Incidental adulteration

Lesson 15 : Food Adulteration

Incidental adulteration

Incidental adulteration is usually due to ignorance, negligency of proper facilities.

The table below shows the lists of adulterants which are used for various food articles & methods for detection of adulterant.

Name of the food article


Simple method for detection of adulterant


Soap stone (pumice stone) or other earthy matter

Shake with water. soap stone or other earthy matter will settle to the bottom

Shake sample with carbon tetralchloride. Asafoetida settle down. Decant the top layer and add dil HCl to the residue. Effervescence shows presence of chalk.


Infested with ergot (fungi)

Long irregular black grain indicates ergot. In 2 per cent salt solution ergot floats.

Bengal gram flour

Yellow maize flour
Metanil Yellow

Rubbing with fingers and roughness indicates presence of maize flour.
Shake portion of sample with cold or warm water. The water becomes yellowish and on treatment with few drops of concentrated HCl turns magnets red.

Black pepper.

Dried seeds of papaya fruit
Light Berries

Papaya seeds are shrunken, oval in shape and greenish brown or brownish black in colour and has repulsive flavour quite distinct from the bite of black pepper.
Light Berries or papaya seeds float on spirit or carbon tetrachloride

Chilli powder

Brick powder,
Soap stone

Artificial colour

Any grittiness that may be felt on tapping the sediment at the bottom of glass confirms the presence of brick powder 'or sand. Smooth white residue at the bottom indicates the presence of soapstone.

Water soluble artificial dye can be detected by sprinkling a small quantity of chilli powder on the surface of water contained in a glass tumbler. The soluble dye will immediately start descending in colour streaks.


Cassia bark

Cinnamon barks are very thin and can be rolled. Cassia barks are thick and stiff.


Volatile oil extracted cloves

Exhausted cloves can be identified by its small size and shrunken appearance. The characteristics pungent taste of genuine cloves is less pronounced in exhausted cloves.




Tamarind or date-seed powder

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 few seconds. The falling chicory powder particles leave behind a trail of colour due to large amount of caramel they contain.

Make decoction of the coffee, decolourise it by adding potassium permanganate and then add a drop of iodine solution. Blue colour indicates presence of starch.

Sprinkle the suspected coffee powder on white blotting paper and spray over it 1 per cent sodium carbonate solution. Tamarind and date-seed powder will, if present, stain blotting paper red.
Shake powder with 2 per cent sodium hydroxide or washing soda solution. Formation of reddish colour indicates tamarind seeds

Common salt

White-powdered stone, chalk

Stir a spoonful of simple salt in a glass of water. The presence of chalk will make the solution white and other insoluble impurities settle down.

Coriander powder

Common salt

To 5 ml of sample add a few drops of silver nitrate. White precipitate indicates adulteration.

Cumin seeds

Grass seeds coloured with charcoal dust

Rub the cumin seeds on palm. If palms turn black adulteration is indicated


Kesari dal

Clay stones, gravels lead, chromate, metanil yellow

Add 50 ml of dilute hydrochloric acid to dal and keep on simmercing water for about 15 minutes. The pink colour if developed indicates the presence of Kesari dal
On visual examination to see wedge like shapes of Kesari dal.
Visual examination will detect these adulterants.
Shake 5 grams of dal with 5ml or water and add a few drops (yellow) of hydrochloric Acid. A pink colour shows the presence of colour.

Edible oils

Argemone oil

Mineral oil

Castor oil

Add concentrated nitric acid to a sample and shake carefully.Red to reddish brown colour in acid layer indicates the presence of· argemone oil.
Take 2 ml of edible oil and add an equal quantity of N/2 alcoholic potash. Heat in boiling water bath for 15 minutes and add 10 ml of water. Any turbidity shows the presence of mineral oil.
Dissolve some oil in petroleum ether in a test tube and cool in ice salt mixture. Presence of turbidity within 5 minutes indicates the presence of oil.

Food grains

Hidden insect infestation

Take a filter paper impregnate with ninhydrin (1% in alcohol).
Put some grains on it and then fold the filter paper and crush the grains with hammer. Spots of bluish purple colour indicate presence of hidden insect infestation.

Ghee or Butter


Mashed potato,
sweet potato and
other starches

Take about one teaspoonful of melted ghee or butter with equal quantity of concentrated hydrochloric acid in a test tube and add to it
a pinch of cane sugar, Shake well for one minute and test it after 5 minutes. Appearance of crimson colour in lower (acidic) layer shows the presence of 'vanaspati'.
Add a drop of iodine solution. Iodine which is brownish in colour turns to blue if starches are present. Iodine solution is prepared by dissolving 2.5 g of iodine crystals and 3 g potassium iodine in water to make solution of 100 ml.


Molasses (sugar and water)

Commercial invert sugar (mixture of glucose and fructose)

A cotton wick dipped in pure honey when lighted with a match stick burns. If adulterated, the presence of water will not allow the honey to burn. If it does, it will produce a crackling sound.

  1. Fiehe's test. Mix 5 g of honey with 10 ml of ether in a mortar using a pestle. Decant the ether extracts into a china dish. Repeat twice or thrice. Allow the ether to evaporate at room temperature.
    To the residue in the dish, add a large drop of I per cent solution of freshly sublimed resorcinol in concentrated HCI (l g of resorcinol resublimed in 5 ml of conc. HCI). Immediate appearance of cherry red colour indicates invert sugar.
  2. Aniline chloride test. Take 5 ml of honey in a porcelain dish. Add Aniline chloride solution (3 ml of aniline and 7 ml of 1:3 HCI) and stir well. Orange red colour indicates presence of sugar.

Jaggery powder

Chalk powder

Metanil yellow

Add few drops of hydrochloric acid. Effervesce indicates adulteration. Stir a spoonful sample of sugar in a glass of water. The chalk settle down.
Same test as for other substances.



Add tincture of iodine. Indication of blue colour shows the presence of starch.


Water/defalted milk


a. The lactometer reading should not ordinarily be less than 1.028,
b. The presence of water can be detected by putting a drop of milk on a polished vertical surface. The drop of pure milk either stops or flows slowly leaving a white trail behind it; whereas milk adulterated with water will flow immediately without leaving a mark.

c. Add tincture of iodine, indication of blue colour shows the presence of starch.
This test is not valid if milk is skimmed and thickening material is added.

Milk, curd

Cane sugar

Add 0.1 g of resorcinol and I ml of concentrated HCI to 10 ml of the sample and boil-A rose red colour indicates the presence of cane sugar.

Mustard seeds

Argemone seeds

Examine under magnifying glass. Seeds more blacken, rough and non-uniform irregular round show presence of argemone seeds. Mustard seeds have a smooth surface. The argemone seed have grainy and rough surface and are blacker hence can be separated out by close examination.

Powdered spices

Grit, talc
sand colour

Shake up a little of the sample in a dry test tube with 5 ml of carbon tetrachloride (CCl4). Allow to settle sand, talc and grit will sink to the bottom leaving spices on the top.

Pulses (green peas)

Colour dye

Sample is kept immersed in water for about half an hour and stirred. Colour separation indicates adulteration


Iron fillings

By moving a magnet through it iron fillings can be separated


Marble or other stones

A simple test is to place a small quantity of rice on the palm and gradually immerse the same in water. The stone chips will sink.


Dyed tendrils of maize cob

Genuine saffron will not break easily like artificial one. The colour dissolves in waler if artificially coloured. Pure saffron when allowed to dissolve in water will continue to give its saffron colour so long as it lasts.


Sand or talcum

On burning leaves no ash. Adulterated sago will leave behind appreciable quantity of ash.

Silver leaves

Aluminium leaves

On ignition, genuine silver leaves burn away completely, leaving glistening white spherical ball whereas aluminium leaves are reduced to ashes of dark grey blackish colour. The silver foil
is very thin and if crushed between two fingers, crumbles to powder Aluminium foil is comparatively thicker and only breaks to small shreds when passed similarly.
Take silver leaves in a test tube. Add dil HCl. Appearance of turbidity to white precipitate indicates the presence of silver leaves. Aluminium leaves reacts with HCl to leave blackish grey fumes.

Soft drinks

Mineral acid other than phosphoric acid

Soak a strip of filter paper in a 0.1 per cent solution of metanil yellow and then dry. Dip one end of paper into the soft drink. Wetted portion turns violet if mineral acid in present.


Chalk powder

Dissolve in a glass of water, chalk will settle down at the bottom.


Colour and saccharine

Colour dissolves in water. Saccharin gives excessive and lingering sweet taste.

Sweet meat, Ice-cream, Sherbat

Metanil yellow (a non-permitted coaltar dye)

Extract colour with luke-warm water from food article. Add few drops of conc. Hydrochloric Acid. If magenta red colour develops, the presence of metanil yellow is indicated

Tea leaves

Exhausted tea or black or Bengal gram dal husk with colour

  1. Tea leaves sprinkled on wet filter paper would immediately release added colour.
  2. 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 dye. In the case of genuine tea, there will be only a slight greenish yellow colour due to chlorophyll which appears after sometime


Metanil yellow

Yellow clay

Take a teaspoon full of turmeric powder in a test tube. Add a few drops of conc. hydrochloric acid. Instant appearance of violet colour which disappears on dilution with water. If the colour persists, presence of metanil yellow is indicated.

Mix powders with water and allow to stand for sometime. The yellow clay will settle down at the bottom leaving turmeric on the top.

Wheat, bajra and other food grains

Ergot (a fungus containing a poisonous substance)

Dhatura seeds

  1. Purple black longer size grains in bajra show the presence of ergots. .
  2. Put some grains in a glass containing 20 per cent salt solution.

Ergot floats over the surface while sound grains settle down.
Dhatura seeds resemble chilli seeds with blackish brown colour which can be separated out by close examination.

Wheat flour


Chalk powder and lime powder

When dough is prepared from resultant wheat flour, more water has to be used and chapathies prepared out of this will blowout. The normal taste of chapathies prepared out of wheat is some what sweetish whereas those Prepared out of adulterated wheat flour will taste insipid(tasteless) .
Extract the sample and petroleum ether and add 13 N H2S04 (Make up 88 ml of conc. H2S04 to 250 ml with distilled water) to the extract. Appearance of red colour which does not disappear with distilled water indicates adulteration.
Treat sample with hot dilute HCl The bubbling of gas indicates carbon dioxide from chalk or other carbonates.

(Source-Manual published by Corporation of Madras. Gupta Rati Ram and Rajeev Gupta. Food Adultration and control Measures processed Food Industry. May 2000).

Incidental adulteration

  1. Contamination of foods with harmful micro organisms
    Some raw foods like meat, fish, milk and vegetables grown on sewage are likely to be contaminated with harmful microorganisms. These are generally destroyed during cooking or processing of food. Some of the micro organisms may survive due to inadequate heat processing. Some foods though they contain low moisture, if they are stored in humid atmosphere, they will get infected with pathogenic fungal which can cause serious illness.
  1. Metallic contamination
    Contamination of food with lead can cause toxic symptoms. Lead brings about pathological changes in the kidney, liver, and arteries. The common signs of lead poisoning are nausea, abdominal pain, anemia, insomnia, mascular paralysis and brain damage. Fish caught from water contaminated with mercury salt contains large amount of mercury. The other elements which are toxic in small doses are cadmium, arsenic, antimony and cobalt.
  1. Packaging hazards
    Polyethylene, polyvinyl chloride and other allied compounds are used to produce flexible packaging material. While this method of packaging is very convenient, it must not contain any noxious thermal breakdown products which could be injurious to health. Further , temperatures used for heat cealing or sterilization should not result in formation of toxic residues. It is essential that only food grade plastic packaging materials be used for packaging foods.
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Last modified: Saturday, 3 December 2011, 11:09 AM