This document provides an overview of various food preservation methods for short and long shelf life foods. It discusses techniques such as heating, cooling, drying, adding natural preservatives like salt or sugar, and using chemical preservatives. It explains how each method works to control microorganisms, deactivate enzymes, and prevent spoilage reactions. Specific methods like drying, acidification, sugar/salt addition, and smoke exposure are then described in more detail regarding their mechanisms and considerations.

1. Principles of Food Science
By
Dr. Chandrajiit Singh
Scientist
Food Science and Technology / Home Science
E:mail: chandar30 @ gmail.com
Mobile and Whats App: 098930 64376
KrishiVigyanKendra- Rewa(MP)
JawaharlalNehruKrishiVishwaVidyalaya
Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (MP)
Krishi Vigyan Kendra- Rewa (MP) 1

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How Food can be Preserved for
Short Shelf Life
Food To be kept for short period of time:
1. Serve the food alive to the consumer and afterwards it is
cooked.
2. If food is to be cooked and then served, the food should be:
• Cleaned
• Covered and
• Cooled

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How food Can be Preserved for
Longer Shelf Life
Various methods applied for preservation for longer shelf life
are:
1. Heating
2. Cooling
3. Drying
4. Radiating
5. Using natural Preservatives ie Sugar, Salt, Oil, Vinegar and
Smoke etc
6. Using chemical preservative ie Sodium Benzoate, Potassium
Meta Sulphite, Sorbic Acid and its salts (eg. Sodium Sorbate,
and Calcium Sorbate, etc) Ascorbic Acid etc.

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Why Preservation Methods are
Applied
Following will happen in the food material if various
methods of preservation are applied :
1. Control (Within safe limit) or elimination of pathogenic or food
spoilage microorganism.
2. Deactivating enzymes,
3. Eliminating chemical reactions in the food to prevent food
spoilage.

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Preservation by Drying : Various
Consideration
Heating and Cooling we have already studied.
Drying:
1. Moisture required in food for the growth of micro-organism is
80%.
2. Drying not only remove water from the food but also from the
bacterial cell.
3. Partial drying is less effective than complete drying.
4. Bacteria and Yeast require more moisture than molds and
hence molds can grow in semi dry food also. For example
moulds can grow on stale bread.
5. Microorganism work at the micro level and in the micro
environment of the food, hence activity of water should be
considered in the food material specifically and pin pointedly.

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Basic Inofrmation
6. Water activity is related to Relative Humidity (RH)
7. Water Activity property of solution is defined as ratio of partial
pressure of water
vapor in the air to the vapor pressure of pure water at the same
temperature
8. Relative humidity refers to the atmosphere surrounding a material
or solution.
9. Moisture requirement is the water activity in the immediate
environment which may be in food particles or solution etc.
10. At favourable temperature for bacteria to grow, 0.90-1.00 is
favourable water activity range.
11. Favourable water activity range for moulds and yeasts is as low
as 0.65.
12. Partial or complete drying may not eliminate the microorganism
completely, it may preserve the microorganism s as it preserves
the food . When food is remoistened or reconstituted bacteria may

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Preservation by Acid
Preservation by Acid :
1. Acid modifies bacterial proteins by denaturing the protein.
2. Acid produced by one microorganism will inhibit growth of another
microorganism, hence controlled fermentation is helpful in
preservation of food against proteolytic and other kind of
microorganism.
3. Acid can be increase in the following tow ways:
• By adding acid forming bacteria to the food
• By adding acid directly to the food eg. Citric Acid Phosphoric Acid
etc.
• Few fruits such as tomatoes, citrus and apples etc contain acid
naturally and act as preservative.
4. Two preservative with same pH may not have same preservative
action .
5. Limit of Acidity which is tolerable to the consumer’s taste may
not make the food sterile.

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Preservation by Sugar and Salt
Preservation by Sugar and Salt :
1. Active microorganism may contain approximately 80 % of
more water.
2. When bacteria, yeast and molds are placed in heavy in heavy
sugar syrup or brine (Containing approximately 40 % water),
water from the cell moves out and hence the cell partially
dehydrates and the process is known as osmosis in order to
equalize the water concentration.
3. Partial dehydration of cell due to osmosis is known as
plasmolysis. It does not allow microorganism to multiply in
number.

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Basic Inofrmation
4. Reverse to the above case, microorganism is placed in distilled
water and due to endosmosis (i.e. movement of water inside the
cell) causes the cell to burst and this process is known as
plasmoptysis. This is rarely done in food.
5. All these phenomenon are closely related to water activity of
solution and foods.
6. Solution high in solute concentration have high osmotic pressure
and low water activity. Dilute solutions have low osmotic pressure
and high water activity.
7. The quantitative contribution of specific solute to total osmotic
pressure, depends upon molecular weight and number of ions it
produces in the solution.
8. Lower molecular weight solute has greater effect on increasing the
osmotic pressure and decreasing its water activity of the solution
than the high molecular weight solute, when the weight of the two
solutes are same.
9. Different microorganism have different level of tolerance towards

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Basic Inofrmation
Preservation with Smoke:
1. Heat and Formaldehyde along with some other chemical
released while smoking have preservative effect
2. But now a days smoke is primarily used for flavour
development.

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Basic Inofrmation
Preservation by Atmospheric Composition :
1. Removing oxygen to control aerobes such as molds eg.
Waxing or covering with plastic sheet if cheese.
2. Putting or adding oxygen to control anaerobes. It can be
dangerous when food piece is large in size because it can
happen that oxygen may not enter the center of the food and
the condition in the center may remain anaerobic and
anaerobes may survive there and can multiply later when the
condition for them becomes favourable.
3. Some aerobes consumes oxygen

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