After reading this article you will learn about the methods for detection of common adulterants in food.
Detection from Milk:
1. Water:
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The presence of water can be by putting a drop of milk on a polished slanting surface. The drop of pure milk either or flows lowly leaving a white trail behind it, whereas milk adulterated water will flow immediately without leaving a mark,
2. Starch:
Add a few drops of tincture of Iodine or Iodine solution. Formation of blue colour indicates the presence of starch.
Iodine solution is easily available in the medical stores.
3. Urea:
Take a teaspoon of milk in a test tube. Add ½ teaspoon of soybean or arhar powder. Mix up the contents thoroughly by shaking the test tube. After 5 minutes, dip a red litmus paper in it. Remove the paper after ½ a minute. A change in colour from red to blue indicates the presence of urea in the milk.
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4. Vanaspati:
Take 3 ml of milk in a test tube. Add 10 drops of hydrochloric acid. Mix up one teaspoonful of sugar. After 5 minutes, examine the mixture. The red colouration indicates the presence of vanaspati.
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5. Formalin:
Take 10 ml of milk in a tests tube and add 5 ml of con sulphuric acid from the sides of the wall without shaking. If a violet or blue ring appears at the intersection of two layers then it shows presence of formalin.
Formalin enhances the life of milk and thus is added for it preservation purpose.
6. Detergent:
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Shake 5-10 ml. of sample with an equal amount of water lather indicates the presence of detergent.
7. Synthetic milk:
Synthetic milk has a bitter after taste, gives a soapy feeling on rubbing between the fingers and turns yellowish on heating.
8. Synthetic milk test for protein:
The milk can easily be tested by Urease strips (available in the Medical stores) because Synthetic milk is devoid of protein.
9. Test for Glucose /inverted sugar:
Milk does not contain glucose /invert sugar, if test for glucose with urease strip found positive. It means milk is adulterated.
If it is made; synthetically by; adding while colour water paint. Oils, alkali, urea and detergent etc. Glucose, inverted sugar syrup is added in milk to increase the consistency and test.
10. Ghee, cottage cheese, condensed milk, khoa, milk powder (Coal Tar Dyes):
Add 5 ml of dil. H2SO4 or conc. HCl to one teaspoon full of melted sample in a test tube. Shake well. Pink colour (in case of H2SO4) or crimson colour (in case of HCl) indicates coal tar dyes. If HCl does not give colour dilute it with water to get the colour.
B. Detection from Milk and Milk Product:
1. Sweet Curd:
Vanaspati:
Take1 teaspoon full of curd in a test tube. Add 10 drops of hydrochloric acid. Mix up the contents shaking the test tube gently. After 5 minutes, examine the mixture. The red colouration indicates the presence of vanaspati in the curd.
2. Rabdi:
Blotting paper:
Take a teaspoon of rabri in a test tube. Add 3 ml of hydrochloric acid and 3 ml of distilled water. Stir the content with a glass rod. Remove the rod and examine. Presence of fine fibres to the glass rod will indicate the presence of blotting paper in rabri.
3. Khoa and its products:
Starch:
Boil a small quantity of sample with some water, cool and add -a few drops of Iodine solution. Formation of blue colour indicates the presence of starch
4. Chhana or Paneer:
Starch:
Boil a small quantity of sample with some water, cool and add a few drops of Iodine solution. Formation of blue colour indicates the presence of starch.
C. Detection from Oil and Fats:
1. Ghee:
i. Vanaspathy or Margarine:
Take about one tea spoon full of melted sample of Ghee with equal quantity of concentrated Hydrochloric acid in a stoppered test tube and add to it a pinch of sugar. Shake for one minute and let it for five minutes. Appearance of crimson colour in lower (acid) of Vanaspati or Margarine.
The test specific seasame which is for oil compulsorily added is to Vanaspati and Mrgarine. Some coal tar colours also give a positive test. If the test is positive i.e. red colour develops only adding strong by Hydrochloric acid (without adding crystals of sugar) then the sample is adulterated with coal tar dye.
If the crimson or red colour develops after adding and shaking with sugar, then alone Vanaspati or Margarine is present.
ii. Mashed Potatoes, Sweet Potatoes and other starches:
The presence of mashed potatoes and sweet potatoes in a sample of ghee can easily be detected by adding a few drops of Iodine, which is brownish in colour turns to blue if mashed potatoes/sweet potatoes/other starches are present.
2. Butter:
i. Vanaspati or Margarine:
Take about one teaspoon full of melted sample of butter with equal quantity of concentrated Hydrochloric acid in a stoppered test tube and add to it a pinch of sugar. Shake for one minute and let it for five minutes. Appearance of crimson colour in lower (acid) of Vanaspati or Margarine.
The test is specific for seasame oil which is compulsorily added to Vanaspati and Margarine. Some coal tar colour also give a positive test.
If the test is positive i.e. red colour develops only by adding strong Hydrochloric acid (without adding crystals of j sugar) then the sample is adulterated with coal tar dye. If the crimson or red colour develops after adding and shaking with sugar, then alone Vanaspati or Margarine is present
ii. Mashed potatoes other starches:
The presence of mashed potatoes and sweet potatoes in a sample of butter can easily detected by adding a few drops of iodine (which is brownish in colour), turns to blue.
3. Edible oil:
Prohibited colour:
Take 5 ml of sample in a test tube and add 5 ml of concentrated hydrochloric acid. Shake gently, let it stand for 5 minutes. Colour will separate in the upper layer of the solution.
4. Coconut oil:
Any other oil:
Place a small bottle of oil in refrigerator. Coconut oil solidifies leaving the adulterant as a Separate layer.
D. Detection from Sweetening Agents:
1. Sugar:
i. Chalk powder:
Dissolve 10 gm of sample in a glass of water, allow settling, Chalk will settle down at the bottom.
ii. Urea:
On dissolving in water it gives a smell of ammonia.
iii. Chalk powder:
Dissolve 10 gm of sample in a glass of water, allow to settle, chalk will settle down at the bottom.
iv. Yellow colour (Non- permitted):
Take 5 ml in a tests tube from the above solution and add a few drops of conc. Hc1. A pink colour in lower acid layers shows the presence of non-permitted colour.
2. Honey:
Sugar solution:
A cotton wick dipped in pure honey when lighted with a match stick burns and shows the purity of honey. If adulterated, the presence of water will not allow the honey to burn, If it does; it will produce a cracking sound.
This test is only for added water.
3. Jaggery:
i. Washing soda:
Add a few drops of solution HC1. Effervescence shows presence of washing soda.
ii. Chalk powder:
Dissolve a little amount sample in water in a test tube, chalk powder settles down. -Or-
Add a few drops of solution Hc1. effervescence indicates the presence of adulterant.
iii. Metanil yellow colour:
Take ¼ of a teaspoon of the jaggery in a test tube. Add 3 ml of alcohol and shake the tube vigorously to mix up the content. Pour 10 drops of hydrochloric acid in it. A pink colouration indicates the presence of metanil yellow colours in jaggery.
iv. Sugar solution:
Add a drop of honey to a glass if water, if the drop does not disperse in water it indicates that the honey is pure. However, if the drop disperses in water it indicates presence of added sugar.
4. Bura sugar:
Washing soda:
Add 1 ml of HC1 to a little of bura sugar. Effervescence occurs if washing soda is present. Dissolve 2 gm of sugar in water; dip a red litmus paper in the solution. If washing soda is present, it will turn blue.
5. Sweetmeats, Ice-cream and beverages:
i. Metanil yellow (a non- permitted coal tar colour):
Extract colour with luke warm water from food articles. Add few drops of concentrated Hydrochloric acid. If magenta red colour develops the presence of metanil yellow is indicated.
ii. Saccharin:
Taste a small quantity. Saccharin leaves a lingering sweetness on tongue for a considerable time and leaves a bitter taste at the end.
E. Detection from Food Grain and their Products:
1. Wheat, Rice, Maize, Jawar, Bajra, chana, Barley etc.:
Dust, pebble, stone, straw, weed seeds, damaged grain, weevilled grain, insects, rodent hair and excreta:
These may be examined visually to see foreign matter, damaged grains, discoloured grains, insects, rodent contamination etc.
Damaged / discoloured grains should be as low as possible since they may be affected by fungal toxins, argemone seeds, Dhatura seeds etc. In moderately excessive amount can resultin risk to health,Discard the damaged undesirable grains before use
2. Maida:
Resultant atta or cheap flour:
When dough is prepared from resultant or left out atta, more water has to be used. The normal taste of chapattis prepared out of wheat is somewhat sweetish whereas those prepared out of adulterated wheat will taste insipid.
3. Maida/ Rice:
Boric Acid:
Take a small amount of sample in a test tube, add some water and shake. Add a few drops of HCl. Dip a turmeric paper strip if it turns red, boric acid is present.
4. Wheat barja and other grains:
i. Ergot (a fungus containing poisonous substance):
(i) Purple black longer sized grains in Bajra show the presence of Ergots,
(ii) Put some grains In a glass tumbler containing 20 per cent salt solution (20 gm common salt to 100 ml water) purple black longer size grain Ergot floats over the surface while sound grains settle down.
ii. Dhatura:
Dhatura seeds are flat with edges with blackish brown colour which can be separated out by close examination.
iii. Karnel Bunt:
The affected wheat kernel have a dull appearance, blackish in colour and rotten fish smell,
5. Spella Rice(Parboiled Rice):
i. Metanil yellow (a non- permitted coal tar colour):
Rub a few grains in the palms of two hands. Yellow would get reduced or disappear. Add a few drops of dilute Hydrochloric acid to a few rice grains mixed with little water, presence of pink colour indicates presence of Metanil yellow
ii. Turmeric (colouring golden appearance):
Take a small amount of sample in a test tube, add some water and shake.
Dip Boric acid paper (filter paper dipped in Boric acid solution) If it turns pink turmeric is present. Take some rice and sprinkle on it a small amount of soaked lime for some time, grains will turn red if turmeric is present.
6. Parched rice:
Urea:
Take 30 numbers of parched rice in a test tube. Add 5ml of distilled water in it. Mix up the contents thoroughly, by shaking the test tube. After 5 minutes, filter the water- contents, and add VI teaspoon of powder of arhar or soybean in it.
Leave it for 5 minutes, and then dip a red litmus paper in the mixture. Take out the litmus paper after 30 seconds and examine it. A blue colouration indicates the presence of urea in the parched rice.
7. Wheat flour:
i. Excess bran:
Sprinkle on water surface. Bran will float on the surface.
ii. Chalk powder:
Shake sample with dil. HC1 Effervescence indicates chalk.
Chalk powder is used as an adulterant due to its weight.
8. Dal whole spilt:
i. Khesari Dal:
(i) Khesari dal has edged type appearance showing a slant on one side and square in appearance in contrast to other dals.
(ii) Add 50 ml of dilute Hydrochloric acid to the sample and keep on simmering water for about 15 minutes. The pink colour developed indicates the presence of Khesari dal.
The test is only for Khesari dal. (Metanil yellow if Present will give a similar colour immediately even without simmering).
ii. Clay, stone, gravels, webs, insects, rodent hair and excreta:
Visual examination will detect these adulterants
Reject if the number of Insects is large or if the odour is unpleasant and taste bitter or gritty
iii. Metanil yellow (a non-permitted coaltar colour):
Take 5 gms of the sample with 5 ml. of water in a test tube and add a few drops of concentrated Hydrochloric acid. A pink colour shows presence o Metanil yellow
9. Atta, Maida Suji (Rawa):
i. Sand, soil, insects, webs, lumps, rodent hair and excrete:
These can be identified by visual examination.
ii. Iron Fillings:
By moving a magnet through the sample, iron filling can be separated
10. Bajra:
Ergot infested Bajra:
Soak bajra in water, swollen and black Ergot infested grains will turn light in weight and will float in water
11. Sago:
Sand or talcum:
Put a little quantity of sago in mouth, it will have a gritty feel, if adulterated. Burn the sago, if pure, it will swell and leave hardly any ash. Adulterated sago will leave behind appreciable quantity of ash.
12. Besan:
i. Mentanil Yellow:
Take 1/2 teaspoon of the besan in a test tube. Pour 3 ml of alcohol in the test tube. Mix up the contents thoroughly by shaking the test tube. Add 10 drops of hydrochloric acid it. A pink colouration indicates presence of metanil yellow in the gram powder.
ii. Khesari flour:
Add 50 ml of dilute Hydrochloric acid to 10 gms of sample and keep on simmering water for about 15 minutes. The pink colour, if developed, indicates, the presence of Khesari flour
The test is only for Khesari dal (Metanil yellow, if present will give a similar colour even without simmering).
13. Pulses
Lead chromate:
Shake 5 gm. Of pulse with 5 ml. Of water and add a few drops of HC1. Pink colour indicates Lead Chromate.
F. Detection from Spices:
1. Whole spices:
Dirt, dust, straw, insect, damaged seeds, other seeds, rodent hair and excrete
These can be examined visually
2. Black pepper:
i. Papaya seeds:
Papaya seeds can be separated out from pepper as they are shrunken, oval in shape and greenish brown or brownish black in colour.
ii. Light black Pepper:
Float the sample of black pepper in alcohol (rectified spirit). The black pepper berries sink while the papaya seeds and light black pepper float.
Press the berries with the help of fingers light peppers will break easily while black berries of pepper will not break.
iii. Coated with mineral oil:
Black pepper coated with mineral oil gives Kerosene like smell.
3. Cloves:
i. Volatile oil extracted (exhausted cloves):
Exhausted cloves can be identified by its small size and shrunken appearance. The characteristic pungent of genuine cloves is less pronounced in exhausted cloves
ii. Coated with mineral oil:
Cloves coated with mineral oil gives kerosene like smell
4. Mustard seed:
Argemone seed:
Mustard seeds have a smooth surface. The argemone seed have grainy and rough surface and are black and hence can be separated out by close examination. When Mustard seed is pressed inside it is yellow while for Argemone seed it is white.
Use magnifying glass for identification.
5. Powered spices:
i. Added starch:
Add a few drops of tincture of Iodine or Iodine solution. Indication of blue colour shows the presence of starch.
Iodine test for added starch is not applicable for turmeric powder.
ii. Common Salt:
Taste for addition of common salt.
6. Turmeric Powder:
Coloured saw dust:
Take a tea spoon full of turmeric powder in a test tube. Add a few drops of concentrated Hydrochloric acid. Instant appearance of pink colour which disappears on dilution with water shows the presence of turmeric. If the colour persists, metanil yellow (an artificial colour) a not permitted coal tar colour is present.
This test is only for Metanil yellow.
7. Turmeric whole:
i. Lead chromate:
Appears to be bright in colour which leaves colour immediately in water.
ii. Chalk Powder or yellow soapstone powder:
Take a small quantity of turmeric powder in a test tube containing small quantity of water. Add a few drops of concentrated Hydrochloric acid, effervescence (give off bubbles) will indicate the presence of chalk or yellow soap stone powder.
8. Chilles powder:
i. Brick powder, salt powder or talc, powder:
Take a tea spoon full of chillies powder in a glass of water. Coloured water extract will show the presence of artificial colour.
Any grittiness that may be felt on rubbing the sediment at the bottom of glass confirms the presence of brick powder/sand, soapy and smooth touch of the white residue at the bottom indicates the presence of soap stone.
To a little powder of chilli add small amount of conc HC1 and mix to the consistency of paste, dip the rear end of the match stick into the paste and hold over the flame, brick red flame colour due to the presence of calcium slats in brick powder.
This test is only for earthy material
ii. Artificial colours:
Sprinkle the chilli powder on a glass of water. Artificial colorants descend as coloured streaks.
iii. Water soluble coal tar colour:
Water soluble artificial colour can be detected by sprinkling a small quantity of chillies or turmeric powder on the surface of water contained in a glass tumbler. The water soluble colour will immediately start descending in colour streaks
9. Asafoetida (Hing):
i. Soap stone or other earthy material:
Shake little portion of the sample with water and allow to settle. Soap stone or other earthy mailer will settle down at the bottom.
In compounded asafoetida due to presence of starch, a slight turbid solution may be produced. However, this will settle down after keeping
ii. Starch:
Add tincture of iodine, appearance of blue colour shows the presence of starch.
Compound of asafetida contains starch which is declared on the label. This test is not applicable for compound as asafoetida.
iii. Foreign resin:
Burn on a spoon, if the sample burns like camphor, it indicates the sample is pure.
Pure hing burn like aromatic camphor
11. Spices:
Powdered bran and saw dust:
Sprinkle on water surface. Powdered bran and sawdust float on the surface.
12. Cinnamon:
Cassia bark:
Cinnamon barks are very thin and can be rolled. It can be rolled around a pencil or pen. It has a distinct smell. Whereas cassia ark comprise of several layers in between the rough outer and inner most smooth layers. On examination of the ark loosely, a clear distinction can be made.
13. Cumin seeds:
Grass seeds coloured with charcoal dust:
Rub the cumin seeds on palms. If palms turn black adulteration is indicated.
14. Green chilli and green vegetables:
Malachite green:
Take a cotton piece soaked in liquid paraffin and rub the outer green surface of a small part of green vegetable. If the cotton turns, green, we can say the vegetable is adulterated with malachite green.
15. Green Peas:
Artificially coloured:
Take a little amount of green peas in a 250 ml beaker add water to it and mix well. Let it stand for half an hour. Clear separation of colour in water indicates adulteration.
16. Saffron:
Dried tendrils of maize cob:
Genuine saffron will not break easily like artificial. Artificial saffron is prepared by soaking maize cob in sugar and colouring it with coal tar colour. The colour dissolves in water if artificially coloured. A bit of pure saffron when allowed to dissolved in water will continue to give its saffron colour so long as it lasts.
G. Detection from Miscellaneous Products:
1. Common salt:
White Powder:
Stir a spoonful of sample of talk in a glass of water. The presence of chalk will make solution white and other insoluble impurities will settle down.
2. Iodized salt:
Common salt:
Cut a piece of potato, add salt and wait minute and add two drops of lemon juice. If iodized salt blue colour will develop. In case of common salt, there will be no blue colour.
3. Tea leaves:
i. Exhausted tea:
Take a filter paper and spread a few tea leaves. Sprinkle with water to wet the filter paper. If coal tar colour is present it would immediately stain the filter paper. Wash the filter paper under tap water and observe the stains against light Spread a little slaked lime on white porcelain tile or glass plate; sprinkle a little tea dust on the lime.
Red, orange or other shades of colour spreading on the lime will show the presence of coal tar colour. In case of genuine tea, there will be only a slight greenish yellow colour due to chlorophyll, which appear after some time.
ii. Iron Filling:
By moving a magnet through the sample iron filling can be separated.
iii. Chicory:
Gently sprinkle the coffee powder sample on the surface of water in a glass. The coffee floats over the water but chicory begins to sink down within a few seconds. The falling chicory powder particles leave behind them a trail of colour, due to large amount of caramel
4. Supari pan Masala:
i. Colour:
Colour dissolves in water
ii. Saccharin:
Saccharin gives excessive and lingering sweet taste and leaves bitter taste at the end.
5. Catachu chalk:
Chalk:
Chalk gives effervescence (gives off bubbles) with concentrated Hydrochloric acid
This a test is only chalk
6. Lemonade soda:
Mineral acid:
Pour 2 drops of the lemonade soda on a metanil yellow paper- strip. A violet colouration indicates the presence of mineral acid in aerated water. The colour impression gets retained even after drying the paper (you can prepare metanil yellow paper strips by soaking filter paper strips in 0.1 % aqueous solution and then drying the paper – strips).
7. Sweet Potato:
Rhodamine B colour:
Take a cotton piece soaked in liquid paraffin, and rub the outer red surface of the sweet potato. If the cotton absorb colour, it indicates the use of rhodamine B colours on the outer surface of the sweet potato
8. Pulses:
Lead Chromate:
Shake 5 gm. Of pulse with 5 ml. Of water and add a few drops of HC1. Pink colour indicates Lead Chromate
10. Iodized salt:
Common salt:
Cut a piece of potato, add salt and wait minute and add two drops of lemon juice. If iodized salt blue colour will develop. In case of common salt, there will be no blue colour.
(i) On ignition, genuine silver leaves burn away completely, leaving glistering white spherical ball of the same mass whereas aluminium leaves are reduced to ashes of dark grey blackish colour,
(ii) Take silver leaves in test tube, add diluted Hydrochloric acid. Appearance of turbidity to white precipitate indicates the presence of silver leaves. Aluminium leaves do not give any turbidity or precipitate
(iii) Take aluminium leaves in palm and rub between both the palms of the hand, silver leaves completely disappear in the hand; however presence of small ball in the palm indicates adulteration with aluminium leaves.
11. Vinegar:
Mineral Acid:
Test with the Metanil yellow indicator paper, in case, the colour changes from yellow to pink, mineral acid is present.