Fruits and vegetables are important sources of vitamins, minerals and dietary fibre. The consumption of fruits and vegetables has increased significantly as consumers have become more health-conscious. Whilst most fruit and vegetables should be eaten fresh, processed fruit and vegetables can be acceptable alternatives. Fruit and vegetables have many similarities with respect to their compositions, methods of cultivation and harvesting, storage properties and processing. Processing (canning, Dehydration & Preservation) increases the shelf life of fruits and vegetables.
Fruits and vegetables are processed into a variety of products such as juices and concentrates, pulp, canned and dehydrated products, jams and jellies, pickles and chutneys etc. The extent of processing of fruits and vegetables varies from one country to another. The technology for preservation also varies with type of products and targeted market. Owing to the perishable nature of the fresh produce, international trade in vegetables is mostly confined to the processed forms.
India is the second largest producer of fruits & vegetables in the world with an annual production of million tonnes. It accounts for about 15 per cent of the world’s production of vegetables. Due to the short shelf life of these crops, as much as 30-35% of fruits and vegetables perish during harvest, storage, grading, transport, packaging and distribution. Hence, there is a need for processing technology of fruits and vegetables to cater the domestic demand.
The major contents of the book are procedures for fruit and vegetable preservation, chemical preservation of foods, food preservation by fermentation, preservation by drying, canning fruits, syrups and brines for canning, fruit beverages, fermented beverages, jams, jellies and marmalades, tomato products, chutneys, sauces and pickles, vegetables preparation for processing, vegetable juices, sauces and soups, vegetable dehydration, freezing of vegetables etc. The book also contains photographs of Production Line & Machinery.
It will be a standard reference book for professionals, entrepreneurs, food technologists, those studying and researching in this important area and others interested in the field of fruits and vegetables processing.
Properties of Fruits
and Vegetables; Chemical Composition and Nutritional Aspects;
and vegetables have many
similarities with respect to their compositions, methods of cultivation
harvesting, storage properties and processing. In fact, many vegetables
considered fruit in the true botanical sense. Botancially, fruits are
portions of the plant which house seeds. Therefore, such items as
cumcumbers, eggplant, peppers and others would be classified as fruit
Vegetables are derived from various
parts of plants and it is
sometimes useful to associate different vegetables with the parts of
they represent since this provides clues to some of the characteristics
expect in these items. A classification of vegetables based on
features as seen in Table 1.
as a dessert item
is the mature ovaries of plants with their seeds. The edible portion of
fruit is the fleshy part of the pericarp or vessel surrounding the
in general is acidic and sugary. They commonly are grouped into several
divisions depending principally upon botanical structure, chemical
and climatic requirements.
important quantities of water. Water plays a vital role in the
reproduction cycle and in physiological processes. It has effects on
storage period length and on the consumption of tissue reserve
water is present in following forms :
bound water or dilution water which is
present in the cell and forms true solutions with mineral or organic
water, directly bound on the
chemical component molecules and which is also removed with difficulty.
contain generally 90-96% water while for fruit normal water content is
80 and 90%.
2. Mineral substances
present as salts of organic or inorganic acids or as complex organic
combinations (chlorophyll, lecithin, etc.) they are in many cases
are more rich
in mineral substances as compared with fruits. The mineral substance
normally between 0.60 and 1.80% and more than 60 elements are present;
major elements are: K, Na, Ca, Mg, Fe, Mn, Al, P, CI, S.
if its content in
the human body is very low, iron (Fe) has an important role as a
haemoglobin. Main iron sources are apples and spinach.
from fruit have a
basic reaction; for this reason fruit consumption facilitates the
neutralisation of noxious uric acid reactions and contributes to the
equilibrium in the blood.
main component of fruit and vegetables and represent more than 90% of
matter. From an energy point of view carbohydrates represent the most
of the food components; daily adult intake should contain about 500 g
properties of sugars. Sugars such as glucose, fructose, maltose and
share the following characteristics in varying degrees, related to
vegetable technology :
l they supply energy for
l they are readily
l in high concentrations
they prevent the
growth of micro-organisms, so they may be used as a preservative;
l on heating they darken
in colour or
l some of them conbine
with proteins to
give dark colours known as the browning reaction.
Some properties of celluloses
and hemicelluloses :
l They are abundant in
the plant kingdom
and act primarily as supporting structures in the plant tissues;
l they are insoluble in
cold and hot
properties of pectins and carbohydrates gums :
l Pectins are common in
vegetables and are gum like (they are found in and between cell walls)
hold the plant cells together.
l pectins in colloidal
to viscosity of the tomato paste;
l pectins in solution
form gels when sugar
and acid are added; this is the basis of jelly manufacture.
Generally fruit and vegetables contain
very low level of fats
below 0.5%. However, significant quantities are found in nuts (55%),
kernel (40%), grape seeds (16%), apple seeds (20%) and tomato seeds
5. Organic acids
Fruit contains natural acids, such as
citric acid in oranges
and lemons, malic acid of apples, and tartaric acid of grapes. These
the fruits tartness and slow down bacterial spoilage.
Acidity and sugars are two main
elements which determine the
taste of fruit. The sugar/acid ratio is very often used in order to
technological charcterisation of fruits and of some vegetables.
6. Nitrogen - containing
These substances are found in plants as
: proteins, amino acids, amides, amines, nitrates, etc. Vegetables
between 1.0 and 5.5 % while in fruit nitrogen containing substances are
than 1 % in most cases.
From a biological point of view vegetal
proteins are less
valuable then animal ones because in their composition all essential
amino-acids are not present.
Vitamins are defined as organic
materials which must be
supplied to the human body in small amounts apart from the essential
amino-acids or fatty acids.
A or Retinol :
This vitamin is found as such only in
aminal mateirlals- meat,
milk, eggs and the like. Plants contain no vitamin A but contain its
beta-carotene. Man needs either vitamin A or beta-carotene which he can
convert to vitamin A. Beta-carotene is found in the orange and yellow
vegetables as well as the green leafy vegetables, mainly carrots,
potatoes, spinach and kale.
Vitamin C is the anti-scurvy vitamin.
Lack of it causes
fragile capillary walls, easy bleeding of the gums, loosening of teeth
joint diseases. It is necessary for the normal formation of the protein
collagen, which is an important constituent of skin and connective
vitamin E, vitamin C favours the absorption of iron.
Enzymes are biological catalysts that
promote most of the
biochemical reaction which occur in vegetable cells.
Enzymes have an optimal temperature -
around +50ºC where their
activity is at maximum. Heating beyond this optimal temperature
enzyme. Activity of each enzymes is also characterised by an optimal pH.
Turgidity and texture
The range of textures that are
encountered in fresh and cooked
vegetables and fruit is indeed great, and to a large extent can be
terms of changes in specific cellular components. Since plants tissues
generally contain more than two-thirds water, the relationships between
components and water further determine textual differences.
The osmotic pressure within the cell
vacuoles and within the
protoplasts pushes the protoplasts against the cell walls and causes
stretch slightly in accordance with their elastic properties. This is
situation in the growing plant and the harvested live fruit and
which is responsible for desired plumpness, succulence, and much of the
Sources of colour and colour changes
These pigments are classified into four
major groups which
include the chlorophylls, carotenoids, anthocyanins, and anthoanthins. pigments
belonging to the latter two
groups also are referred to as flavonoids, and include the tannins.
The Chlorophylls. The chlorophylls are
contained mainly within
the chloroplasts and have a primary role in the photosynthetic
carbohydrates from carbon dioxide and water. The bright green colour of
and other parts of plants is largely due to the oil-soluble
in nature are bound to protein molecules in highly organised complexes.
In food processing the carotenoids are
fairly resistant to
heat, changes in pH, and water leaching since they are fat-soluble.
they are very sensitive to oxidation, which results in both colour loss
destruction of vitamin A activity.
Properties of the anthocyanins include
a shifting of colours
with pH. Thus many of the anthocyanins which are violet or blue in
media become red upon addtion of acid.
of Living Systems
Fruit and vegetables are in a live
state after harvest. Continued
respiration gives off carbon dioxide, moisture, and heat which
storage, packaging, and refrigeration requirements. Continued
adds to moisture evolved and further influences packaging requirements.
It is important to note that the
reduction of acid content on
ripening influences more than just the tartness of fruit. Since many of
plant pigments are sensitive to acid, fruit colour would be expected to
Additionally, the viscosity of pectin gel is affected by acid and sugar
contents, both of which change with ripening.
Stability of Nutrients
One of the principal responsibilities
of the food scientist
and food technologist is to preserve food nutrients through all phases
acquisition, processing, storage and prepartion. The key is in the
sensitivities of the various nutrients, the principles of which are
in Table 3.
The ultimate nutritive value of a food
results from the sum
total of looses incurred throughout its history- from farmer to
Nutrient value begins with genetics of the plant and animal. The
fertilisation program affects tissue composition of plants, and animals
consuming these plants. The weather and degree of maturity at harvest
The structural unit of the edible
portion of most fruits and
vegetables is the parenchyma cell. While parenchyma cells of different
and vegetables differ somewhat in gross size and appearance, all have
essentially the same fundamental structure.
The protoplast has inner and outer
layers; the cytoplasm and its nucleus are held between them. The
contains various inclusions, among them starch granules and plastids
the chloroplasts and other pigment-containing chromoplasts. The cell
cellulose in nature, contributes rigidly to the parenchyma cell and
outer protoplasmic membrane. It is also the structure against which
parenchyma cells are cemeted to form extensive three-dimensioonal
Procedures for Fruit
and Vegetable Preservation
Fresh fruit and vegetable storage :
Once fruit is harvested, any natural
resistance to the action
of spoiling micro-organism is lost. Changes in enzymatic systems of the
also occur on harvest which may also accelerate the activity of
Harvest method : Considerable
research is continuing on
mechanical harvesting of perishable crops with a view to minimising
fruit trees, controlling their height by use of dwarfing rootstocks,
and growth regulating chemicals will lead to easier, cheaper more
Handling systems : Field
packing of various vegetables
for export has been carried out for many years. In the last decade or
has been applied, in selected cases, to a few tropical fruit types.
systme can be practised it has considerable economic advantages in
cost of building, labour and equipment and can result in lower levels
Chemicals : There
is a very stong health lobby whose
objective is to reduce the use of chemicals in agriculture and
during the post harvest period. Every year sees the prohibition of the
commonly used post-harvest chemicals. New ways need to be developed to
post-harvest diseases, pest and sprouting.
Coatings : Slowing
down the metabolism of fruit and
vegetables by coating them with a material which affects their gaseous
is being tested and used commerically on a number of products.
transport : Recent innovations in this technique have
progress as a result of the development and miniaturisation of
measure carbon dioxide and oxygen. Several companies now offer
the levels of these two gases can be controlled very precisely.
Preservation by reduction of
Water Content: Drying
/ Dehydration and Concentration
and water activity (aw)
Micro-organisms in a healthy growing
state may contain in excess
of 80% water. They get this water from the food in which they grow. If
water is removed from the food it also will transfer out of the
and multiplication will stop. Partial drying will be less effective
drying, though for some micro-organisms partial drying may be quite
to arrest bacterial growth and multiplication.
When we speak of moisture requirements
of micro-organisms we
really mean water activity in their immediate environment, whether this
be in solution
in a particle of food or at a surface in contact with the atmosphere.
Two foods with the same water content
can have very different
aw values depending upon the
degree to which
water is free or otherwise bound to food constituents. Fig. 1 is a
water absorption isotherm for a given food at a given temperature. It
final moisture content the food will have when it reaches moisture
with atmospheres of different relative humidities.
Preservation by drying / dehydration
technique of drying
is probably the oldest method of food preservation practised by
removal of moisture prevents the growth and reproduction of
causing decay and minimises many of the moisture mediated deterioration
substantial reduction in weight and volume minimising packing, storage
transportation cost and enable storabliity of the product under ambient
tempertures, features especially important for developing countries.
rise in energy costs has promoted a dramatic upsurge in interest in
world-wide over the last decade.
Several types of dryers and drying
methods, each better suited
for a particular situation are commercially used to remove moisture
from a wide
variety of food products including fruit and vegetables.
While sun drying of fruit crops is
still practised for certain
fruit such as prunes, figs, apricots, grapes and dates, atmospheric
processes are used for apples, prunes, and several vegetables,
processes as tunnel, belt trough, fluidised bed and foam-mat drying are
used for vegetables.
Spray drying is suitable for fruit
juice concentrates and
vacuum dehydration processes are useful for low moisture/high sugar fruits like
peaches, pears and apricots.
As far dryers are concerned, one useful
division of dryer
types separates them into air convection dryers, drum or roller dryers,
vacuum dryers. Using this breakdown, table 1 indicates the
applicability of the
more common dryer types to liquid and solid type foods.
Fruit and vegetable
natural drying-sun and solar drying
Surplus production and specifically
grown crops may be
preserved by natural drying for use until the next crop can be grown
harvested. Natural dried products can also be transported cheaply for
distribution to areas where there are permanent shortages of fruit and
Preservatives are used to improve the
colour and keeping
qualities of the final product for some fruits and vegetables.
include items such as sulphur dioxide, ascorbic acid, citric acid, salt
sugar and can either be simple or compound solutions.
In osmotic dehydration the prepared
fresh material is soaked
in a heavy (thick liquid sugar solution) and / or a strong salt
then the material is sun or solar dried. During osmotic treatment the
loses some of its moisture. The syrup or salt solution has a protective
on colour, flavour and texture.
protective effect remains
throughout the drying process and makes it possible to produce dried
of high quality. This process makes little use of sulphur dioxide.
The main problems for sun drying are
dust, rain and cloudy
weather. Therefore, drying areas should be dust free and whenever there
threat of a dust storm or rain, the drying trays should be stacked
placed under cover.
The trays should be placed on a
framework at table height from
the ground. This allows the air to circulate freely around the drying
and it also keeps the food product well away from dirt. Ideally the
be exposed to wind and this speed up drying, but this can only be done
wind is free of dust.
With 80 cm x 50 cm trays, the
approximate load for a tray is 3
kg; the material should be spread in even layers. During the first part
drying period, the material should be stirred and turned over at least
Shade drying is carried out for
products which can lose their
colour and/or turn brown if put in direct sunlight. Products which have
naturally vivid colours like herbs, green and red sweet peppers,
green beans and okra give a more attractive end product when they are
Identification of Suitable Designs of
Solar Dryers for
In the selection of appropriate solar
dryers for commercial
scale operation, it is imperative that economics be kept in view at all
total Energy System should be employed and due consideration be given
parasitic energy consumption.
Construction of Solar Dryers
In the case of simple natural
convection dryers it may be more
appropriate to build and operate a number of small units. Multiplicity
diversity, since more than one crop can be dried at a time. A further
is that if one dryer is out of operation due to damage, drying can
continue at reduced capacity using the other dryers.
On the other hand, more sophisticated
dryers, such as forced
convection solar dryers, benefit from economies of scale due to the
tied up in the fan and the source of heat.
Construction methods and materials
available materials may vary considerable from location to location. It
within the scope of this document to discuss individual, local
Some general guidelines regarding factors which must be considered can,
however, be given :
l Dimensions of standard
materials - Where
possible , design should take account of the sizes of material locally
availabe. For example, it would be poor design to specify the width of
corrugated iron collector as 1.1 m if the standard width of a
sheet is 1 m.
l Before finalising a
commercial availability of materials must be ascertained.
l Use of rural materials
- The cost of
building of solar dryer can be minimised if the producer is able to use
cut straight from the forest rather than prepared timber. Careful
design in the
development stage of a dryer can often facilitate the use of cheaper
Difficulties caused by these materials are in joining pieces of the
in sealing the structure against air leaks, and in attaching the
to the (wooden) frame. There is obvious scope for designs which use
timber for strategic points and unprepared at others.
factors must be established:
l the throughput of the
dryer over the
l the size of batch to be
l the drying period(s)
l the initial and desired
content of the commodity (if known);
l the drying
characteristics of the
commodity, such as maximum drying temperature, effect of sunlight upon
product quality, etc.;
l climate conditions
during the drying
season, i. e. sunlight intensity and duration; air temperature and
wind speed (such data may be available from local meteorological
l availability and
considerations, estimates of the capital costs of the dryer, the price
commodity to be dried, and the likely selling price of the dried
have been made. Other question that need to be considered are the
l who will own the dryer?
l is the dryer to be
constructed by the
end-user (with or without advice from extention agencies), local
or other organisations?
l who will operate and
l how can the drying
incorporated into current
/ Solar drying tray
The drying tray described requires
seasoned timber 22.5 mm
thick x 50 mm wide.
Cut the timber into lengths of 900 mm
long for the sides of
the tray and 600 mm long for the ends - 4 pieces of each length will be
The ends of each piece are cut as shown in the drawing - this is to
fitting joints. Join the corners using small brass screws 20 mm long.
extra strong joints use good quality wood glue as well as the screws.
netting or grass woven mesh can be fitted between the frames as shown
bottom drawing. Cut the mesh a little larger than the size of the
drawing pins, pin the mesh to the OUTSIDE edges of one of the frames -
should be pulled tight as the pins are put in around the edges.
4 to 19
illustrated various types of sun / solar dryers along with examples of
and dehydration equipment.
Foods are also concentrated because the
have become desirable components of diet in their own right. Thus fruit
plus sugar with concentration becomes jelly. The more common
and vegetable products include items as fruit and vegetable juices and
jams and jellies, tomato paste, many types of fruit purees used by
candy makers and other food manufacturers.
of preservation by concentration
level of water in
virtually all concentrated foods is in itself more than enough to
microbial growth. Yet while many concentrated foods such as non-acid
vegetable purees may quickly undergo microbial spoilage unless
processed, such items as sugar syrups, jellies and jams are relatively
to spoilage; the difference of course is in what is dissolved in the
water and what osmotic concentration is reached.
concentration. As in food dehydration, one of the simplest methods of
evaporating water is with solar energy. A typical example of this
production at farm level in developing countries of fruit
as apricot or plum pastes).
Some foods can be satisfactorily concentrated in open kettles that are
by steam. This is the case for jellies and jams, tomato juices and
for certain types of soups. High temperatures and long concentration
should be avoided in order to reduce or eliminate damage. It is also
to avoid thickening and burn-on of product to the kettle wall as these
gradually lower the efficiency of heat transfer and slow the
chemicals will kill
micro-organisms or stop their growth but most of these are not
foods; chemicals that are permitted as food preservatives are listed on
page. Chemical food preservatives are those substances which are added
low quantities (up to 0.2%) and which do not alter the organoleptic and
physico-chemical properties of the foods at or only very little.
Chemical food preservatives are applied
to foods as direct
additives during processing, or develop by themselves during processes
fermentation. Certain preservatives have been used either accidentally
for centuries, and include sodium chloride (common salt), sugar, acids,
alcohols and components of smoke.
acid is the main
product of many food fermentations; it is formed by microbial
sugars in products such as sauerkraut and pickles. The acid produced in
fermentations decreases the pH to levels unfavourable for growth of
organisms such as putrefactive anaerobes and butyric-acid-producing
Yeast and moulds that can grow at such pH levels can be controlled by
inclusion of other preservatives such as sorbate and benzoate.
acid is general
preservative inhibiting many species of bacteria, yeasts and to a
moulds. It is also a product of the lactic acid fermentation, and its
preservative action even at identical pH levels is greater than that of
acid. The main applications of vinegar (acetic acid) includes products
pickles, sauces, and ketchup.
used lipophilic acid food
acid in the form
of its sodium salt, constitutes one of the most common chemical food
Sodium benzoate is a common preservative in acid or acidified foods
fruit juices, syrups, jams and jellies, sauerkraut, pickles, preserves,
cocktails, etc. Yeasts are inhibited by benzoate to a greater extent
moulds and bacteria.
are used for
mould and yeast inhibition in a variety of foods including fruits and
vegetables, fruit juices, pickles, sauerkraut, syrups, jellies, jams,
preserves, high moisture dehydrated fruits, etc.
chemical food preservatives
sulphites. Sulphur dioxide (SO2)
has been used for many centuries as
a fumigant and especially as a wine preservative. It is a colourless,
suffocating, pungent-smelling, non-flammable gas and is very soluble in
water (85 g in 100 ml. at 25ºC).
dioxide is used
as a gas or in the form of its sulphite, bisulphite and metabisulphite
which are powders. The gaseous form is produced either by burning
sulphur or by
its release from the compressed liquified form.
stable to oxidation than bisulphites, which in turn show greater
various forms of
chlorine constitute the most widely used chemical sanitiser in the food
industry. These chlorine forms include (CI2),
hypochlorite (NaOCI), calcium hypochlorite (Ca(OCI)2)
dioxide gas (CIO2).
compounds are used
as water adjuncts in processes such as product washing, transport, and
of heat-sterilised cans; in sanitising solutions for equipment
Food irradiation is one of the food
available to the food industry to control organisms that cause food
diseases and to reduce food losses due to spoilage and deterioration.
irradiation technology offers some advantages over conventional
application should be evaluated on its own merit as to whether
provides a technical and economical solution that is better than
irradiation is permitted, commercial applications depend on a number of
including the demand for the benefits provided, competitiveness with
alternative processes and the willingness of consumers to buy
products. There are a number of applications of food irradiation. For
application it is important to determine the optimum dosage range
achieve the desired effect. Too high a dosage can produce undesirable
in texture, colour and taste of foods.
Preservation of Foods
value of selected chemical compounds in preserving foods, the benefits
by their judicious applications, and the general principles governing
uses have received attention in most governments and their laboratories. The matter is so important
that it was and is
the subject of many national and international conferences.
the United States the National Academy of Sciences (NAS) - National
Council (NRC), the President’s Science Advisory Committee Panel on
and Health, and expert committees from governmental agencies,
industries have focused on the area.
Food and Agriculture Organisation (FAO) and the World Health
(WHO) of the United Naitons have also been active in this field,
the matter from an international point of view, generally embracing the
important features of the thinking of most nations in the world.
a result, a growing body of knowledge has become available which has
and yielded insights into this important subject.
the United States the Food Protection Committee of the NAS/NRC defined
additive a substance or a mixture of substances, other than a basic
which is present in food as a result of any aspect of production,
storage or packaging. The
term does not
include chance contamination.
is clear that there are intentional additives which are added to
specific functions. There
additives which really have no function in a food product but become
part of a
food product through some phase of production, processing, storage or
additives do not include
those substance which may find their way into food accidentally,
or unintentionally. The
terms do not
include pesticides,. for example, nor color additives, new animal drugs
substance used in accordance with a sanction or apporval granted prior
effective date of the Food Additives Amendment of 1958.
Uses in Food Processing
additives have a legitimate use in the food processing and distribution
of both technologically advances and of less well developed countries,
use of food additives to the advantage of the consumer may be
justified when it serves the following purposes :
of the nutritional quality of a food.
(2) The enhancement
keeping quality or stability with resulting reduction in food losses.
attractive to the consumer in a manner which does not lead to deception.
essential aids in food processing.
Federal Food, Drug and cosmetic
designates any chemical which when added to a food tends to prevent or
its deterioration as a chemical preservative.
chemical added to a food during the process of its fabrication is not
necessarily considered to be a preservative.
For example, in canning, if the air in the headspace is
nitrogen, the gas is not considered a chemical preservative added to
the United States chemical preservatives added to foods must be stated
label, stating the chemical as an ingredient.
The name of the chemical must be declared
in terms understandable to consumers.
It two or more chemical preservatives are
added to a food, each must be stated individually.
are two large categories of microbial antagonists useful in food
those of inorganic nature and those of organic nature.
Examples of each will be discussed.
Agents. - Sulfur Dioxide. - Sulfur containing
compounds are extremely
useful to mankind. Sulfur
been used in food preservation for centuries.
It currently still finds widespread use throughout the
principally in treating foods of plant origin. Being more effective
molds than yeasts, Sulfur dioxide has found wide use in the fermentation industries, such as wine
dioxide is much more toxic to molds
and bacterial than in yeasts.
dioxide is used in concentrations upwards to 2000 ppm in the
fruit concentrates. Sulfur
thought to be an enzyme poison, and finds use in controlling enzymatic
drying of foods. The
burning of sulfur, and the occurrence of
sulfur houses of one form or another in drying yards, has been observed in most countries.
proposed process for sterlizing fluid
whole milk involves the addition of 0.1% hydrogen peroxide to fluid milk allowing a
reaction time of
several minutes for sterilizatrion, adding sterlized catalase to
residual hydrogen peroxide, then heating to inactivate the enzyme. Combined with aseptic
packaging, the process
therotically has potential. One
objection is the damaging influence of the liberated oxygen.
spore forming bacteria can be killed with hydrogen peroxide. Surface sterlization of
many commodities may
be accomplished. In this regard, hydrogen peroxide finds wide usage in
controlling surface infections of man.
peroxide is not a permitted additive to foods in the United States.
- Chlorine is a widely used chemical disinfectant, finding
as important use
in the treatment of water for drinking and processing purposes. Its action is most
effective at low pH
Living tissues produce metabolic
products. Some of
these products from microorganisms
have been found to have germicidal properties, and are called
tissues contain other materials which
have antimicrobial activity, but the term antibiotic is restricted to
materials yielded in metabolism by microorganisms. spices may
contain antimicrobial compounds, yet the active
ingredients are not called antibiotics.
Preservation by Canning
Appert, a french
working in a simple kitchen, observed that food heated in sealed
preserved if the container was not reopened or the seal did not leak.
modestly called the process “the art of Appertizing”. Appert received
from Napoleon after spending ten years proving his discovery.
should be appreciated that the cause of spoilage of food was unknown.
scientists of the day were summoned to evaluate Appert’s process and
explanations for its apparent success. The conclusion reached was that
process was successful because in some mysterious and magical fashion
combined with food in a sealed container, preventing putrefaction. This
quite incorrect. Neverthless, the canning process was discovered and
for the next 50 years with some success, but in the darkness of
OF FOOD CAUSED BY MICROORGANISMS
the Academy of Sciences in France in 1864, Pasteur reported that he had
the cause of the disease of wine and beer to be a microscopic
given favorable conditions this vegetation grew and spoiled the
However, boiled wine sealed from contamination in jars with even cotton
would not sour. In fact, it was possible to isolate this microscopic
from the cotton plugs! It was this microscopic growth which spoiled
it was necessary for such organisms to gain entrance to heated foods if
were to spoil! Here was an explanation for the success of Appert more
a century before. The concept of heat treating foods to inactivate
organisms is termed appropriately “pasteurization” today.
had established that containers of food must be carefully sealed and
Cleanliness was important to his process, although he did not know that
were the agents of spoilage. Pasteur established several important
Most changes in wine depended on the development in it of
were themselves the spirits of disease. Germs were brought by air,
machinery and even by people. Whenever wine contained no living
material remained undiseased. Some of Pasteur’s flasks remain, and are
presumably still sterile today.
Resistance of Microorganisms Important in Canning
are two important genera of bacteria which form spores. Both genera are
forms, one (Bacillus) is aerobic and the other (Clostridium) is
a rod is about to sporulate a tiny refractile granule appears in the
granule enlarges, becomes glassy and transparent, and resists the
of various chemical substances. All of the protoplasm of the rod seems
condense into the granule, or young spore, in a hard dehydrated,
state. The empty cell membrane of the bacterium may separate off, like
of a seed, leaving the spore as a free, round or oval body. Actually a
an end product of a series of enzymatic processes. There is no
opinion either of spore function in nature or of the factors concerned
appear to be formed by healthy
cells facing starvation. Certain chemical agents (glutamic acid) may
the development of spores. No doubt sporulation consists of a sequence
integrated biochemical reactions. The sequence can be interrupted at
may be applied in two ways for the destruction of bacteria. Oven heat
considered as dry heat, used in the sterilization of glassware. Other
are heated when moist or in the presence of moisture; this is commonly
moist heat. Dry cells exhibit no life functions; their enzyme systems
active. Cell protein does not coagulate in the absence of moisture.
OF FOODS FOR CANNING
is possible to classify foods to be
canned on the basis of acidity and pH value. Plant tissue (except
berries) and animal tissue (including meat, fish and dairy products)
classed as low acid foods. Manufactured items with several ingredients
into the medium acid group. Fruits are in the acid group. Berries,
products and certain citrus products fall into the high acid group as
and jellies. Few foods are basic in reaction if considered in their
of Food Ingredients on Heat Resistance of Spores
and pH Value of Heating Medium.-Of the many factors which influence the
resistance of spores, the pH values of the heating medium has profound
For most spore-forming bacteria maximum resistance generally occurs in
region of neutrality. Bacterial spores are not heat resistant at low pH
For foods with pH values higher than 5.0 apparently factors other than
important in the resistance of spores. For instance, the heat
spores of Cl. botulinum in fish products with a
range in pH from 5.2 to
6.8 is approximately the same. at
a pH lower than 5.0, a marked reduction in resistance occurs. This
utilized in the processing of certain vegetables and other low acid
do not withstand sterilization under usual canning conditions. The
which these foods are packed are acidified, with the result that the
of the contaminating organisms is lowered.
the pH of tomato juice with citric, lactic or acetic acid greatly
heat resistance of B. thermoacidurans. If the same
percentage of acid is
added, they differ in their degree of effectiveness in lowering the
tolerance of the organisms in the order of lactic, citric and acetic.
on the pH, the order would be acetic, lactic and citric. Evidently the
undisassociated acid molecule is important in this phenomena.
of Enzymes After Heating -
substantial attention has been given to the destruction of enzymes in
methods of food preservation (freezing, dehydration) relatively little
given in canning foods. The assumption has been that the heat process
to kill microorganisms is sufficient to inactivate all enzymes. While
true that heating to 79 C will inactivate many enzymes, it is only
that studies have been undertaken to evaluate the heat resistance of
canned foods. Enzymes play a role in the deterioration of canned acid
acid foods. Also, enzymes are in some instances reactivated after
peroxidase). This problem has developed from studies of extremely high
temperature processing (121º to 149ºC flash-heat treatments).
are heat inactivated but indications are that some enzymes do survive
peroxidase in pickles is able to withstand heating to 85ºC. The heat
destruction of this enzyme is increased by the addition of vinegar.
solutions are protective to enzymes to heat inactivation in pears and
The enzymes of the tomato are not altered in heat resistance by the
amount of salt added. Some suggestions that the enzymes of canned
remain active after the canning process are available. Peroxidase
turnip and cabbage have been found to be reactivated after heating.
destruction curves obtained for ascorbic acid oxidase and peroxidase in
foods indicate that standard methods may be used in evaluating the heat
inactivation of enzymes.’
internal temperature of fruit and vegetables in the high acid food
receive relatively low heat processes in canning, may not rise
high to inactivate enzymes normally present internally in these
pectinesterase in canned grapefruit juice is active after an adequate
the standpoint of microbial spoilage has been administered.
Chemical Index of Efficiency-In
the inactivation of enzymes may be used as an index of the degree of
foods. For instance, the pasteurization of milk can be evaluated by its
phosphatase enzyme activity. The destruction of phosphatase in milk
with the heat treatment designed to kill B. tuberculosis and
pathogenic organisms. An evaluation of milk for this enzyme indicates
minimum degree of heat treatment.
peroxidase system in fruits may be useful in evaluating the relative
of acid food canning processes. Unless the enzymes are destroyed, they
continue to function in the container, causing deterioration. So too,
presence of one enzyme is found, what conclusions are possible relative
hundreds of others which may be functional, but for which there are no
Penetration Characteristics of Canned
When a can of food is sealed at 98ºC and
placed in a steam pressure vessel which is brought to 121ºC, the steam
is the reservoir of high heat energy and the can of food is the
lower heat energy. Heat then is transferred from the hot body to the
mechanism of heat transfer in canned food during such thermal
processing may be
divided into several rather definite classes. To a certain extent it is
possible to place food into heat transfer classes by knowing their
characteristics. The heat is transferred by conduction from the steam
can, and from the can to the contents.
the Heat Penetration into Canned Foods- While thermometers
can be used to
follow certain heating characteristics of foods, the most satisfactory
involves the use of thermocouples. A thermocouple is formed when two
metal wires are fused together at the ends. If the ends of these wires
placed at different temperatures a measurable voltage is developed,
related to the temperature difference between the two ends or
junctions. By attaching a suitable measuring device (potentiometer) to
thermocouple, it is possible to calibrate it and follow the temperature
inside a can which itself is being heated in a retort under steam
commonly used thermocouple system is composed of copper-constantan
wires and a
potentiometer, reading directly in degrees centigrade. Recording
are also available.
METHOD FOR CALCULATING THE PROCESS TIME FOR
information relative the heat resistance of spoilage organisms to be
in canning and the heating characteristics for the food in question,
information necessary to calculate the processing time for the product
available. Each time-temperature interval during the heating and
cooling of the
containers has a lethal effect on food spoilage organisms, if the
are above the maximum for growth for the organisms. By correlating the
effects of these high temperatures with the heating rate of the food,
length of time theoretically required to destroy any specific bacterial
present in the container of food may be calculated for any given
order to ensure that the calculated processing time for a product is
established, it is desirable to prepare inoculated packs. The product
prepared and filled into containers. An inoculum of spores of the
organism, important in the food group in which the product falls, is
approximately the cold point in the containers. With viscous foods,
strained pumpkin, the inoculum will remain somewhat at the position
convection heating foods, the inoculum will be carried in the
formed during heating the containers. For solid packed foods such as
the inoculum should be injected with needle
into the flesh of a potato
at the cold point. Excessive processing would be required to kill
spores in the
center of a 2-in, diameter potato. The inner surfaces are assumed to be
of Heat Processes
are two considerations relative to safe processing schedules developed:
relative to the heat resistance of spoilage microorganisms, and the
to the heat penetration characteristics of the food in the containers.
Evaluation of Heat Processes.- When process time is plotted against its
value, the relationship between the two variables, if considering a
processes, is generally linear. In view of this, a linear regression
be fitted to the lethal value-process time data for each product and
standard error of estimate computed.
process times determined for products by the three methods (i.e.,
heating-fastest cooling composite data from heat penetration studies,
inoculated pack studies, and the statistical evaluation) contain
margins of safety. Under certain sanitary conditions they may be
Under poor processing conditions they may be inadequate!
OF CANNED FOODS
ends of normal cans of food with a vacuum are slightly concave. Ends
bulged may be caused by microbial, chemical or physical actions. A hard
is one which resists being pushed back to a normal position. The ends
soft-swelled can may be forced back slightly but will not resume a
condition. A springer swell is one which is bulged but which may be
into normal position causing the opposite end to bulge by hitting
solid object. The opposite end flips into the bulged end. Cans may
through the flipper, springer, soft swell and hard swell stages. The
is to have the can explode.
anaerobic spore-forming organisms are causes of spoilage, it is usual
contamination comes from the raw material. It is unlikely that
conditions in a
plant are favorable for inoculation of anaerobes into products.
products such as meat which have spoiled may have center portions still
sterile. The growth may be centered outside te product or on the
Internal tissues of plants and animals normally do not contain
organisms if the
tissues are not diseased.
Sour.-Spoilage of canned foods needs not be accompained by bulged ends.
sour spoilage, as the term implies, is a condition of high acid
unaccompanied by gas production. Thermophilic bacteria are
the production of such spoilage. In flat sour spoilage, either the cans
been under-sterilized or the cans have leaked.
cans may be more easily perforated than plain cans, due to the fact
of exposed iron are not afforded cathodic protection or the protection
dissolved tin. Imperfections in the lacqured surface tend to
chemical activity to small areas, and perforation may be rapidly
on glass container may be attacked chemically by some foods.
Induced Swells - Overfilling cans at low temperatures may cause
bulging to cans by heating. Expansion of the solids and liquid of the
may permanently distort it.
packed with low vacuums may bulge when placed at high altitudes where
lower atmospheric pressure.
OF CANNED FOODS
the canning processes have been successful, the containers should be in
condition where biological spoilage will not occur. Thermophilic
be present, but unless temperature conditions in the storage chamber
excessive such spoilage is unlikely. However, while the biological
not be operative, chemical reactions are not eliminated. Chemical
bring about many changes in canned foods during storage.
Corrosion of Cans
presence of moisture on the surfaces of cans leads to rust formation.
conditions may result from “sweating” of containers when moisture from
condenses on cans when their temperature is below the dew point of the
When the relative humidity is high and the temperature of the cans is
may be expected. Warehousing at dry atmospheric conditions and constant
temperatures is important to prevent deterioration of cans and
air circulation, heating or cooling, and ventilation around stacks of
products with adequate temperature control, reduce danger to corrosion
no doubt outnumber other living entities on this
planet and can be found existing actively or passively wherever living
organisms occur. While the energy for life on this planet is captured
plants in the photosynthetic process, microorganisms are generally
for the final decomposition of the photosynthetic products. Animals
minor role in the cycle.
microorganisms were not identified as the important agents in food
until a century ago, wine making, bread baking, cheese making and
foods have been practised for more than four thousand years. For all
years mankind practiced food preservation using unknown, invisible,
word fermentation has undergone evolution itself. The term was employed
describe the bubbling or boiling condition seen in the production of
prior to the time that yeasts were discovered. However, after Pasteur’s
discovery, the word became used with microbial activity, and later with
activity. Currently the term is used even to describe the evolution of
dioxide gas during the action of living cells. Neither gas evolution
presence of living cells is essential to fermentative action, however,
in lactic acid fermentations where no gas is liberated, and in
accomplished solely with enzymes.
Important Organisms in Food Preservation
application of microorganisms to food preservation practices must be
a positive protection is available to control contamination.
microorganisms used in fermentations are notable in that they produce
amounts of enzymes. Bacteria, yeasts and molds, being single cells,
functional capacities for growth, reproduction, digestion, assimilation
repairs in a cell, that higher forms of life have distributed to
Therefore, it is to be anticipated that single celled complete living
(such as yeasts) have a higher enzyme productivity and fermentative
than found with other living creatures.
are contaminated naturally with microorganisms and will spoil if
type of action which will develop is dependent upon the conditions
imposed. The most favorable to a given type of fermentation under one
will be altered by slight changes in a controlling factor. Untended
naturally mold and putrefy. If brine or salt is added, entirely
organisms will take over.
of Energy - Inasmuch as the immediate need of microorganisms is a
energy, the soluble, readily available carbohydrates influence the
population that will dominate. In milk the sugar is lactose; those
which quickly mount in numbers are the lactose fermenting organisms.
suitable energy sources are generally available to microorganisms in
foods, energy sources are not usually a limiting factor, with certain
exceptions (such as milk).
held at 0ºC has little microbial activity, and retarded expansions in
numbers. At 4ºC there is slight growth of organisms and more rapid
temperature at which a food is held will determine within certain
nature of the organisms capable of either yielding the desired
spoilage, whichever the case may be.
and beer or similar fermented products originated in antiquity.
beverages were discovered by man in many areas on earth, with the
the early American Indian. There was a fermented cactus juice known to
tribes in the Southwest, but evidently alcohol was not a commodity in
as it was in the ancient Egyptian, Greek, Roman, and oriental
civilizations. The ability to produce pleasant,
palatable effervescent beverages by fermentation of natural fruit
juices is a
demonstration of man’s in-herent ingenuity. From earliest recorded
and beer have been important items of trade.
of wines imporves the flavor and bouquet due to oxidation and formation
esters. These esters of higher acids formed during aging give the
pleasing bouquet to well aged wine. Aged wine may be polished by
give a clear, bright appearance prior to bottling.
is applied in one of three ways : (1) by flash pasteurizing and
the storage tank; (2) flash pasteurizing into the final bottle; and (3)
pasteurization by heating the filled and sealed bottle. There is also
pasteurization and hot holding at a temperature of 49ºC for several
stabilize wines, usually dessert types.
flash pasteurizing in bulk,. wine is heated for about 1 min to 85ºC and
cooled continuously against the incoming wine and water or refrigerant
time-temperature relationship for pasteurization of wines is:
cells are killed at 40ºC while yeast spores are only killed at 57ºC.
and fruit juices can be rendered sterile, germ or yeast free, by
through sterile, very tight filter pads. The Seitz process of sterile
filtration includes three stages : sterilizing, filling and corking.
Sterilizing of bottles is accomplished by use of sulfur dioxide gas, by
of the gas with sterile water, filling under pressure, and corking with
corks. When sulfurous acid solutions are employed to sterilize the
bottles must be well drained in order to prevent excessive pickup of
dioxide.. The filter plates, pipes, hose lines, etc,. beyond the filter
bottling machine, and the latter, and the bottles and corks, must be
and kept sterile during filtration and bottling.
making remains an art and a science, dependent on nature to yield
conditions for grape culturing. Certain localized areas have the proper
combination of soil type, sunlight, temperature, and rainfall required
grape growing. These regions have become know throughout the world.
are found in the Rhine and Rhone valleys of Europe, and in areas of New
and California. Expert wine tasters are able to locate generally the
area from which the grapes for a wine have come.
and ale are fermentation products with characteristic flavor and aroma
malt and hops. The aclcoholic content ranges from 3 to 7%. The strain
used, the composition of the wort, and the temperature of fermentation
controlling factors. Hops has at least two antibacterial components in
to having a role in flavoring. Boiled wort must be innoculated with
the start of the fermentaion. Packaged beer is usually pasteurized
barrelled beer is not. Pasteurization temperatures of 64ºC are commonly
many years attempts were made to capture the unheated flavor of casked
beer in bottles and cans for home use. Recently success was achieved by
cold pasteurization technique. This employs newly developed microporous
membrane filters which physically remove the majority of bacteria and
yeasts. Using filtration of this kind rather than heat, microbial
effectively decreased and the flavor of draft beer is largely
is a condiment prepared from various sugary or starchy materials by
and subsequent acetic fermentation. It consists principally of a dilute
solution of acetic acid in water, but also contains flavoring, coloring
extracted substances, fruit acids, esters, and inorganic salts, varying
according to its origin. Although acetic acid is the active ingredient
vinegars, these additional substances give distinctive and pleasing
the product. Vinegar may be produced from the juices of most fruits
such as apples,
grapes, cherries and pears, but cider vinegar has always been the most
in the American home. The principles involved and method of preparing
vinegar will be discussed herein.
vinegar which during the course of manufacture has developed in excess
of 4% of
acetic acid, may be reduced to a strength of not less than 4%. Cider
reduced is not regarded as adulterated, but must be labeled to this
diluted cider vinegar.
of Vinegar Fermentation
manufacture of vinegar requires two fermentation processes. The first
transforms the sugar into alcohol, by yeast. The second changes the
into acetic acid and is brought about by vinegar bacteria. One of the
causes of failure in preparing vinegar, and a factor not often
that vinegar-making involves two very distinct and different
first must be completed before the second begins.
juice of ripe apples has been found to vary in the sugar content
between 7 to
15% with an average for a large number of varieties in several states
near 11%. Generally, the juice from summer apples has the lowest sugar
winter apple juice the highest, and fall apple juice somewhere between
Mature apples in the ripe stage contain the largest amount of sugar,
apples a much smaller amount, and over-ripe fruit less than ripe fruit.
juice should be expressed and collected.
Preservation by Drying
is one of man’s oldest methods of food preservation. It
is a process copied from nature; we have improved certain features of
operation. Drying is the most widely used method of food preservation.
the cereal grains are preserved by drying, and the natural process is
efficient it hardly requires added effort by man. However, there have
periods in history when climatic factors were such that grains failed
properly in the fields. In these instances, man attempted to assist the
action by supplying heat to the grains which otherwise would decompose.
legumes, nuts and certain fruits nature on the plants and dry in the
More fruits are preserved by drying than by any other method of food
preservation. The natural sun drying of foods yields highly
materials of enduring quality, yet a highly complex civilization cannot
dependent upon the elements-they are unpredictable. Sun drying remains
greatest food preservation action.
Driers -The drier consists of a chamber in which trays of product can
placed. In large driers the trays are placed on a truck for ease of
In small units trays may be placed on permanent supports in the drier.
blown by a fan past a heater (usually finned steam coils) and then
trays of material being dried.
cabinet drier is usually the least expensive drier to build, is easy to
maintain, and is quite flexible. It is commonly used for laboratory
the dehydration of vegetables and fruits, and in small scale and
TRANSFER THROUGH A SOLID SURFACE
Driers.-Steam heated rotating drums 1 to 2 m in diameter are used for
dehydration of fluid products. The slurry is deposited on the drum in a
film. Heat is transferred through the drum wall to the product film.
may be exposed to the atmosphere or it may be held under a vacuum. The
product is removed from the drum by a scraper blade. The dried film
then may be
ground to a fine powder.
Shelf Driers -These consist of a cabinet with hollow shelves.
is placed in pans on the shelves or, if solid, it can be laid directly
shelves. The unit is closed and a vacuum drawn, Steam, hot water, hot
Dowtherm or some other suitable heating medium is circulated through
shelves, heating the product. These units are expensive and have been
mainly on such products as “puff-dried” citrus powder, tomato powder
Vacuum Driers -These driers consist of a stainless steel belt on which
product is deposited. The film on the belt passes over a heating
heating drum or a grid of steam coils, and heat passes through the belt
product film. In some cases, additional heat may be supplied from the
infrared lamps. The entire unit is enclosed and held under a vacuum.
using high vacuum condition it is possible to establish specific
temperature and pressure whereby the physical state of a food substrate
maintained at a critical point for successful dehydration, with greatly
improved rehydration potentialities. Such is a system developed in
which has been called freeze-dehydration.
OF DRYING ON MICROORGANISMS
bacteria are occasionally able to withstand the unfavorable environment
them in dried foods, then create a public health hazard when eaten.
infections by enteric organisms and food poisoning organisms in
general. It is
a common technique to dry cultures (by lyophilization techniques) for
Under these conditions there is a slow, steady decrease in the number
surviving populations. Similar experiences are found with bacterial
contaminants of dried food.
OF DRYING ON ENZYME ACTIVITY
are sensitive generally to moist heat conditions, especially where
range above the maximum for enzyme activity. Moist heat temperature
boiling point of water finds enzymes nearly instantaneously
are exceptions, but as a rule a minute at 100ºC renders enzymes
exposed to dry heat at the same temperature, such as used in drying,
are notably insensitive to the effect of the energy. Short exposure to
temperatures near 204ºC have
effect on enzymes if the heating medium and the enzyme preparation is
great volume of fruit is sold as dry fruit with a moisture content of
25%. This can be achieved by placing fruit in trays for either sun
drying or tunnel drying. Some fruit juice powders have been produced by
a corn syrup to the juice and vacuum or spray drying.
dehydration of vegetables, enzyme systems must be inactivated. This is
accomplished usually by heating in boiling water or steam. Many
more stable if given a treatment with sulfur dioxide or a sulfite. The
content of vegetables should be less than 4% if satisfactory storage
quality retention are to occur. Residual moisture contents can be
these levels in practice by in-package desiccants.
are usually dried in tunnel, cabinet or belt driers. For some powdered
vegetable products, drum driers and spray driers have been used. The
dried vegetables on the market is relatively small and limited in
Potatoes are the largest single item. Most of the other products are
as onion, celery, parsley, and their powders which can be used as
ingredients. Some dehydrated vegetables are sold in soup mixes and some
used in manufacturing canned products. Much developmental work needs to
OF ANIMAL PRODUCTS
is usually cooked before it is dehydrated. The moisture content of the
the time of entry into a drier is about 50% and when dried should be
approximately 4% for beef or pork. Mildly cured vacuum packed bacon
because of the growth of many species of microorganisms. Mildly cured,
packed, sliced bacon has a shelf-life of at least six months if it is
sufficiently dehydrated before canning to have moisture content to salt
OF DEHYDRATED FOODS
meat, milk and vegetables are ordinarily packaged in tin containers.
Occasionally fiberboard or flexible film material may be employed,
they are not as satisfactory as tin. Tin offers protection against
moisture loss or gain, and permits packaging with an inert gas. If
dehydrated foods are to be stored for a considerable period of time, it
advisable to use low temperature storage.
long-term storage, of dehydrated foods, functional containers which are
hermetically sealed and resistant to penetration by insects are
packaging requirements of dried foods are product specific.
are not canned to any great extent, since they can be kept in
refrigerated or controlled
atmosphere storage for practically the whole year from one season to
Canned apples, which are usually available in the larger sizes of cans,
generally used in pies. The varieties commonly employed for canning are
Yellow Newton, Pippin, Spitzenberg, Winesap, Baldwin, Russet, Jonathan,
Delicious, and Rome Beauty.
are canned largely in the U.S.A. In India, these grow mostly in
Hills and Uttar Pradesh, where considerable scope exists for their
are not peeled for canning. They are merely cut into halves and the
removed. Sometimes, they are canned whole. According to Cruess, on as
a ton of apricots yields about 55 cases of 24 A 2 ½ size cans. Siddappa
reported an average yield of 58 cases per ton of apricots.
is one of the most important fruit crops of India. More than 200
varieties are grown over an area of about 1,60,000 hectares.
ripe fruit is peeled by hand and cut laterally into slices of 1.27 cm
cm thickness. Sugar syrup of 25 to 30º Brix, containing 0.2 per cent
acid is used as covering liquid. The pH of the banana has been found to
from 4.5 to 5.3. Butter size cans (1 lb squat) are processed for 15
minutes in (i)
boiling water (100ºC), if the pH of the fresh fruit is 4.8 or less, and
a pressure cooker at 5 lb psi (0.35 kg per cm2) steam pressure (sea
the pH is higher than 4.8. Cooling after processing should be quick and
thorough to prevent pink discolouration of the slices in the can during
berries are canned to some extent in the U.S.A. and in the U.K. They
available in any large quantity in India for commercial canning.
Mammoth and Himalaya are the more important canning varieties. The
should be handled without any delay after harvesting.
cherries are packed in barrels of brine containing calcium hydroxide,
dioxide, and occasionally alum. According to Cruess in California, the
for this purpose is made up of about
0.75 to 1.0 per cent
SO2 and about 0.4 to 0.6 per
cent of slaked lime in Oregon, approximately 1.5 per cent of SO2 and about 0.9 per cent
of lime are used. The brined cherries are stored for 4 to 6 weeks for
During this period , the colour of the cherries changes to white or
pale-yellow. The cured cherries are washed well in water and dyed with
dye such as erythrosin,
colour fixed with citric acid. These coloured cherries are used for
and Thompson Seedless are good canning varieties. Only large sized
used for canning. Syrup of 20º to 40º Brix is used. Loss in canning is
20%. According to Siddappa and Ishaq, the Seedless Kishmish and the
Haitha grapes give good canned products. Coloured grapes should be
(Artocarpus integrifolia) is available in plenty in
Orissa, Karnataka, Kerala and some parts of Tamil Nadu. It is an
staple food for certain sections of the people in these areas. The tree
annually 60 to 75 fruits, each weighing 10 to 20 kg. In exceptional
fruit weighs even 35 to 40 kg. The unripe green and immature fruit is
a vegetable. Experiments have shown that green jack-fruit can be canned
curried vegetable. The crisp bulbs (seeds removed) of the ripe fruit
for canning in syrup. The yield of bulbs varies from 25 to 40 per cent
weight of the fruit.
are found in Uttar Pradesh, Bihar and Orissa. For canning, the fruit should be
tree-ripened. The outer
shell is first cracked, then the pulp inside is separated, and finally
stones are removed. Plain can and 40º Brix syrup with 0.5 per cent
are used. Prompt and thorough cooling of the cans after processing is
to prevent development of pink colour in the product. Canned litchies
China are well known in foreign countries.
can be cut into halves and canned to get an attractive product.
slices or cubes, can be used for canning. About 0.5% citric acid should
added to the syrup to counteract the high pH of the fruit. Papaya could
canned along with other fruits like pineapple, mango, banana, etc. to
product similar to the one commercially packed in Australia. Papaya
quick growing fruit, can from the basis for a thriving canning
also yields valuable by-products such as the enzyme papain and
pectin. An integrated approach to the utilization of this fruit has
investigated by Siddappa and his co-workers at the Central Food
Research Institute, Mysore.
Brines for Canning
canning fruits and vegetables, different covering liquids
are employed. Syrup of sugar, glucose or corn is used for fruits, and
salt solution for vegetables. The process of preparing these for
requirements, on commercial as well as domestic scale, are dealt with
canning fruits, sugar in the form of syrup is used to bring out the
flavour of the fruits, care being taken not to make the contents
sweet. Strength of the syrup would depend on the kind and variety of
Generally, the more acidic fruits require denser syrups.
can be made either by the ‘cold process’ or by the ‘hot process’. In
process, sugar is placed in a tank and cold water poured over it and
The solution is then filtered through a thick flannel bag, muslin
fine brass wire gauze to remove insoluble impurities. Sometimes warm
also be added to facilitate the dissolving of the sugar. In the hot
sugar and water are placed in a steam jacketed kettle, boiled and the
removed. The syrup is clarified further by nitration. Steam helps to
the syrup and to prolong its keeping quality. The quantities of sugar
required to prepare syrups of a given Brix are given in Table 1.
of the canned product depends on the accuracy of measuring and
syrup, because any mistake in syrup making cannot be rectified later.
cost of syrup forms an important item in the total cost of the finished
product, it is essential to control the syrup strength and thereby
wastage. Accurate thermometers and hydrometers are necessary for this.
different kinds of hydrometeres used are the Brix or Balling, Baume,
gravity and Twaddell hydrometers. A refractometer can also be more
Brix or Balling hydrometer gives directly the percentage of sugar by
the syrup. It is calibrated at 20ºC, and corrections are needed for
temperatures. On the Baume’s hydrometer, the divisions range from 0 to
degrees. The relation between the Brix and Baume scales is given in
8. Specific gravity
in the case of
Baume’s reading may be deduced by adopting the formula:
it will be found necessary in practice to dilute a syrup or increase
strength. This is facilitated by what is known as the ‘square method’.
most commonly used for preparing beverages are sweet
orange, mandarin (sangtra) loose jacket orange,
sour lime (kagzi
nimboo or limboo), lemon, grape fruit, grape, apple, mango,
phalsa, (Grewia asiatica), jamun (Eugenia
passion fruit, pineapple, etc. Tomato juice also has become quite
Among the squashes, sweetened orange juice known as orange squash,
and pinepapple squash are the most popular ones.
plums like the alucha plum are preferred for the
preparation of plum
squash. To extract the colour from the skin, the plums are heated at
about 30 minutes, in half their weight of water. The heated fruit is
through a pulper to extract juice. The juice is made into squash of 45
degrees Brix. Sodium benzoate is added as preservative.
and syrups can also be made from several other fruits like mulberry,
strawberry, pear, apricot, pumelo, guava, musk melon etc. The methods
preparation are broadly the same as those described in the case of
mango, pineapple, etc. Ingredients required can be deduced from basic
principles involed in the preparation and preservation of squashes.
fruit juices like orange juice, apple juice, pineapple juice, etc.,
highly prized as nutritive breakfast foods are packed in large
several coutries. Apple juice is generally bottled, while other juices
apple juice is highly popular in Europe. In this country also, it is
popularity. With the increase in area under apples, the demand for
is likely to increase in the near future. A method has been
the preparation of juice from Kulu valley apples like the Yellow Newton
Baldwin varieties. The apples are washed with a weak solution of
acid (22.7 litres of acid in 454 litres of water) to remove any arsenic
lead spray residues, and are then crushed in an apple grater to pieces
cm to 1.2 cm size. The pieces are placed in a basket press and pressed
apples are available in large quantities on the West Coast, where there
thriving cashew kernel processing industry. Large areas are being
cashew to meet the increasing world demand for the kernel. At present,
fruit, which is the fleshy portion to which the nut is attached, goes
practically to waste. The fruit is highly perishable. It is fairly rich
vitamin C, and as such is worth preserving, by organising its
processing at convenient centres. The resulting sweetened juice has a
taste and the characteristic aroma and flavour of the cashew apple.
citrus juices, canned orange juice and frozed 4:1 orange juice
the most popular fruit juices on account of their nutritive avalue,
content and universal appeal in almost all countries. To retain the
taste and flavour as well as vitamin C content of the juice highly
sophisticated processing equipment and technique are employed.
improve its quality and retain its vitamin C content, the juice is
deaerated and flash-pasteurised. Preservation of orange in its pristine
with all its natural flavour, is still a technical problem. It develops
characteristic stale or off-flavour during storage.
a suitable modification of the method of a extraction and preliminary
of the juice, it is possible to minimise the development of bitter
taste in the
equipment comprising of fruit washers, juice extractors, depulpers,
flash pasteurizers, fillers etc., have quite recently been installed in
two factories in the country for canning orange juice and manufacture
density (6:1) orange juice concentrate.
as well as white grapes can be used for making grape juice. In the case
coloured varieties, it is necessary to heat the crushed berries for 10
minutes at 60 to 63ºC to extract the colouring matter. White grapes are
heated. Juice is extracted from the crushed grapes by means of a basket
The extracted juice is filtered through cloth and bottled by the
method. In the bottled juice, cream of tartar (argol)
down during storage.
already mentioned earlier, pineapples are cultivated fairly extensively
Assam, West Bengal, Kerala and recently in Coorg. The production in
is nearly 95 percent of the total production of pineapples in the
Although there are a number of varieties, namely kew, giant Kew,
Mauritius, Jaldhoop, Singapore, etc., Kew and
Giant Kew are preferred for canning whereas other varieties can be used
preparation of juice. Pineapple juice is generally but not always a
in the canning of pineapples.
the HTST process, the juice is quickly heated to 88ºC, held at that
for 2 to 3 minutes, and then immediately filled into clean and steamed
which are closed, inverted for a minute or two and then cooled.
kandhari variety of pomegranate, which contains
richly coloured purple
grains, gives a highly delicious juice. The fruit is cut into quarters
grains separated and pressed in a basket press. The juice can also be
from the cut quarters as such by applying gentle pressure in a basket
The juice is filtered through thick cloth. It is then bottled and
pasteurization or by addition of sodium benzoate. The flavour is rather
delicate and becomes less intense gradually during prolonged storage.
can also be converted into an attractively coloured pleasant-tasting
55 to 60 degrees Brix. The well-known syrup of grenadine is prepared
of fruit juices in the preparation of carbonated beverages was
negligible till very recently, although large quantities of aerated
sherbets, and synthetic drinks containing
sweetening agents like
saccharin, are consumed all over the country. There products have
very little or of no nutritive value. If real fruit juices are
instead, the nutritive value of these beverages could be increased
which is a highly desirable objective.
prepare orange syrup for carbonation, a heavy syrup is made by mixing
4.5 kg of
orange juice, 6.8 kg of sugar and 198 g of citric acid. Of this, 42 to
56 g are
filled into 283 to 340 g bottles for carbonation. Other syrups like
pineapple, lemon, lime, etc. can also be prepared in a similar manner.
beverages have been known to mankind from times
immemorial . Grape wine is the most important among these. The Vedic “Soma
Rasa” also is a kind of fermented juice. Wines made from
fruits are narhed
after the particular fruit employed. Thus we have apple cider from
perry from pears and oranges. Starch and sugar also are fermented to
special types of liquors. In India, such liquors are known as nira
of palm tree, sake from rice, country liquors from molasses etc.
Material. Grapes intended for wine making are sorted to
bunches and then crushed between fluted rolls. In the case of white
crushed mass is pressed directly in basket-type presses. In the case of
coloured grapes, on the other hand, they are fermented slightly before
the juice. This helps in the extraction of colour and also facilitates
of the juice. Generally, the yield of juice is 60 to 70 per cent.
ferment the juice, which is popularly known as ‘must’ in fermentation
is a culture of pure wine yeastlike Saccharomyces
ellipsoideus is added
as a starter. Sulphur dioxide is added to the ‘must’ at the rate of 50
ppm (about 226 g of potassium metabisulphite per 1016 kg of grapes) to
the action of wild yeasts and bacteria which are undesirable in
fermentation. The temperature should be maintained between 27ºC and
Fermentation virtually ceases at about 38ºC.
the Brix of the majority of grape variteties grown in the country
12 to 16 degrees, except in the case of seedless Kishmish grapes, which
Brix as high as 23 to 26 and, therefore, dry satisfactorily under
conditions. In the case of grapes of low Brix value, case sugar is
added to the
juice sometimes to raise the Brix to about 23 degrees.
the maturation process, there is natural clarification of the wine.
aids, white of egg, etc, can also be employed to bring about the
Jellies and Marmalades
preserved fruits, jams, jellies and marmalades form an
important class of products. During World War II, fairly large
these were imported into India from the U.S.A., the U.K., and
Nowadays, such products are being manufactured extensively in several
in this country, as by-products or joint products in fruit canning
are also made in many of the homes all over the country. Their
demand can be increased manifold by making better use of cull fruit
being wasted at present.
is a fruit jelly in which the slices of the fruit or of the peel are
The term ‘marmalade’ is generally associated with the product made from
fruits like oranges and lemons, in which shredded peel is in included
term fruit jelly covers, in a general sense, jams and marmalades also
possess the consistency of jelly (whether made from clear juice or from
pectin is the main ingredient in the fruit which gives a set to the
jam, it is
preferable to use some green fruit which is rich in pectin along with
fruit to secure the desirable jellying effect in the jam. Over-ripe
should not be used as it produces pasty product. In some cases, where
is deficient in pectin, pectin from other fruits or commercial liquid
pectin may be added to supplement it.
Preserved by Heat Treatment
fruit is prepared in the same way as for canning, and heated to a
temperature in hermetically sealed containers. Sometimes, a small
sugar is also added to preserve the aroma, colour, and texture of the
Plums, apricots, pineapples, and peaches are stored without addition of
whereas strawberries and raspberries are stored after adding sugar. The
sugar is taken into account at the time of making the jam. This method
however, generally used largely for the following reasons :
storing the fruit in barrels;
Loss of colour
in fruits such as strawberries and raspber ries during the treatment
A certain amount
of loss of pectin while the fruit remains hot for a long period in bulk
preserving fruits in bulk, sulphur dioxide is universally employed in
of sodium or potassium meta-bisulphite, sulphurous acid or calcium
Calcium sulphite provides an additional advantage in that it hardens
tissues of soft fruit and thereby prevents their disintegration.
dioxide toughens the skin of some fruits such as gooseberries and red
These fruits should, therefore, be heated to boiling temperature and
cooled before adding SO2.
This preliminary heating will destroy the
enzyme in the fruit that would, otherwise, destroy the jellying power
pectin present in the fruit.
fruit is washed thoroughly to remove any adhering dust and dirt.
and other undesirable portions are removed. The fruit is then subjected
preliminary treatment which varies with the type of fruit. For example,
strawberries are crushed between rollers. Raspberries are steamed
passed through sieves to remove the hard cores. Plums are heated with a
quantity of water until they become soft, and are then passed through a
mesh sieve to separate the stones. Sometimes, the stones are not
making whole fruit plum jam. Cherries are treated in a similar way.
are whirled in a rotary vertical cylinder lined with carborundum to rub
tops and tails.
in excess of the requisite quantity
should not be added because, if the percentage of total soluble solids
very high, the jam becomes gummy and sticky. In case excess of sugar
added, the remedy lies in adding pectin or acid or both, to counteract
effect of excess sugar. If, on the other hand, the percentage of
is low and there is premature setting of the jam, indicating thereby
material contains excess of pectin, it is advisable to add more sugar.
exceptional circumstances where more sugar is not added, it would be
to and a small quantity of sodium bicarbonate to reduce the acidity and
TYPICAL JAMS AND JELLIES
jam. Both White and yellow apricots can be used for the
apricot jam. The method is similar to that employed in the case of
except that the quantity of acid added should be increased to 0.5 per
especially in the case of the sweeter white varieties. The kernels can
decuticled like almonds and added to the jam to improve its taste and
appearance. Besides fresh apricots, sulphited apricot pulp packed in
during the fruit season and also dried apricots, are extensively
large-scale manufacture of apricot jam. Apricot jam is a popular
several parts of the country.
jam. White as well as yellow peaches of free and also
olingstone type are
employed for the preparation of peach jam. The fruit is peeled with a
with lye solution, and the stones removed. The pulp is softened by
with about 1/4th its weight of water. An equal weight of sugar and 0.2
citric or tartaric acid are added to get a jam having good taste, set
jam. Pears are peeled and cut into small pieces which are
then crushed and
boiled with 3/4th of their weight of water. To that pulp 0.25 to 0.5
citric acid is added towards the end point of boiling the jam. Pear jam
an important by-product in the canning of pears.
the preparation of marmalades, all the conditions necessary for
are applicable. The pectin and acid contents of the marmalades should
slightly higher than what has been recommended for jellies. Citrus
are generally of two kinds, namely sweet marmalade and bitter
well-known English marmalades such as golden shred marmalades, are of
bitter type; bitterness being accepted as a desirable characteristic of
product. A mixture of sweet and bitter oranges like the Seville oranges
in their preparation.
is desirable to add a small amount of flavour to the product, because
the natural flavour volatilizes during the boiling and cooking
Generally, a small quantity of orange oil may be added to the marmalade
time of filling into jars or cans.
tomatoes are highly refreshing and appetizing. They are a
good source of vitamins, particularly vitamin C. In this country,
grown both in summer and winter, but those grown in winter are superior
they contain more solids.
tomato changes in colour during different stages of its maturity and
i.e., from green to pale-white, yellow and finally red. The yellow
owing to the presence of carotene. The red colour appears when the
formed in the fibres.
this product, only plant-ripened and fully red tomatoes should be used.
green, blemished and over-ripe fruits should be rejected as they
affect the quality of product. Juice got from over-ripe tomatoes is
thin and not quite pleasant in its taste and aroma.
rinsing of tomatoes in water is not enough, because mould filaments and
micro-organisms found in the cracks, wrinkles, folds and stem cavities,
easily dislodged by gentle washing alone. For thorough cleaning,
should be washed in plenty of running water. For commercial production,
washers, or trough washers fitted with moving conveyor belt and soft
brushes, are generally employed.
trimming, tomatoes are cut into 4 to 6 pieces for boiling to soften the
tissues. Alternatively, they may be crushed by means of fluted wooden
concentrated tomato juice or pulp without skin and seeds, and
less than 25 per cent of tomato solids, is known as tomato paste. If
is further concentrated so as to contain 33 per cent and more of tomato
it is called concentrated tomato paste. Common salt, basil leaf or
sweet oil of
basil leaf also may be added. Part of its acidity may be neutralized
sodium carbonate or bicarbonate. Ordinarily, tomato juice can be
to 14 to 15 per cent times solids in open pans, but for higher
vacuum pans are required. The initial concentration is generally
carried out in
open pans and the product is then finished in vacuum pans.
the product is very thick, the total solids in it are determined with
cocktail is gaining popularity in many of the high class hotels and
restaurants. It is prepared just before serving and sometimes is also
from stock. In the latter case, the cocktail is preserved by
bottles. Although the recipes vary, the main constituent is tomato
which common salt, vinegar, Worcestershire sauce, lemon or lime juice,
sauce etc., are added in different proportions to suit the palate.
ketchup is a fairly common and popular tomato product in this country.
made by concentrating tomato juice or pulp without seeds and pieces of
Spices, salt, sugar, vinegar, onion, garlic, etc., are added to the
the ketchup contains not less than 12 per cent tomato solids and 28 per
sauce is a highly spiced product which is prepared from plant ripened
peeled tomatoes. It is mostly used as a flavouring material in cooking,
also as a table relish to some extent.
tomatoes are washed thoroughly, rejecting any blemished or rotton
They are then blanched in hot water or in steam till the skin is
are then dipped in cold water to stop further cooking and softening.
then peeled by lifting the peel easily by means of pointed end of a
chopped. The seeds are not removed. During cooking of the chopped
spices are added, tied loosely in a muslin cloth bag, just as in the
Sauces and Pickles
sauces and pickles of various kinds are prepared in
Indian homes and also on a commercial scale. They find a ready market
countries. Standard recipes have been modified to suit local taste in
country and consumer acceptability in other parts of the world. Fruits
apple, peach, plum, apricot, and mango and vegetables like turnip,
carrot, etc, are the basic raw materials. Onion, garlic, spices, herbs,
are added for flavour. Vinegar, common salt and sugar are also used to
products more palatable. Vinegar serves as a preservative also to some
chutneys such as mango and apricot chutneys are generally cooked to
of jam to avoid fermentation of the proiduct during storage. Where
used in fairly large quantities, the amount of sugar may be reduced
correspondingly, because vinegar itself serves partly as a preservative.
clean and dry bottles and jars earlier sterilized in boiling water
used and they should be warm at the time of filling. If the bottles and
jars are not properly cleaned, fermentation is likely to set in through
fermentation organisms adhering to the walls of the containers. It is
pasteurize the filled bottles are sealing them at 82oC for about 30
0.45 kg size jars.
is a typical product of India. For its preparation, slightly under ripe
of seedling vrieties are preferable. Fresh as well as brined and peeled
slices can be used in its preparation. Both types of raw material are
by the industry. The latter is used to extend manufacture of chutney
mango season. In this case, the slices are preserved in a brine of 15
strength, the percentage of salt being maintained by adding salt from
time. Some of the manufacturers prefer to dd dry slat to the slices.
sauce is made from soya beans. the sauce has usually a predominant
taste and has a dark brown colour. It is made by cooking soya beans and
and yhen allowing the mass to undergo mould fermentation for 3 to 4
moudly mass is then mixed with strong brine (15 to 20 per cent) to form
which is filled into wooden barrels to bring about bacteriological and
changes in the presence of a high concentration of salt. In due course,
brown liquid is formed. It is boiled and filtered. To the filtered
molasses are added to improve the flavour. the finished product, which
as soya sauce, is bottled in the usual way.
AND SOUP MIXES
soups such as tomato soup, mushroom soup, mixed vegetable soup,
dried vegetable mixtures for quick preparation of soups at home, are
popularity nowadays. Liquid soups are generally canned. They are warmed
time of serving. In the case of typical soup, namely tomato soup, the
two recipes; one for home scale preparation and the other for
production will be useful as guidelines.
of the vegetable in a salt solution of pre-determined concentration for
certain length of time is called brining. This type of treatment is
the case of cucumbers and similar vegetables, which do not contain
juice to form brine with dry salt.
can be prepared by dissolving common salt in water and filtering it
jelly bags to remove insoluble impurities. The amount of brine
cover the vegetable is usually equal to about half the volume of the
to be fermented. To be more precise, if a keg of 45.4 litres capacity
is to be
packed, the amount of brine required would be 22.7 litres. It is
make the whole quantity of brine needed for the day in one lot.
are several kinds of pickles sold in the Indian market. Mango pickle
first. Then comes cauliflower and turnip pickles followed by those of
chilli, bamboo etc. Pickles are classified according to the method of
pickles are the most important ones in other countries. Their are sour,
spiced and mustard pickles. Pickled onions occupy a prominent place
pickles imported into this country. Then come mixed pickles, followed
piccalilli, dill, walnut, beetroot, cabbage and all other kinds of
form different fruits and vegetables.
bamboo shoots can be used for preparing different types of pickles.
tender bamboo shoots and remove the outer leaves Cut the shotts into
pieces and boil them for half an hour twice with 2 to 3 changes of
remove the poisonous bitter principle namely, hydrocyanic acid. Drain
well. Dry the pieces for 2 to 3 hours in the sun. Mix them with the
spices and a small quantity of rapeseed oil or gingelly oil. Fill them
into a stone
jar. Place the jar in the sun for about a week. To imporve its keeping
add sufficient oil to keep the pieces fully covered.
begins in the field for many vegetables. This is
true with mobile cutters for greens, viner/shellers for peas and beans,
extractors for tomatoes, and graders/washers for many vegetables. The
advantages of such operations are that harvesting/processing can be
started at any point to accommodate variations in the field; there is
no lag in
time in which freshly harvested, sometimes badly bruised, product can
deteriorate while waiting for the next step in processing; and most of
refuse, including vines, shells, leaves and other organic waste, is
over the fields to be incorporated into the soil. There are several
common to the preparation of most vegetables for processing.
STEPS IN PREPROCESSING
operations involved in preprocessing vegetables for canning, freezing,
dehydration, or pickling can be summarized as follows :
Harvest in the
immature, tender stage, before any portion becomes fibrous and tough.
should be full grown, but tender; peas and beans should be “green” ;
asparagus, stems of greens, and shells of snap beans should be without
There is a tendency for most vegetables to be harvested after the peak
Grade to remove
trash, overmature, diseased, insect-infested vegetables, and other
that would impart an off-flavor to the product. This may be done with a
roller-grader/sizer, a blower, or rod/shaker, followed by hand
Bruising or cutting, which may cause loss of juices, should be avoided.
ascertain pay rate, yield, and production rate.
Rinse in water
to remove surface dirt, insects and small trash not removed by the
detergent may be used on vegetables taken from the soil (e.g. potatoes,
potatoes, and turnips) and leafy vegetables (e.g. spinach and turnip
provided it is thoroughly rinsed off.
Prepare as required for individual
vegetables. This includes peeling (beets, carrots, parsnips, potatoes,
potatoes); shelling (beans, lima beans, peas, blackeye peas); shucking
cauliflower, Brussels sprouts); trimming (snap beans, okra, broccoli,
others as needed); and cutting and dicing (carrots, beets, sweet
okra, and others as desired).
Blanch or scald at 190ºF (88ºC) to stop
all life processes
and destroy yeast and
mold; to inactivate enzymes that would cause discoloration and changes
flavor and aroma; to render the product limp and easier to pack in
to fix the green color; and to remove certain harsh flavors common in
vegetables such as turnip greens, collards, spinach, okra, and snap
harvesting has aggravated the waste disposal problem and decreased
the potential. Even though plant breeders have developed tomatoes with
skins and firm flesh, rough handling during mechanical harvesting still
significant damage. Once damaged, tomatoes deteriorate rapidly because
microbiological and enzymatic actions. This causes a 10-20% loss in
solids during the usual 24 hr interval between harvest and factory
including an allowance for hauling mold losses. The damaged fruit ends
urban waste and is a direct loss.
Peeling. Tomatoes can be lye-peeled by immersion in a
using a principle successfully applied to fruits. In this procedure, a
conveyor spreads tomatoes uniformly into machines, where they are
picked up by
travelling buckets on an endless conveyor that takes them through the
tank filled with 14-17% lye solution. A short time exposure at
temperatures, combined with vigorous agitation, results in high
efficiency (87-90% removal) . Exposure time, temperature, and lye
be varied to give optimum results with the particular characteristics
lot being peeled.
Peeling. A process of peeling tomatoes using low temperature
freezing was reported by Brown et al. and Anon.
Liquid nitrogen (-196ºC)
is used as the refrigerant for freezing the skin and a thin layer of
beneath the skin. The fruit is immediately thawed, after which the skin
quickly and easily removed from the fruit.
in Calcium Chloride Solution. Another method of
peeling tomatoes is by submerging them in a hot solution of calcium
In this method, the underskin or
mesocarp of the tomato is not removed; therefore, the finished product
better appearance and color than product obtained by lye peeling.
drained weights and original shape were obtained, and the firm whole
be sliced in a manner similar to whole fresh tomatoes.
purpose of blanching is to prepare vegetables for the next step in
There are many ways of doing this, depending upon the kind of vegetable
end product desired. Many methods of blanching have been used in an
reduce the leaching of nutrients and to get uniform heating throughout
about 1945 considerable public monies have been invested in research on
of irradiation to prevent postharvest losses in vegetables for the
and processing. Early optimistic reports were based on results with
equipment. Extensive studies in California and elsewhere, employing
simulated transit equipment, have yielded largely negative results.
show that conventional refrigeration is still the best means of
postharvest losses. Furthermore, refrigeration is cheaper,
more effective than irradiation.
juice blends were initially developed as a way to utilize vegetable
because of their high natural pH, required destructive high temperature
sterilization procedures. Acidulation with organic acids would have
been been a
logical way to use low-acid juices, except that vegetable juices with
appropriate acids apparently were not accepted by many consumers.
then, became the popular natural acidulant almost 30 years ago.
sauce is the liquid element accompanying every culinary preparation.
sauces are as numerous as they are varied, they can broadly be
(1) those comprising both the essential solid and liquid elements, such
stews containing vegetables and/or meat or (2) accompanying sauces,
tomato sauce, white and brown sauces. The vegetables used in a sauce
either fresh, canned, or dried. Special flavorings, including herbs and
and oil can be added to give special characteristics to a sauce.
is an ancient method for
preserving food. It lowers the costs of packaging, storing, and
by reducing both the weight and volume of the final product. Sun drying
certain fruits, such as apricots and peaches is common, whereas there
limited application of sun drying with vegetables, except for a small
of come-dried mushrooms and experimental use of solar driers for
wide variety of methods is available for drying food products, each
definite effect on the quality and physical properties of the product.
vary with drying methods, and they vary widely for different products
the same drying method.
frozen peas are the least costly item to manufacture, its cost
disappears if the cost associated with one month of home storage is
In that case, compressed freeze-dried peas is as equally cost-effective
of the tightening supplies and increasing costs of various forms of
utilization of solar energy for drying vegetables has been evaluated.
of wind and radiant solar energy in combination for drying vegetables
promote conservation of food and energy resources.
common kinds of vegetable-drying equipment are tray, tunnel, continuous
conveyor-belt, belt-trough, air-lift, fluidized-bed, spray, drum and
drying of vegetables is still the most widely used method. In the early
tunnel and cabinet driers were in general use, buyt continuous
dryers and belt-trough dryers are rapidly replacing these devices.
the past decade, the growth of the frozen-food industry
has been greater than that of any other segment of the food industry.
Production value of frozen fruits and vegetables increased about 12%.
most important vegetable crop preserved by freezing is the white
important frozen vegetables are green peas, corn, snap beans, broccoli,
carrots, lima and green beans, and mixed vegetables. Cauliflower,
sprouts, and green asparagus are also frozen in significant quantities.
OF VEGETABLES FOR FREEZING
were first successfully frozen commercially about 1936, with green peas
spinach as leaders. The key to holding the fresh flavor was not
se, but inactivation of the flavor-deteriorating enzymes by
before freezing. Once this problem was solved, the list of commercially
vegetables grew to more than 25 by 1944, and by 1950 included most
of the early research on blanching and freezing vegetables was done at
Frozen Food Laboratory, Seattle, Washington. This research team moved
Western USDA Utilization Laboratory, Albany, California after the
deterioration is so rapid after harvesting, all vegetables harvested on
particular day should be processed on that day unless immediately
For this reason, during the peak of the processing season, a high
the crop is harvested, transported, and processed at night. Most of the
in handling (e.g., inspection, grading, trimming, shelling, and
washing) can be
done better before the vegetables wilt.
list of vegetables considered unsuitable for freezing continuously
shorter as (a) methods of preparation for freezing are improved; (b)
knowledge is obtained about maintaining the color, flavor, aroma, and
in vegetables before, during, and after freezing; (c) improvements are
defrosting and serving frozen vegetables; (d) more vegetables are
combinations with other products; and (e) more vegetables are fully
may be accomplished in various ways. Common methods include air-blast
freezing of packaged vegetables, and air blast belt, fluidized bed, and
liquid-contact freezing of vegetables before packaging.
freezants can be classified into two types: (1) those operating at or
-73ºC and (2) those operating in the range of approximately -18ºC down
to -34ºC. Rasmussen and Olson refer to the former as cryogens;
include liquid nitrogen (LN), liquid air, and liquid or solid carbon
Dichlorodifluoromethane (R-12) has attracted much attention as a
liquid-contact freezing. This
boils at -30ºC, high compared with the cryogens, but freezing rates are
comparable. The use of brines for direct freezing has been reported to
better result than air blast freezing for IQF items. Several
freezants have found some applications in the frozen food industry, but
quality vs. freezing costs with these methods, compared with more
freezing methods, continues to be debated, and equipment improvements
In dehydrofreezing, the product is partially dehydrated (a
threefold concentration) just before packaging and freezing.
procedures (i.e. harvesting, handling, storage, washing, peeling,
blanching, and cooling) for vegetables that are to be dehydrofrozen are
to the conventional methods.
products must be stored and transported in the same manner as other
foods. The advantages of dehydrofreezing over conventional freezing
(1) savings in packaging, shipping,. and storage costs; (2) reduction
and drip losses; and (3) increased freezing capacity. Dehydrofrozen
are still very limited in production and are used only for the
and remanufacturing trades.
AND QUALITY OF FROZEN VEGETABLES
is one of the best approaches to preserving quality in vegetables.
Olson and Dietrich, properly blanched, frozen and packaged vegetables,
including cauliflower, green beans, peas, spinach, etc, can be kept at
for 5 years without measurable change in color, flavor, chemical
and physical attributes. The same authors reported that properly
packaged frozen vegetables are stable enough to maintain high quality
harvest to another at -18ºC. However, rigorous evaluations by trained
panels can detect minor color and flavor deterioration in some frozen
vegetables stored at -18ºC for 1 year in comparisons with identical
‘Blue Lake’ cultivar of green beans (Phaseolus vulgaris L.) which
pole bean type, is considered highly desirable for freezing. It yields
tons/acre, whereas bush bean cultivars usually yield 1-4 tons. However,
labor cost of growing and harvesting ‘Blue Lake’ pole beans is
high, and in recent years, because of the development of mechanical
for bush beans, many acres have been switched to bush types. Some
bush-type green bean cultivars grown in the West are ‘Tendercrop’,
‘Asgrow 274’, and ‘Cornelli’ 14'. The Italian green bean, or ‘Romano’
has become increasingly important in recent years.
size graded beans are fed into snippers, which remove the stems and
blossom ends from the pods. Some processors prefer to snip beans before
grading. Beans to be used for cuts pass to mechanical cutters where
cross cut to lengths of 2.54-3.81 cm. Beans to be used as boil-in-bag
frequently cut diagonally, at a 45-degree angle. Nubbins and small
removed as the cut beans pass over a series of vibrating screens. After
cutting operations, beans are blanched in steam or in water at 99ºC for
min. The large No. 5 and 6 beans used for French cut are first blanched
then cut. Although smaller beans can also be cut after blanching, a
that reduces the flavor loss encountered when cut beans are blanched,
practice frequently leads to sanitation problems. In either case, the
is quickly cooled after blanching, then sorted, packed, and frozen.
are frequently individually quick-frozen on belts or frozen by
Refrigerant-12, and then bulk-stored.
than 75% of frozen potato products are used by restaurants and
Because of the dominance of this one vegetable in total frozen
considerable space is devoted here to the principal form, the frozen
potato products are not only convenient but also dependable in quality.
of frozen potato products, rather than fresh potatoes, has several
especially for institutional and foodservice operations. These
include stable price, greater flexibility in meal preparation,
of storage and inventory control, uniform quality and reduced labor
are usually suitable for processing into frozen French fries
harvest, but a buildup of reducing sugars during prolonged storage
may render many cultivar unsuitable for processing. If potatoes are
a few months after harvest, storage at 4-10ºC should permit production
high-quality French-fried product. However, French fries prepared from
stored for 2-3 months at 10-16ºC have been reported to have better
flavor, and color than those prepared from potatoes stored below 10ºC.
are stored at 4ºC or lower in many commercial storage cellars to
sprouting, withering, and spoilage. Under these conditions reducing
to accumulate. If the concentration of reducing sugars becomes
resulting French fries will be too dark in color. In such instances,
must be conditioned before processing, i.e. held at 21ºC or higher for
weeks just prior to use. This treatment lowers the reducing sugar
at the cost of weight losses due to shrinkage. It is generally
a reducing sugar content above 2-3% of the potato solids is undesirable.
fry strips are usually water-blanched before frying. Blanching makes
color more uniform, reduces fat absorption by gelatinizing the surface
starch, reduces frying time, and improves texture. Adjustments are made
blanching time and temperature to accommodate the variations
different lots of raw material. Blanching may be done at 90ºC in water
min. It is common to operate two blanchers in series for greater
The first blancher may be used, for example, in the manner just
while the second may contain a dilute sugar concentration to a level
a product with the best color on frying. Various compounds, such as
lactate for improvement of texture and sodium acid pyrophosphate for
after-cooking darkening, have been used with varying success.
blanching, excess moisture is removed from the strips by dewatering
warm-air blowers before the strips are fed into a fryer at a carefully
regulated rate. Various types of conveyors are used to carry strips
hot fat at 121-191ºC. In one method strips are conveyed through the fat
perforated trays or baskets mounted on an endless chain. Close
attention to and
control of frying conditions are essential in order to obtain a product
has the desired surface color and internal textural characteristics
for institutional use or home consumption. Restaurants, for example,
French fries that can be prepared as needed by finish-frying in deep
develop color and crispness. To meet this need, the processor gives the
a minimum of frying, i.e. “par-fries” them. Products destined for home
consumption are fried more completely.
wide variety of frozen potato products is made from the slivers and
from the French fry line and from chopped or sliced small potatoes.
include whole, diced, mashed, hash-browned, au gratin, O’Brien,
stuffed, home-fried, rissole, and Delmonico potatoes, potato pancakes,