Mayonnaise is best described as:

An oil-in-water emulsion stabilised by lecithin

Which of the following reduce the loss of water-soluble vitamins when vegetables are cooked? Select all that apply.

Cooking in the minimum amount of water and using that water

Covering the pan to shorten cooking time

Cooking in the minimum amount of water and using that water

Cutting vegetables into small pieces hours in advance and soaking them

Covering the pan to shorten cooking time

Adding a pinch of baking soda to keep the colour green

Why is potassium metabisulphite unsuitable for preserving jamun squash?

The sulphur dioxide it releases bleaches the anthocyanin pigment

It raises the water activity of the squash

It is not a permitted preservative in India

It is ineffective in acidic foods

Assertion (A): Green vegetables cooked for a long time with a lid on, or with tamarind, turn olive-brown. Reason (R): Acid replaces the magnesium of chlorophyll with hydrogen, forming pheophytin. Choose the correct option.

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Which statements about anthocyanins and anthoxanthins are correct? Select all that apply.

Anthocyanins are red in acid and turn violet to blue in alkali

Cauliflower cooked in hard, alkaline water turns yellowish because of its anthoxanthins

Anthocyanins are red in acid and turn violet to blue in alkali

Anthocyanins are fat-soluble and so do not leach into cooking water

Anthoxanthins are the main vitamin A precursors in vegetables

Cauliflower cooked in hard, alkaline water turns yellowish because of its anthoxanthins

Dried fruit with a water activity of 0.65 is unlikely to be spoiled by most bacteria mainly because:

Most bacteria need a water activity above about 0.91 to grow

Bacteria cannot survive in the presence of sugar at any level

Most bacteria need a water activity above about 0.91 to grow

Drying sterilises the fruit completely

Food Science I: Food Science and Nutrition, Properties of Food, Quality Evaluation, Effects of Cooking and Processing, Preservation, and Pigments and Additives

This chapter takes items 1 to 5 of Unit I. Food science studies what food is made of and what happens to it between the field and the plate; nutrition studies what the body does with it. The two meet in the kitchen and the processing plant, where heat, water, acid, air and time change colour, texture, flavour and nutrient content. The chapter works through the physical and chemical properties of food, the two ways of judging food quality (instruments and trained human senses), the losses and gains that cooking and processing cause, the principles behind every method of preservation, and the pigments and additives that decide how food looks and how long it keeps. Food safety law, HACCP, menu costing and institutional food service follow in the next chapter.

1. Food science, nutrition and the properties of food

Food science applies chemistry, physics, microbiology and engineering to food: its composition, its changes during handling, and its safety. Nutrition is the science of how nutrients are ingested, digested, absorbed, transported, used and excreted, and of how diet relates to health. Home Science joins them at the household and institutional level, where the practical question is always how to keep food safe, acceptable and nourishing at a cost the family can bear.

Physical properties include colour, size and shape, density and specific gravity, viscosity, surface tension, texture and the colloidal state. Many foods are colloids: milk is an emulsion of fat in water, mayonnaise an oil-in-water emulsion stabilised by egg-yolk lecithin, butter a water-in-oil emulsion, whipped cream and meringue are foams (gas in liquid), and jelly, custard and set curd are gels (liquid trapped in a solid network). A sol flows; a gel holds its shape.

Chemical properties of food components that decide cooking results
Nutrient group	Change on heating or handling	Kitchen example
Starch	Gelatinisation: granules absorb water and swell on heating; on cooling some amylose re-crystallises (retrogradation)	Thickening of kheer; staling of bread
Starch, dry heat	Dextrinisation: breakdown to dextrins, browning	Roasting suji or besan
Sugar	Caramelisation above its melting point, with no protein needed	Caramel custard topping
Reducing sugar with protein	Maillard (non-enzymatic) browning; reduces available lysine	Crust of bread, roasted groundnuts
Protein	Denaturation and coagulation by heat, acid, salt or beating	Setting of egg; paneer from acidified hot milk
Fat	Hydrolytic and oxidative rancidity; smoke point falls with repeated frying	Stale smell of old ghee; reused frying oil

⚠️ Caramelisation is not Maillard browning

Both brown food, but caramelisation needs only sugar and high heat, while the Maillard reaction needs a reducing sugar and an amino group, and runs at lower temperatures. A question that mentions amino acids, protein or loss of lysine is describing Maillard browning.

2. Quality evaluation: objective and subjective

Food quality is the sum of characteristics that decide acceptability: appearance (colour, size, shape, defects), texture and consistency, flavour (taste plus aroma), and nutritive and safety value. It is judged in two complementary ways. Objective evaluation uses instruments that give the same reading whoever operates them; subjective (sensory) evaluation uses a panel of people, because only people can say whether a food is liked.

Objective method	What it measures
Colorimeter / Hunter L, a, b values	Lightness and colour coordinates
Refractometer	Total soluble solids in degrees Brix (juices, jams)
Viscometer; line-spread test	Flow and consistency of sauces, batters
Penetrometer; texture analyser	Firmness, hardness, chewiness
pH meter; titratable acidity	Acidity, which also governs safety and colour

Sensory tests fall into three families. Difference tests ask whether a difference exists: the paired comparison, the duo-trio (which of two samples matches a reference) and the triangle test (three coded samples, two identical, pick the odd one; the chance of guessing right is one in three). Preference and acceptance tests ask how much a food is liked, most often on the nine-point hedonic scale running from "like extremely" to "dislike extremely". Descriptive tests, such as the flavour profile and quantitative descriptive analysis, use trained panellists to score the intensity of named attributes. Tests are run in booths under controlled light, with samples coded by random three-digit numbers, served in random order, with water to rinse the palate between samples.

🧠 Which test for which question

"Can people tell them apart?" is a difference test (triangle, duo-trio, paired). "Do people like it?" is a hedonic test with an untrained consumer panel. "What exactly is different and by how much?" is a descriptive test with a small trained panel.

3. Effects of cooking and processing, and the principles of preservation

Cooking improves digestibility, destroys many micro-organisms and anti-nutritional factors, and develops flavour, but it costs nutrients. Water-soluble vitamins leach into cooking water; vitamin C is destroyed by heat, air, alkali and copper; thiamine is heat-labile and is destroyed rapidly when baking soda is added to dal or vegetables; riboflavin is sensitive to light, which is why milk in clear bottles loses it; fat-soluble vitamins are comparatively stable, though carotene oxidises on long exposure. Losses are reduced by cooking in the minimum water, using the cooking water, covering the pan, cutting close to cooking time and avoiding soda.

Milling and polishing remove the bran and germ of cereals and with them much of the thiamine, fibre and minerals.
Parboiling rice drives water-soluble vitamins from the bran into the grain before milling, so parboiled rice keeps more thiamine.
Germination raises vitamin C and some B vitamins and lowers phytate, improving iron and zinc availability.
Fermentation (idli, dosa, dhokla, curd) raises some B vitamins, lowers anti-nutrients and improves digestibility.
Blanching before freezing or drying inactivates enzymes that would otherwise cause off-flavours and browning in storage.

Every preservation method rests on one or more of three principles: preventing or delaying microbial decomposition (by keeping microbes out, removing them, hindering their growth or killing them), delaying self-decomposition by the food's own enzymes, and preventing damage by insects, rodents and physical causes. Low temperature slows growth (refrigeration at about 0 to 5 degrees Celsius, freezing at minus 18 degrees or below). High temperature kills: pasteurisation destroys pathogens in milk by the low-temperature long-time method (about 63 degrees Celsius for 30 minutes) or the high-temperature short-time method (about 72 degrees for 15 seconds), while sterilisation and canning aim at commercial sterility. Drying lowers water activity; most bacteria need a water activity above about 0.91, most moulds above about 0.80. Sugar and salt preserve by raising osmotic pressure, acids and fermentation by lowering pH, and chemical preservatives by inhibiting microbes. Irradiation is a cold process for sprout inhibition, insect disinfestation and pathogen reduction.

🎯 Why potassium metabisulphite is kept for pale fruit

Potassium metabisulphite releases sulphur dioxide, which bleaches the anthocyanin pigments of red and purple fruit, so it is used for light-coloured products such as squash of lemon or guava. Sodium benzoate, which does not bleach, is used for coloured products such as jamun or kokum squash and tomato ketchup; it works best in acidic foods.

4. Food pigments

Colour is the first quality a consumer judges, and each natural pigment reacts in its own way to acid, alkali, heat and metals. Knowing these reactions explains why a vegetable turns dull or bright in a given recipe.

Pigment	Found in	Behaviour
Chlorophyll (magnesium at the centre)	Green leafy vegetables, peas	Acid and long cooking replace magnesium, giving olive-brown pheophytin; alkali keeps it bright green but softens texture and destroys vitamins
Carotenoids	Carrot, mango, papaya, pumpkin, tomato (lycopene)	Fat-soluble, fairly heat-stable; beta-carotene is a vitamin A precursor; oxidise on drying and long storage
Anthocyanins	Jamun, red cabbage, black grapes, brinjal skin	Water-soluble; red in acid, violet to blue in alkali; turn dull with iron or tin
Anthoxanthins (flavones, flavonols)	Cauliflower, onion, potato, rice	White in acid, yellowish in alkali or hard water
Betalains	Beetroot	Water-soluble red-violet; leach readily
Myoglobin	Meat	Purple-red; bright red as oxymyoglobin; brown as metmyoglobin; pink as nitrosomyoglobin in cured meat

ℹ️ Enzymatic browning

Cut apple, potato, brinjal and banana brown because polyphenol oxidase acts on phenolic compounds in the presence of oxygen. It is prevented by blanching, by acid (lemon juice), by keeping cut pieces under water, or by sulphiting.

5. Food additives

A food additive is a substance not normally eaten as a food by itself, added intentionally for a technological purpose in manufacture, processing, packing or storage. Additives are identified internationally by the International Numbering System (INS) of the Codex Alimentarius, are evaluated for an acceptable daily intake (ADI), and in India are permitted only for the foods and at the levels laid down in the food additive regulations framed under the Food Safety and Standards Act 2006.

Class	Purpose	Examples
Preservatives	Inhibit microbes	Sodium benzoate, potassium metabisulphite, sorbic acid
Antioxidants	Delay oxidative rancidity	BHA, BHT, TBHQ, tocopherols, ascorbic acid
Emulsifiers and stabilisers	Keep oil and water mixed; give body	Lecithin, mono- and diglycerides, pectin, gums, CMC
Colours	Restore or give colour	Natural: turmeric, annatto, caramel; synthetic: tartrazine, sunset yellow FCF, carmoisine
Flavour enhancers and sweeteners	Intensify taste; replace sugar	Monosodium glutamate; aspartame, sucralose, saccharin
Acidity regulators, leavening agents, anti-caking agents	Control pH; aerate; keep powders free-flowing	Citric acid; baking powder; silicon dioxide

⚠️ An additive is not an adulterant

An additive is permitted, declared on the label and used within a legal limit for a technological purpose. An adulterant is an undeclared substance that lowers quality or endangers health, such as metanil yellow in turmeric or argemone oil in mustard oil. A permitted synthetic colour becomes an adulterant when used in a food for which it is not permitted or above the limit.

Key takeaways

Foods are colloids (emulsions, foams, gels, sols), and starch gelatinisation, dextrinisation, caramelisation, Maillard browning, protein coagulation and fat rancidity explain most cooking results.
Objective evaluation uses instruments; sensory evaluation uses difference tests (triangle, duo-trio, paired), hedonic tests (the nine-point scale) and descriptive tests.
Vitamin C and thiamine are the most vulnerable nutrients in cooking; soda destroys thiamine, light destroys riboflavin; parboiling, germination and fermentation raise nutritive value.
Preservation works by keeping microbes out or killing them, slowing enzymes, lowering water activity or pH, or raising osmotic pressure.
Chlorophyll dulls in acid, anthocyanins turn red in acid and blue in alkali, anthoxanthins yellow in alkali; additives are permitted, declared and limited, unlike adulterants.

Practice questions (10)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

Mayonnaise is best described as:
1. A foam of air in fat
2. A gel of protein
3. An oil-in-water emulsion stabilised by lecithin
4. A water-in-oil emulsion
Show answer
Answer: C — An oil-in-water emulsion stabilised by lecithin
Mayonnaise disperses oil droplets in a watery phase of vinegar and egg yolk, and the lecithin of the yolk is the emulsifier. Butter is the classic water-in-oil emulsion; whipped cream is the foam.
Browning of the crust of bread, which also lowers the availability of lysine, is due to:
1. Retrogradation
2. Enzymatic browning
3. Caramelisation
4. The Maillard reaction
Show answer
Answer: D — The Maillard reaction
The Maillard reaction joins reducing sugars with amino groups, so it browns the crust and ties up lysine. Caramelisation involves sugar alone; enzymatic browning needs polyphenol oxidase in cut produce; retrogradation is the re-crystallising of starch that stales bread.
In a triangle test, 30 panellists each receive three coded samples, two of them identical. If the samples were truly indistinguishable, how many panellists would be expected to pick the odd sample correctly by chance alone? Type the number.
Numerical answer — type the value.
Show answer
Answer: 10
The probability of guessing the odd sample in a triangle test is 1/3, so the chance expectation is 30 × 1/3 = 10. Only a number of correct answers significantly above 10 shows a real perceptible difference.
Which of the following reduce the loss of water-soluble vitamins when vegetables are cooked? Select all that apply.
1. Cooking in the minimum amount of water and using that water
2. Cutting vegetables into small pieces hours in advance and soaking them
3. Covering the pan to shorten cooking time
4. Adding a pinch of baking soda to keep the colour green
Show answer
Answer: A — Cooking in the minimum amount of water and using that water; C — Covering the pan to shorten cooking time
Minimum water that is then eaten, and a covered pan that shortens heating, both cut losses. Baking soda destroys thiamine and vitamin C, and cutting small pieces early and soaking them multiplies the surface from which vitamins leach and oxidise.
Why is potassium metabisulphite unsuitable for preserving jamun squash?
1. The sulphur dioxide it releases bleaches the anthocyanin pigment
2. It raises the water activity of the squash
3. It is not a permitted preservative in India
4. It is ineffective in acidic foods
Show answer
Answer: A — The sulphur dioxide it releases bleaches the anthocyanin pigment
KMS releases sulphur dioxide, which decolourises red and purple anthocyanins, so coloured products such as jamun squash are preserved with sodium benzoate. KMS is a permitted preservative and works well in acidic light-coloured products.
Assertion (A): Green vegetables cooked for a long time with a lid on, or with tamarind, turn olive-brown. Reason (R): Acid replaces the magnesium of chlorophyll with hydrogen, forming pheophytin. Choose the correct option.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: A — Both A and R are true, and R is the correct explanation of A
Both are true and R explains A. A lid traps the volatile plant acids released on cooking, and tamarind adds acid; in both cases magnesium is lost and olive-brown pheophytin forms. Cooking uncovered for a short time lets the acids escape.
Which statements about anthocyanins and anthoxanthins are correct? Select all that apply.
1. Anthocyanins are red in acid and turn violet to blue in alkali
2. Anthocyanins are fat-soluble and so do not leach into cooking water
3. Anthoxanthins are the main vitamin A precursors in vegetables
4. Cauliflower cooked in hard, alkaline water turns yellowish because of its anthoxanthins
Show answer
Answer: A — Anthocyanins are red in acid and turn violet to blue in alkali; D — Cauliflower cooked in hard, alkaline water turns yellowish because of its anthoxanthins
Anthocyanins are pH indicators, red in acid and blue in alkali, and anthoxanthins yellow in alkali. Anthocyanins are water-soluble and leach readily, and the vitamin A precursors are carotenoids such as beta-carotene, not anthoxanthins.
Which instrument measures the total soluble solids of a fruit juice in degrees Brix?
1. Penetrometer
2. Refractometer
3. Viscometer
4. Colorimeter
Show answer
Answer: B — Refractometer
The refractometer reads the refractive index of a solution, which rises with dissolved solids and is calibrated in degrees Brix. The penetrometer measures firmness, the colorimeter colour and the viscometer flow.
Which of the following are antioxidants used to delay rancidity in fats and fried snacks? Select all that apply.
1. Tocopherols
2. BHA
3. Sodium benzoate
4. Carboxymethyl cellulose
Show answer
Answer: A — Tocopherols; B — BHA
Butylated hydroxyanisole and the tocopherols interrupt the free-radical chain of fat oxidation. Sodium benzoate is an antimicrobial preservative and carboxymethyl cellulose a thickener and stabiliser, so neither slows rancidity.
Dried fruit with a water activity of 0.65 is unlikely to be spoiled by most bacteria mainly because:
1. Bacteria cannot survive in the presence of sugar at any level
2. Most bacteria need a water activity above about 0.91 to grow
3. Drying sterilises the fruit completely
4. Drying raises the pH above 7
Show answer
Answer: B — Most bacteria need a water activity above about 0.91 to grow
Water activity measures the water available to microbes; most bacteria need about 0.91 or more and most moulds about 0.80, so at 0.65 only some xerophilic moulds and osmophilic yeasts remain a risk. Drying does not sterilise and does not make fruit alkaline.