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II- Identification tests

1- Identification of proteins

Proteins ensure the growth and the multiplication of the cells as well as the normal maintenance
of the body.
The Biuret test allows us to detect the presence of proteins and peptides by obtaining a violet

coloration.
Proteins are formed of long chains of amino acids. Many amino acids form peptides.

2- Identification of glucose

Carbohydrates are sugars:
- Simple sugars or monosaccharides such as glucose, fructose and galactose…
- Complex sugars or polysaccharides such as starch, cellulose and glycogen.
The Fehling test allows us to detect the presence of reducing sugars (all simple sugars and
disaccharides except sucrose) by obtaining a brick red precipitate when heated.

3- Identification of starch

Iodine water test: Iodine water is the reagent of starch. It gives a dark blue coloration.
N.B.: Cellulose doesn’t have any specific digestive enzyme. It is eliminated intact in the feces.
However, it facilitates the progress of food in the digestive tract and prevents constipation.

4- Identification of lipids

Lipids leave a persistent translucent spot on a paper.

5- Identification of mineral substances

a- Water: after heating, water vapor condenses on the cold border of the tube.
b- Mineral salts (chlorides) react with the silver ions. They form a white precipitate of silver
chloride.

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