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Write the methods of food preservation detailed for each method-coolingheatingadding salt or sugardehydrationadding oil or vinegarchemical preservativescanning and vaccum packingpasteuristaioni will mark brainiliest for the ones who type it detailed

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Principle of food preservation:

Various chemical and physical methods are available for preservation of food. But selection of appropriate method is very important to protect the quality and nutritional value of the food.

During preservation by these methods, following principle are involved.

Prevention or delay of microbial decomposition of food by:

Preventing contamination of food by spoilage organisms (Asepsis).

Removing micro-organisms from contaminated food. by washing.

Slowing down the growth and activity of micro-organisms in food. by freezing the food.

Killing micro-organisms present in the food. by heating the food or by adding some chemicals.

Prevention of self-decomposition of food by:

Damaging self-enzyme of food that cause self-decomposition. damaging of ripening enzyme of fruits by washing it in hot water.

Preventing purely chemical reaction occurring in food that damage the food. prevention of oxidative rancidity of lipid by addition of anti-oxidant.

Prevention of mechanical damage of food caused by insects, bird, food handling device etc.

Methods for prevention of microbial spoilage of food:

Various methods of food preservation include:

1. By preventing food contamination (Asepsis):

Process of preventing contamination of food by spoilage micro-organisms is called asepsis.

Inner tissue of healthy animal and plants do not contain micro-organisms and if present they usually do not spoil food.

Most spoilage micro-organisms enter into the food by contamination from external sources like water, air etc.

Therefore, microbial decomposition of food can be prevented by preventing contamination of food by spoilage organisms.

Several foods like egg contains natural covering around food that prevent entry of spoilage organism into the food.

Nowadays, variety of such artificial barrier are made around the food to prevent contamination. fruits and vegetables are stored for years by coating the wax around them.

Some other artificial barriers that prevent the contamination includes wrappers, cartoons and cans.

Safe handling of food and good personal hygiene of food handler are important method to prevent or minimize contamination of food by spoilage organisms.

2. By removing microorganisms from contaminated food:

It is second level of preservation of microbial decomposition of food.

If contamination of food by spoilage organism is not prevented, spoilage of food still can be prevented by removing contaminated micro-organisms from the food.

Some techniques that preserve food by removing micro-organisms include:


It is only one successful method for removing micro-organisms from contaminated food.

Unfortunately, this method is applicable only for clear liquid like clear fruit juice, beverages etc.

To remove micro-organisms, liquid food is filtered through sterile bacterial filter.

Centrifugation/ sedimentation:

Centrifugation removes some but not all micro-organisms from contaminated liquid food.

When liquid food is centrifuged suspended particle, debris and some micro-organisms settle to the bottom which is later separated and remove from the food.

This technique is commonly used for milk in dairy industries.


This method is commonly used for vegetable and fruits. Dusts and micro-organisms present on the surface of whole vegetable and fruits are removed by washing with sterile water.

One limitation of washing is that it increases water activity of some food and hence facilitates growth of remaining spoilage organisms.

Furthermore, if washing water isnot sterile, it adds spoilage organisms in food.


Trimming is the process of removing spoiled parts of food like vegetables and fruits by cutting.

Trimming prevents spread of micro-organisms from spoiled part into inner healthy tissue.

3. By inhibiting or killing microorganisms:

Different methods that preserve food either by killing micro-organisms or by slowing down their growth and activity includes:

Preservation of High temperature (Heat)

Preservation by low temperature

Preservation by Drying

Preservation by Radiation (irradiation)

Chemical agents used in preservation of food

I. Preservation of food by High temperature (Heat):

Heat is the most commonly used method of food preservation.

Heat kills spoilage of micro-organisms by denaturation of cytoplasmic protein and enzyme.

Two types of heat i.e. dry heat and moist heat are used in preservation of food.

Moist heat is more effective in killing micro-organisms than dry heat.

Heat causes denaturation of protein and enzyme by breaking down their bonds.

Breaking of bond occurs by two mechanisms i.e. hydrolysis and oxidation.

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