Food Chemistry, Nutrition and Adulteration Testing
What this domain tests
Proximate analysis, nutrient-energy arithmetic, nutrition labelling rules and the rapid adulteration tests in FSSAI's DART manual. Questions are usually calculation-plus-detection pairs.
Proximate analysis
- Moisture: hot-air oven at 105 degrees C to constant weight.
- Ash: muffle furnace at about 550 degrees C; ash reflects total mineral content.
- Crude protein: Kjeldahl (digestion, distillation, titration); nitrogen factor 6.25 general, 6.38 for milk, 5.70 for wheat flour.
- Crude fat: Soxhlet extraction with petroleum ether; crude fibre by acid-alkali digestion.
- Carbohydrate is obtained by difference, not measured directly.
- Energy: 4 kcal/g protein, 9 kcal/g fat, 4 kcal/g carbohydrate; fibre about 2 kcal/g in labelling.
Adulteration quick tests
- Starch in milk - iodine gives blue-black colour.
- Metanil yellow in turmeric or sweetmeat - dilute HCl gives magenta-pink.
- Argemone oil in mustard oil - nitric acid gives red colour.
- Papaya seeds in black pepper - float in water, light colour.
- Khesari dal - long-term consumption causes lathyrism (neurolathyrism).
- Rhodamine B or lead chromate in chilli powder; sawdust and exhausted tea leaves in tea; ergot in bajra.
Worked example
1.00 g of milk powder gives 0.035 g nitrogen on titration. Protein = 0.035 x 6.38 = 0.223 g, so the sample is 22.3 per cent protein. Using the general factor 6.25 wrongly would give 21.9 per cent - close but enough to change a pass or fail verdict at a specification boundary.
Traps
- Using 6.25 for milk products instead of 6.38.
- Reporting carbohydrate as measured when it is calculated by difference.
- Confusing iodine (starch) with nitric acid (argemone) test colours.
- Forgetting that table sugar and glucose fractions are separate labelling declarations.