principles of food preservation

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PRINCIPLES OF FOOD PRESERVATION
Activities of spoilage agents depend on several
factors
Change in any of these results in their
decreased performance
Principles of food preservation based on:
Knowledge about spoilage agents
Understanding of how:
chemical reactions
physical changes
pest attack
collectively reduce quality of foods
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PRINCIPLES OF FOOD PRESERVATION
Principle 1
Autolysis in food may be prevented or delayed
by:
destruction or inactivation of enzymes
by treatment and handling of food in such
a manner so as to inhibit reactivity of
chemically active molecules

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Principle 2
Spoilage in foods as a result of microbial
activity may be prevented or delayed by:
either prohibiting entry of microorganisms
into the food
physically removing them from the food
hindering their growth and activity or
even destroying them, if they are already
present in the food.
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Principle 3
Quality defects and losses in food caused by
insects, rodents and birds may be controlled
by:
adequate packaging and
by instituting a sustained population control
programme of such pests

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Principle 4
Deterioration in food caused by the physical
phenomenon occurring during processing,
handling and storage may be reduced by:
development of optimal handling, processing
and storage conditions
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PREVENTION OR DELAY OF AUTOLYSIS
Enzymes require specific pH range to catalyze
life reactions
Enzymes sensitive to changes in pH of
environment
Information utilized to preserve foods by
merely altering their pH

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PREVENTION OR DELAY OF AUTOLYSIS
For example
Biological preservation of vegetables (pickling):
pH of raw materials reduced through activities of
lactic acid bacteria
Some meat and milk products preserved or
produced as a result of change in pH
Sometimes organic acids, as acetic acid
(vinegar), added to foods for the purpose
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PREVENTION OR DELAY OF AUTOLYSIS
Enzymes thrive best in particular temperature
range
Deviation - higher or lower side has adverse
effect on enzyme activity
Food subjected to high temperature will either
destroy or inactivate enzymes
Process called blanching or scalding

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PREVENTION OR DELAY OF AUTOLYSIS
Blanching or scalding
Some fruits, most vegetables normally
subjected to around 100°C for few seconds to
few minutes
Destroys some damaging enzymes – catalase
Usually pre-treatment in food preservation
methods as:
Canning
Dehydration
Freezing
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PREVENTION OR DELAY OF AUTOLYSIS
Use of low temperature - procedure employed
to delay autolysis
Low temperatures that prevail in refrigerator or
cold storages retard enzyme reactions
Refrigeration delays ripening process in fruits
Freezing inactivates enzymes and sometimes
destroys them
Hence frozen foods have much longer shelf
life than fresh or those kept at above 0°C

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PREVENTION OR DELAY OF AUTOLYSIS
Enzymes require moisture for biochemical
reactions catalysed in foodstuffs
Absence of water means no reaction
Property utilized, partly, in preservation of
foods by:
Removal of moisture
Binding of moisture
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PREVENTION OR DELAY OF AUTOLYSIS
Moisture in foods removed by:
Sun drying
Dehydration
Concentration
Evaporation
Available moisture bound by using chemicals:
production of intermediate moisture foods
(jam)

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Prevention or Delay of Autolysis
Chemically induced autolysis:
minimized by applying good manufacturing
practices (GMP) based on experience and
scientific knowledge
Most chemical reactions retarded by:
Maintaining low temperature
Use of chemical inhibitors
Packaging
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Prevention or Delay of Autolysis
Non-enzymatic changes prevented by:
Use of some chemicals
Sulphites to inhibit colour changes
Antioxidants check rancidity

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Prevention or Delay of Autolysis
Further control achieved by:
Employing low temperature
Controlling water activity in dehydrated foods
Reduction of reducing sugars in potatoes by
storage
Reduction of amino-nitrogen content in juices
by ion exchange
Packaging with oxygen scavengers
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Prevention or Delay of Microbial Activity
Microorganisms invaders
Where undesirable treat like any other invader
1. Take precautions to prevent their entry into
food
2. Where already gained access, may be thrown
out
3. When such strategy not feasible, control
microbial activities by creating unfavourable
conditions
4. Destroy by any suitable means

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Keeping Microorganisms Out
Nature creates all foods free from
microorganisms
Provides protective covering to prevent entry
All fruits, vegetables free from microorganisms
when produced
Skin, peel, husk and shell provide protection
Tissues of healthy animals free from
microorganisms
Skin and fatty tissues give animal protection
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Keeping Microorganisms Out
When outer covering injured, microorganisms
invade and start growing, cause infection
Industry provides protective covering to guard
against entry of microorganisms from outside
source:
Pack fruits, vegetables, meat, etc in tin cans
or glass containers
Coat cheese, eggs etc with wax or other
inert material

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Removal of Microorganisms
During food processing difficult to keep
microorganisms out
Gain entry into food during
harvesting
storage
processing operations
Microorganisms very small, not easy to pick
and throw out
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Removal of Microorganisms
Fruits and vegetables carry microflora on their
surface or in bruised, damaged and decaying
tissues
Wash raw material thoroughly to remove
contaminants
Trim bruised, damaged and decayed portions
Filter or centrifuge liquid foods such as clear
beverages (water, fruit juices)
Centrifuge milk to separate cream – removes
microorganisms

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Creation of Unfavourable Conditions
Most food spoilage and pathogenic microorganisms
aerobic
Spores of some organisms need oxygen to germinate
Creating anaerobic conditions:
Prevents growth of vegetative cells
Prevents germination of spores
In canning use mechanical vacuuming or
exhausting
Air from product removed, can sealed airtight
Even if microorganisms gained entry, under prevailing
anaerobic conditions, will not grow
Anaerobic organisms may pose problem if their
activities not checked or not subsequently destroyed.
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Creation of Unfavourable Conditions
Removal or binding of moisture
All microorganisms require available
moisture for activity
Growth inhibited if no or low moisture
Preserve food by removal or binding of
moisture
remove by drying, dehydration,
concentration

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Creation of Unfavourable Conditions
Moisture made unavailable by chemicals:
Sugar
Glycerine
Humectants (water-binding substances)
Microorganisms unable to grow in changed
environment
Food does not deteriorate or spoil as a result of
microbial activity.
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Creation of Unfavourable Conditions
Chemicals produce unfavourable conditions:
Some chemicals intentionally added
Sulphur dioxide - as potassium
metabisulphite
Benzoic acid as sodium benzoate
protect fruit juices from spoilage in sealed
containers
Some chemicals developed
Lactic acid

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Creation of Unfavourable Conditions
Lactic acid produced by normal growth of lactic
acid bacteria
Activities of lactic acid bacteria encouraged in:
Vegetable pickles - Grow, produce lactic
acid, reduce pH of vegetable material
In dairy and meat industries some products
produced and preserved by lactic acid
bacteria
Examples - Sour cream, butter, cheeses,
yoghurt and sausages
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Creation of Unfavourable Conditions
Low temperature another effective tool to create
unfavourable conditions
Chilling slows microbial growth
Freezing completely stops activities
Holding foods at freezing temperature or in
frozen state helps destroy or kill some
microorganisms.

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Destruction of Microorganisms
Destroy microorganisms to prevent spoilage
High temperatures (above maximum growth
temperature) adversely affect microorganisms
Blanching destroys or inactivate enzymes
Also kills some vegetative microorganisms
Pasteurization temperatures (65°C to 88°C)
kill pathogenic organisms including bacteria
and yeasts in some liquid foods
Sterilization employs much higher
temperatures (100°C or above) to destroy
all microbial forms
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Destruction of Microorganisms
Sterilization not possible in food processing
Hence commercial sterilization or heat
processing employed
Some microorganisms or spores remain viable
after this
With combination of other techniques
employed in preservation method, these
remain dormant and unable to cause trouble

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Destruction of Microorganisms
Heat treatment necessary to kill microorganisms or
their spores varies:
Organism to organism
State - vegetative or spore
Environment
Depending on effectiveness of heat treatment, only
part of vegetative cells, or all or most of the cell may
be destroyed
Some bacterial spores also killed at high temperature
Heat treatment applied temperature/time dependent.
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Destruction of Microorganisms
Some chemicals very effective in controlling
microbial activity in foods
Sulphur dioxide and benzoic acid common in
fruit and vegetable preservation industry
Propionates employed in baking for moulds
Microorganisms also destroyed by radiations
Ultraviolet waves from electromagnetic
spectrum have germicidal properties
Gamma rays, emitted from by-products of
atomic fission germicidal, preserve food.

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Control of Pest Activities
Pests - Insects, rodents and birds
Only those so designated that:
exhibit prolific reproductive capabilities
compete with humans for food and space
may transfer diseases to man
Constant threat to man's survival
Seemingly harmless species a necessary part
of balanced ecological system in which we live.
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Insects
Insects destroy and waste almost 50% annual
cereal grain crops in some developing
countries
Attack food everywhere - field, processing
plants
Eat sizeable quantities
Damage and create easy entry for
microorganisms
Control - fumigation with methyl bromide,
ethylene oxide and phostoxin

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Insects
Protect from further infestation - packing in
containers
Insect-proof packaging not feasible for all dried
foods, especially in developing countries for
both economic and logistic reasons
Use integrated systematic insect control
program:
preventive measures
curative measures
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Insects
Typical preventive measure for insect control:
Treatment with long-acting insecticides
Treatment with insect repellants for seeds
Use of insect predators
Other biological means
Curative insect control program - extermination
of insects and insect eggs from food by:
Physical methods
Chemical methods
Biological methods

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Insects
Popular physical method for destroying insect
eggs in wheat flour and other similar size-
reduced dry foods involves use of impact-based
instrument, the entolater
Insect eggs thrown to metal body of this
revolving instrument instantly destroyed by
impact
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Insects
Heat disinfection another physical method to
destroy insects in stored products
Temperature of food raised to about 50°C since
insects cannot survive such high temperature
Infrared devices popular heat sources for heat
disinfection of grains - effective and relative low
cost

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Insects
Most desirable control measures:
Demonstrate effective insect control over
long periods without creating intractable
adverse effects on man and the environment
Control measures which momentarily and
indiscriminately reduce insect populations may
introduce serious health hazards and
environmental problems in the long run.
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Rodents
Gross rodent infestation readily discovered by:
presence of burrows
dark oil and dirty stains on rodent runaways
odour of mice
filth deposited on food
damaged food and other materials
Dry urine appears as darkened stain on food
and containers
These stains will fluoresce under ultraviolet light
Presence of rodent filth in food processing and
storage premises calls for prompt control
measure.

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Rodents
Complete eradication almost impossible
Situation worse in developing countries
rodent populations overwhelm available
control facilities due to poor environmental
sanitation
Systematic control of mice and rats practiced
with reasonable degree of success in most
industrialized countries
Typical systematic control includes
use of poison baits
rat-traps
biological methods
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Rodents
Rodent harbourages usually destroyed or
sealed off after treatment with long-acting
rodenticide
Foods packaged and stored in environments
that make rodent invasion difficult
Sustained control effort can yield positive
results
Must be backed by reasonable measure of
sanitation around food handling and storage
sites.

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Birds
Birds consume substantial quantities of grains
in field
Some birds, as weaverbird, known to
devastate entire corn crop in field
Loss by bird invasion traditionally checked by
installing noise-making dummies at strategic
points on farm to scare birds away
Birds consume grains, contaminate food and
water
Prevention
Erect bird screens over important water supply
sources and food handling areas.
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Reduction In Physical Defects
Interactions induced by series of treatments
that accompany food manufacture, handling
and storage
No simple rule of thumb to predicts best
processing conditions for all types of foods
Experimentation, experience and current
exchange of scientific and technical information
on effects of various processing variables on
food quality have helped in development of
optimized processes aimed at keeping physical
defects in foods to minimum.

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Surface Drying
Desiccation or drying out observed on surface
of certain foods during frozen storage an
important physical defect
Control - adequate packaging and
maintenance of steady storage temperature
Refrigerated storage of flesh foods - moisture
loss and surface drying minimized by
maintaining higher than conventional average
relative humidity in storage chamber
Increase in microbial activity induced by such
high relative humidity kept under check by use
of ultraviolet lamp as storage atmosphere
sterilants
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Crystallization
Common physical defect - crystallization of
sugar in syrups and sugar-based products
Products develop distasteful sandy texture
Unwanted sugar crystallization prevented by
using mixture instead of single sugar
60 % sucrose solution at ambient temperature
develops crystals
Solution containing 75 % total sugars, blend
of sucrose, glucose and fructose no crystals
Knowledge applied in production of high
sugar products – jams, sugar-based jellies

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Other Defects
Attempts at reducing physical and textural defects in
foods during processing and storage are seen in
process handling and storage controls applied by the
industry
Relative humidity and drying rates controlled in
dehydrators to minimize incidence of case-
hardening;
Stabilizers used to prevent collapse of emulsions
during handing and storage
Freeze-drying removes moisture from heat-sensitive
foods and enhances retention of natural nutritional
and textural properties on rehydration.