Theory:

Test for carbohydrate:
 
There are many types of carbohydrates present in our food. Starch and sugars are very important and most abundant carbohydrates present in our food.
 
How do we identify starch in our food, we can perform the below-mentioned test.
 
Test for Starch:
  • Take small quantity of the food items to be tested.
  • Put 2-3 drops of iodine solution on it.
  • Observe the colour of the food item.
  • Blue-black colour indicates the presence of starch in the tested food item.
Blue-black colour indicates the presence of starch in the tested food item.
 
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Test for sugar:
 
Benedict's test:
 
Benedict's solution is used to test for simple sugars, such as glucose. It is a clear blue solution of sodium and copper salts.
In the presence of simple sugars, the blue solution changes colour to green, yellow, and brick-red, depending on the amount of sugar.
 
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Test for protein:
 
Add a few drops of copper sulphate and caustic soda in food.
Change in colour to violet indicates the presence of protein.
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Test for fats:
 
Very simple test, crush the food inside a tissue paper. Shake or crush the food to make it dissolve.
 
Another test for fats:
 
Filter or dilute the food and mix it with ethanol so that you get a clear liquid (a solution of fat in ethanol). Add this to a test tube of water. A white (milk-like) emulsion indicates the presence of fats or oils.
A white (milk-like) emulsion indicates the presence of fats or oils.
 
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Important!
The nutrients such as carbohydrates, proteins, vitamins, minerals, fats are highly essential to make a person healthy and make a meal balanced. These are the major nutrients of a meal. In addition to it, we also need dietary fibres and water to make the absorption of all the nutrients easier.
Let us see how each of these nutrients helps us to keep healthy and active, and how to make a balanced diet which will contain all the above nutrients.  
Reference:
Iodine test for starch: http://www.docbrown.info/ebiology/foodtests.htm .copyrighted image.
Benedict's test for sugar: http://www.docbrown.info/ebiology/foodtests.htm .copyrighted image
Test for protein: https://www.tuttee.co/blog/biol-biological-molecules-carbohydrates-proteins-and-lipids. copyrighted image
Test for fat: https://socratic.org/questions/what-should-you-use-to-test-if-a-type-of-food-has-starch-sugar-or-fat . copyrighted image