Lyophilisation, used to make instant coffee and to preserve vaccines, is the technical name for which process?
- A.Pasteurisation
- B.Freeze-drying
- C.Canning
- D.Irradiation
Correct answer
Explanation
The correct answer is B, freeze-drying. In lyophilisation the material is first frozen and then placed under a strong vacuum, so that the ice changes directly into vapour without passing through the liquid state. This change of state is sublimation, and because the product never becomes wet and never gets hot, its aroma, colour, shape and biological activity survive almost unchanged; the dried solid rehydrates instantly in water. That is why instant coffee, dried fruit for ready-to-eat meals, bacterial cultures and many vaccines are freeze-dried. Option A is wrong because pasteurisation is a mild heat treatment of liquids such as milk and does not dry them at all. Option C is wrong because canning seals food in an airtight container and then heats it, so the water stays in the can. Option D is wrong because irradiation exposes food to gamma rays to kill insects and microbes and remove sprouting, while the water content is untouched.
Read the full article: Food Preservation, Adulteration and Food Safety Notes
Practice Questions
View allFruits stored in a cold chamber exhibit longer storage life because
- A.exposure to sunlight is prevented
- B.concentration of carbon dioxide in the environment is increased
- C.rate of respiration is decreased
- D.there is an increase in humidity
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A harvested fruit is still a living tissue that keeps respiring, using up its own sugars and acids and giving off heat, carbon dioxide and ethylene.
Read the full explanation →The adulteration of mustard oil with argemone oil causes which disease?
- A.Lathyrism
- B.Epidemic dropsy
- C.Fluorosis
- D.Minamata disease
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Argemone mexicana, the prickly poppy known in India as satyanashi, has seeds that look very like mustard seeds, so its oil is a classic adulterant of mustard oil.
Read the full explanation →Lathyrism in human beings is caused by the prolonged consumption of which of the following?
- A.Khesari dal
- B.Argemone seeds
- C.Metanil yellow
- D.Chicory
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Khesari dal, botanically Lathyrus sativus and also called grass pea, is a hardy pulse that survives drought and is therefore sometimes mixed with arhar dal or besan.
Read the full explanation →In the high-temperature short-time (HTST) method of pasteurisation, milk is heated to about:
- A.63 degrees Celsius for 30 minutes
- B.72 degrees Celsius for 15 seconds
- C.100 degrees Celsius for 10 minutes
- D.150 degrees Celsius for 2 seconds
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Pasteurisation is not sterilisation: it is a mild heating that kills disease-causing organisms such as Mycobacterium tuberculosis, Salmonella and Brucella and most spoilage bacteria, while leaving the taste and nutritive value of milk largely unchanged.
Read the full explanation →Which of the following is a Class I preservative under Indian food standards?
- A.Sodium benzoate
- B.Sulphur dioxide
- C.Common salt
- D.Potassium sorbate
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Indian food standards divide preservatives into two classes. Class I preservatives are the natural ones that cooks have always used, and no limit is placed on the quantity: common salt, sugar, dextrose, spices, vinegar or acetic acid, honey and edible vegetable oils.
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