describe the principle on which the following methods of food preservation are based :

a) boiling

b) canning

c) freezing

d) dehydrations

Boiling: Boiling increases the temperature of the food in such extent that all microorganisms die.

Freezing: The food can be kept in frozen condition inside the freezer for a long time. The temperature inside the freezer is very low (lower than the freezing point). We know that usually microbes cannot grow in extreme conditions. For this reason by keeping food inside the freezer growth of microorganisms can be avoided. Without microbes the food materials remain fresh for a long time.

Canning: Food materials like fruits, vegetables, fishes etc. are boiled in sugar syrup or canning salt solution and are packed inside a can. Then the can is boiled in water bath or pressure canning is done for sterilization. Due to boiling in high temperature all microorganisms will die and airtight packing will prevent new microorganisms from entering in side.

Dehydration: The moisture of the fruits are taken out by drying them in sun or drier and then stored. As moisture is absent bacteria fail to grow there.


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boiling : in boiling the temperature of the liquid to be boiled is increased , due to this the harmful germs find it difficult to survive in such environment and this sudden extreme chane in their env. leads to death. so in boiling it is killing of germs......

canning : over here the food product is processed (To prevent the food from being spoiled before and during containment, a number of methods are used: pasteurisation, boiling, refrigeration, freezing, drying, vacuum treatment, antimicrobial agents that are natural to the recipe of the foods being preserved, a sufficient dose of ionizing radiation, submersion in a strong saline solution, acid, base, osmotically extreme (for example very sugary) or other microbially-challenging environments.)and then sealed in airtight container......thus here also the env. gets changed......

freezing : in freezing the food is freezed...itis a common method offood preservationthat slows both food decay and the growth ofmicro-organisms. Besides the effect of lower temperatures onreaction rates, freezing makes water less available forbacterialgrowth.

dehydration : in this method the water content is totally removed ..... commonly knwn as drying.... this stops the bacterial growth ....{ Bacteria, yeasts and molds need the water in the food to grow, and drying effectively prevents them from surviving in the food.}....... grapes are dried to mahe raisins.... due to this no microbe is able to survive......

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