Food adulteration and simple tests to detect it
Adulteration makes food unsafe, sub-standard or misbranded. Simple tests with water, iodine and acids, such as iodine turning starch in milk blue, screen common foods quickly.
What adulteration means
Adulteration lowers the quality of food by adding a cheaper or harmful substance, substituting a cheaper ingredient, or removing a valuable part. Under the Food Safety and Standards Act, 2006, an adulterant is any material that is or could be used to make food unsafe, sub-standard or misbranded, or containing extraneous matter. In simple words: unsafe food can harm health (argemone oil in mustard oil); sub-standard food does not meet its quality standard but may not be harmful (watered milk); misbranded food carries a false or misleading label or claim (a blend sold as 'pure ghee'); extraneous matter is foreign material such as sand, stones or hair. Adulteration cheats the buyer, lowers nutritive value and can cause serious disease.
Types and methods of adulteration
| Type | Meaning | Examples |
|---|---|---|
| Intentional | Added deliberately for profit | Water and starch in milk, chalk in sugar, brick powder in chilli powder, papaya seeds in pepper |
| Incidental | Enters through carelessness, ignorance or poor handling | Pesticide residues, insect fragments, rodent hair and droppings, stones in grain |
| Metallic | Toxic metals get into food, by accident or on purpose | Lead from lead chromate on turmeric, arsenic from pesticides, mercury in fish from polluted water |
| Abstraction | A valuable part is taken out | Fat skimmed from milk sold as whole milk; oil extracted from cloves or cardamom (exhausted spices); used tea leaves re-dried and sold |
| Colouring and concealment | Hiding poor quality or making food look fresh | Malachite green on peas and chillies, metanil yellow on dal, calcium carbide to ripen fruit |
Common adulterants and simple tests
| Food | Adulterant | Test | Positive result |
|---|---|---|---|
| Milk | Water | Put a drop of milk on a polished, slanting glass plate | Pure milk flows slowly and leaves a white trail; watered milk runs down at once without a trail |
| Milk | Starch | Boil 3-5 mL milk, cool, add 2-3 drops iodine solution | Blue colour; without starch the iodine stays brown |
| Milk | Detergent | Shake 5-10 mL milk with an equal amount of water | Dense, lasting lather; pure milk gives only a thin foam |
| Ghee or butter | Mashed potato, sweet potato or other starch | Melt half a teaspoon (in the lab, boil with a little water), cool, add 2-3 drops iodine | Blue colour |
| Ghee | Vanaspati (hydrogenated fat) | Baudouin test: 5 mL melted ghee + 5 mL conc. HCl + about half a teaspoon of sugar; shake 2 minutes and let it separate | Crimson or pink colour in the lower acid layer that stays after adding water (the test detects sesame oil, which Indian standards require in vanaspati as a marker) |
| Chilli powder | Brick powder, sand, soapstone | Stir a teaspoon into a glass of water; rub the sediment between the fingers | Gritty sediment means brick powder or sand; a smooth, soapy white sediment means soapstone |
| Chilli powder | Artificial colour | Sprinkle the powder on water in a glass | Coloured streaks run down from the particles |
| Turmeric powder | Metanil yellow | 1 g turmeric + 5 mL water + a few drops conc. HCl | Pink-violet colour that stays when more water is added; with pure turmeric it fades on dilution |
| Black pepper | Papaya seeds | Drop the berries into a glass of water (in the lab, into alcohol) | Papaya seeds (lighter and oval) float; mature pepper sinks |
| Tea leaves | Used tea leaves coloured with dye | Place the leaves on a white filter paper and add water drop by drop | Pink or red streaks spread on the paper; pure tea gives no colour |
| Coffee powder | Chicory | Sprinkle gently on water in a glass | Coffee floats; chicory sinks within seconds, leaving a brown trail |
| Honey | Sugar syrup | Drop honey into a glass of water (in the lab, Fiehe's test with resorcinol in HCl) | Pure honey stays as a lump and adulterated honey disperses; Fiehe's test gives pink to cherry red with invert sugar |
| Sugar | Chalk powder | Dissolve 10 g in a glass of water; add dilute HCl to the sediment | White chalk settles; it fizzes (effervescence) with acid |
| Edible oil (mustard) | Argemone oil | Shake 5 mL oil with 5 mL conc. nitric acid and let the layers separate | Orange-red to reddish-brown colour in the lower acid layer |
| Green peas, green chillies | Malachite green | Rub with cotton dipped in liquid paraffin, or soak peas in water | The cotton turns green; the water turns green |
| Toor or chana dal | Metanil yellow | Shake 1 g dal with lukewarm water, add a few drops conc. HCl | Pink colour at once |
| Silver leaf (vark) on sweets | Aluminium foil | Burn a small piece | Pure silver burns away leaving a shiny white ball; aluminium leaves dark grey ash |
| Rava, tea | Iron filings | Spread on paper and run a magnet through it | Iron filings cling to the magnet |
Activity: detecting adulteration in different foods
Done in the food lab in small groups. Wear an apron, gloves and goggles; handle concentrated acids in a fume hood with a dropper or pipette filler. Never taste a sample.
- 1Collect samples: buy loose and packed milk, ghee, chilli powder, turmeric, pepper, tea, honey, sugar and oil from different shops; label each with source, date and price.
- 2★Keep a control: test a sample of known purity alongside each unknown, so that colours and behaviour can be compared.
- 3Set up: clean, dry test tubes, a glass plate, filter paper, glasses of water and a magnet; reagents: iodine solution, conc. HCl, dilute HCl, conc. nitric acid, sugar, liquid paraffin.
- 4Run each test from the table, one food at a time, using the stated amounts.
- 5Observe and record at once in a table: food, test, observation, inference (pure or adulterated); photograph results if possible.
- 6Conclude: a positive home test is only a screening result; confirm in an accredited laboratory and report suspected adulteration to the local Food Safety Officer.
- 7Clean up: dilute and dispose of acids as the lab instructs; wash all glassware.
★ one-way, controls the pace
Home screening tests vs laboratory tests
In the exam, write the reagent and the exact colour for each test; that is where the marks are.
A canteen or hotel purchase manager can screen incoming milk, ghee, oil and spices with these quick tests, buy only from FSSAI-licensed suppliers, and refuse loose, unlabelled spices. Adulteration also lowers nutritive value: watered milk gives less protein and calcium per glass.
2 marks: “Define an adulterant.” Under the FSS Act 2006, any material that is or could be used to make food unsafe, sub-standard or misbranded, or containing extraneous matter.
5 marks: “Give simple tests to detect any five common adulterants.” Table of food, adulterant, test and result: starch in milk (iodine, blue), metanil yellow in turmeric (HCl, pink that persists), argemone in oil (nitric acid, orange-red), papaya seeds in pepper (float), chalk in sugar (settles, fizzes with acid).
10 marks: “Define food adulteration. Explain the types of adulteration and the methods to detect common adulterants.” Definition with the FSS Act terms (unsafe, sub-standard, misbranded); types (intentional, incidental, metallic, abstraction); table of 8-10 tests; home vs lab tests; harmful effects; consumer's role.
Pair the colour with the culprit: iodine blue = starch; HCl pink that stays = metanil yellow; nitric acid red = argemone; crimson acid layer = vanaspati; fizz = chalk; float = papaya seeds.