Food Selection, Storage, Processing, Cooking Effects and Quality Evaluation

What to remember

• Choose fresh, clean, whole and seasonal foods; store them dry, cool and covered; cook in a way that keeps nutrients (little water, short time, no soda).
• Pasteurisation (HTST) heats milk to 72 °C for 15 seconds; sterilisation and UHT destroy all organisms; the danger zone for germs is about 5 to 60 °C.
• Quality of food is judged by sensory methods (taste panel) and by physical, chemical and microbiological tests; grade marks such as Agmark, FSSAI and BIS show standards.

Selection of foods

A good buyer checks freshness, cleanliness, colour, smell, weight, price and the label. Buying food in season is cheaper and fresher.

• Cereals and pulses: should be dry, uniform in size, free of insects, stones, husk and mould. Old, damp grains smell musty.
• Vegetables and fruits: should be fresh, firm and bright, without bruises, spots or wilting. Leafy vegetables should be crisp and green.
• Milk: should be fresh, white, with a pleasant smell and no sourness. A lactometer measures its specific gravity; pure cow milk is about 1.028 to 1.032. Adding water lowers the reading; removing cream raises it.
• Eggs: a fresh egg has a clean, rough shell, sinks in a salt (brine) solution and lies flat at the bottom; an old egg floats because its air cell has become larger. Candling (holding the egg to a bright light) shows a small air cell, a firm yolk and clear white in a fresh egg.
• Fish: bright eyes, red gills, firm flesh and no foul smell. Meat: firm, with good colour and no sliminess.
• Fats and oils: no off smell or rancid taste.

Packed foods should be bought with the label read: date of manufacture, expiry or "best before" date, ingredients, net weight, and the licence mark.

Food standards and marks

Food adulteration means adding a cheap or harmful substance to food or removing a valuable part. A few simple home tests: iodine drops turn starch-adulterated milk blue; metanil yellow in turmeric turns the colour pink or violet with hydrochloric acid.

Storage of foods

Foods are classed by shelf life. Perishable foods (milk, meat, fish, leafy vegetables) spoil in hours or days. Semi-perishable foods (potato, onion, eggs, flour) last weeks. Non-perishable foods (dry grains, pulses, sugar, salt) last months if kept dry.

Spoilage is caused by moisture, warmth, air, light, insects, rodents, moulds and bacteria.

• Grains and pulses: store at low moisture (cereals about 12-14% or below) in clean, airtight, moisture-proof bins. Dry in sun before storage. Use neem leaves or dry chillies to keep insects away. Common pests are weevils and the grain moth.
• Flour: spoils faster than whole grain because of the larger surface; keep in dry containers.
• Fats and oils: store in a cool, dark, covered container; air, light and heat cause rancidity (an off flavour).
• Eggs: store cool with the pointed end down.
• Refrigerator: about 4-5 °C for most foods; freezer about −18 °C or below. Bacteria multiply fastest between about 5 and 60 °C (the "danger zone"). Cooked food should not be left at room temperature for more than two hours.
• Raw and cooked foods are kept apart to avoid cross-contamination. The first-in, first-out (FIFO) rule should be followed in a store.

Food processing and preservation

Food processing changes raw foods into forms that last longer or are easier to eat. Preservation prevents spoilage by controlling micro-organisms and enzymes.

Milk processing

• Pasteurisation kills disease-causing germs without much change in nutrients. LTLT (holder) method: about 63 °C for 30 min. HTST: about 72 °C for 15 sec.
• UHT: about 135-150 °C for a few seconds; packed aseptically; long shelf life.
• Sterilisation heats in the sealed bottle at higher temperature to destroy all organisms.
• Homogenisation breaks up fat globules so cream does not rise. Toned milk is made by adding skim milk powder and water to whole milk to lower the fat.
• The alkaline phosphatase test checks if milk has been properly pasteurised.

Jam, jelly and marmalade: fruit, sugar, acid and pectin set to a gel. A jam must have total soluble solids of not less than 65% and a minimum fruit content of 45% (FSSAI standard; the older FPO figure was 68% TSS). Jelly is made from clear fruit juice; marmalade from citrus fruit with peel. Squash and cordial are sweetened fruit drinks. Fruit juices and pickles preserved with salt, oil or acid do not need refrigeration.

Canning has these steps: select and clean the food, blanch, fill the can, exhaust air, seal, heat sterilise, cool. Blanching (a short hot water or steam treatment) stops enzyme action and keeps colour.

Effect of processing and cooking on nutrients

Cooking makes food safe, soft, digestible and tasty. It gelatinises starch, coagulates protein, kills germs and removes some anti-nutritional factors.

Points about different cooking methods:

• Boiling: loses water-soluble vitamins and minerals into water; use the cooking water in dal, soup or kneading.
• Steaming: retains more nutrients than boiling (idli, dhokla, steamed vegetables).
• Pressure cooking: short time, less loss of vitamins; saves fuel.
• Frying: adds energy; high temperature destroys some vitamins; oil must not smoke (the smoke point is the temperature at which oil gives off smoke).
• Roasting and baking: dry heat; browning gives flavour but may cause loss of lysine.
• Microwave cooking: quick, with good retention of nutrients.
• Starch: on heating with water it swells and gelatinises; dry heat forms dextrins.
• Maillard (browning) reaction: reaction between reducing sugar and amino acids on heating.
• Fermentation (idli, dosa, curd, bread) raises B vitamins and improves digestibility. Germination (sprouting) raises vitamin C and B vitamins. Parboiling retains B vitamins of rice. Soaking and cooking reduce phytates and trypsin inhibitors in pulses.
• Hand-pounded rice keeps more thiamine than machine-milled polished rice.
• Fortification adds nutrients to a food (iodised salt, vitamin A in oil, iron in salt or flour); enrichment restores nutrients lost in processing (thiamine, niacin and iron in refined flour).

Good practices: wash vegetables before cutting; cut into large pieces; cook with a lid in a small amount of water; do not add soda; avoid reheating again and again; do not throw away the water.

Quality evaluation of food

Quality means the total features of a food that make it acceptable and safe. It is checked by:

• 1. Sensory (subjective) evaluation: done by human senses of appearance, flavour, aroma, taste and texture. A trained or untrained taste panel is used in a clean, quiet room with coded samples. Common tests: paired comparison, triangle test (three samples, two the same), ranking and the hedonic scale (9-point scale from "dislike extremely" to "like extremely").
• 2. Objective evaluation: by instruments and laboratory tests.
• *Physical:* texture meter, colorimeter, viscosity, specific gravity.
• *Chemical:* moisture, protein, fat, ash, fibre, acidity, peroxide value for rancidity.
• *Microbiological:* total plate count, tests for coliforms and specific pathogens.
• 3. Nutritive quality through food analysis (proximate principles: moisture, ash, crude protein, fat, fibre, carbohydrate).

Panel members should not smoke, eat strongly flavoured food or be ill before testing. Water or plain bread is used to cleanse the mouth between samples. All samples are given random codes to avoid bias.

Exam traps

• Pasteurisation does not sterilise milk; sterilisation and UHT destroy all organisms.
• HTST is 72 °C for 15 seconds, not 63 °C for 30 minutes (that is the holder method).
• Baking soda destroys thiamine (and vitamin C) and is not good for cooking pulses or vegetables.
• Riboflavin is light-sensitive; thiamine is heat- and alkali-sensitive; vitamin C is air- and heat-sensitive.
• Steaming retains more nutrients than boiling in water.
• Fortification adds new nutrients; enrichment restores lost ones.
• A fresh egg sinks in brine; an old egg floats.
• Agmark is for farm produce grading; FSSAI is the food safety regulator; ISI is a BIS mark.

One-liners

• 1. Lactometer measures the specific gravity of milk.
• 2. Pure cow milk has a specific gravity of about 1.028 to 1.032.
• 3. HTST pasteurisation is 72 °C for 15 seconds.
• 4. The danger zone for bacterial growth is about 5-60 °C.
• 5. Freezer temperature is about −18 °C.
• 6. Blanching stops enzyme activity before freezing or canning.
• 7. Jam sets with sugar, acid and pectin.
• 8. Rancidity is the spoilage of fats.
• 9. Fermentation increases the B vitamin content of food.
• 10. Sprouting increases vitamin C.
• 11. Hedonic scale is used to judge liking in sensory tests.
• 12. FSSAI works under the Food Safety and Standards Act, 2006.

Practice questions

1. Specific gravity of pure cow milk is about

   1. 1.50 to 1.60
   2. 0.90 to 0.95
   3. 1.10 to 1.15
   4. 1.028 to 1.032
   Answer

   D. 1.028 to 1.032

   A lactometer reading in this range indicates unadulterated milk.

2. In HTST pasteurisation milk is heated to

   1. 90 °C for 5 minutes
   2. 100 °C for 1 hour
   3. 63 °C for 30 minutes
   4. 72 °C for 15 seconds
   Answer

   D. 72 °C for 15 seconds

   HTST is 72 °C for 15 s; holder (LTLT) is 63 °C for 30 min.

3. The holder (LTLT) method of pasteurisation uses

   1. 135 °C for 2 seconds
   2. 72 °C for 15 seconds
   3. 100 °C for 10 minutes
   4. 63 °C for 30 minutes
   Answer

   D. 63 °C for 30 minutes

   Low temperature long time method.

4. UHT treatment of milk uses a temperature of about

   1. 72 °C for 15 minutes
   2. 63 °C for 30 minutes
   3. 50-55 °C for a minute
   4. 135-150 °C for a few seconds
   Answer

   D. 135-150 °C for a few seconds

   Ultra-high temperature gives a long shelf life when packed aseptically.

5. The temperature range called the 'danger zone' for bacterial growth is about

   1. −18 °C to 0 °C
   2. 100 °C to 120 °C
   3. 5 °C to 60 °C
   4. 70 °C to 100 °C
   Answer

   C. 5 °C to 60 °C

   Bacteria multiply fastest in this range.

6. The usual freezer storage temperature is about

   1. 4 °C
   2. 10 °C
   3. −18 °C
   4. 0 °C only for 1 hour
   Answer

   C. −18 °C

   Frozen food is kept at −18 °C or lower.

7. A fresh egg placed in brine (salt) solution will

   1. Sink and lie flat
   2. Float at the surface
   3. Break open
   4. Turn the water cloudy
   Answer

   A. Sink and lie flat

   Air cell enlarges with age, so old eggs float.

8. Holding an egg before a bright light to see the air cell and yolk is called

   1. Homogenisation
   2. Blanching
   3. Parboiling
   4. Candling
   Answer

   D. Candling

   Candling is a quick test for egg quality.

9. Quick dipping of vegetables in hot water or steam before freezing or canning is

   1. Pasteurisation
   2. Candling
   3. Fermentation
   4. Blanching
   Answer

   D. Blanching

   Blanching stops enzyme action and fixes colour.

10. The statutory body for food safety standards under the Food Safety and Standards Act, 2006 is

    1. BIS
    2. APEDA
    3. FSSAI
    4. Agmark Directorate only
    Answer

    C. FSSAI

    FSSAI licenses food businesses and sets standards.

11. Agmark is a grade mark for

    1. Agricultural produce
    2. Drugs
    3. Textiles
    4. Electrical goods
    Answer

    A. Agricultural produce

    Agmark certifies the quality of farm products such as ghee and spices.

12. Which is a chemical preservative commonly used in squash and jam?

    1. Calcium carbide
    2. Metanil yellow
    3. Sodium benzoate
    4. Washing soda
    Answer

    C. Sodium benzoate

    Benzoate and KMS are permitted preservatives.

13. Jam sets properly because of the combination of

    1. Sugar, acid and pectin
    2. Salt, fat and starch
    3. Oil, vinegar and protein
    4. Water, soda and gluten
    Answer

    A. Sugar, acid and pectin

    Fruit pectin gels with sugar and acid.

14. Which method of cooking generally retains more water-soluble vitamins than boiling in a lot of water?

    1. Boiling and discarding water
    2. Soaking in hot water
    3. Deep frying
    4. Steaming
    Answer

    D. Steaming

    Steam does not dissolve vitamins into water.

15. Which vitamin is destroyed by baking soda during cooking?

    1. Vitamin K
    2. Thiamine
    3. Vitamin D
    4. Vitamin A
    Answer

    B. Thiamine

    Thiamine is unstable in alkaline medium.

16. Which vitamin is most easily destroyed by sunlight in milk kept in clear bottles?

    1. Thiamine
    2. Riboflavin
    3. Vitamin B12
    4. Niacin
    Answer

    B. Riboflavin

    Riboflavin is light-sensitive (photolysis).

17. Cooking of starch in water leading to swelling of granules is called

    1. Dextrinisation
    2. Caramelisation
    3. Gelatinisation
    4. Rancidity
    Answer

    C. Gelatinisation

    Starch absorbs water and swells on heating.

18. Breakdown of starch by dry heat into smaller units is called

    1. Gelatinisation
    2. Pasteurisation
    3. Fermentation
    4. Dextrinisation
    Answer

    D. Dextrinisation

    Roasting flour forms dextrins.

19. The browning reaction between reducing sugars and amino acids is

    1. The Maillard reaction
    2. Saponification
    3. Hydrogenation
    4. Blanching
    Answer

    A. The Maillard reaction

    It gives colour and flavour and can reduce lysine.

20. Spoilage of fats giving an off flavour is called

    1. Pasteurisation
    2. Gelatinisation
    3. Rancidity
    4. Fortification
    Answer

    C. Rancidity

    Rancidity is oxidation or hydrolysis of fats.

21. Adding nutrients such as iodine to salt is called

    1. Enrichment of lost nutrients only
    2. Fortification
    3. Blanching
    4. Homogenisation
    Answer

    B. Fortification

    Fortification adds nutrients, even those absent originally.

22. Restoring nutrients lost in milling, such as thiamine in refined flour, is called

    1. Enrichment
    2. Candling
    3. Adulteration
    4. Pasteurisation
    Answer

    A. Enrichment

    Enrichment returns nutrients lost during processing.

23. A 9-point hedonic scale is used to measure

    1. Specific gravity
    2. Moisture
    3. Peroxide value
    4. Degree of liking of food
    Answer

    D. Degree of liking of food

    It ranges from like extremely to dislike extremely.

24. In a triangle test the panelist is given

    1. Three samples, two alike and one different
    2. Two samples both different
    3. Five samples in order
    4. One sample only
    Answer

    A. Three samples, two alike and one different

    The panelist picks the odd one.

25. Which is an objective (instrumental) method of food quality evaluation?

    1. Rating colour by eye
    2. Judging aroma by smell
    3. Tasting by a panel
    4. Measuring viscosity with a viscometer
    Answer

    D. Measuring viscosity with a viscometer

    Instruments give measured, not human, results.

26. 100 g of fresh fruit with 80% moisture is dried until it has 20% moisture. The weight of dried fruit from 100 g is

    1. 20 g
    2. 25 g
    3. 50 g
    4. 40 g
    Answer

    B. 25 g

    Solids = 20 g; dried product has 80% solids; 20/0.8 = 25 g.

27. 1 kg of flour at 14% moisture contains dry matter of

    1. 900 g
    2. 714 g
    3. 860 g
    4. 140 g
    Answer

    C. 860 g

    1000 × (100−14)/100 = 860 g.

28. To prepare 500 mL of 10% sugar syrup (w/v), the sugar needed is

    1. 50 g
    2. 100 g
    3. 10 g
    4. 5 g
    Answer

    A. 50 g

    10 g per 100 mL × 5 = 50 g.

29. Milk of specific gravity 1.028 after adding water would show a reading that is

    1. Exactly 1.000 always
    2. Lower
    3. Higher
    4. Unchanged always
    Answer

    B. Lower

    Water has a specific gravity of 1.0, so mixing lowers the reading.

30. A cook discards the rice cooking water. The main loss will be of

    1. Fat-soluble vitamins
    2. Dietary fibre only
    3. Water-soluble vitamins and minerals
    4. Cholesterol
    Answer

    C. Water-soluble vitamins and minerals

    B vitamins and minerals dissolve into the water.

31. Cut vegetables left in the open for hours lose mainly

    1. Iron
    2. Vitamin D
    3. Calcium
    4. Vitamin C
    Answer

    D. Vitamin C

    Vitamin C oxidises on exposure to air.

32. Cooked food should not be left at room temperature for more than about

    1. One day
    2. Three days
    3. Ten hours
    4. Two hours
    Answer

    D. Two hours

    Beyond this, bacteria multiply to unsafe levels.

33. Which of the following statements is/are correct? 1. Pasteurisation destroys all micro-organisms in milk. 2. Sterilisation heats milk to destroy all organisms.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Pasteurisation only kills disease-causing germs.

34. Which of the following statements is/are correct? 1. Fermentation increases B vitamin content of idli batter. 2. Germination increases vitamin C in pulses.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

35. Which of the following statements is/are correct? 1. Steaming retains more nutrients than boiling in excess water. 2. Baking soda protects thiamine.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Soda destroys thiamine.

36. Which of the following statements is/are correct? 1. Fortification adds nutrients to a food. 2. Enrichment restores nutrients lost in processing.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both definitions are right.

37. Which of the following statements is/are correct? 1. Fresh eggs float in brine. 2. Candling shows a small air cell in a fresh egg.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Fresh eggs sink; old eggs float.

38. Which of the following statements is/are correct? 1. Prolonged boiling increases vitamin C in vegetables. 2. Pressure cooking reduces cooking time and loss of vitamins.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Long boiling destroys vitamin C.

39. Which of the following statements is/are correct? 1. FSSAI sets standards for food safety. 2. Agmark is a regulator for food business licences.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Agmark is a grading mark; FSSAI licenses food businesses.

40. Which of the following statements is/are correct? 1. Parboiling helps retain B vitamins in rice. 2. Hand-pounded rice keeps more thiamine than polished rice.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

41. Which of the following statements is/are correct? 1. Jam needs sugar, acid and pectin to set. 2. Jelly is made from whole fruit pulp with seeds.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Jelly is made from clear fruit juice.

42. Which of the following statements is/are correct? 1. Rancidity is a type of fungal spoilage of cereals. 2. Blanching inactivates enzymes in vegetables before freezing.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Rancidity is deterioration of fats.

43. Which of the following statements is/are correct? 1. Salt and sugar preserve foods by drawing out water. 2. Pickling in acid helps stop bacterial growth.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

44. Which of the following statements is/are correct? 1. Refrigeration kills all bacteria in food. 2. Raw and cooked foods should be stored separately.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Cold only slows growth.

45. Which of the following statements is/are correct? 1. The first-in, first-out rule is useful in a food store. 2. Spices stored damp last longer than dry spices.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Dry storage is needed.