Principles and Methods of
FRUIT AND VEGETABLE PRESERVATION
Knowledge of Spoilage agents
Environmental conditions
 Physical Damage
 Action of enzymes
 Growth and multiplication of
Microorganisms
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Preservation aims to increase the shelf life of
food and ensuring the safety of human
consumption.
This involves
Prevention and delay of microbial
decomposition
Prevention and delay of self
decomposition
Prevention of Damage caused by poor
handling, insects and mechanical means
Methods of Preservation
Preservation by drying
Preservation by use of low temperature
Preservation by use of high Temperature
Preservation by use of food additives
Preservation by irradiation
Asepsis
Methods of Preservation
Preservation by exclusion of Air
Preservation by exclusion of moisture
Preservation by fermentation
Preservation by filtration
Preservation by carbonation
Hurdle technology and combination of methods
Preservation by drying
Reducing free or available moisture
Most foods contain enough moisture to permit
the action of their own enzymes and growth of
microorganisms.
Large surface area provides maximum contact
with the heating medium and the moisture to
escape.
Preservation by drying
Methods of drying
A. Sun Drying
A. Sun drying
Sun drying of fruits, vegetables, cereals, pulses etc. is done by
exposing the food material to the sun rays
Method widely practiced in tropical and subtropical regions where
plenty of sunshine is available
Cheapest method
Sun Drying
Disadvantages
no control over temperature, humidity ,
wind velocity
Products not very hygienic
Requires more labor
Loss of original flavor and texture
Contamination of the food with dust, dirt,
rodents and animal excreta
a. Sun drying
b. Mechanical dehydration
Passage of heated air with
controlled relative humidity
over the food material
• Ovens, Solar driers, kiln driers,
tray driers etc.
Drying can also be achieved by passing the food
through hot air or hot surface
e.g, Tunnel drier,, spray drier, and drum drier
Advantages:
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uniform drying
better quality product
saving of time and labour
environmental changes do not effect the drying process
2. Preservation by use of low temperature
Retards
Chemical
Reactions
Low
Temperature
Actions of food
enzymes
Microbial
Growth
2. Preservation by use of low temperature
Low Temperature does not kill
the microorganisms present in
the food but prevents growth
of some microorganisms and
slows the growth of others
2. Preservation by use of low temperature
Methods
a. Common or cellar storage (about 15° C)
Root crops, cabbage, apples and similar
foods are stored in bulk
The deterioration of foods in cellar
storage due to their own enzymes and
microorganisms is not prevented but can
be slowed down
B. Chilling or Cold storage (0-5°C)
Cooling by ice or refrigeration
Temporary preservation method
Most perishable foods including eggs, dairy products, meat, sea
foods, vegetables and fruits are kept in chilling storage for a
limited period of time with little changes from their original
condition
c. Freezing or Frozen Storage (-18 to -40°C)
Microbial
growth
prevented
Enzymes
retarded
Slow freezing
• -23°C in 3 to 72 hours
• Butter , peas, carrot,
meat
Quick Free
Freezing
• -20 °C in 30 minutes
d. Cryogenic Freezing ( below -60 °C)
Freezing is done at
very low temperature
( below -60 °C) by
means of liquid
nitrogen.
Certain fruits and
vegetables, fish,
mushrooms are frozen
this way
e. Dehydro freezing

Foods especially fruits and vegetables are
frozen this way where half of the
moisture present in them is removed
before freezing
3. Preservation by use of High Temperature
Denaturation of proteins
Inactivation of Enzymes
Killing of microbes
• Bacteria more resistant than yeasts and
molds
• Spores of bacteria even more resistant
Temperatures employed in preservation of
food by means of heat are:
Pasteurization (Temperature below
100°C)
Heating at 100°C
Sterilization (temp above 100°C)
a) Pasteurization
Liquid foods, milk, fruit juices, vinegar etc.
 Heated below 100°C and immediately
cooled
 Ways of Pasteurization

◦ HTST: High Temperature Short Time 72°C for 15 seconds
◦ LTLT: Low Temperature Long Time 62.8°C for 30 minutes
Pasteurization kills all bacteria, yeasts and molds except
thermoduric and thermophiles
Therefore, some other method should supplement
pasteurization
a) Pasteurization
Methods of Pasteurization
• A. Flash Pasteurization
• B. Bottle method or holding
pasteurization
• C. Pasteurization by over-flow
method
b) Heating at about 100°C
Many acid foods(PH <4.5) can be
successfully processed at 100°C or less
 100°C temp obtained by boiling a liquid
food, Immersing food containers into
boiling water or by exposure to flowing
steam
 e.g Blanching of vegetables, baking of
bread, roasting of meat
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c) Temperature above 100°C
(sterilization)
Temp above 100°C is obtained by steam
under pressure in sterilization
 Complete destruction of all kinds of
microbes
 Milk , fruit, fruit juices
 Sterilization can be done by heating in
sealed containers in case of
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◦ Canning
◦ Ultra high temperature (UHT)
◦ Hot filling and sealing method
4. Preservation by use of Food
Additives
A food additive is a substance or a mixture
of substances which is added to food to
improve its quality.
 Those additives which prevent the
deterioration or decomposition of food are
known as preservatives
 They have antibiotic, fungistatic, germicidal
and anti-oxidative properties or act as
neutralizers of acidity, firming or coating
agents to prevent the spoilage of foods

Two types of preservatives
Class I and
Class II preservatives
Class I preservatives
Common salt, sugar, honey, wood smoke,
spices, vinegar, or acetic acid
Salt at concentration of 15-25% preserve
food products by inhibiting enzymatic
browning, discoloration of food,
inhibitory action of microorganisms,
causes high osmotic pressure and death
of microbial cells
Class I preservatives
Sugar when added in high
concentrations( > 40%)reduces
the availability of free moisture to
the microbial cells, reduces their
activity and causes death of cells
Addition of acids like acetic acid,
citric acid, lactic acid etc. reduces
pH of he medium- unfavorable for
the growth of microorganisms
Class I preservatives
Vinegar arrests enzymatic activity,
prevents undesirable browning
reaction and has germicidal and
antiseptic properties
A Layer of oil on the top of food
products creates anaerobic
condition and prevents growth of
yeast and mold
Wood smoke- Bacteriostatic
Class II Preservatives
Chemical Preservatives
Benzoates, Sulphites, Ascorbic acid,
Propionates, Nitrites etc. are
commonly used chemical preservatives.
Class II Preservatives
Sodium Benzoate: water soluble, anti-microbial
substances used in concentration 0.06-0.1 percent
It is used to preserve fruit juices, pickles, squashes
etc.
Potassium meta bisulphite- for fruit juices
Propionates- anti microbial used in bakery products
Nitrates and nitrites are very effective against
Clostridium botulism (food poisoning)
5 Preservation by Irradiation
The radiations used in food preservation
include UV rays, Beta rays, Gamma rays,
X- rays and microwaves
 UV radiations widely used
 Rays are passed through or absorbed by
the food have germicidal effect
 This method is known as cold sterilization
 Fish, poultry, meet, vegetables, milk eggs,
onion carrot are treated this way
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6. Asepsis
It means keeping out microorganisms
 Protective covering
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◦ Nuts with shells, Pea pods, Skin of fruits and
vegetables, shells of eggs
Careful picking, proper packaging and
transportation increases shelf life of fruits and
vegetables
Washing dirty food commodities
7. Exclusion of Air
Some foods (nuts and oils) spoiled by
simple oxidizing actions of oxygen in air
 Others by actions of microbes which
need air
 Maintaining anaerobic conditions by filling
Nitrogen gas in food packs or by creating
vacuum
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8. Exclusion of Moisture
Moisture necessary for development of
microbes
Lowering availability of moisture by
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Concentration
Dehydration
Freeze drying of food
Addition of salt and sugar
Chemical preservatives
9. Preservation by fermentation
Where end product of fermentation is highly
desirable
In contrast to the other methods of preservation,
fermentation process encourages multiplication of
microorganisms and their metabolic activities
Fermentation by bacteria, molds and yeasts or
combination of these organisms
9. Preservation by fermentation
Preservation by fermentation
Foods are preserved by organic acids (lactic
acid, acetic acid) and alcohol formed by the
microbial action during fermentation
Fermenting microbes also produce vitamins like
riboflavin, vitamin B12 and precursor of vitamin C
Digestion of Cellulose, hemicellulose which are
otherwise very resistant to digestion
Preservation by fermentation
Alcoholic fermentation by yeasts
Decomposition of simple hexose sugars into alcohols
and CO2
Preservation by fermentation
Lactic acid fermentation
by lactic acid bacteria
Intra molecular oxidation- reduction process
Decomposition of simple hexose sugars into lactic acid
Preservation by fermentation
Acetic acid fermentation
by acetic acid bacteria (Acetobacter aceti)
Acetic acid is produced by the oxidation of ethyl alcohol
10. Preservation by filters
Liquids filtered through bacteria proof
filters
Asbestos, sinestered glass,
diatomaceous earth, unglazed porcelain
Differ in their pore size
Bacterial filters
11. Preservation by Carbonation
Dissolving CO2 in aqueous solutions like
fruit juices
 Incorporation of CO2 gas at high pressure
 Carbonated beverages
 H2CO3--------- H2O + CO2
 Good mouth feel, fizzy taste, burning
sensation
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11. Preservation by Carbonation
Carbonation reduces availability of
free oxygen and reduces pH and
establishes anaerobic conditions
Reduces oxidation of Ascorbic
acid and enzymatic browning
12. Combination of methods
(Hurdle Technology)
Temperature, water activity,
pH, Chemical preservatives
etc. is used to design a
series of hurdles that
ensure safety and stability of
processed foods
Thanks