analysis of lipids- Identification of fats or oils

Lipids

Lipids are a heterogeneous group of organic substances related actually to the fatty acids. Chemically they are various types of esters of different alcohols

The common properties of lipids:

Relatively soluble in water

Soluble in nonpolar solvent such as ether, chloroform and benzene.

Classification of lipids

Simple lipids:

Neutral fats (triglycerides & fats and oils).

Wax, which is ester of fatty acids with high molecular weight.

Conjugated lipids:

Phospholipids (fatty acid + phosphoric acid).

Glycolipids (fatty acid + carbohydrate).

Derived lipids:

Fatty acid, which may be, saturated e.g stearic acid or unsaturated e.g Oleic acid.

Sterol and steroids e.g cholesterol.

Glycerol.

Soaps alkaline salt of fatty acids

analysis of lipids

Identification of fats or oils

Solubility of lipids:

a)     Obtain 5 test tubes, label them from 1 to 5 .

b)     Put 2 drops of olive oil to each of test tubes.

c)     Add 2ml of the following solvents; distilled water ,ether, chloroform, aceton, and ethanol to each of test tubes respectively.

d)     Shake the test tubes well.

e)     Record your observations.

Emulsification test:

Oils can be formed of  emulsification unstable with water but formed of emulsification stable with soap or detergent.

Procedure :

1.      Obtain 3 test tubes, label them from 1 to 3 .

2.      Add 0.5 ml of olive oil to each of test tubes.

3.      Then pour 2ml of the following solutions; distilled water, 2%     sodium carbonate, and 2% soap to each of test tubes respectively.

4.      Shake the test tubes well.

5.      Record your observations.

Cupper acetate test:

Carry out this is test to distinguish between neutral triglycerides (fats & oils)and between fatty acids , so that to distinguish between saturated fatty acid and unsaturated fatty acid.

Procedure:

0.5 g of lipids or fatty acid + 5 ml of petroleum ether + 5 ml of cupper  acetate solution ,shake well, then leave of solution until separation of solution to two layer .

In this case the upper layer will be ether layer and lower layer will be aqueous layer.

Observations:

a)     In state neutral glyceride will be two layer of solution is clear and the upper layer is colourless.

b)     In state saturated fatty acid will be the upper layer is colourless  and formed green ppt. in lower layer.

c)     In state unsaturated fatty acid will be the upper layer is green colour.

Saponification test:

Hydrolysis of a fat by an alkali is saponification. The alkali salts of the fatty acids, which are called "soap".

Soaps are cleansing agents because of their emulsifying action . some soaps of high molecular weight.

Procedure:

1 ml of oil or lipid in a test tube + 4 ml of KOH ((alcohol))+water bath for 10 min. ,then add 10 ml of D.W + heat for 4 min. and then cool the test tube.