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Answer: C

Dextrinisation takes place in toasting bread.

Dextrinisation is the breakdown of starch into shorter chains called dextrins under dry heat, at about 150-160 °C or more. When bread is toasted, the starch on its surface is dextrinised, which, together with the Maillard reaction, gives toast its brown colour and slightly sweet flavour.

Boiling milk and flour for custard and steaming idli are moist-heat processes in which starch is gelatinised, not dextrinised. Fermentation is the action of yeasts or bacteria on sugars and is not a heat process.

Answer: B

The acid formed during rigor mortis is lactic acid.

After an animal is slaughtered, the oxygen supply to the muscle stops. Muscle glycogen is then broken down anaerobically, by glycolysis, to lactic acid, and the pH of the meat falls from about 7 to about 5.5. As ATP runs out, actin and myosin lock together and the muscle stiffens, which is rigor mortis.

Citric acid belongs to the TCA cycle, which needs oxygen. Oxalic acid occurs in plants such as spinach, and gluconic acid is made by oxidising glucose; neither is formed in post-mortem muscle.

Answer: B

Such products are probiotics.

A probiotic is a preparation of live micro-organisms, such as the lactobacilli and bifidobacteria in curd and fermented milks, which in adequate numbers benefit the host by improving the balance of the intestinal flora.

Prebiotics are the near miss: they are non-digestible food ingredients, such as inulin and fructo-oligosaccharides, that feed the beneficial bacteria but contain no living organisms. Antibiotics kill or inhibit bacteria rather than adding them, and enzymes are proteins, not micro-organisms.

Answer: B

The answer is waiter service.

In waiter (table) service the guest is seated, the order is taken, the food is brought course by course and the bill is presented at the table. Each step waits on staff, so a table is occupied longest and the number of customers served per seat in a given time, the turnover, is lowest.

Self service, buffet service and cafeteria service all have customers collect their own food, which cuts waiting time and is chosen precisely for fast turnover in canteens, hostels and industrial catering.

Answer: A

Sugar alcohols are low calorie sweeteners.

Polyols such as sorbitol, mannitol, xylitol and maltitol are only partly absorbed from the gut, so they provide about 2 to 3 kcal per gram against 4 kcal for sugar. They are used in sugar-free sweets and chewing gum, and do not promote dental caries.

They are not non-calorie sweeteners: that term belongs to intense sweeteners such as saccharin, aspartame and sucralose, which are used in tiny amounts. Preservatives prevent spoilage and stabilisers keep emulsions or textures stable; neither describes a sugar alcohol's main role.

Answer: D

Fresh cow's milk has a pH of about 6.6 - 6.9, slightly on the acid side of neutral.

The mild acidity comes from the casein, phosphates, citrates and dissolved carbon dioxide in milk. Dairy tests use this narrow range: when lactic acid bacteria sour the milk, the pH falls and the casein begins to curdle at around 4.6.

A pH of 7.1 - 7.6 is alkaline and is a sign of mastitis milk rather than normal milk. The lower ranges, 6.0 - 6.4 and 5.0 - 6.0, describe milk that has already begun to sour.

Answer: D

Milk lipase is inactivated by pasteurisation.

Native milk lipase is heat-sensitive, and the time and temperature of pasteurisation (for example 72 °C for 15 seconds) destroy most of it. This is important because active lipase would split milk fat into free fatty acids and give the milk a rancid flavour.

Homogenisation does the opposite of protecting the fat: by breaking the fat globules it exposes more fat to lipase, which is why raw milk is pasteurised before or immediately after homogenising. Gelatinisation is the swelling of starch granules in hot water, and caramelisation is the browning of sugar by heat; neither is a milk enzyme treatment.

Answer: D

The natural colour among the options is Annatto.

Annatto is a yellow-orange pigment (bixin and norbixin) extracted from the seed coat of the tropical shrub Bixa orellana. It is widely used to colour butter, cheese, snacks and bakery products.

Carmosine (a red), tartrazine (a lemon yellow) and metanil yellow are synthetic coal-tar dyes. Carmosine and tartrazine are permitted synthetic colours in India, while metanil yellow is a non-permitted dye that is a well-known adulterant of turmeric and sweets.

Answer: B

Organisms that grow at refrigeration temperature are called psychrotrophic.

Psychrotrophs have an optimum above 20 °C but can still multiply slowly at 0-7 °C, which is why they spoil refrigerated milk, meat and fish. Pseudomonas and Listeria are common examples.

Thermoduric organisms survive heat treatment such as pasteurisation without necessarily growing at high temperature. Mesophiles grow best at about 20-45 °C, the range of body and room temperature, and do not grow well in a refrigerator. 'Thermotropic' is not a term for a growth group of microorganisms.

Answer: A

Baking powder contains sodium bicarbonate, cream of tartar and corn starch.

Sodium bicarbonate is the source of carbon dioxide. Cream of tartar (potassium hydrogen tartrate) is the acid that reacts with it when the powder is moistened, so the dough or batter rises without the bitter, soapy taste of unreacted soda. Corn starch is the filler that keeps the powder dry and stops the two from reacting in the tin.

Sodium bicarbonate alone is baking soda, not baking powder. Calcium bicarbonate is not a leavening agent and exists only in solution, so the two options built on it are wrong.