Chemical composition of lipids
Lipids are made of carbon, hydrogen and oxygen atoms.
Higher proportion of hydrogen atoms compared to oxygen atoms.
Egs of lipids include (1) fats, (2) phospholipids and (3) steroids.
Importance of fats
(i) Important store of energy. For the same mass of triglyceride stored in the body, the amount of energy contained is twice that of carbohydrates.
(ii) Being large, uncharged and insoluble in water, fats are easily stored in spaces around organs eg kidneys, and in the layers under the skin.
(iii) Solvent for some substances, eg fat-soluble vitamins and hormones.
(iv) Constituent of protoplasm.
Risk of consuming too much fats
- Increased risk of developing coronary heart disease.
- Higher cholesterol level.
- Higher blood pressure.
- Obesity and diabetes.
Ethanol-emulsion test for identifying fats
Step 1: Place food sample into 2 cm3 of ethanol and shake thoroughly. (Ethanol is capable of dissolving fats.)
Step 2: After shaking thoroughly, decant the clear supernatant into a test-tube containing 2 cm3 of water.
(+): If fats are present, a white emulsion would be formed.
(-): If fats are absent, there will be no emulsion and the liquid remains clear and colourless.