Answer:
1. Heating - Heating at 135 degree Celsius for few seconds will kill more bacteria than the traditional method of heating. Milk is prepared in factories using the Ultra Heat Treatment.
2. Cooling - Cooling prevents the growth of microbes. Placing food in refrigerator about 5 degree Celsius will delay the spoilage of food for few days.
Deep freezer provides a temperature as low as -18 degree Celsius which will delay the growth of microbes for few months.
3. Adding Salt/ Sugar - They reduce the moisture content of the food. It also prevents the growth of microbes in food items. These microorganisms tend to loose water from their bodies in the process of Osmosis. Salt is used as a preservative in pickles, fish, meat and chips while Sugar is used as a preservative in Jams and Squashes.
4. Adding Vinegar or oil
These both will create an unfavorable environment which will delay the growth of microbes. For example : Fish, Pickles and Meat.
5. Chemical Preservatives
Example : Sodium Benzoate and Sodium Metabisulphite are used as preservatives in Jams, Sauces and Ketchups. They inhibit the growth of microbes.
6. Dehydration
Extracting moisture from food.
Some more methods are 7. Canning & Vacuum Packing and 8. Pasteurization.
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