Gums are plant flours (like starch or arrowroot) that make foods & other products thick. Gums are used in foods for many reasons besides being used as a thickener. Gums are important ingredient in producing food emulsifier, food additive, food thickener & other gum products. The main reason for adding a gum or hydrocolloid to a food product is to improve its overall quality. India is the largest producer of gums specially guar gum products. Similarly stabilizers are an indispensable substance in food items when added to the food items, they smoothens uniform nature and hold the flavouring compounds in dispersion. Gum technology stabilizers are carefully controlled blends of various food ingredients. Most processed foods need some sort of stabilization at some point during production, transportation, storage and serving. The science and technology of hydrocolloids used in food and related systems has seen many new developments and advances over recent years. The breadth and depth of knowledge of gums and stabilizers has increased tremendously over the last two decades, with researchers in industry and academia collaborating to accelerate the growth. Gums as food constituents or as food additives can influence processing conditions in the following ways; retention of water, reduction of evaporation rates, alteration of freezing rates, modification of ice crystal formation and participation in chemical reactions.
Some of the fundamentals of the book are functions of gum, typical food applications, gums in food suspensions, rheology and characters of gums, natural product exudates, flavor fixation, ice cream, ices and sherbets, gelation of low methoxyl pectin, seaweed extracts, microbial gums, transformation of collagen to gelatin, cellulose gums, dairy food applications, bakery product applications, analysis of hydrocolloids, gums in food products, general isolation of gums from foods, identification of gums in specific foods, group analysis and identification schemes, group identification methods, qualitative group analysis etc.
This book contains rheology of gums, plant sheet gums, microbial gums, cellulose gums and synthetic hydrocolloids different stabilizers used in food industry. The book will be very resourceful to all its readers, new entrepreneurs, scientist, food technologist, food industries etc.
Functions of Gum
army marches on its stomach is
an old expression, widely attributed to Napoleon. It is unfortunate,
that many advances in technology have been greatly accelerated and
the contingencies of war. The need for preserving foods for long
time during the Napoleonic campaigns led directly to the development of
canning process by Nicholas Appert in 1810. Considering the state of
and general lack of information at that time, this ranked as a
with the proliferation of little wars that eventually culminated in the
and Second World Wars, the logistics of supplying food for armies
over the world, led to many other advances in food science. Marked
made in the preservation of foods by quick freezing, irradiation,
additives, dehydration, and other methods.
dehydration technology were spurred by the need for transporting foods
distances by ship or plane. It is a rare soldier that does not recall
nostalgia perhaps, but not regret the powdered eggs and dehydrated
that were part of the daily rations of the American soldier overseas
World War II. It is encouraging to report that these products were
improved during the years after the war, and today they can be
considered to be
quality products of the convenience food type.
convenience foods with the built in maid ushered in a period of great
and technological advances in the food industry. This era, which also
during World War II, was primarily a result of the great changes, which
place in the American home at that time. Many women, employed in war
industries, had limited time for the every day kitchen tasks, and were
for any time saving devices and foods that might be offered. After the
feeling of emancipation from the kitchen remained and became a way of
which exists today.
food industry were quick to perceive this trend and took advantage of
beckoning market by plunging into the development of all types of
foods. For a period of time it might be said that the prevailing
that of the famous gastronome Brillat Savarin when he made the
appears, at the beginning of this chapter.
One of the
successful post war developments is that of instant coffee. Although
coffee was known before the war, it was not a widely accepted commodity
it varied in
quality, had poor stability, did
not dissolve too well, and was expensive. In short, it did not enjoy
consumer acceptance. War time needs, being the mother of inventions,
technological improvements in the development of good quality soluble
to be included in military rations. These products had good
stability, and taste characteristics as a result of drying the coffee
fillers such as sugar or dextrose.
breakthrough was achieved subsequently with the development of a spray
process for a 100% coffee product that had good flavor, performance,
stability. This 100% flavor bud product met with great success and
way for many similar products, resulting in continuous market growth
past two decades. Today, instant coffee is so well entrenched in the
market, that it now outsells regular ground coffee. It has also been
that the current generation of teen agers who grew up on soluble coffee
become an adult market with a preference for soluble rather than
coffee. This, of course, is conjecture and only time will tell.
quick freezing foods as a preferred method of preservation was
developed by Clarence Birdseye in 1925. Applications of his methods led
host of food products that could be processed in season and preserved
height of their flavor and textural development until ready to use. No
does the housewife have to screen the sand from her spinach, or remove
discolored and damaged leaves, or even core the vegetable. It is not
necessary to cook it, watching carefully until the vegetable is soft
tender, but not too soft and crumbly. Now all she has to do is remove a
package of cleaned, cooked spinach from her freezer, put it in a pot of
water, and heat it until thawed.
and high quality of frozen vegetables, fruits, meats, etc., met with
consumer acceptance in the period after World War II and resulted in
products, the outstanding example of which is frozen orange juice
Freeze Dried Foods
processing combination of quick freezing followed by low temperature
dehydration was the logical outcome of a series of technological
new freeze dried food products have been developed, the most recent of
have been dry breakfast cereal combinations with freeze dried
bananas, and other fruits. Upon the addition of milk, the fruits
form truly fresh high quality fruits.
the reader might rightly ask, What does all this have to do with gums?
answer is, Everything. Gum constituents are present in almost every
food and are largely responsible for the structure and textural
the plant. In prepared foods, gums are used as food additives to impart
desirable textural and functional properties to the finished products.
rare that a convenience food does not have one or more gums listed
ingredients. Gums are so necessary in many foods covered that they are
in these standards and are not required to be listed on the label.
The use of
to obtain superior quality in many products has become so accepted in
foods that it is difficult to find a sample without it, even if one
want it. This is best illustrated by ice cream. In the good old times,
ice cream like mother used to make suffered from poor textural
as presence of ice crystals, sandiness, and lack of smooth melt down.
commercially prepared ice creams contain various hydrocolloids as
and stabilizers to eliminate such defects of quality. It is almost
to find a brand of ice cream that does not contain gums.
Effect on Processing
processes inherently involve the modification or denaturation of the
characteristic food texture. The properties of the gum constituents
many food materials have an important bearing on processing conditions
resultant properties of the final food product.
food processing there is a change in the moisture content or the
of water. The water is either completely or partially removed, as in
foods or it is
physically changed to gas
in cooking and blanching operations or
it is converted to the solid form of ice in freezing operations. The
the water content or its physical form is largely responsible for
texture of the processed food product, and is one of the most important
to be considered in manufacturing high quality processed foods. Since
residual gum constituents and hydrocolloid additives greatly influence
of physical transformation and rate of migration of the water
substances are important factors in food processing.
Pertinent Processing Parameters
constituents or as food additives can influence processing conditions
following ways: (1) retention of water (2)
reduction of evaporation rates (3)
alteration of freezing rates (4)
modification of ice crystal formation (5)
participation in chemical reactions. These
functional effects are not isolated phenomena, which can be followed
easily they are
only evident in the textural
qualities or rheological behaviour of the final product. While the
effects of a gum are its most important characteristics in determining
in foods, these effects must be considered in context with many other
including price, availability, ease of handling, and legal restrictions
to their use.
Function in Food Applications
a wide range of specific food applications, ranging from adhesives to
agents. Typical specific functions and food applications are shown in
but the general function of gums can be limited to their two major
hydrocolloids, by definition and usage have a thickening, or viscosity
effect when dispersed in a water medium. This property is the basis for
use as bodying, stabilizing, and emulsifying agents in many foods. A
comparatively few of the important gums i.e., agar, algin, carrageenan,
furcellaran, gelatin, pectin, and starch also have the ability to form
under specific conditions of use. Gels, when referring to foods, are
that will retain their shape and will not flow unless pressure is
Probably the most common gelled food product is gelatin dessert gel,
enjoyed enormous popularity in this country for many years. Other well
food gels are starch based milk puddings, gelatin aspics, and pectin
cranberry sauce. In Europe, milk puddings of the blanc mange type are
pupular and are usually made with seaweed extracts of the carrageenan
There is an
interplay between the viscosity and gelling characteristics of any
and these factors must be taken into consideration when these gums are
used for example,
depending on the type of gelatin
and on its concentration, gelatin can be used as a thickening agent
a gelling medium. In a related way, temperature also plays an effect as the temperature
increases, the viscosity
decreases, thus decreasing the effective thickening properties of the
temperature increase is in most cases the same as an effective
reduction in gum
Definition and Meaning
resistance to flow of a liquid system. In colloidal suspensions it is
by the thickening of the liquid phase as a result of liquid absorption
consequent swelling of the dispersed colloid. This thickening, or
effect of gums in food products is, in turn, responsible for other
effects such as the suspension of solid particles, the emulsification
and water phases, the stabilization of liquid solid gas phases, the
of solid and liquid phases, and related phenomena.
hydrocolloids are used as viscosity producing agents for the purpose of
suspending, emulsifying, or stabilizing a food system, shelf stability
extremely important and the selection of the proper hydrocolloid is
Degradation of the hydrocolloid and the resulting reduction in the
polymer solutions may impair the flow properties and appearance of the
sufficiently to reduce its consumer acceptability.
are long chain polymers, they are subject to the type of molecular
caused by cleavage of molecular bonds, resulting in lower viscosities.
Determination of the exact causes of degradation or loss of viscosity
difficult. Frequently, polymers are degraded by the use of high
equipment used to put them into solution, or by the high temperatures
processing. In general, the low viscosity natural gums are more stable
high viscosity types. Studies on the comparative stabilities of gums
valid if comparisons are made between solutions of equal viscosity
of equal concentrations, which is so often the case.
Factors Effecting Hydrophilic Viscosities
of hydrocolloid systems are effected by many factors and listed ten
that cause variations in the viscosities of hydrophilic systems: (1)
concentration, (2) temperature, (3) degree of dispersion, (4)
electrical charge, (6) previous thermal treatment, (7) previous
treatment, (8) presence or absence of other lyophilic colloids, (9) age
lyophilic sol, (10) presence of both electrolytes and nonelectrolytes.
importance of viscosity to the textural quality and consistency of most
is so great that above factors to be the ten commandments of food
She illustrated the importance of some of these in the preparation of a
custard dessert: concentration of egg or protein micelles temperature of cooking degree of dispersion of the
micelles degree of
hydration which is influenced by the
type of reaction and presence of salts beating
of the egg use of
milk or water aging
of the custard as well as the age of the
eggs and milk presence
in egg and milk and addition of salt presence
of nonelectrolyte, sugar. The
viscosity of any food system is subject to the influence of many
parameters, and the hydrocolloids present or added are likewise subject
same forces encountered in the preparation of quality food products.
Typical Food Applications
The use of
solely for thickening purposes is common in such products as pie
beverage dry mixes. In pie fillings, especially fruit type fillings,
used to thicken the fruit juice to prevent the flow of the filling from
shell. In beverage mixes that are reconstituted with water, gums are
thickening agents to give the final product the necessary body. This is
especially true for the sugar free, dietetic products.
mixes are thickened with starches and gums to improve their body and
consistency. Likewise, sauces and sauce mixes contain gums to impart
texture and flow characteristics. For low pH sauces, it is necessary to
thickening agents that are resistant to acid degradation. Gum
propylene glycol alginate are two of the preferred additives, since
more acid stable than the other common gums.
agents are incorporated into many breading mixes, so that they will not
meats and fish. Gums have also found a novel use in dog foods where
added to dry meatlike pieces, which, upon the addition of water,
thicken to form a thick gravy like sauce containing meatlike chunks.
food gels are rigid, two phase systems that show resistance to flow
pressure and are capable of retaining a firm, distinct structural form.
are liquid solid systems with a continuous network of solid material
the gel matrix and enmeshing or holding a continuous or finely
phase. The solid, backbone phase is usually composed of long chain
the form of a mass of intertwined fibrils linked by primary or
at widely separated sites along the molecule.
can be considered primarily to be solids, they exhibit properties of
solids and liquids. They resemble solids in their structural rigidity
elastic response when distorting forces are applied, and they resemble
in their vapor pressure, compressibility, and electrical conductivity.
Mechanism of Gel Formation
gelation is shown initially by the gradual decrease in Brownian
movement of the
colloidal particles concluded within the gel. This decrease is caused
exertion of long range forces between the molecules, which in turn
the hydration and coherence of the particles. The viscosity then begins
increase as gelation proceeds and the solvent (liquid) is absorbed by
swelling solute (solid) and is gradually immobilized. As the process
a three dimensional network containing enmeshed portions of the liquid
gradually built up. The various fragments of the gelling polymer
react and finally form one large continuous structure. At this stage
rigidity of the system becomes apparent. Parts of the large molecular
the network can still react with other parts by cross linking to
increase the rigidity of the whole structure.
Gelation from Sol State
induced in both sol or solid state systems. From the sol state,
gelation can be
achieved by increasing or establishing forces between solute molecules
or more of the following ways: addition of a nonsolvent evaporation of the solvent
present in the
system addition of
a cross linking agent
solubility of the solute by
chemical reaction changing
Gelation from Solid State
state, gels can be formed by allowing the solid phase to remain
immersed in the
solvent until sufficient liquid is imbibed to form a gel. Thus, a gel
considered to be in an intermediate state of hydration between a sol
Types of Gel Linkages
gels from solutions of long chain polymers can be explained as being
due to the
cross linking of adjacent molecules to form a continuous network
mechanical stability in the final gelled state. Entrapped within this
is a continuous liquid phase consisting of the solvent and solutes,
which may include non cross linked polymeric materials.
cross linking that may take place depend on the chemical properties of
constituent groupings on the polymers forming the gel matrix and the
conditions existing in the system.
Rheology and Characters of Gums
The main reason for adding a
gum or hydrocolloid to
a food product is to improve its overall quality. This improvement may
to its appearance, convenience, stability, cost, texture, etc., all of
are eventually judged by the consumer. The consumer usually judges the
by simply eating it and seeing how it tastes. At this point he does not
the added gum is a galactomannan or a sulfated galactan, nor does he
about whether the vitamin A in the product is naturally derived from
liver or synthesized from b ionone. He is concerned with the taste and
feel of the product. If it tastes good, he is happy
it tastes bad, he is unhappy, and so
eventually is the manufacturer of that specific food item.
objective of every company selling food is directly related to food
flavor. At the risk of oversimplifying, it can be assumed that these
factors, texture and flavor, are the two most important properties of a
comestible, although it is conceded that other factors such as
color, packaging, convenience, price, calorie content, etc., are also
and often supersede texture and flavor. But for mass market acceptance,
flavor and texture are essential. With products such as soluble coffee
frozen orange juice concentrates, the flavor characteristics alone have
sufficient to separate the products of good quality from the inferior
In the case of ice cream, the textural qualities predominate and serve
distinguish the good from the bad. Poor quality ice creams may have a
consistency due to ice crystal formation, while good quality ice creams
uniform and have a homogeneous texture leading to smooth melt down in
mouth. It is obvious that no one would buy a product that had a poor
texture at least
not the second time.
Oldfield makes the point that
foods that cease to
yield flavor before they have been sufficiently chewed for comfortable
swallowing tend to produce an aversion towards further chewing together
involuntary inhibition of the swallowing mechanism. He illustrates this
the impulse to spit out over cooked, tough steak. Another common
that afforded by chewing gum. Most people will chew gum until the
leached out and will then discard it even though the textural and
have not been impaired.
somewhat influenced by gums, in that gums play a part in flavor release
flavor retention in foods and are used to stabilize and fix flavor
the most important effect of gums is on texture. Texture is an abstract
of a concrete property. All foods have texture if we think of texture
the structural matrix of the food, but it is the perception of texture
food is eaten that is important. This was most clearly stated by
defined texture as the composite of the structural elements of the food
manner in which it registers with physiological senses. The importance
physiological stimuli during eating is best described by Oldfield. Once
and chewing start, an immensely complex pattern of stimulation is set
the help of the tongue the food is rolled across the gums and the hard
palates. The teeth themselves play a part in signalling the textural
rheological properties of the food and
these properties are progressively changed by the process of
a changing pattern of stimuli results. As the food is broken up by the
the increased surface area releases taste and smell stimulus substances
greater quantity. All these stimulus elements contribute to supply the
with the material out of which it constructs the complex perception,
also serve, some without entering consciousness, to maintain and modify
activity of the mouth. Eventually the food is swallowed.
eating (i.e., chewing and swallowing) can be visualized as a process of
breaking down (or deforming) the food product in the mouth, with the
character of the breakdown being dependent on the structure or texture
food. In recent years this important area of investigation has been
into a branch of science known as rheology, the science of the
flow of matter.
While it is
the purpose of this chapter to delve deeply into the subject of
subject, which is still regarded by some as a messy science, it is
be able to understand the methods and instruments of rheology in order
measure and explain the effects of hydro colloids on food textures. Any
gives a meaningful number to a textural parameter, which in turn can be
to consumer acceptability, is useful to the food scientist. The phrase
number must be carefully qualified, because many numbers are not
bear no relationship to the textural acceptance of the product in
Thus the viscosity of beverages is not necessarily correlated with the
mouthfeel or acceptability of the beverage. Beverages of identical
can be either slimy and mouthcoating or smooth and pleasant. Likewise
strength measurements on standard instruments such as the Bloom
give satisfactory data on the overall strength and rigidity of the
will completely fail to characterize the parameters of elasticity and
brittleness which may be more important from the viewpoint of consumer
measurements, however, can be objectively correlated with mouthfeel and
consumer approval. Recent work established a correlation between the
organoleptic characteristics of hydrocolloid solutions and their
behavior. Measurements of solution viscosities at various rates of
a relationship between the shape of the curve and degree of sliminess.
subsequently confirmed in work on gum thickened sucrose solutions.
various hydrocolloid solutions showed that they could be grouped into
categories slimy, slightly slimy, and nonslimy–depending upon the shape
curve (Fig. 1). This was a practical way of measuring rheological
gums and using the physical data to select the ones preferred with
mouthfeel or texture.
behaviour of hydrocolloids is of special importance when they are used
artificially sweetened foods where large amounts of sugars are replaced
for bodying and textural effects. The organoleptic properties and
of such foods are more critically related to their rheological
general, the overall objective in studying the rheology of food
products is to
measure the various parameters of foods under stress and to define them
mathematically so that they can be related to the subjective,
textural properties of the food.
word rheology is only about 40 years old, the science and practice of
goes back many centuries. The first known rheologist, Amenemhet, an
who lived about 1540 B.C., studied the effects of temperature on the
of water and then described his observations in hieroglyphics. This
scientist invented a clock, which consisted of a conical vessel from
water could be made to flow steadily. Time was measured as the height
water remaining in the funnel. The angle of the cone puzzled modern
because it was not corrected to provide a fall in height proportional
However, when a replica of the clock was built and operated through the
temperature differences which exist between Egyptian days and nights,
constructed by Amenemhet was found to be correct. Cold water has a
viscosity, or resistance to flow, than warm water
angle of the cone had thus been calculated
and constructed to allow for this difference as the water was cooled by
cold Egyptian night.
of the world, the Indians developed a crude system of rheology in about
A.D. which classified different substances into groups according to the
responses of feel, temperature, sound, taste, and odor.
the sixteenth century, though, that any real progress in rheology was
this time, Leonardo da Vinci investigated the flow of water through
and channels, a series of experiments, which was followed in the next
by Galileos studies on the cohesion of ropes. Hooke subsequently
the elastic properties of solids and stated that stress is proportional
strain in elastic solids. Newton, in the same era, made the first
viscometer in the course of his studies of the rotation of the planets
solar system. He used a rotating cylinder in a pool of water and
resistance to flow is proportional to the rate of shear in liquids.
of ideal relationship was later termed Newtonian flow in honor of its
nineteenth century, Poiseuille studied the flow of water through glass
capillary tubes and found that the quantity of water flowing through
increased directly with the fourth power of the diameter of the tube
with the pressure of the water. In addition, the quantity of water
with increased viscosity and with the length of the tube. For his work,
Poiseuille was honored by having the basic unit of viscosity, the
modern rheology is considered to be Eugene C. Bingham who coined the
rheology from the Greek rheos meaning flow. His classic book, Fluidity
Plasticity established a firm basis for this new science. Later, like
other scientific endeavors, the study of the rheology of polymers was
accelerated by the contingencies of war. For example, gasoline
aluminum stearates used in flame throwers during the Second World War
marked elasticity and peculiar flow properties. Rheological studies
in an effort to understand and to improve the cohesiveness of the
ejected fuels. The flow peculiarities were attributed to normal
were pressures acting across or normal to the shear planes. After the
study of rheology led to the development of many useful products such
plastics, paints, foods, drugs, etc., and proved to be helpful in
technologies of all of these industries.
science of the deformation and flow of matter. It includes the study of
deformation and other phenomena not necessarily associated with flow.
deformed, or starts to flow, only when it is acted upon by force. The
be supplied deliberately, accidently, or may be all pervading as in the
gravity. Rheology is concerned with forces, deformations, and time, and
also include temperature and other secondary parameters.
a complex property comprising several interrelated physical parameters,
which viscosity in liquids and elasticity in solids are among the most
important. Other related properties are tackiness, smoothness,
particle size, density, and temperature. Most foods do not have simple
invariant rheological properties such as viscosities and elastic
are independent of stress and strain conditions and which can be
defined by a
single number. But the behaviour of these materials, even when they are
variable, can be expressed according to defined rheological
must be represented by flow curves (rheograms) rather than single
For a more
complete description of the rheological behaviour of fluid foods, Charm
believes that the parameter of tensile strength must also be considered
with shear strength and viscosity measurements. This property, although
measured, may play an important role in textural qualities and coating
of fluid foods. Charm measured the tensile strengths of catsup, tomato
and mayonnaise, and found them to be about twice the value of the shear
strength. The overall significance of tensile strength has not yet been
established, but it may be an important factor in defining the complete
rheological picture of specific food products.
the perfect, or ideal, (Newtonian) liquid is one that flows at a steady
constant pressure and at a rate strictly proportional to each pressure
series of pressures is applied. Other liquids whose rates of flow are
proportional to the pressure applied are called non Newtonian liquids.
respect to solids, elasticity and plasticity are two of the more
attributes of their structures.
defined these properties
quite clearly. When a shearing stress is applied to a perfectly elastic
a certain strain is developed which disappears completely when the
removed. The process is reversible and no work is done. Likewise,
play no part in the movement. This is a classic case of elastic
not of flow.
the ideal elastic solid is based on Hookes Law and must meet the
criteria: (1) the deformation must be proportional to the applied force
(2) it must be
completely recovered when the
force is removed (3)
both the original
deformation and its recovery must not be delayed by internal
stress is applied to a body that is imperfectly elastic, it will be
at least a part of the deformation will remain long after the stress is
removed. In this situation, work has been done in overcoming some kind
internal friction. Plasticity can therefore be defined as a property of
by virtue of which they hold their shape permanently under the action
shearing stresses but are readily deformed, worked, or molded, under
The line of
demarcation between a liquid and a solid is sometimes very thin and
difficult to define, let alone, measure but
various situations will be reviewed in the
discussions of the different types of flow behavior found in food
way of characterizing a liquid or fluid material is by measurement of
viscosity, which is actually a measure of fluid friction. The force of
can be considered as the energy required to move an object that rubs on
another, i.e., viscosity is the measure of the internal friction
movement of each layer of fluid as it, moves past an adjacent layer of
highly viscous material is one possessing a great deal of internal
friction it will
not pour or spread as easily as a
material of lesser viscosity.
systems, where the shearing stress is directly proportional to the rate
shear, the viscosity is constant and a single point viscosity
sufficient to characterize the system. It is only necessary to plot the
point measurement and draw a straight line to the origin to indicate
fluid foods are non Newtonian systems where the viscosities are not
but are dependent on the rate of shear. In addition, yield values and
of change in resistance to flow with increased shear are also needed in
to define the flow picture of some systems accurately.
The rate of
change in resistance to flow is a measure of the magnitude of the
systems non Newtonian
behaviour and can be ascribed to various factors such as: (1) the ease
alignment of long chain molecules in solutions
the nature and uniformity of the particle
size of the ingredients in dispersions or suspensions
the way the particles pack together in the
dispersion (4) the
amount of dispersion
liquid and the extent of voids created when the system is disturbed.
seen, therefore, that single point measurements with any type of
limited in meaning because they do not describe the flow behaviours at
rates of shear and thus cannot adequately characterize the physical
of the liquid.
depending upon their behaviour under imposed shearing forces, materials
categorized as Newtonian or non Newtonian. Only a few of these systems
present in food products, the more important ones being those where the
independent of time. These consist of Newtonian, Bingham plastic,
and dilatant systems. Two other systems often encountered are
rheopectic materials in which the flow is dependent on time.
can best be described by considering two parallel plates, A and B, of 1
(A), with the intervening 1 cm space being filled with the liquid under
consideration (Fig. 2).
equal to the force (F) that is required to induce a unit rate of shear.
depth (d) of the substance in between is 1 cm. If a force (F) of 1 dyne
required to move plate A with constant speed of 1 cm per second, then
viscosity of this substance will be 1 poise. The innumerable parallel
the substance must move past each other once plate A is moved.
If plate A
moved to the right, the layer next to the stationery plate B remains
moving. The layers above it travel, depending upon the distance from
with an increasing speed to the right. Each single layer of the
therefore, passes the one below it and remains a little behind the one
it. Because the layers adhere to each other, a force is encountered
opposes this sidewise movement. This tenacity is called viscosity (h),
internal friction, of a system which, per unit area, is the same on
Viscosity, then, is a measurement of the combined effect of adhesion
cohesion. The transmitted force (F) is therefore proportional to the
coefficient of the inner friction as follows:
D, is the rate of shear and is directly proportional to the applied
and flow starts under the slightest pressure. The characteristic flow
line of a
Newtonian substance goes through the origin of a plot (or rheogram) of
exhibit direct proportionality between shear stress (F) and shear rate
any given temperature, these materials have a viscosity that is
the rate of shear. In simple terms, it will take twice as much force to
the liquid twice as fast. As shown in Fig. 3, the relationship between
force and rate of shear is a straight line and the viscosity, in
units, is the inverse slope of the line. The viscosity of Newtonian
remains constant as the rate is changed.
behaviour has been found to be common to all gases and to all liquids
solutions of low molecular weights i.e., non polymeric materials and
solutions of low concentrations of some high molecular weight polymers.
common denominator of these solutions is that the dissipation of
in them is due to the collision of fairly small molecular species.
foods include most simple solutions, such as sugar syrups, broths,
soups, soft drinks, and milk. Most foods, however, fall into the non
Natural Product Exudates
Origin of Gums
plants exude viscous, gummy liquids, which when exposed to air and
dry, form clear, glassy masses. The shapes of these masses vary from
teardrop balls typical of gum arabic producing Acacia trees to curved,
strands of tragacanth from Astragalus bushes. The colors of these
vary widely from almost clear white to dark brown, depending on the
climate, soil, and absorbed impurities.
reason for the formation and exudation of gums by plants, is still not
understood, and many theories have been formulated to explain these
One theory suggests that gum formation is a protective mechanism
a pathological condition. This hypothesis is supported by evidence
the production of gum arabic. Healthy Acacia trees, grown under
conditions of soil and climate, produce little or no gum, while trees
under adverse conditions of high elevation, excessive heat, and
moisture produce sizeable quantities of gum arabic. And the yield of
gum can be
further increased by deliberately injuring the tree by stripping away
investigators believe that gum formation is part of the normal
of the plant as in the case of the gums in sugar beets and yeasts.
consider gums to be synthesized as a result of an infection of the
microorganisms in an effort to seal off the infected section of the
prevent further invasion of the tissue. This would probably be similar
formation of a scab on a human wound. The formation of gum has also
attributed to fungi attacking the plant and releasing enzymes that
the tissues and transform the constituent cellulose materials of the
into gum. This has been suggested to be the mechanism of formation of
found in the gummosis disease of various deciduous trees. Yet another
particularly with respect to Acacia species, claims the formation of
gums to be
caused by bacterial action and suggests that specific bacteria are
producing different kinds of gum.
reasonable explanation however, seems to be the simplest one, namely
plant produces the gum in order to seal off the injured part, primarily
prevent the loss of moisture and not necessarily to prevent infection.
concept is supported by the fact that gum arabic and gum tragacanth are
produced immediately by healthy trees that have been deliberately
whatever the cause, it is fortuitous that many species of plant produce
quantities of gums that can be utilized in a constructive manner.
appearance and properties of the natural gums are of utmost importance
determining their commercial value and their end use. These vary
with gums of different botanical sources, and there are even
differences in gum from the same species when collected from plants
under different climatic conditions or even collected from the same
different seasons of the year. The physical properties may also be
the age of the exudate, treatment of the gum after collection, such as
drying, sun bleaching, and storage temperatures.
exuded in a variety of shapes and forms, the best known being the
globular shape of various grades of gum arabic. Other characteristic
flakes or thread like ribbons as with gum tragacanth. Still others
stalactites and after collection and fracturing yield irregular rod
most gums is perfectly smooth when fresh but may become rough or
small cracks or striations upon weathering, resulting in an opaque
These fissures or striations are often restricted to the surface, but
deep in some gums, causing the tear drops to break up into smaller
during handling and shipping.
gums in their natural exudate shape varies from almost water white
through shades of yellow, amber, and orange, to dark brown. The best
gum arabic are almost colorless with slight traces of yellow. Some gums
pink, red, or green lines and
or brownish gums are also found.
first secreted appear to be colorless, and it is believed that color is
mainly to the presence of various types of impurities. Color often
the gum ages upon the tree and may be due to extraneous substances that
washed onto the gum. Bush or grass fires can cause discoloration by
Tannins from the sap or tissues of the parent tree are frequently the
discoloration and are believed to account for some of the very dark
yielded by certain trees.
plant gums are usually odorless and in this respect differ markedly
oil soluble resinous exudates which have distinctive smells. The gums
usually tasteless and bland, except for some species which have a
carbohydrate taste and some types that have been contaminated. Gums
contaminated with tannins usually have a harsh, bitter flavor that is a
disadvantage in food applications.
hardness, but since this is usually dependent upon the amount of
present (12 16%), it cannot be used as a means of classification as
minerals. Density is also variable and depends upon the amount of air
when the gum was formed.
plant gum exudates known all over the world, but only four are of real
importance to the food industry. Many of the other gums are known and
local areas where they are available, but only to a very limited
gums have similar properties and can be used for similar applications
necessary. Some of the more common ones are damson, plum, cherry,
lemon, almond, cashew, brea, chagual, mesquite, shiraz, cactus, neem,
cholla, khaya, jeol, and many more too numerous to mention.
best known of all natural gums is gum arabic, also known as gum acacia,
gum, gum Senegal, and by many other descriptive and colorful local
arabic is the dried, gummy exudation obtained from various species of
trees of the Leguminosae family. About 500 species of Acacia are
over tropical and subtropical areas of Africa, India, Australia,
America and southwest North America, but only a comparatively few are
commercially important. The important producing areas are the Republic
Sudan, French West Africa, and several smaller neighboring African
earlier, the trees produce gum arabic only when they are in an
from poor nutrition, lack of moisture, or hot weather. The gum is
breaks or wounds in the tree bark, and exuded in the form of spherical
resembling teardrops. These exudates are collected by hand by the local
and transported to central collecting stations where they are sorted by
and exported gum suppliers in all Parts of the world. There the gum
sorted again, ground, processed, and graded to meet various
standards for good
quality gum arabic have been defined in the Indian Pharmacopeia as
total ash (maximum), 0.5% acid insoluble ash (maximum), and 1% water
residue (maximum). In line with recent efforts to define standards for
grade additives, more rigid specifications have been established for
karaya, and tragacanth, and published in the Food Chemicals Codex.
not yet been included, probably because of its comparatively minor use
exists in nature as a neutral or slightly acidic (D glucuronic) salt of
complex polysaccharide containing calcium, magnesium, and potassium
ions. It is
a heterogeneous material and may be composed of several slightly
molecular species. The most recent opinion is that the main structural
of the molecule is a main chain of b galactopyranose units linked
1®3, with side chains of 1,6 linked galactopyranose units terminating
glucuronic acid or 4 0 methylglucuronic acid residues. Additional
also attached to the C 3 positions on the galactose side chains.
hydrolysis of the molecule yields the four basic sugar constituents D
L arabinose, L rhamnose, and D glucuronic acid. These sugars are found
arabic from all species of Acacia, but the proportions vary among the
species. A recent study by Anderson has reported the presence of
groups in certain Acacia gums and suggested that the methoxyl content
structural significance that has yet to be defined.
weight is believed to vary from about 250,000 to 1,000,000, and also
to the method of measurement. The shape of the molecule is believed to
of a short stiff spiral, or coil, with the length of the main molecule
varying between 1050 Å and 2400 Å according to the amount of charge on
unique among the natural hydrocolloids because of its extremely high
in water. Most common gums cannot be dissolved in water at
higher than about 5% because of their very high viscosities. Gum
however, can yield solutions of up to 50% concentration. At these high
it can actually form a highly viscous, gel like mass similar in
character to a
strong starch gel. In addition to forming high solids gels of this
arabic can be used at much lower concentrations in combination with
as thickeners and binders. Comparative viscosities of the common
exudates are shown in Fig. 1 and Table 1.
the gum give solutions that are essentially colorless and also impart
to the solution. Poor quality dark grades of arabic have an unpleasant
astringent flavor and odor, probably due to the presence of tannins.
should never be used in food products.
insoluble in oils and in most organic solvents. It is soluble in
ethanol up to a limit of about 60% ethanol. Limited solubility can also
obtained with glycerol and ethylene glycol.
gums form highly viscous solutions at low concentrations of about 1 5%,
is unique in that it is extremely soluble and is not very viscous at
concentrations. High viscosities are not obtained with gum arabic until
concentrations of about 40 50% are obtained. This ability to form
concentrated solutions is responsible for the excellent stabilizing and
emulsifying properties of gum arabic when incorporated with large
gum arabic solutions will depend upon the type and variety of arabic
Measurements of the relationship of concentration to viscosity made by
showed slight, but not unreasonable inconsistencies, considering the
differences in raw materials and methods of measurement. Their results
given in Table 2.
concentrations up to 40%, gum arabic solutions exhibit typical
behavior. Above 40%, solutions take up pseudoplastic characteristics as
by a decrease in viscosity with increasing shearing stress.
Effect of pH
on gum arabic solutions has been reported by several investigators who
agree that arabic acid is a strong monobasic acid. The viscosity of gum
rises sharply with increasing pH to a maximum at about pH 5 7, then
slowly to about pH 10 14. The data reported by Thomas are shown in
Normally, solutions of gum arabic are slightly acidic, having a pH of
5.5 and hence are in the area of maximum viscosity.
Effect of Electrolytes
electrolytes to a gum arabic solution results in a lowering of the
even in a very dilute solution. This lowering is much more pronounced
concentrated solutions. The decrease in viscosity is proportional to
increase in the valence of the cation or the increase in the
electrolyte. The addition of more than one electrolyte gives an
viscosity, which is accompanied by a lowering of the interfacial
produces favorable emulsifying conditions. Thus, while a good kerosene
emulsion can be obtained with a 10% gum arabic solution, equally good
can be obtained with 0.5 % gum arabic solutions in the presence of
sulfate or sodium bicarbonate.
Effect of Aging
solutions of gum arabic showed that all solutions underwent a decrease
viscosity with age. Unpreserved solutions showed the greatest drop in
viscosity, while solutions preserved with benzoic acid (0.2 %)
smallest loss of viscosity.
solutions will produce precipitates with many salts, particularly
metallic salts. It is incompatible with some gums, such as gelatin and
alginate, but quite compatible with methylcellulose,
and larch gum. In many cases, compatibility is subject to the influence
and concentration, and compatibility of gum arabic with other
components can be
obtained by proper adjustment of these parameters.
very effective emulsifying agent because of its protective colloid
functionality and has found widespread use in the preparation of varied
oil in water
food emulsions. It produces stable emulsions with most oils over a wide
range and in the presence of electrolytes without the need for a
stabilizing agent. The gum arabic forms a visible film at the oil
but the mechanism of emulsification still is not understood. It is
that arabic, as a film forming agent, prevents coalescence of the oil
thus permitting a high degree of dispersion by diminution of the
It has been
found that the chemical nature of the oil used can cause marked changes
properties of acacia stabilized emulsions. The relative viscosity of
made with gum arabic changed in accordance with the oil used as the
phase. It has been suggested that the differences might be due to the
of a stabilizing layer, the thickness of which varied with the oil
layer is presumably large enough to contribute noticeably to the volume
and thus the emulsion viscosity.
A few other
minor gum exudates from fruit trees also have been said to have
emulsifying properties. Solutions (10%) of apricot, prune, and sweet
have been reported to have protective properties similar to a
solution of gum arabic, but since these gums are only available in
quantities in certain geographic areas, they have not been used in any
important food applications.
Plant Seed Gums
important food plants produce seeds containing starch as the
reserve. This starch serves as the principal food stored for use by the
embryonic plant in its initial growth stages. Many plant seeds,
contain polysaccharide food reserves that are not starch (glucose
but are polymers of other sugar molecules such as galactose and
polymers also have constructive hydrocolloid properties, and when
be used like gums from other sources.
these seed gums are known and have been investigated, only a very few
are important in the food industry, and at present only locust bean gum
guar gum enjoy a substantial degree of acceptance. Although psyllium
and quince seed gum have also been utilized to some extent in the food
industry, they still find their most extensive uses in the related
pharmaceutical and cosmetic industries. The gums of flaxseed, tamarind
tara seed, flamboyant seed, and other seeds also have interesting
properties and may eventually prove to be economically and practically
in food applications.
above, at present only locust bean gum and guar gum are of importance
hydrocolloids with possible applications seen for psyllium seed and
gums. This chapter will therefore be restricted to a discussion of
Locust Bean Gum
or carob bean, plant is an ancient leguminous plant (Ceratonia siliqua
which is indigenous to the near East and Mediterranean areas. That it
known for thousands of years is shown by the fact that the ancient
used carob paste for binding their mummies. Arabs used the carob seeds
kernels as weight stones to weigh precious metals and gems such as gold
As a matter of fact, the word carat is cognate with the botanical name
ceratonia. Dioscorides, a Greek physician in the first century A.D.,
to the curative laxative and diuretic properties of the carob tree
times, the pods of the tree were widely used for feeding cattle,
pigs (hence the name swines bread). The pods were used for human
times of scarcity, and perhaps regularly by the poorer people. The
food was immortalized in the Bible in the passage where the sojourn of
the Baptist in the wilderness is described. His meat was locusts and
is believed to refer to wild carobs (Matthew 3:4) and one of the names
carob bean that has lasted through the centuries is St. Johns bread, or
Johannisbrot. The Prodigal Son in the Bible also longed in vain to
feast on the
carob: and he would fain have filled his belly with the husks that the
did eat and no man
gave unto him (Luke
Biblical meaning of carob trees is commemorated in a traditional Jewish
holiday. Jewish Arbor Day, TuBishvot, marks the tree planting season of
Israel and usually falls in February. It is the custom at this time to
display the fruits distinctive to Israel and one of the fruits honored
occasion is the carob, or boksor as it is called in Hebrew.
of carob as animal feed and human food slowly grew over the centuries
tree was gradually introduced from the near East to other parts of the
The Greeks were responsible for carrying it from Syria and neighboring
Greece and Italy while the Arabs, by virtue of their extensive
trade routes, made the carob plant known in northern Africa and Spain.
In more modern
times, the carob was introduced to the Americas, Australia, and other
the world where climatic conditions were favorable to the cultivation
beans have been used extensively as coffee substitutes, especially in
In North Africa the poorer inhabitants of the carob growing areas still
pulp as a preferred sweet for children because of its high (30 to 50%)
content. During the Spanish Civil War in 1936 to 1939, the inhabitants
carob growing area ate the locust bean as food. In southern Greece
War II, after the German army had stripped the country of livestock and
other foods, the rural inhabitants lived largely on carob pods.
years in the early 1920s there was considerable interest in California
various food products made from carob pods. Carob flour mixed with
was used to make an acceptable quality bread that was sold in the Los
area for a short period. Another use was a sweet carob syrup with a
flavor made by grinding the pods to a coarse powder, dissolving the
water, and boiling the solution down to the thickness of honey.
made by beating the seedless pods into a powder were sold both as
carob or mixed with wheat products according to the amount of fiber
Some very extravagant claims were made for the health and medicinal
of some of these products until public interest waned. Today some carob
products are still being sold but mostly as a chocolate substitute in
foods. Recipes have been developed by suppliers for the use of carob in
cookies, candies, ice cream, malted milk, and other foods in which
carob, tree (Ceratonia siliqua L.) is a member of the legume family and
only species in the genus. It is a large, handsome evergreen tree, 40
high, which has been used extensively for shade and avenue planting
southern California where the climate is similar to that of the
countries where the carob tree thrives.
It is very
drought resistant and grows readily in areas where water is not
However, it is a slow maturing tree and begins to bear fruit 5 years
budding and increases slowly to a maximum by the twenty fifth year when
tree is full grown. This feature of the carob tree is illustrated
in an old Hebrew legend.
Honi ha Ma aggel, saw on his travels an old man planting a carob tree.
asked by the sage when he thought the tree would bear fruit, the old
replied, After seventy years. And dost thou expect to live seventy
eat the fruit of thy labor? he was asked. The gentle reply was, I did
the world desolate when I entered it, and as my fathers planted for me
was born, so do I plant for those who will come after me.
carob, fruit itself has the shape of a long pod similar to a string
measures 4 12 inches in length, depending upon the variety. Within this
pod are flinty, brown seeds approximately the size and shape of
seeds. The weight of these seeds is 5 14% of the total weight of the
seeds, or kernels, are the commercial source of locust bean gum, though
part of the seed is useful for that purpose. The seed is composed of a
hard, yellow embryo germ portion (25 30%) that is surrounded by a large
of white semi transparent endosperm (35 45%). This whole mass is in
covered by a tenacious, dark brown husk, or outer coating (30 35%). The
endosperm contains the gum and is therefore the desired part of the
Successful production of a high quality locust bean gum involves the
of the endosperm from the germ and from the seedcoat.
practice, the husk is first removed by mechanical abrasion or by
processes. The dehusked kernels are then split lengthwise and the
separated from the germ or embryo. The isolated endosperm is then
ground, graded according to accepted standards of color, impurities,
viscosity, and sold as commercial locust bean (or carob) gum. It is
that the purity and quality of the gum depends on the efficiency of the
separation of the endosperm from the other portions of the kernel.
locust bean gum of commerce is usually a white powder with the
typical composition: galactomannan, 88% pentosan,
3 4% protein, 5 6% cellulose, 1 4%
and ash, 1%.
parts of the world, locust, or carob, bean gum is marketed under other
including: St. Johns bread, gum gatto, gum hevo, jandagum, lakoe gum,
lupogum, luposol, gum tragon, tragasol, tragarab, honey locust, and
is a galactomannan polysaccharide with a molecular weight of about
structure is essentially a straight D mannose polymer linked C1 C4
relatively regular branching on every fourth or fifth mannose group on
single D galactose units (Fig. 1). The ratio of D galactose to D
to vary according to reports from various workers, but this is believed
due to varying origins of the gums and possibly to the stage of growth
development of the plant at time of gum production. The structure of
bean gum is similar to that of guar and differs only in having a
of D galactose side chains.
is only partly soluble in cold water and must be heated in order to
optimum viscosity. Leo claimed that locust bean gum could be made
soluble in cold water by intimately mixing 4 parts locust bean gum with
corn sugar, then wetting, heating, steaming, drying, and finally
grinding to an
appropriate mesh size but
viscosity still required heating.
order to obtain the greatest efficiency as a thickener, it is best to
the gum in hot water and then cool the solution. The solution is
viscous and sticky, and 1% concentration of a good quality gum may have
of about 3500 cps (Fig 2). One of the earliest recorded uses of this
was the use of locust bean paste by the Egyptians in preparing the
cloth with which they bound their mummies.
bean gum contains small amounts of insoluble protein and cellulose
solutions of the gum show a cloudy, whitish opacity, which is a serious
drawback in food applications where clarity is desired.
bean dispersions or solutions in themselves do not gel, they have the
synergistic effect of imparting desirable elastic properties to
agar gels. This effect is discussed in detail in the section on
bean gum is a neutral polymer, its viscosity or stability is very
affected by pH within the range of pH 3 11. The chemical reactions of
are also similar to those of the other neutral polysaccharides. Its
ethers have been made commercially, some of which, such as the
ethers, have found interesting industrial applications but are not
Ice Cream Stabilization
has found an important application as a primary stabilizer in ice cream
because of its unusual swelling and water imbibing qualities, as well
smooth meltdown and excellent heat shock resistance it imparts to the
manufacture of soft cheese, locust bean gum speeds up coagulation,
the yield of curd solids by as much as 10%, and makes separation and
the curd easier. The resulting curd has an excellent soft and compact
and the separated whey is limpid. The finished cheese has an excellent,
resilient body and texture. It is also more homogeneous, and exudation
from fresh cheese is reduced. These improved properties are believed to
to the buffer function of the acidified locust bean gum solution, which
a protective colloid and maintains a constant pH in the finished cheese.
and melted cheese products can be prepared from very soft cheese having
water content. The incorporation of locust bean gum ties up the water
results in a firm, spreadable texture and a highly homogeneous product
quality. It is even possible to add water to the cheese products if
The gum, usually used in a concentration of about 0.6%, is mixed with
ingredients, homogenized, pasteurized, and packaged in a stable form.
that locust bean gum improved the baking characteristics of spray dried
cheese products made with acidified milk cream combinations.
has been used in the manufacture of processed meats such as salami,
and sausages, where it acts as a binding and stabilizing agent and
more homogeneous product of improved texture and quality. It also has a
lubricating effect on the meat mix, facilitating extrusion and
stuffing. Due to
its water retention properties, locust bean gum reduces loss of weight
meat products in storage. Locust bean gum has also been used as a
canned meat and fish products.
preparation of synthetic meat products, locust bean gum has been used
important additive to contribute specific properties of meatlike
Protein food products simulating the nutritional and textural
of meat were prepared from plant proteins extracted and isolated by
patented methods. The eating qualities of these chewy protein gels were
beneficially modified by the incorporation of locust bean gum as an
additive to impart the essential meatlike chewiness.
used to supplement flour in the manufacture of bread and other leavened
products, produces doughs with constant functional properties and good
characteristics. Higher yields are obtained and the baked products have
textures, are much softer, and have a longer shelf life.
gum to cake and biscuit doughs also gives higher yields and a
saving of eggs. Further, the cakes and biscuits are softer and have a
shelf life. The cakes have a firmer texture, are easily removed from
pans, and are cut or sliced without difficulty.
investigated the effect of periodic acidoxidized locust bean gum on the
and baking characteristics of wheat flour. It was assumed that the
of reactive groups (aldehydes) into the polysaccharide molecule would
further reaction with flour proteins, leading to an increase in the
and rigidity of the dough. Locust bean gum, with, degrees of oxidation
from 10 to 100% of theoretical, were incorporated into wheat flour at
0.1 0.5% of flour weight. Dough properties were measured on the
Extensograph, and bread baking tests were also made. At a certain
level, the oxidized locust bean gum distinctly improved the dough
extensibility and resistance of the doughs could be manipulated to give
which from experience, are considered to be brought about by flour
Neukom and Deuel concluded that these modified polysaccharides react
flour constituents, and that the improving effect is enhanced as the
oxidation is increased (i.e., as the number of aldehyde groups
the polysaccharide is increased).
bean gum has been found to be a very satisfactory stabilizer for canned
and berry apple pie fillings. In frozen pie fillings, it has also
satisfactorily in conjunction with certain starches. Carlin also
use in stabilizing meringue toppings for pies in order to increase
dietetic foods, locust bean gum has often been used for various
Arobon, a locust bean gum preparation, has been added to infant diets
treatment of diarrhea. Martins suggested using locust bean gum
an additive at 0.25 0.50% levels in fresh or dried milk in order to
the product viscosity, thus giving the consumer a higher degree of
without increasing caloric content.
locust bean flour to be an effective antioxidant for butterfat when
ghee (processed butter) at levels of about 0.5%. It was believed that
exerted a synergistic effect upon the natural antioxidants in the
locust bean gum to stabilize citrus juice products, i.e., to maintain
natural cloudiness of the citrus fruit beverages, or at least to make
longer. Recommended use levels for this application in citrus beverage
concentrates were about 1 30 ppm locust bean gum, preferably in
with 20 400 ppm sodium hexametaphosphate.
bean gum in preparing a base material for frozen desserts and
base material, which was capable of floating on water, was a mixture of
tasting edible oil, sugar, locust bean gum, and propyl 3,4,5
in the form of a solid, aerated slab. Another aerated dessert,
Mancuso, was based on gelatin, with locust bean gum or guar as an
mixture of gelatin, locust bean gum, partially degraded soy protein,
an organic acid forms an aerated, flavored, chiffon type of gel dessert
and whipped in hot water, and then allowed to set.
bean gum continues to be
used as an effective thickening agent in salad dressings and various
Guar gum is
derived from the seed of the guar plant. Cyamopsis tetragonolobus, of
Leguminosae family. This plant has been grown for thousands of years in
and Pakistan where it is a most important crop that has been long used
for humans and animals. Some guar seeds have even been found in a
excavated tomb of an ancient Egyptian pharaoh.
was well known in Asia, it was not introduced into the United States
when it was evaluated as a possible cover crop in the Texas, Arizona,
California areas by the United States Department of Agriculture.
little interest was shown at the time, and until the advent of the
War, very little headway was made in the cultivation of the plant in
country. At that time supplies of locust bean gum, which was widely
used in the
paper and textile industries and usually imported from Europe and North
became more and more limited and difficult to get. Therefore,
groups, made a concerted effort to find a domestic plant that could
provide a substitute
for locust bean gum. This search led to the reexamination of guar gum,
was found to be the best answer to the problem.
of its extensive milling experience, General Mills undertook a study of
with respect to: (1) agricultural production of the plant in the
milling, and (3) adaptation of the product to industrial requirements.
not until 1953, however, that the gum was produced in commercial
Stein, Hall & Co., as well as General Mills, built plants in
States for domestic production of guar gum, and some time later, the
producers of locust bean gum also began to process guar gum.
is a pod bearing, nitrogen fixing legume. The seeds of the plant are
of the hull (14 17%), germ (43 47%), and endosperm (35 42 %). In the
manufacture of guar gum, the endosperm must be separated as cleanly as
from the hull and germ. In practice, there are several methods for
accomplishing this. The
hull can be
removed by treatment with sulfuric acid to loosen it, by heating and
the hull by flame treatment, or by mechanical grinding and sifting.
hull is removed, differential grinding is used to separate the germ.
endosperm and germ can be separated in this manner because of the
hardness of each constituent. After the endosperm is separated from the
and germ, it is ground to a fine particle size and sold as guar gum.
trade names are often used for guar, such as Jaguar, Supercol, and
locust bean gum, is a galactomannan. But there are significant
their chemical structures and properties. Guar is structurally composed
straight backbone chain of D mannopyranose units with a side branching
D galactopyranose on every other unit. Locust bean gum differs in this
branching structure by having an average of one D galactopyranose unit
on every fourth D mannopyranose unit (Fig. 1). The greater branching of
believed to be responsible for its easier hydration properties as well
greater hydrogen bonding activity. Guar gum has an average molecular
the range of 200,000 300,000.
is derived from the Greek phctoV meaning to congeal or solidify. The
chemical compound was discovered by Vauquelin in 1790, but it was not
characterized until Braconnot first described it as the principal
of fruit and gave it the name pectin. Braconnot understood that pectin
substance that gave fruits the ability to form jellies when boiled with
He also recognized that sugar and the proper pH were necessary for the
reaction, and he mentioned that he had to add a small amount of acid
or sulfuric acid) to break up the pectates when making his jellies.
work on pectin, a great deal of scientific research was done during the
century from both the chemical and biological points of view.
As a result
the vast amount of confusion that had been created over the years by
investigators in the field, the American Chemical Society finally
standard nomenclature for these materials in 1927. The standard was
revised and broadened in 1944. Pectin was then defined functionally as
pectinic acids capable of forming the standard type of fruit jellies
and acid were present in the correct proportions.
definitions adopted at that time and still in use today are as follows:
substances are those complex colloidal carbohydrate derivatives that
or are prepared from, plants and contain a large proportion of
anhydrogalacturonic acid units, which are thought to exist in a
combination. The carboxyl groups of polygalacturonic acids may be
esterified by methyl groups and partly or completely neutralized by one
the water insoluble parent pectic substance that occurs in plants and
restricted hydrolysis, yields pectin or pectinic acids.
are the colloidal polygalacturonic acids containing more than a
proportion of methyl ester gropps. Pectinic acids, under suitable
are capable of forming gels in water with sugar and acid, or, if
in methoxyl content, with certain ions. The salts of pectinic acids are
normal or acid pectinates.
pectins) are those water soluble pectinic acids of varying methyl ester
and degree of neutralization and are capable of forming gels with sugar
acid under suitable conditions.
term applied to pectic substances composed mostly of colloidal
acids and essentially free from methyl ester groups. The salts of
are either normal or acid pectates.
is the enzyme that converts protopectin into a soluble product. It has
been called pectosinase and propectinase.
(PE), or pectinmethylesterase, is the enzyme that catalyzes the
the ester bonds of pectic substances to yield methanol and pectic acid.
name pectase does not indicate the nature of the enzyme action and has
way to these more specific names.
(PC), or pectin polygalacturonase, is the enzyme that catalyzes the
of glycosidic bonds between de esterified galacturonide residues in
substances. Pectinase is frequently used to designate the glycosidase
as pectic enzyme mixtures.
substances, which are all modifications of galacturonic acid polymers,
differentiated by the degree of methoxyl substitution
the current accepted industry practice. Thus, Bender groups commercial
into five distinct categories according to their degree of methylation
(1) 30 DM pectin for low sugar gels (2)
45 DM pectin for rapid setting, calcium precipitatable pectin suitable
sugar gels and emulsions (3)
60 DM or
slow set pectin for high sugar gels and confectionery jellies (4) 74 DM for typical rapid
set pectin for
jams and jellies (5)
higher DMs for
special purpose applications.
however, prefer a simpler, though arbitrary, classification of gelling
into three groups: (1) rapidset, (2) slow set and (3) low methoxyl. The
lines are not sharp, and the distinction between the three groups seems
related to their solubility and degree of esterification (DE): (1)
pectin 70% DE or higher (2)
pectin 50 70% DE (3)
low methoxyl pectin
–50 % DE or lower.
even simpler classification,
which is preferred and used herewith by the author, is to consider just
types of pectin: (1) regular pectins which require sugar and acid for
and (2) low methoxyl pectins which have methoxyl contents below 7% and
calcium for gelation.
Function in Plants
substances, in combination with cellulose and starches, are structural
components of all green land plants. Although they are found mainly in
and vegetables, traces have also been discovered in cereals where their
contribution to structure is of minor importance.
substances are integral components of the cell structures and function
cementing substances in the middle lamellae. They are present in the
stages of molecular development and transformations, which are
dependent on the
specific morphology, and taxonomy of the plant as well as the stage of
and maturity. The chemistry and interrelationship of these materials
pectinic acids, pectic acids) are still not completely elucidated and
continues to be the subject of continuing research by many scientific
all parts of the world.
pectins in fruits and vegetables is primarily concerned with the
form and firmness of the plant. Pectins also seem to play a role in the
of the movement of water and plant fluids through the rapidly growing
The action of pectins as intercellular substance in plants is similar
action of intercellular substance of animals, e.g., collagen, the
gelatin. Protopectin, the water insoluble precursor of pectin, is
immature fruit tissues. The normal process of ripening and maturing
hydrolytic changes of protopectin to form pectin, followed after
enzymatic demethylation and depolymerization of pectin to form pectates
eventually soluble sugars and acids.
manner, nature has provided not only enzymatic means for pectin
plants but has also provided the human digestive system with a somewhat
enzymatic mechanism to digest the pectins normally ingested as a part
natural fruitstuffs. This ease of digestibility of pectic substances is
different from that observed for the hydrocolloids derived from natural
and sea plants. Most of the gum exudates from trees or bushes have an
aldobionic acid nucleus for the gum structure that is very difficult to
down. The seaweed extracts also consist of gel forming polyuronides
complex nuclei that are very resistant to hydrolytic breakdown. The
substances, on the other hand, can be broken down quite easily by
pectins of fruits at very early stages of growth are almost completely
methylated and have a very high molecular weight. As growth proceeds
fruit matures, pectic enzymes are believed to attack the pectin and
it into smaller polymers with lower methoxyl contents, higher carboxyl
contents, and lower molecular weights. As the fruit continues to mature
catabolic process continues. Commercial pectin is usually extracted
pectin still has a relatively high methoxyl content and molecular
complex heterogenous structure, is composed chiefly of
having a wide variety of molecular weights. Some of the carboxyl groups
esterified with methyl alcohol, some are neutralized with cations, and
free acids. In addition to variations in its molecular weight and
content, pectin may also vary with respect to the distribution of ester
along the chains. Small amounts of acetate and other groups are also
attached to the molecule.
molecule consists of D galacturonic acid units in pyranose
together by a 1, 4 glycosidic linkages. In nature, the carboxyl groups
partially methylated to form the ester known as pectin. In addition,
secondary hydroxyl groups may be partially esterified by acetic acid.
degree of esterification in natural products may vary within a wide
macromolecules may be changed by saponification or esterification. The
configuration and relationship of the basic pectic acid molecule to
and alginic acid is shown in Fig. 1.
of the pectic substances depend greatly on their molecular weight and
degree of substitution. Properties such as water solubility, viscosity,
coagulability, gelling tendency, and stability toward enzymes change
with increasing degree of esterification. These changes can be
explained by the
alteration of the electric charge and the form of the pectin
Solubility of pectin decreases with an increase in chain length and
decrease in methoxyl groups.
pectin solutions depends on several factors, namely, the DM of the
concentration, temperature, pH, and presence of salts and their
Decreasing the concentration or the grade of pectin increases the
would be expected. Temperature changes decrease the viscosity in a
manner. However, if alkaline earth salts are present in pectins of 60
lower, the decrease might be larger than expected.
Effect of pH
sufficient pectin and sugar are present in the system, no gel will form
the pH is reduced below the critical value of about 3.6 known as the
pH value. Most slow setting pectins give optimum performance at pHs
and 3.2, while rapid setting pectins perform best in a range of 3.0
effect of pH is not entirely predictable, since it depends upon the DM
salts that may be present. The tendency of a 30 45 DM type of pectin to
would be decreased by a change in pH and prevented by lowered pHs.
dispersions of pectinic acids free of alkaline earth salts will
viscosity and finally gel at very low pHs.
added alkali metal salts such as sodium chloride is also not very
The salt effect depends on the amount of salt, the type of pectin, and
of the solution. Small amounts of sodium chloride (as low as 0.6%) will
a great increase in viscosity or gelation of a 0.8%, 40DM pectin
the pH is 2.9. But the viscosity will be decreased at a pH of 4.4. At
higher pHs (about 6) salt effects are minimized if phosphates are also
It is believed that viscosity is solely dependent on the length and
Effect of Calcium Salts
calcium salts on pectin viscosity are very important. These effects
show up as
an increased viscosity even for pectins of 75 DM or higher, and show a
viscosity at pHs of 8.55. The viscosity increasing effect of added
increases sharply as the degree of methylation decreases, thus freeing
carboxyls for cross linking of the chains by calcium ions. The
viscosity is very evident at 60 DM and becomes greater as the DM
until it reaches a maximum of 80.
can be stated that pectins of the same type can be compared with
viscosity when they are in solutions of the same grade, pH,
salt content. Viscosities of different pectin types can also be
even small variations in pH or salt content of the media can noticeably
the final viscosities.
Low Methoxyl Pectins
pectins, as opposed to regular pectins, do not require sugar for gel
and are also not as sensitive to pH. On the other hand, they are
divalent metallic cations such as calcium.
Effect of Cations
ions can react with carboxyl groups from adjacent pectinate chains to
gel network. This ionic cross linking by normal valence forces of
can be slowed down temporarily by such monovalent ions as sodium which
react with the free carboxyl groups. Usually, the effect of such ions
curtail the cross linking reaction of calcium and to improve the
low methoxyl pectin in the presence of calcium. Sometimes a better gel
when salts such as sodium citrate are present in low concentrations.
pectins can form gels without the need for sugar, but the presence of
amounts (10 20%) of sugar tend to impart desirable textural properties
gels. High concentrations of sugar (60% or higher) interfere with gel
because the dehydrating effect of the sugar favors hydrogen bonding and
decreases cross linking by ordinary valence forces. It is therefore
to determine the optimum sugar level for any specific gel application.
pectin gels can be prepared within a comparatively wide pH range. Good
gels can be made at pHs up to 6.5, while fruit or vegetable gels can be
pHs as low as 2.5. The practical and most desirable range for most
dessert gels is 3.2 4.0. Regular pectin gels have a limiting pH near
3.5 above this,
gels cannot be formed.
an important factor in the formation of low methoxyl pectin gels. Low
pectin will form gels that are much more stable at much higher
than can be made with other gelling systems such as gelatin. The
gel formation and the stability of the gel will depend upon the initial
composition. Gels made with high concentrations of pectin, such as
aspics, will form and be stable at temperatures of 120 150°F, while
low levels of pectin are not stable at temperatures above 100°F.
pectin has the unique property of dispersing in water to form a viscous
colloidal sol, which will gel in the presence of appropriate
sugar and acid. The structure of these pectin sugar acid gels is
different from that of gelatin, and indeed, the mechanism involved in
gel formation is also quite different.
belong to a major division of the plant kingdom, are composed of those
bearing plants that contain photosynthetic pigments. The plants, which
in size from single cells to giant conglomerates, all share a common
feature in the absence of a vascular or food conveying system. Since
must be submerged in the medium from which they acquire their food,
found in ponds, lakes, and streams and in the salt seas and oceans
attain maximum size. The larger forms of these plants are known as
although they are not really weeds, but flowers of the sea as the poets
millenia of evolution, several parallel evolutionary branches of these
algae developed, each branch using different pigment systems for
photosynthesis. The largest and most numerous forms are the two major
comprising the red and brown algae, while the smaller groups consist of
green and blue green algae, which are confined, in general, to fresh
contain structural substances that hold the various cells together and
form a large proportion of the plant weight. These substances are
hydrocolloid polymers composed of sugar units. In land plants, neutral
such as cellulose and hemicellulose are the major components, while in
plants, the structural polymers are the more flexible, negatively
or Rhodophyceae, contain predominantly red pigments and are the source
several important hydrocolloids, namely agar, carrageenan, and
of which are polymers of galactose. The second important group is the
Phyophyceae, or brown algae, which contain predominantly brown
largest and most numerous of the brown algae are commonly referred to
inclusive term kelp, a term generally reserved for those forms growing
masses such as the floating giants of the Pacific coast.
hydrocolloids of the brown seaweeds are the salts of polyuronic acids
(mannuronic and guluronic acids). The soluble salts of this polymer,
sodium salts, are generally referred to as algins. Any salt of the
an alginate, while the organic salts or esters are called algin
seaweed species that are used for the production of commercial seaweed
are shown in Table 1. These are not all inclusive, and undoubtedly
botanical species are often used, but in general, these specific types
and brown algae form the basis of the industry today.
of seaweeds for food and medicine can be traced as far back as 3000
Shen Nung, a famous oriental physician used the plants for their
value. Later, in the time of Confucius the food uses of seaweed were
the Chinese Book of Poetry, which extolled a housewife who cooked
doubt that agar was the first seaweed hydrocolloid isolated as an
the parent plant. It had been known in oriental countries for ages and
in the form of a sweetened, and sometimes flavored, gel. The use of
foods and the extraction of similar gel forming seaweed extracts, were
spread through the Orient and the western Pacific areas by the various
migrations of the Chinese and Japanese. In areas such as Indonesia and
Philippines, the native weeds were exploited in a similar manner by the
inhabitants, and a great deal of intercultural applications of the
were developed as evidenced by the host of colloquial names still in
similar seaweed extracts.
world, the seaweeds utilized were those found off the coasts of Europe,
and North America and were mainly the carrageenan bearing red seaweeds
algin bearing brown seaplants.
many respects, was to the Occidentals what agar was to the Orientals.
It was known
for many years in the seacoast areas of Ireland, Great Britain, France,
and other European countries. And its vernacular name, Irish moss is
indicative of its origins in the coastal Irish town of Carragheen
current name carrageenan is derived.
of the carrageenan seaweeds to these various geographic communities is
difficult to assess. Although they have been used locally for
centuries, it was
not until the nineteenth century that they became an article of
it has only been in modern times that they have been extracted as a
hydrocolloid. Prior to this carrageenan was eaten as a whole plant or
indirectly by the housewife who wanted to make a pudding of the blanc
type. During the Irish potato famine in the middle of the nineteenth
these Chondrus crispus seaweeds were used to make a not very nourishing
alginate first became a commercial product due to the perspicacity of
English chemist, who observed that the viscous fluid found in the
sacks on the surface of kelp plants was a unique substance of
properties. Although his initial commercial venture was not successful,
Stanford had sown the seed of a new industry. Today alginate products
manufactured in various parts of the world and are standard commodities
most recent seaweed hydrocolloid to achieve commercial importance in
industry, was a result of the search for agar substitutes during World
As the story goes, a barber in Denmark was investigating various kinds
seaweeds in an effort to make a permanent wave liquid product. He found
the seaweed Furcellaria fastigiata, which is found off the coast of
gave a shiny, gummy material with good thickening properties. This
was commercialized. The extracts sold as Danish agar are now used in
quantities in the food industry.
ever growing realization that the sea is the last remaining great food
on earth, a great deal of research is being done to find new seaweed
of commercial use. Many plants and extracts are being studied, and
many new hydrocolloids will become available in the future for food
are quite different from higher plant forms because large amounts of
polysaccharides are accumulated in the cell walls or intercellular
nature of the polysaccharide sulfate from each alga is distinctive and
characteristic of each plant type and is useful for the classification
differentiation of the algae. For example, the polysaccharides of the
Rhodophyceae usually contain galactose as the D
as the D and L
enantiomorphs, often together with such
derivatives of each enantiomorph as the 3,6 anhydride, the 6 0 methyl
and/or various sulfate esters.
variation that has been consistently observed among red seaweed
extracts is in
ester sulfate content this may range from as low as 0% in the agarose
of agar to as high as 36% in carrageenan. The common red seaweed
the following amounts of ester sulfate:
their studies of the red algae structure have come to the conclusion
close relationship exists between many of these polysaccharides, and
same basic structure is common throughout many of these polymers. This
structure is, namely, a chain of galactose units linked alternately a
l,3 and b
1,4. This basic structure is modified by different algae to produce
variations on the same structural theme. They differ from each other in
either the D or L configuration, the 3,6 anhydro group, the ester
group, or by being methylated. These variations alone can yield
structures of these various seaweed gums become more accurately
begins to appear that all of the seaweed gums may be composed of a
of basic building blocks that form different types of polymers
according to the
type of plant and its stage of growth or development. This least common
denominator theory is being investigated by studies of enzymes which
exact specificities for the various building blocks in the molecules.
would appear that the sulfated galactans of the red seaweeds are a
related polymers, each with properties appropriate for a particular
growing in a particular environment.
the only important extract of brown algae at this time. It was
considered to be
primarily a polymer of anhydro l,4 ,b D mannuronic acid until Fischer
established the presence of L guluronic acid in the hydrolysis products
alginic acid. Based on this and other confirmatory work, alginic acid
currently regarded as a polyuronide comprising D mannuronic and L
acids, the relative proportions of which vary in different species of
blocks or molecular entities that have been isolated and identified in
commercially important seaweed extracts are shown in Table 2.
In spite of
Malayan name, agar agar is of Japanese origin and was first fully
Japan. According to Tseng, Chinese settlers in the East Indies
use of Japanese agar as a food to the natives. To avoid a Chinese or
name, they called it agaragar, a name used by the Malayans to indicate
seaweeds and the jellies made from them.
agar is called kanten, meaning cold sky. This name refers to the fact
material used to be prepared on cold winter days or high up in the
where it was always cold. In other areas it is also known as Japanese
isinglass, Chinese isinglass, vegetable isinglass, seaweed isinglass,
gelatin, bar kanten, square kanten, slender kanten, tungfen (frozen
and many other colloquial names common to specific geographic areas.
other Europeans living in Indonesia later learned to use this Japanese
for making fruit and vegetable jellies and seem to have introduced this
jelly making to their friends and relatives in Europe.
But it was
until 1882 that the world wide fame of agar was truly established when
Koch introduced the product into bacteriology as a culture medium. Koch
did not realize the importance of this discovery as a major technical
improvement, for in his famous experiments on the isolation of the
bacillus, he disposes of this new culture medium in a single,
sentence, So wachsen sie beispielsweise auf einer mit agar agar
Blutwaren hart bleibenden Gallarte, welche einen Zusatz van
Pepton erhalten hat.
credit for first using agar
as a culture medium rightly belongs to a housewife, Frau Fanny Hesse,
been using agar for years in her kitchen for the preparation of
had received the recipe from Dutch friends living in Indonesia. When
husband, Dr. Walther Hesse, complained about the difficulty of using
cultivating microbes, she suggested agar instead. His successful
was communicated to the famous Dr. Koch, who in turn, introduced it to
world. The rest is history. Today, almost a century later, agar is
best culture medium available. The gelling and colloidal properties
agar the excellent bacteriological medium are the ones that have been
in various food applications, as will be discussed later.
Collection of Agar Weed
agar bearing seaweeds are gathered from rocks between mid and low tide marks, or else
them from the sublittoral regions. In certain areas of Japan, the
seaweed by diving has developed into a unique industry largely carried
female divers. These diving, girls, known as amas, inhabit the Chiba
(province) along the seacoast. They are trained from early childhood to
for various seaweeds. The word ama originally meant the sea and was
calling the divers when the boats were full. These women operate from
boats, or even large wooden tubs, which are paddled to the collecting
There, they dive for the weeds and store them in the tubs or rafts.
sufficient material has been collected, the tubs are towed to shore by
women who swim with them. These bare breasted women develop an
chest expansion and lung capacity and would probably do well in
Hollywood if a
seaweed shortage should occur. They use no equipment except goggles and
in water depths down to 30 feet. In deeper waters, below 60 feet, male
equipped with diving apparatus gather the harvest. After the weed has
collected, it is dried on the shore and partly bleached. It is then
manufacturers for final processing. The deep water weed is considered
the best gelling extracts, and the optimum harvesting time is from
agar was produced by simply boiling seaweeds to obtain a jelly mass.
method of purification and preparation was discovered by accident.
to legend, it was in
the year 1658 or thereabouts that the Emperor of Japan and his royal
caught in a sudden snowstorm and took refuge in a nearby inn. The
Minoya by name prepared a dish of
seaweed jelly for his royal guests. The left over jelly was thrown
and it froze solid during the night. The next day, when the sun came
frozen jelly thawed and the watery part drained off, leaving a dry,
translucent substance. The acute innkeeper found that this residue
remade into a jelly by boiling it up with more water. The new jelly was
and of better quality than the original product.
was subsequently adopted by producers of agar. The process of purifying
seaweed extracts by consecutive freezing and thawing operations became
standard procedure that is still used in commercial practice today in
agar is manufactured essentially by hot water extraction followed by
for purification. Agar weeds appropriate to give a final product of
properties are blended in carefully predetermined proportions. The
weeds is soaked and washed with fresh water and then extracted by
water in open iron kettles or by pressure autoclaving in modern plants.
calcium hypochlorite or sodium bisulfate is introduced in order to
decolorize, the agar so as to obtain the lightest possible product. The
is filtered hot and the residue is re extracted one or two times. The
is allowed to cool, and when gelled, the solid mass is allowed to
naturally or is frozen by refrigeration. The frozen gel is allowed to
the impurities are drained off with the excess water. The gel is then
ground, and packed for shipment.
agar has been studied for many decades, primarily by Japanese
of whom have spent their entire professional lives in this area of
first to isolate agarose, and subsequent work by other workers led to
currently fairly well established opinion that agar is a mixture of at
two polysaccharides–agarose, a neutral polymer, and agaropectin, a
polymer. The ratios of these two polymers vary widely and the
agarose in agar bearing weeds can range from 50% to 90%. The two
components can be fractionated either by acetylation in chloroform to
soluble agarose acetate and an insoluble agaropectin acetate or by
precipitation of the agaropectin with quaternary ammonium salts.
know of no society in which fermentation has not been employed to make
more pleasant. The cave man discovered that meat allowed to age a few
after the kill was more pleasing to the taste than meat eaten
also learned that intoxicating drinks could be made from rotting grains
fruits. These two unconscious uses of the fermentation process, the
meat and the manufacture of alcohol were the first applications of what
is a vast science. To primitive man, fermentation was a type of magic.
not aware that he was using the natural activity of tiny living
as molds and yeast, to improve the taste and texture of his foods. But
knowing that these creatures existed, ancient man learned how to put
work. For thousands of years, the soy sauces of China, Japan and other
countries were made from fermented beans. For centuries, the Balkan
Europe enjoyed fermented milk or yogurt, while in Central Asia, the
tribesmen enjoyed an alcoholic beverage called kumiss, made from
or camels milk. The preparation of one of mans oldest foods, bread,
been used in some form virtually everywhere on earth, involves
fruit fermentation by which wine is made, was made so long ago that the
Greeks believed that wine had been invented by the god Dionysus. Beer
an ancient discovery, and a Mesopotamian clay tablet written about 500
B.C. tells that brewing had been a well established profession for
thousand years. Beer was also a commodity that the Babylonian Noah,
Utanpishtim, took on board his ark to make his trip more pleasant.
documents dating back to the Fourth Dynasty (about 2600 B.C.) describe
malting of barley and the fermentation of beer, and it is well known
Pharaohs enjoyed a cloudy, unreliable beer made in this fashion. A
beer, kiu, has been traced back to 2300 B.C. More recently, when
landed in Central America, he found that the Indians drank a beer made
middle Ages, experimenters learned how to improve the taste of wine,
beer, and cheese, but they had no idea that they were dealing with a
life too small to be seen by the naked eye. The true cause of
not understood until the latter part of the nineteenth century when
Pasteur arrived on the scene.
art to science, which was initiated by Pasteurs discovery that
brought about by living yeast cells, signaled the beginning of a new
in the last 100 years has wrought such miracles as the discovery of
streptomycin, and other antibiotics, as well as the food additives that
make our foods more nutritious and appetizing.
In the area
hydrocolloids, fermentation technology has also played an important
part in the
development of polysaccharide gums having unique functional properties
capable of making important contributions to the food industry.
polysaccharides can be roughly divided into two groups
heteropolysaccharides. The homopolysaccharides include those polymers
from sucrose by a variety of bacteria, of which the best known members
was first used to describe the slimy material formed in the juices of
beets, wine, and other sugar based food products. It was a well known
in the sugar industry because it sometimes clogged up the pipes through
sucrose containing juices and solutions were transferred. Pasteur
these slimes were caused by microbial action. Shortly thereafter,
found that dextran is a carbohydrate with the empirical formula
Since the material was closely related to starch and dextrin, he coined
name dextran for it. Later investigations showed that dextran can be
many microorganisms and is not a well defined substance with specific
properties. It is more accurate to refer to dextrans when no clear
of the bacterial origin and chemical properties of the substance are
Much work on these microorganisms was erratic due to the study of
preparations, but comparatively recently Hucker
classified the microorganisms
responsible for producing dextran from sucrose. The main dextran
bacteria belong to the Leuconostoc genus, species mesenteroides and
dextranicum, tribe Streptococceae, and family Lactobacteriaceae.
work isolated other strains of bacteria that are capable of producing
dextran materials. All of the species, however, have one common
in that sucrose is the only suitable carbohydrate source for the
the polysaccharide. The organisms can grow on any medium containing
together with a few inorganic salts and a suitable source of nitrogen.
number of microorganisms capable of synthesizing dextran, it was seen
of the factors determining the properties of the polysaccharide
the strain of the particular bacteria used. Likewise, the final
dextran obtained was closely related to the particular strain that
and it appeared that individual strains of bacteria have the ability to
over the years to the extent that the branches on the resultant
eventually become attached at points on the main chain different than
found originally. Most of the work with dextran has been conducted on
produced by various strains of Leuconostoc mesenteroides, which was
the designation B 512. Among the different types of bacteria that can
dextrans, the Leuconostoc mesenteroides strain has been most thoroughly
studied, and most scientific investigations are based on dextrans of
dextran depends upon dextran sucrase, an enzyme of the dextran
microorganism. This enzyme is active outside the bacteria cells and
the culture medium either through secretion or autolysis of the cells.
can therefore be produced either by the cultivation of these organisms
synthesis using the cell free enzyme extract. Only the first method has
used in large scale industrial production.
of dextran by cultivation of Leuconostoc mesenteroides is carried out
suitable temperatures and pH in a fluid medium containing sucrose,
substances necessary for the growth of the bacteria, and the buffer
which limits the pH displacement during fermentation.
takes place in two phases. First, the bacterial cells divide, releasing
dextransucrase into the medium. Second, the enzymatic polymerization of
units to dextran takes place. Gradually, as the dextran is formed, the
thickens into a tough, viscous mass. When the viscosity is greatest,
maximum yield is obtained, and the dextran is precipitated by the
methanol, ethanol, or acetone. The white, rubberlike precipitate is
and pulverized to give a white to slightly yellowish dextran
influence the type of dextran obtained are the following: (1) strain of
organism, (2) optimum pH of the synthesis, (3) incubation time, (4)
innoculation, (5) composition of the culture medium.
studies by Sloan have shown the dextran produced by B 512 to contain
(1®6) linked units of a D anhydroglucopyranose, and 5% of (1®3) linked
Van Cleve subsequently demonstrated that the B 512 dextran contained a
repeating segment of approximately 23 anhydro D glucopyranosyl units.
21 units are (1®6) linked, 1 unit is a branch (1®3) linked, and 1 unit
end group. About 80% of the external branches are only one D glucose
A typical structural segment is shown in Fig. 1.
weight of the polymer is dependent upon the fermentation medium. If no
or acceptor is present, the dextran formed has a molecular weight of
100,000,000. If a primer such as maltose is used, the dextran molecules
predominantly below 50,000 molecular weight. If a dextran primer of
is employed, the majority of the resultant dextran will have a
of 75,000±25,000, the preferred type for use as a blood extender.
polysaccharide, readily soluble in hot or cold water to give clear,
solutions. It is tasteless, chemically inert, and compatible with most
ingredients normally used in foods.
hydrocolloidal characteristics such as emulsifying and stabilizing
in oil water systems. It is also known for its humectant and water
qualities, and it imparts effective bodying attributes to liquid foods.
structure, due to its low degree of branching, affords a high degree of
stability to hydrolytic depolymerization, which makes it useful as a
blood plasma extender.
dextran, when ingested, is hydrolyzed slowly to form absorbable
which are utilized. This was shown by feeding tests on animals and
Dextran, given by mouth, produced a modest but sustained increase in
substances and liver glycogen. The evidence suggested that the
breakdown of dextran is not ascribable only to bacterial action, but
likely to an enzyme or enzymes present in the intestinal mucosa.
Baker reported that biological tests demonstrated that when dextran
a high proportion of a (1®6) linkages is included in a normal diet on a
regimen, gain in body weight is inhibited. Even though dextran is
assimilated without unfavorable effect on the human system, it appears
a (1®6) linkages are resistant to attack by bacteria and enzymes
present in the
gastrointestinal tract. This may suggest its use in low calorie foods
been proposed for use in a large number of industrial and medical
but the greatest use has been in medicine where partially hydrolyzed
have successfully been used as blood plasma extenders in the treatment
shock. For this application, a dextran possessing a molecular weight in
range of 50,000 100,000 is required, and a great deal of experimental
been done to produce dextrans in this range.
the incorporation of small quantities of dextran in yeast raised bread
containing both yeast and gluten produced breads that were softer and
greater volume and longer shelf life than ordinary breads made from
without dextran. The dextrans preferred were derived from Leuconostoc
mesenteroides and had molecular weights of about 20,000,000 40,000,000.
amount of dextran used ranged from about 0.01 10% by weight of the
contained in the dough. The addition of dextran to the doughs increased
water absorptive properties of the resultant dough and also made the
extensible by softening the gluten.
edible containers, such as ice cream cones, from dextran. The dextran
with sugar, milk, and water or oily plasticizer to give a mash that
molded and baked in the usual manner after forming.
dextran to replace 10 20% of the malt in the production of pilsener
dextran beers were reported to have good flavor and foam stability and
same color as pure malt beer. The carboxymethyldextran derivative is an
effective foam stabilizer when added to beer or other fermented malt
at about 0.5% concentrations.
used as a stabilizer for chocolate milk beverages. Mahoney also found
effective in the stabilization of the soft drinks and flavor extracts.
Likewise, Wadsworth found it to be useful in the production of
sugar syrups where stability and viscosity were important qualities.
has also been suggested for use as a bodying agent in low calorie,
described dextran as a desirable constituent for use in all foodstuffs
there is a sugar component. Its value was in its capacity to prevent
crystallization, improve moisture retention, improve body, and maintain
and appearance. It was effectively used in candies, fondants, jellies,
subsequently combined the entire sterile culture liquor of dextran with
syrup to prepare a noncrystallizing sugar syrup of exceptionally high
purified dextran sucrase to convert a sucrose solution enzymatically to
higher viscosity, fruit additive, dextran syrup, containing all the D
originally present in the sucrose molecule. The product had enhanced
and superior odor and flavor over that from the whole culture process.
Viscosity could be controlled by reaction conditions and by the
addition of the
employed for preserving a large variety of foods by preventing the food
drying out during storage and by protecting it against the deleterious
of exposure to air.
aqueous solution for dispersion of native or hydrolyzed dextran to
shrimp and other products. Similarly, other foods, such as meats, dried
and cheese, could be coated with a film of dextran, which protected the
against drying in storage, and yet permitted the product to vent the
aqueous dextran dispersions containing antibiotics as a preservative
for quick frozen foods, such as fish or spinach. The dextran film
the storage life and retarded decay during thawing by absorbing and
In a similar manner, Woodmansee and Abbott coated sub scalded chicken
parts with dextran to protect them against dehydration and skin
carboxymethyldextran derivative, Novak found it to be effective as a
fixative. Citrus oils emulsified in gelatin to prevent deterioration
protected against insolubilization of the gelatin by incorporation of
1% of carboxymethyldextran. In a related fashion, coating monosodium
crystals with carboxymethyl dextran offers protection against potency
agglomeration of the granular material.
the use of dextran as a conditioner in chewing gums as well as a
ice cream products. It could also be used in the manufacture of
synthetic creams. In general, dextran could replace, in whole or in
gums as gum arabic, karaya, locust bean gum, tragacanth, or alginates.
B 1459 (Xanthan Gum)
work on the fermentation of sucrose to produce dextran (B 512) led to
efforts by the Northern Utilization Research and Development Division
other microbial polysaccharides that might be industrially useful. They
particularly interested in using glucose (corn sugar) as a fermentation
since one of the functions of the Northern Regional Laboratory at
Illinois, was to find new uses for the agricultural crops in that area,
which corn was a major one.
were quite successful in achieving their objective. One new gum,
B 1459, had such interesting properties that several industrial
investigated the possibility of commercializing it. The Kelco Co.
it commercially under the trade names Kelzan (industrial grade) and
(food grade), while Archer Daniels Midland Co. carried it through
development stages as Product 7097 and patented an improved biochemical
for synthesizing it. Two other large companies, Eli Lilly & Co.
Commercial Solvents Corp., also explored the commercial potential of
material for food, drug, and cosmetic applications, but apparently the
did not go into production. The Jersey Production Research Company
gum to be a very effective water and brine thickening agent for oil
drilling operations and developed a new and novel process for making it.
epigraph aptly describes one of the most popular and widely eaten
foods gelatin desserts. The shimmering, tender texture and brilliant
a quality gelatin dessert have widespread esthetic as well as
appeal to a broad majority of consumers. And the properties of gelatin
lend themselves to the preparation of such gelled food products are
cannot be exactly duplicated by any other hydrocolloid. This has given
a tremendous advantage in the area of packaged dessert mixes, so that
majority of gelatin produced in this country is used in dessert foods.
defined in the Pharmacopeia as a product obtained by the partial
collagen derived from the skin, white connective tissue and bones of
The fact that gelatin is obtained with ease and in relative purity from
abundant starting material probably has much to do with the fact that
become the classic protein of colloid chemistry, and has been the
subject of an
enormous amount of experimental work.
Of all the
common natural hydrocolloids, gelatin is the only protein of
largely because of its novel gelling and thickening properties.
advances in technology, other protein gums are becoming subjects of
for the hydrocolloid chemist. The most important of these are the soy
which, like gelatin, also have interesting and exploitable gelling,
and other colloidal properties. Egg albumin, a relatively old protein,
given new functional properties, which permit its use in a much wider
of foods. In addition, the milk protein caseinates have been found to
effective emulsifying and stabilizing proper properties, while cereal
make excellent whipping agents.
gelatin is by far the most important protein hydrocolloid, this chapter
limited to gelatin.
from the Latin verb gelare meaning to congeal, has been known for
years. The extraction of glue by cooking hides dates back at least to
of the ancient Pharaohs of Egypt. Bogue cites a 3000 year old stone
found in the ancient city of Thebes and belonging to the period of
III, which describes the gluing of a thin piece of rare red wood veneer
yellow plank of sycamore.
Roman era, Pliny, Lucretius, and others referred to the manufacture of
Pliny wrote, Glue is cooked from the hides of bulls. Elsewhere in his
he referred to glue, which had been mixed with gums, milk, eggs, and
wax as a
vehicle for paints, used by the ancient Egyptians. Much later, in the
Elizabethan period, Shakespeare and Bacon made frequent references to
their writings. Indeed, a commercial glue industry appears to have been
established in England about 1700. A similar industry developed in the
States within the following century.
years of the Napoleonic era, gelatin was manufactured on a large scale
attempt to alleviate the food shortages resulting from the English
blockade of Europe. The first manufacture of edible gelatin is credited
Arney, who was granted a patent in 1846 for the preparation of a
gelatin for forming compositions from which may be prepared jellies and
manges also, when
mixed with falina, or
starch, or starchy vegetable flour, for thickening soups, gravies, etc.
present, gelatin is manufactured in the United States by at least
companies in the amount of about 60 70 million lb annually.
means glue producing material, is the principal protein component of
connective tissues, which serve as the major stress bearing elements
mammals and fishes. Although much of the collagen is located in major
such as skin, tendon, and bone, collagen fibers pervade almost every
tissue. Collagen is unique among proteins because of its unusual amino
composition. It owes its distinctive structure to its high content of
cyclic amino acids, proline and hydroxyproline. In addition to these
collagen also contains large quantities of glycine and alanine, the
nonpolar amino acids with short side chains.
It is now
believed that proteins consist of long chains of amino acids connected
their a amino and a carboxyl groups to form peptide linkages
be either stretched out or folded. Additional bonds, between adjacent
between adjacent parts of the same chain after folding, become a
of the structure and stabilize the functional protein configuration.
collagen polymer unit, sometimes called tropocollagen, is thought to
three helical polypeptide chains wound around each other to form a
which behaves as a firm, rigid rod. Recent work indicates that
source, collagen has a molecular weight of about 350,000, a length of
and a diameter of about 14Å. As shown in Fig. 1, it has now been
that two types of bonds contribute to the secondary and tertiary
collagen: (1) intramolecular cross links existing between the
of the collagen molecules, and (2) intermolecular cross links.
collagen fibers are capable of undergoing considerable mechanical and
changes, which may vary from reversible swelling and partial, melting
irreversible disorganization of the entire structure. But all these
occur without solubilization of the fiber.
Transformation of Collagen to Gelatin
water soluble product of the dissolution or degradation of water
collagen fibers. The transformation or transition of collagen to
gelatin is the
process whereby the highly organized, quasi crystalline, water
collagen fiber is transformed from an infinite assymetric network of
tropocollagen units to a system of water soluble, independent molecules
much lower degree of internal organization. Since the original collagen
structures are not all the same, and since there are many paths by
structure may be broken down, there are obviously a great many
gelatin formed by the destruction of collagen.
configuration of the collagen macromolecule can be broken down by
collagen solutions in acid to about 40°C. The transition is sharp and
within a few minutes over a small temperature interval, and the
molecule falls apart in one of three ways, as shown in Fig. 2.
If there are no additional
restraining bonds between chains, three randomly coiled single strand
chains result (Path 1). The three chains, known as a chains, are not of
identical composition and probably not of equal molecular weight.
In those cases (Path 2) where
two chains are joined by one or more covalent cross linkages,
leads to the appearance of two particles, one an a chain and the other
a two stranded
molecule with approximately twice the molecular weight of the a chains.
stranded b component may be composed of two similar or two dissimilar a
The weight distribution would be 67% b and 33%a.
In the final case, it can be
assumed that at least two covalent cross linkages hold the three chains
together. The disordering process (Path 3) melts out and removes all
secondary structure, but the three chains cannot separate and remain as
in solution. This three chain structure is called the g component.
that there is no reason why every molecule of tropocollagen should have
same number of identically disposed intramolecular cross linkages, and
is most reasonable to assume that any given preparation is
respect to the degree of intramolecular polymerization. The ideal
the collagen monomer to gelatin is therefore the one via Path 1. The
molecular weight of the gelatin system should be one third the
of the collagen monomer, and the weight average molecular weight should
slightly higher due to the nonidentity of the chains. The best values
collagen monomer molecular weight are substantially above 300,000, and
the minimum molecular weight of the parent gelatin must be greater than
100,000. Reports of lower molecular weights for gelatin probably
peptide bond hydrolysis was a factor in those studies. Reports of the a
having molecular weights of about 80,000 are not consistent with recent
on acid soluble collagen.
can be assumed that native collagen fiber is an ordered array of
tropocollagen rods, staggered by approximately one fourth of their
tropocollagen rod is composed of three chains of a character but
different chemical composition, and may contain intra tropocollagen
to produce the b sub unit of two chains or the g units with bonds
of the three chains. All g units may not be of the same degree of
intramolecular polymerization and may in addition be bonded together
interunit cross linkages to form g polymers.
Manufacture of Gelatin
The bulk of
gelatin manufactured is derived from three basic sources and consists
types of finished gelatin product. Type A gelatin is derived from acid
materials, primarily pork skin. Type B gelatin is derived from
lime processed, materials, primarily cattle hides and bone (ossein). In
a substantial quantity of type A gelatin is made from ossein.
Pig Skins. One of the major
sources of gelatin in the United States is pig skins. They are frozen
after removal at the meatpacking plants and delivered to the gelatin
refrigerated cars. Since some of the fat remains on the skins, it is
to process these by acid pre treatment in order to avoid forming a
emulsion that would make extraction of the gelatin extremely difficult.
Cattle Hides (Tanners Stock).
These are calf or cattle hide trimmings not usable for the manufacture
leather. The whole hides are shipped to tanners and the trimmings from
hides in various stages of the process, before actual tanning, are used
Ossein (Bone). Although this
is one of the best known gelatin raw materials, it is the one least
used in the
United States. Ossein is the residue of dried cattle bones remaining
pre treatment to remove the calcium phosphate. Even though ossein is a
expensive raw material, if properly processed, it makes an excellent
for photographic use and one that can command higher prices.
of gelatin is shown in the flow diagram in Fig. 3. In general, all
manufactured by one of the two following processes or modifications
Processing (Type A)
is usually based on the use of pig skins and ossein, and the most
commercial acid process in the United States is the preparation of
gelatin from, frozen pig skins. The pig skins are thawed, washed in
and soaked in approximately 5% solutions of inorganic acids. This
process hydrates and swells the skin without causing appreciable
acid, sulfuric acid, phosphoric acid, and sulfurous acid are the most
frequently used acids. The acid soak usually takes 10 30 hours, after
supernatent acid is removed and cold water is used to wash away the
and raise the pH of the soaked skins to about pH 4. Most of the
proteins have isoelectric points in the pH 4 5 range and are thus most
coagulated and removed. The acid conditioned skins are then subjected
to a series
of hot extractions where the two variables are time and temperature.
initial extraction (first run) is carried out for the longest time at
lowest (about 60°C) temperature. The temperature is raised about 5 10°C
successive extraction and five to ten extractions may be made. In
gelatin made from the first extract excels subsequent extracts in gel
and each run is kept separate and blended later to match various
gelatin extract is pressure filtered and concentrated by vacuum
The warm concentrated solution is then cooled almost to its gelling
poured onto a belt conveyor, and immediately conveyed into a
chamber where it is chilled rapidly until it gels. Upon emerging from a
refrigerator chamber as a continuous sheet, it is cut into suitable
placed on wire frames, which are then placed into a drying room or
tunnel, where the temperature is carefully controlled. Continuous
now in use where both temperature and humidity are controlled. The rate
drying is closely regulated to avoid melting or surface dehydration.
moisture has been reduced to approximately 10%, the gelatin is removed
ground or pulverized to form the final product. Each batch of dried
graded and stored separately. Gel strengths and viscosities are the
for grading and the different grades of gelatin are blended to give a
product with the desired specifications.
Processing (Type B)
initially demineralized with dilute acid to remove the calcium salts,
particularly the phosphate, and then both the ossein and cowhides are
in a similar manner. The raw collagen stock is washed and thoroughly
in cold water in large tanks or pits. Excess water is drained and lime
in sufficient amounts so that when fresh water is added a saturated
calcium hydroxide is formed. An excess of calcium hydroxide must be
to make up for the amount consumed in the conditioning reactions. The
left in the liming pits for periods of 3 12 weeks or longer, depending
nature of the stock, ambient temperature, type of operation, alkalinity
lime liquors, etc.
treatment removes most of the extraneous albuminoids such as globulins,
mucopolysaccharides, albumins, as well as carotenes and various other
After liming is complete, the lime is washed from the surface of the
running water for a day or so. The residual base is then neutralized by
with dilute hydrochloric acid until the collagen is deplumped, or until
becomes limp and flaccid. At this point, the collagen has a pH of 5 8
ready for conversion to gelatin.
stock is then loaded into extraction kettles and gelatin is extracted
series of cooks at successively higher temperatures. The highest
gelatins are obtained in the first few extractions and the liquors from
cook are filtered, concentrated, and dried separately as for the Type A
gelatins. Again, the overall balance of viscosity and gel strength for
particular quality of gelatin is usually achieved by blending gelatins
several different extractions.
gelatins have similar functional properties, there are differences
Type A and Type B gelatins, which are important in the selection of the
appropriate gelatin for any specific application. These differences in
properties are shown in Table 1 and will be discussed in more detail in
of 19 amino acids joined by peptide linkages to form long polymer
gives a typical protein reaction and may be hydrolyzed by any of the
proteolytic enzymes to yield its constituent amino acid or peptide
Gelatin is not a nutritionally complete protein in that it is lacking
essential amino acid, tryptophan. However, it contains a small amount
rare amino acid hydroxylysine. Gelatins from different sources may
small variations in amino acid composition, as shown in Table 2.
in chemical structure between the Type A and Type B gelatins produce
differences in the physical properties, including the isoelectric and
amphoteric substance, i.e., one that has both acidic (carboxyl) and
(amino, guanidino) groups. The overall charge of the molecule depends
pH of the solution and other ions present. The pH at which the
both the acidic and basic groups are equal is called the isoionic point
At this point, the net charge is zero. If electrolytes are added to the
solution, this point may be shifted to a new pH. This new pH, known as
isoelectric point (IEP), is defined as the pH at which gelatin
molecules do not
migrate in an electrical field (because they are neutrally charged at
point). In some cases, the pI and the IEP are identical.
gelatin varies with the type of raw material and the method of
Type A or pork skin gelatins contain small amounts of chloride, while
gelatin contains principally calcium phosphates. The J.P. limit on ash
but most commercial gelatins have lower ash contents.
of gelatin is rigidly controlled, and the presence of such materials in
gelatins is unlikely unless impure acids or chemicals are used in the
of manufacture. The D.S.P. limit for arsenic is 1 ppm and for heavy
ppm. Most gelatins meet these requirements without difficulty.
Sulfur Dioxide Content
sulfur dioxide gives hard gelatin capsules an increased transparency,
brilliancy, and improved stability all qualities that are desired in
manufacture. The J.P. permits not more than 0.004 % sulfur dioxide in
cases, but for gelatin used in capsules, as much as 0.15 % is
However, these are special grade gelatins that are not used in normal
hydrocolloids in foods has until very recently been the story of
materials derived from seaweed extracts, tree and bush exudates, plant
flours, and similar sources. Almost all these natural materials are
polysaccharides or mixtures of polysaccharides. Today a new and growing
category of gums, which is still in its infancy, is that of the
modified natural gums. Although these man modified polymers are
a small fraction of the total gum market (food and industrial) about
lb of the total 3 billion lb of water soluble gums sold domestically
steadily pressing at the position of the natural gums and enlarging
foothold in the field as newer and better modified hydrocolloids become
gums, pointing to the giant advances of organic chemistry, feel that as
was replaced by nylon, rubber by neoprene, waxes by plastics, so the
gum polymers are targets for the organic research chemist. Although
duplications may not be possible, or even desirable, a sufficient
number of the
functional properties of the natural materials can be reproduced by
synthesis or modifications to create marketing opportunities for these
inexpensive natural materials such as cellulose and starch yields
gums that have many of the properties of natural gums. They also have
advantages of low cost, steady and inexhaustible supply, constant
properties, tailor made functionality designed to meet specific
domestic availability, and sometimes new unique properties not
natural gums. Moreover, pure synthetic gums, derived from the
air, and flame of the ancient alchemists, are also being created, some
are already being used as food additives. These materials, usually much
expensive to make, offer the promise of completely novel hydrocolloids
materials, the organic chemist has available two of natures cheapest
abundant raw materials starch, at about $0.06 0.09 per pound, and a
pulp, at about $0.09 0.14 per pound. Both of these readily available
polysaccharides are excellent starting materials for the production of
They both can be chemically modified easily by heat, oxidation, or
treatment. Proper control of the modification makes possible a great
products. As Whistler pointed out, it is conceivable that as more is
about the relationship of structure to the physical properties of
specific gum properties will probably be custom tailored into starch
cellulose molecules so that the properties of the custom made products
more closely match the properties desired in special gum applications.
is urged, however. It must be remembered that although sophisticated
procedures may modify a polysaccharide to give the desired end product,
materials and processing costs may be so high that the new gums will
competitive in price with the natural gums. This chemical modification
natural polysaccharides is both a stimulating challenge for industrial
and a substantial protective barrier for the lowercost natural gums. It
probable that in the foreseeable future, chemically modified starches
celluloses, as well as the purely synthetic gums, will continually
the natural gums for the expanding markets for these materials.
In 1961, as
previously mentioned, the traditional market for watersoluble gums was
estimated to have been 3 billion lb. Of this total, the largest
far was held by the natural gums, including the starches, whereas only
100 million lb were composed of the synthetic gums. However, this
is not complete, since it does not include data on such hydrocolloids
Gantrez An, Polyox, Carbopol, and other newer and less well known gums.
addition, estimates of the potential market for water soluble films
up to 20 million lbs per year.
In the food
industry, the chemically modified and synthetic gums at present occupy
role. Of the total market of 100 million lb in 1961, only an estimated
million lb was consumed by the food industry. The modified or synthetic
used in foods were chiefly well established gums such as carboxymethyl
and methylcellulose. The newer chemically synthesized polymers will
difficult, up hill, and expensive battle to develop markets in the food
industry because the stringent Food and Drug Administration regulations
extensive animal feeding tests and experimental assurance of
allowing their use as food additives. As a result, most companies
water soluble gums tend to look for industrial applications and strive
develop profitable markets in these nonfood industries before
penetrate the food industry. The ease of penetration or acceptance is,
course, dictated by the novel and unique functional properties offered
new gum that cannot be matched by the current available ones, or by the
advantage of a cost reduction or product quality improvement.
chemically derived hydrocolloids tend to offer some of the following
over the natural gums: (1) uniform properties and specifications, (2)
prices, (3) unlimited availability (not affected by crop failures,
shortages, etc.), (4) low biological oxygen demand (B.O.D.) (5)
products not subject to import fluctuations.
major constituent of most land plants and is the most abundant natural
in the world. Together with the hemicelluloses and lignins, it forms
walls and intercellular layers, which are the primary structural
natural cellulose is cotton fibers or linters, which on a dry basis
about 98% a cellulose. Wood contains about 40 50%, and together with
linters, it is the most important commercial source for raw material
Agricultural residues, such as corn stalks, corncobs, and wheat straw,
about 30% cellulose and are available as a vast reservoir of
available raw material.
molecule is composed of a chain of repeating cellobiose units, each of
of two anhydroglucose units it
more briefly described as a linear polymer of b D glucopyranose (Fig. 1
studies have shown the degree of polymerization of cellulose to be
3000 so that, with the spatial arrangement of the glucose residues, the
molecules are long and threadlike. X ray measurements, however, show
native cellulose, the molecules are aligned to form fibers, some
which are highly ordered and have a crystalline structure due to
association by hydrogen bonding. The crystalline regions vary in size
represent areas of great mechanical strength and high resistance to
chemical reagents and hydrolytic enzymes. The physical and chemical
of cellulose are largely dependent on the relative amount and
the crystalline regions. The cellulose molecules tend to remain
may normally undergo a degree of turning and twisting. Because of its
strong associative forces, it can only be brought into solution under
conditions, usually by chemically modifying the polymer and forming
derivatives. In this way, many diverse and useful functional properties
imparted to the cellulose molecule.
other notable discoveries, the first chemically modified cellulose
made by accident. Christian Schonbein, a professor of chemistry at the
University of Basel in 1846, was conducting some experiments in his
The flask in which he had been distilling nitric and sulfuric acids,
accidentally broke and the corrosive liquid spilled all over the floor.
story goes, Schonbein, unable to find a mop, wiped up the mess with his
cotton apron, which he then washed and hung up over the hot stove to
Instead of drying, however, the apron flared up suddenly and
Schonbein had invented guncotton (cellulose nitrate). This accidental
was a major factor in the advances of polymer chemistry and stimulated
development of many other synthetic cellulose derivatives.
derivatives commonly encountered in the food industry are ethers in
or hydroxyalkyl groups have been substituted upon one or more of the
available hydroxy groups in each anhydroglucose unit of the cellulose
The effect of the substituent groups is to disorder and spread apart
cellulose chains so that water or other solvents may enter to solvate
chain. By controlling the type and amount (degree) of substitution, it
to produce products that have a wide range of functional properties.
derivatives of cellulose made by chemical substitution, a modified
made by acid hydrolysis has recently been developed that has functional
properties. This hydrolyzed cellulose, called microcrystalline
Avicel, has found novel uses in the food industry, primarily in low
foods. Although not soluble in water, Avicel has a great water
capacity. Thus it functions as an effective thickening and bodying
similar to many hydrocolloids.
starch are both condensation polymers of glucose. The differences in
between the glucose units however are sufficiently great to cause great
differences in properties. Pure cellulose is substantially insoluble in
while starch can be readily dissolved in hot water.
developments in cellulose technology have led to the preparation of
pure a cellulose
products, which have hydrophilic properties and which can function as
hydrocolloids in various food applications. One of the most important
products is a microcrystalline a cellulose sold under the trade name of
The normal a cellulose found in natural plants is a fibrous material,
does not absorb water and is comparatively inert under most conditions,
Avicel, a specially hydrolyzed a cellulose, is nonfibrous and has water
prepared by the acid treatment of a cellulose under special processing
conditions, as disclosed by the patent of Battista. By controlled
with hydrochloric acid, a cellulose is converted to two components an
fraction and an acid insoluble fraction. The acid insoluble crystalline
is washed and separated. It is called cellulose crystallite material or
microcrystalline cellulose. Essentially, the amorphous regions of the
are hydrolyzed completely, leaving the crystallite regions as isolated
microcrystallites, which are defined as the level off degree of
cellulose, or DP cellulose. In other words, if the hydrolysis reaction
continued, the degree of polymerization would not change, indicating
level off period or limit of reactivity, has been reached. The reported
DP consists of 15 375 anhydroglucose units, the constituent chains of
aggregate being separate from those of neighboring aggregates. These
are characterized by sharp X ray defraction patterns indicative of a
substantially crystalline structure.
available microcrystalline cellulose comes as a white, fine flour which
in ash, metals, and soluble organic materials. It is insoluble in
acid, common organic solvents, and oils. It is partially soluble, with
swelling, in dilute alkali. Table 2 summarizes the chemical and
properties of this material.
of this Avicel product has been the fact that it requires a great deal
energy to completely disperse and hydrate the dry material. In
many food applications, the incorporation of large amounts of Avicel
chalky, drying mouth feel to the food that makes it organoleptically
have been recently overcome by the addition of carboxymethylcellulose
to the a cellulose
prior to drying the final product. The addition of
improves the functional properties so that the material can hydrate and
disperse with comparatively little mechanical effort. It also reduces
eliminates the chalky taste in many food formulations. This new
trade name is Avicel RC, has substantially different properties from
original Avicel. Specifications and properties of Avicel RC are given
3. A great deal of the previous literature describing Avicel
not valid for Avicel RC. Therefore a clear cut distinction should be
between these two products in food applications and evaluations.
applications for the original microcrystalline cellulose were described
Trauberman: (1) Avicel in dry form or as a gel can be incorporated as a
agent in many food products to effect significant calorie reduction
impairing the palatability or appearance of the food. (2) Avicel
water produces stable gels containing up to 20% or more of solids.
are spreadable, and at lower concentrations creamy colloidal
suspensions can be
obtained. (3) In dry form, Avicel is an effective absorbent and can
base foods, such as cheese and peanut butter, and also syrups, such as
and honey, to free flowing, granular powders for use in dry package
similar convenience foods.
application proposed for Avicel was as a new ingredient for the control
calories in a wide range of food products. The promotional literature
manufacturer, Food Machinery Corp., proclaimed Avicel to be a
ingredient and stated that it contributes functional properties, such
stability, body bulk, opacity, texture, and palatability. These
were disclosed and illustrated by Battista in a broad spectrum of
food uses. They were all basically reduced calorie food compositions.
examples covered are methods and formulations for making a wide variety
of low calorie
products, such as honey flavored doughnuts, peanut butter cookie dry
muffins, layer cake, fibrous breakfast food, chocolate pudding,
dessert topping or sauce, soft pudding, peanut butter streusel type
topping, low calorie cream salad dressing, imitation butter or
mayonnaise type salad dressing, cheddar cheese spreads, dry mix ice
malted milk shake, catsup, caramel candy, and milk chocolate.
novel rheological properties, which makes it useful in the preparation
stable emulsions and suspensions such as pourable salad dressings and
drinks. When properly dispersed, the particles of microcrystalline
and carboxymethyl cellulose form a gel network of weakly bound
gel structure stabilizes and prevents the coalescence of liquid
emulsions as well as the settling out of solid particles in
suspensions. If a
shear force (such as shaking) is applied to this thixotropic system,
the bonds break when the yield value is exceeded and the system flows.
standing, the gel structure gradually reforms to give the original
emulsion or suspension. This property can be quite useful in the
many food products.
Canned Shelf Stable Spreads and Salads
development has been the use of Avicel RC in the manufacture of canned
and spread type products that are sterilized in the container. This
was made possible because of the ability of Avicel stabilized
as salad dressings, to withstand sterilization conditions as severe as
for 75 minutes even in the presence of food acids. Discoloration was
experienced except where other heat sensitive substances were present.
salad dressings could be blended at any desired ratios with pieces of
meats or vegetables. It is now possible to retort in the container such
products as ham spread, chicken salad, tuna salad, salmon salad, potato
and macaroni salad. Durkee Famous Foods Co. has marketed a ready to
canned tuna salad made with Avicel RC.
The use of
Avicel with water at solids levels of 30 36% gives gel like materials
in degrees of thixotropy, viscosity, and opacity. These gels make it
to prepare colloidal spreads containing up to 20% solids or more. These
colloidal gels are particularly useful in the formulation of smooth
products such as dressings, spreads, dips, sauces, and aerosol type
contents, the gels have the physical characteristics of animal fats or
hydrogenated vegetable oils. Vegetable oils and fats normally used in
similar to mayonnaise or salad dressing can be partially replaced with
reducing the caloric values by more than 50%. By combining the gels
oils or fats and using the proper dispersing agent, calorie control
taste like sour cream, hollandaise sauce, and cheese dips can easily be
such product, a low calorie
salad topping containing 82 % fewer calories, has been marketed by Otto
Seidner, Inc., of Westerly, Rhode Island. This product, made with
contains only 3½ calories per teaspoon instead of the normal 20 per
Frozen desserts with better
eating quality, added
heat shock stability and improved control of ice crystal formation have
claimed through the use of microcrystalline cellulose. The cellulose
a source of solids, are said to give body, bite resistance, and
frozen desserts. In addition, the added stiffness improves the
the products. Avicel RC has been used in ice cream, sherbet, ice milk,
ice cream, and artificially sweetened ice cream.
especially suited for frozen baked goods have been formulated with
These stable emulsified toppings can withstand several freeze thaw
(foamable) preparations, such as toppings, possessing excellent body,
spreadability, and stability, are easily prepared using Avicel RC. The
Avicel in aerosol or foamed food toppings has been illustrated in a
Herald. In addition to reduced caloric content, toppings made with
have the desirable properties of foam retention (no sagging),
appearance and eating quality, and a rich mouth feel despite the lower
of fatty materials. In addition, it was claimed that the products after
extrusion and foaming do not leak water, collapse, or develop a coarse
Dairy Type Products
found application in the formulation of various synthetic or simulated
products. A synthetic product, Sour Kreme dressing, containing 40% less
calories than sour cream has been proposed for special dietary needs.
nondairy synthetic cream has
been prepared in the form of a stable, white emulsion resembling real
yet containing no dairy ingredients. In addition, coffee whiteners made
Avicel RC exhibit superior keeping qualities and an ability to
several freeze thaw cycles.
nondairy product, Cheez Spread, which also maintains its texture and
consistency through many freeze thaw cycles is made possible by the
properties of Avicel RC.
Free Flowing Spreads
cellulose, which has a vast surface area because of the many fissures
in the submicroscopic surface area, is extremely absorbent,
fatty materials. This function or property makes it possible to convert
syrupy products into dry, free flowing powders. It has been suggested
butter flavored mixes can be formulated that will produce smooth,
bread spreads upon the addition of water and stirring. By use of other
such as cheese and spices, other flavored spreads may also be prepared.
characteristics of Avicel offer advantages for use in various meat
When used on the surface of bacon, it was claimed to curb curling and
sticking of the slice strip during storage. When used as a coating on
of hamburger patties, it was claimed to prevent loss, of some of the
to reduce shrinkage. A suggested use for the material is in meat
be added by housewives or institutional operators to ground meat in
meat loaf dishes, sauces, etc. It could also be used as a vehicle for
oily seasonings or flavor components and for incorporating these
be absorbed by the microcrystalline cellulose aggregates. The latter
be used to carry edible dyes into fat based products, such as butter or
margarine, without causing speckling or blooming in the product.
suggested that since many of the oil soluble dyes have been banned for
use, this application may be helpful for coloring fatty foods with
nontoxic natural vegetable dyes.
accomplished this by binding suitable colors, lakes, pigments, etc.,
cellulose crystallite aggregates. These were then used to color various
particularly those that tolerate little or no water, such as hard
bakery icings, confectionery coatings, cake mixes, and beverage powders.
Bakery and Pasta Products
Avicel powder, which resembles flour, can be easily incorporated into
blending or homogenization. In baked goods, it has been used for the
of low calorie cookies marketed by Weston Biscuit Company. The cookies,
Sweet 16 cookies, contain only 16 calories apiece and are fortified
A pasta of
Avicel in water can be extruded into ribbons and other shapes. In this
way low calorie
spaghetti, macaroni, and other products can be made.
It has been
suggested that Avicel can be used as a clouding or opacifying agent for
beverages at concentrations of less than 0.5%. This was tried by the
Company in its Keen soft drink powder in order to impart cloudiness to
effective film forming properties. It therefore has been suggested for
use as a
water soluble, edible protective coating for foods and has been claimed
particularly suitable for frozen foods such as vegetables, meats, ice
confections, butter, and cheese.
two or three decades, various synthetic and chemically modified
have been created and investigated. Some of these polymers have
traditional natural gums in various food applications, and increasing
commercialization of improved synthetic gums will undoubtedly stimulate
competition between these and the natural gums.
organic chemists who believe that the day will come when every natural
will be synthesized in the laboratory, and at the same time improved
functionally in such a way as to overcome inherent undesirable
the other hand, there are those who believe that synthetic gums will
economically replace the cheaper natural gums such as starch ($0.10
pound), gum arabic ($0.35 per pound), and guar and locust bean gum
pound), and that at best the semisynthetics (chemically modified
celluloses, etc.) will be the limit of practicality for the synthetic
But in all cases, the economic incentive and specific quality will be
guiding force behind these decisions.
gum field at present, most research efforts seem to be directed toward
objectives: (1) synthesis and development of gums having properties
to and superior to those of the well known natural gums, and (2)
development of gums having completely new and novel properties for
and yet undefined applications.
synthetic gums have been developed which have already been used
the food industry or which have the potential of finding food
the future. The main hurdle for employment in foods is the lack of Food
Drug Administration clearance, which is based on lengthy feeding
of which are in progress. But in general, these hydrocolloids have been
reported to be nontoxic and must eventually be considered for food
is a comparative newcomer to the field of industrial water soluble
was developed by W. Reppe in Germany in the late 1930s and was first
during the Second World War as a blood plasma expander. After the war,
uses, primarily in nonfood fields, were developed, and in 1956, the
Aniline and Film Corporation began full scale production of this
the United States.
is a polymeric N vinyllactam known chemically as poly 1 vinyl 2
but more generally as PVP. Its chemical structure is shown in structure
is produced commercially by a purely synthetic route involving
formaldehyde, ammonia, and hydrogen as shown in Eq. (1).
General Aniline and Film Corp. produces four different viscosity
are offered in both powder form and aqueous solutions. These differ
in molecular weight, as in the tabulation.
special pharmaceutical grades of PVP are available under the trade name
Plasdone, and food additive grades are supplied as Polyclar.
present these materials range
in price from a low of about $1.25 per pound to $3.20 per pound for the
pharmaceutical injectable grade. It is felt that its physiological
and its protective colloid function remain to be exploited in the food
and that only a fraction of the market potential for PVP has been
realized to date.
With the growth of markets and long range development of PVP, the price
eventually come down to the range of 60 70 cents per pound and offer
competition to other water soluble gums in this price range.
is very versatile and offers various functional properties for a
applications. It has a wide solubility and compatibility range. It is
excellent protective colloid and suspending agent and has very good
properties. It is also a good binder and stabilizing agent and has
adhesive properties. It is a complexing agent and can be used for
commercial versatility of
PVP, which has led to the increasing use of this polymer in a wide
fields, is due primarily to the following outstanding properties: (1)
solubility and compatibility range, (2) complexing and detoxifying
physiological acceptability, (4) protective colloid action, (5) film
ability, (6) adhesive qualities.
is readily soluble in cold water and gives fairly viscous solutions
With lower molecular weight material, concentrations as high as 60% can
dissolved in aqueous media. The viscosity of PVP is not affected by pH
broad range of 0 10. Solutions of PVP also have a high tolerance for
inorganic salts, particularly the lower molecular weight types. PVP
are stable over long periods if they are protected from mold growth by
antimycotics such as sorbic acid.
with other commercially available water soluble gums, PVP has unusual
solubility in organic solvents. It is soluble in the lower alcohols,
nitroparaffins, methylene dichloride, amines, and organic acids, and
when it is
anhydrous the solubility range is increased to include ketones, esters,
complexing action of PVP is
demonstrated by its ability to form molecular adducts with other
some cases, the result is a solubilizing action, as with iodine in other cases the result is
action, as with tannins in beverages.
One of the
unusual properties of PVP is in its film forming nature. PVP can be
cast from a
variety of solvents to give films that are clear, glossy, and hard at
humidities. They are very hygroscopic and exhibit excellent adhesion to
variety of surfaces, such as glass, metals, plastics, and human hair.
most water soluble resins, PVP films are hygroscopic and the degree of
absorption is a function of relative humidity. Because of its unique
properties, PVP film has found widespread application in the cosmetic
where it is used extensively in the formulation of various hair sprays
fixative preparations. In this field it has also been used in barrier
hand cleaners, hand lotions, dentifrices, and shaving preparations as
in deodorant sprays and after shave lotions.
having the same stability, physiological compatibility, and other
soluble PVP can be made by reacting PVP with polymeric carboxylic acid
physiological background of PVP has been well explored because of its
uses as a blood plasma extender, and a long history of use has shown it
essentially a physiologically inert material. PVP is essentially
given by oral administration, skin absorption, inhalation, or
intraperitoneal injection. It is not a primary irritant, skin fatiguing
material, or sensitizer and
the acute oral toxicity (LD0) is greater than 100 g per kilogram of
weight. Acute intravenous toxicity (LD50) is equal to 12 15 g per
body weight. Chronic oral toxicity was also investigated by feeding
dogs 1 10% PVP K 30 by weight of their total diet for up to 24 months.
effects or significant pathological changes attributable to the PVP
In the food
industry, PVP has found an important application in beverage
manufacture as a
clarifying agent. It is known that PVP forms insoluble complexes with
tannins. This property is applied to clarification and chill proofing
vegetable and fruit beverages, such as beer, whiskey, wine, vinegar,
juices. Usually, taste and clarity are improved and other desirable
are enhanced. The trade name for PVP offered for beverage uses is
the United States. PVP has been approved for use as a clarifying agent
beverages under prescribed conditions by Food and Drug Administration.
The use of
as a selected precipitant for tannins in beer was discovered. In
find a method of getting rid of the tannins in beer in order to extend
life, McFarlane et al. conducted a long search for these selective
precipitants. They found that PVP was the most effective and useful.
is generally regarded as being due to a proteintannin complex formed by
reaction between barley protein, b globulin, and a tannin of unknown
but probably of high molecular weight. Proteolytic enzymes such as
active ingredient of most chill proofing agents, break down and
protein of the protein tannin complex. The chill stability imparted to
by this process may be of a temporary nature, since upon storage for
periods the components of the protein tannin complex may recombine and
haze. On the other hand, PVP is concerned with a tannin rather than a
component, and since PVP removes all the tannins it would appear that
precipitation will result in a more permanent chill proofing of the
McFarlane et al. found that under certain specified conditions PVP
removed the chill haze material from beer without harming palate
flavor, or head retention. They found the optimum requirement to be
about 1 lb
of PVP per 100 barrels but
for beers brewed under different conditions. Insufficient PVP failed to
adequate protection, whereas an excess caused the appearance of haze
pasteurization. However, a method was described whereby the optimum
PVP for a given beer could be easily determined before proceeding to
brewing trials. In addition, the use of PVP to remove these tannins
taste and taste stability, foam retention, chill haze stability, and
ease, and gave cleaner worts from the cooler, cleaner, better tasting
beer, shorter storage time, a saving on hops, and lower enzymatic chill
amount of PVP used generally falls within the range of 120 200 parts
million, or about 3 5 lb of PVP per 100 barrels of beer but the optimum must be
experimentally for a given brewery. The usual practice in breweries is
the malt cereals and hops with water for a specified period, after
hot liquid, called hot wort, is strained free of hops. It is
the PVP be added a few minutes before the end of the kettle boil. At
stage, the PVP content after filtration of the finished beer is
(less than 1 ppm). A different mechanism for preventing chillhaze takes
advantage of the observation that a large excess of PVP (an extra 100
forms a soluble complex with the critical materials.
PVPs for preventing chill hazes in beer are the ones with molecular
less than 30,000. They are used at a level of less than 2lb per 100
Stone, in a
later patent, claimed that McFarlanes clarification procedure could be
by using the low molecular weight PVP polymers ( K 15), or copolymers
of PVP with
olefinic compounds such as vinyl acetate or vinyl alcohol. These
would stabilize the beer or ale without causing precipitation of the
a unique advance in brewing technology involving the use of an
of PVP. This material (once known as AT 496, now called Polyclar AT),
reported to have the advantages of water soluble PVP, such as the high
selectivity for tannins (anthocyanogens), without the disadvantages
that may be
associated with the presence of residual PVP in the finished beer. In
it appears to possess a particular affinity for the part of the
that combine specifically with protein to form chill haze materials.
advantages stated are that Polyclar AT did not absorb bittering
that there is no effect on the foam properties of treated beer. In
copper content is reduced significantly and the flavor is not adversely
affected. In fact, it was reported that beers treated with Polyclar AT
less astringent after bitterness, which seems to help accentuate the
associated with the isohumulones. The levels recommended are about 3 4
that the haze forming constituents in beverages are precipitated by the
0 8 g PVP per hectoliter of beverage, with the preferred PVP having a
weight of 7,500 40,000.
developments in this field led to the production and sale of a
product, Polyclar H, for use in the fining and stabilizing of beer
Aniline and Film Corp., 1958). Polyclar H, currently sold by the
Aniline and Film Corporation for specific use as a clarifying and
agent for the brewing industry, is claimed to contribute the following
attributes: (1) markedly increases the amount of trub removed as hot
break (2) modifies
the characteristics of trub,
facilitating removal by decanting, filtering, or centrifuging (3) reduces potential haze
materials in the
significantly reduces the
amount of chill proof required (5)
enhances the flavor and foam properties of finished beer (6) improves the clarity and
stability of beer
(7) exerts a hop
sparing action (8)
improves stability to taste.
developments have led to the use of the insoluble, cross linked form of
(Polyclar AT) as a clarifying and stabilizing agent for beer and also
whiskey, fruit juices, and tea. Sucietto used a combination of cross
and activated charcoal to render aged distilled whiskeys haze resistant.