Micro Organism of Class 8
You have already studied about the preservation of stored food grains. How do we preserve cooked food at home?
Spoilage of cooked food takes place very often due to the action of microorganisms like bacteria and fungi. Spoilt food shows the following changes:
- Emits bad or foul smell
- Taste is changed
- Nutritive value is affected
- Colour changes
Food preservation can prevent food spoilage and can be done by different methods.
BY SUN DRYING:
Drying of food materials like vegetables (spinach, methi, cauliflower) and fruits in sun results in dehydration (reducing the moisture content). Microorganisms cannot grow in dry condition.
Smoking is used for dehydrating food items like meat, fish and their products. Small pieces of fish or meat are dried with heat and smoke of the fire lit below.
Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
PRESERVATION BY COMMON SALT:
Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
PRESERVATION BY SUGAR:
Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
PRESERVATION BY OIL AND VINEGAR:
Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
HEAT AND COLD TREATMENTS
You must have observed your mother boiling milk before it is stored or used. Boiling kills many microorganisms. Similarly, we keep our food in the refrigerator. Low temperature inhibits the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 70ºC for 15 to 30 seconds and then suddenly pasteurization.
STORAGE AND PACKING:
These days dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes. NCERT solutions for class 8 Science prepared by Physics Wallah will help you to solve your NCERT text book exercise.