composition of food

1. Chemestry laboratory

2. Composition of food
The majority of the food we eat is composed by some
nutrients like : proteins, sugar, fats and mineral salts,
vitamins.

3. Energetic function
Carbs lipids

4. Structural function
Proteins

5. Bio-regulating function
Vitamins

6. The experiment
In this experince we will learn to recognize the
presence of sugar(simple and complex) and proteins
using some reagents that change their colour in
presence of a specific nutrient.

7. Materials Required
Watch glass
Test tubes
Support for tubes
Bechers
Droppers
Mortar with pestle
Hotplate
Reagents: Fehling A and B, Lugol, Biuret.
Two kinds of food

8. The reactives that we
will use are:
Fehling’s solution
to identify the presence of
simple sugars
Lugol to identify
the presence of
starch
Biuret to identify
the presence of
proteins

9. Fehling A stirred with Fehling B gives a blue reagent
solution .
In the presence of simple sugars , the blue solution changes
its colour into green, yellow and brick-red, depending on
the amount of sugar.
Warning
Fehling B solution is dangerous.
Care needs to be taken to avoid conctact with skin.

10. Lugol reagent is a yellow Iodine solution that
changes its colour into blue –black when it reacts
with starch .

11. Biuret reagent is a blue solution that changes its
colour into pink-purple when it reacts with proteins.
Warning
Biuret solution is dangerous.
Care needs to be taken to avoid conctact with skin.

12. Now enjoy youself finding out the nature of
these nutrients!!