Lab Manual: Food Sample Test for Starch and Adulteration | Extra Documents & Tests for Class 9 PDF Download

Objective

To test

• The presence of starch in the given food sample
• The presence of adulterant metanil yellow in dal

Theory

• Carbohydrates: The energy-giving food, that contains carbon, oxygen,and hydrogen.
• Glucose: It is the simplest form of carbohydrate, formula: C6H12O6. It instantly gives energy on oxidation during respiration.
• Starch: The long chain of glucose forms starch, e.g., rice, potato.
• Iodine: It is a halogen, brown coloured liquid solution present in lab used for starch test.

  Iodine + Starch ⟶ Blue black colour.

Adulteration

• When food is mixed with undesirable substances which can cause harm to our body, this is called adulteration.
• Long time consumption of adulterated food causes severe health problems which may lead to cancer, stomach ulcers, brain damage, etc.
• Adulterant: Any substance that is added to the food and degrades the quality of food material is called an adulterant.
• Adulteration of food affects the health of the people.
• Foodstaff and their common adulterants
  

Harmful effects of Adulteration on health:

• Mixing of argemone oil in mustard oil results in dropsy, gastrointestinal disturbances, swelling of limbs etc. Dropsy has also caused death in some cases.
• Mixing of Kesari dal in Arhar dal causes crippling of lower limbs.
• Mixing of lead chromate in turmeric causes paralysis, mental retardation, brain damage and stiffening of limbs.
• Mixing of artificial colour (coal tar) in tea leaves causes cancer.

Diseses caused by adulterants :

Metanil Yellow

• It is a yellow colour dye, generally used for colouring food material. For e.g., starch when dyed with metanil yellow looks like turmeric. Poor quality dal when dyed with metanil yellow looks superior quality dal.
• Test for Metanil Yellow: On addition of hydrochloric acid, the metanil yellow solution turns into pink colour.
• Disease caused by metanil yellow consumption: Paralysis, brain damage, anaemia and abortion.
• Prevention of Food Adulteration (PFA): It is an act passed by Government of India to check the adulteration in food.
• Food articles with “Agmark” and FPO (Food Products Order) label are safe with unadulterated food in it.

1. To test the presence of starch in the given food sample.
Materials Required
Test tube, test tube stand, dropper.
Chemicals required
Given food sample, Iodine solution.
Procedure

• Take a clean test tube and add a little given food sample and water in it.
• Add few drops of iodine solution in the given food sample. Shake the contents of the test tube. Observe the change in colour.

Starch Test

Observation
The colour of the given food sample changes to blue-black on adding iodine solution to it.

Conclusion
The given sample of food contains starch (only if iodine changes its colour to blue-black).
Given food sample + Iodine solution ⟶ Blue-black colour

2. To test the presence of the adulterant metanil yellow in dal.
Materials Required
Test tubes, test tube holder, test tube stand, dropper.
Chemicals required
Any yellow dal (arhar), cone, hydrochloric acid
Procedure

• Take any yellow dal in a test tube in powdered form. Add 2-3 mL of water and shake well.
• Add 2-3 drops of concentrated hydrochloric acid in the test tube, shake the contents.

Metanil Yellow Test

Record your observation.

Observation
A pink colour solution appears in the test tube.
Conclusion
The given sample of dal contains metanil yellow adulteration.

Precautions 

• Use clean and dry test tubes.
• Handle concentrated HC1 carefully.
• Use chemical judiciously. Do not waste unnecessarily.