A few drops of iodine solution added to a sample of milk or khoa turn it blue-black. This indicates the presence of:
- A.Urea
- B.Starch
- C.Detergent
- D.Vanaspati
Correct answer
Explanation
The correct answer is B, starch. Iodine forms a deep blue-black complex with the long coiled chains of amylose in starch, and this colour change is the standard classroom and field test for starch. Dishonest sellers add boiled arrowroot, maida or rice starch to milk and khoa to thicken them and hide the water they have added, so the iodine test is the quickest check for that fraud. Option A is wrong because urea in milk is detected by a different reaction, the yellow colour given with a soyabean or arhar powder extract and red litmus paper, or by a urease strip. Option C is wrong because detergent is detected by shaking the sample with water, when a persistent dense lather forms. Option D is wrong because vanaspati in ghee is shown by the crimson colour of the hydrochloric acid and sugar test, and not by iodine at all.
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 →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
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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.
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