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Pathset Publications

Food Preservation

Why do we need to Preserve Food?
We need to preserve food because microorganisms that grow on food can sometimes produce toxic substances which are poisonous to us. If we consume this spoilt food, we can become seriously ill or die. Hence, we need to preserve food from being spoilt.

Food Preservation: -
Preservation began as a necessity when ancient people searched for methods to preserve their crops for prolonged periods of time. Most food is destroyed in storage by spoilage caused by living organisms such as moulds, bacteria, and yeast. Preservation is an attempt to create an environment that is inhospitable to these microorganisms.

Ways of preservation of Food: -
Drying, Pickling and Freezing are some of the methods of preservation being followed from generations all across the world.
By using ancient methods:
▪ In frozen climates, ancient people froze seal, whale, and fish meat under the ice. In tropical
climates, they dried foods under the sun.
▪ India’s Achaar, Korea’s,’ Kimchi’ a popular pickled cabbage dish, Preserved Lemons in Middle Eastern Cuisine, Scandanavians’ Pickled Herrings, USA’s Pickled Cucumbers, Mexico’s Pickled Carrots, are some of the examples of Pickling.
Walk through any grocery store you will find dried, pickled, and canned food like jalapenos,
beans, olives, canned tuna, sun dried tomatoes and dried herbs like Kasuri methi, oregano, basil, sage leaves etc.

By using chemical preservatives:
Chemicals called preservatives may be used to prevent the growth of microbes in food.
▪ They can prevent the growth of microbes.
▪ e.g. dry salt is used to preserve meat, fish, raw mangoes, tamarind, and amla.
▪ They create an environment unviable for the microbes.
▪ Sugar reduces moisture content. Bacteria cannot grow in dry conditions. (This is used to preserve jams, jellies and fruit juice).
▪ Oil and vinegar contain a chemical that prevents the growth of bacteria. (This is used to preserve pickles, vegetables, fruits, fish, and meat)
▪ S odium benzoate and sodium metabisulphite are chemical preservatives used to retard bacterial growth. They are used in jams and squashes.

Pasteurization: -
Pasteurization is the process of heating the milk to a high temperature followed by sudden cooling, this prevents the growth of bacteria.
▪ This process is called Pasteurization after Louis Pasteur-the scientist who discovered it.
▪ Milk is heated to 700 C for 15-30 seconds and then suddenly cooled.

Food Preservation
Food preservation is a process by which edible items such as fruits
and vegetables are prevented from getting spoilt. The nutritive value,
flavour and color of the foods preserved remain intact. This is done to
increase the life of the food product and enable its storage and supply.
What principles is food preservation based on?
The main aim of food preservation is to prevent the food that is being
preserved from decay by microorganisms.
The principles it works on are:
1.Preventing microorganisms in the food that is being preserved i.e
maintaining asepsis.
2. Removal of microorganisms
3. Preventing or hindering the growth of microorganisms by various
methods such as low temperatures, drying, use of chemicals etc.
4. Killing the microorganisms by various methods such as heating and
Some food substances can self-decompose due to the enzymes that are
present in them. In these cases, the enzymes are deactivated at the
time of food preservation.
Some foods are also susceptible to insects or animals and so the
utilization of appropriate chemicals to kill them and prevent them
from destroying the food.
Let’s now look at the methods that are used for
food preservation
Food preservation methods are broadly divided into three:
1. Biological
2. Physical
3. Chemical
The commonly used methods of food preservation fall into one of the
above categories. The main purpose of all these methods is to either
prevent or retard spoilage of food items.

1.    Filtration
This is done for liquids such as juices. The process applies pressure
while the liquid is passed through a very fine sieve. This results in the
liquid passing through while the microbes cannot and thus the liquid
obtained is sterile.

2. Heat treatments
There are different kinds of heat treatments that can be done such as
boiling at 100 degrees Celsius, boiling above 100 degrees
Celsius(sterilization)or pasteurization (as done in case of milk) 

3. Low- Temperature Treatments
The most commonly used method even in households- using a
refrigerator. The refrigerator maintains a low temperature such that it
slows down the growth of microbes and keeps food fresh for longer.
Freezing is another low-temperature method used to preserve food
where the temperature is maintained at -18 degrees Celsius.

4. Using Chemicals or Preservatives
These are substances that are added to foods to prevent or slow down
their spoilage. The preservatives that are added, need to fulfill certain
criteria before they are deemed fit to be added to foods. Few
properties of preservatives are – they should be able to inhibit a wide
range of microbes, should be safe for human consumption, should not
affect the taste, flavor, color or properties of the food being preserved,
should not activate any other change in the food being preserved.

Commonly used preservatives are sulfites, sorbic acids, sodium
nitrate, and benzoic acid.

5. Acids
Citric acid and Acetic acid are commonly organic acids that are used
to preserve food substances such as pickles, sauces chutneys, and
vegetables. Being acidic, they inhibit the growth of the
micro-organisms and thus are effective food preservatives.

6. Drying
Many foods such as chips, papad, vegetables like methi or ginger are
dried or dehydrated and preserved. By dehydrating, the moisture
inside these substances is removed and thus micro-organisms are
unable to thrive on them, thus, preserving them.

7. Radiation
This method of preservation is used commonly for increasing the shelf
life of meat, seafood and poultry. Irradiating these food substances
helps to kill any pathogens and microbes that are present in them and
prevent the growth of others.
Humans have always tried and preserved their food items and other
perishable items. The methods have either changed or evolved, but the
purpose remains the same.
Look around and observe how many of these methods you have seen
at home or around you.

Common Methods of Preserving food are:


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