Theme XIV: Lipids

Properties of lipids. Functions, importance.

Oils and fats are distinguished by their physical properties. They are completely insoluble in water but are soluble in chloroform, ether and some water immiscible solvents. Very few of them as castor oil (Ricinus communis Oil), are soluble in alcohol.

When they are purified have a slight odor and taste, with few exceptions. The yellowish color of fat is due to the frequent presence of carotene.

When heated moderately, fats and oils are liquefied and become less viscous. When are strongly heated, they decompose with the production of flammable vapors that burn with a flame of incomplete combustion (soot produced). The acrid smell that occurs when an oil or fat is overheated is due to the formation of acrolein (propenal).

The common property of oils and fats is its ability to hydrolyze forming free glycerin and the corresponding fatty acids. Without catalyst, the reaction is very slowly but may be accelerated with higher temperatures and pressure and the presence of acid or alkali. If used alkali the process is called saponification, the final result is the formation of soap. The term is often used to refer to the hydrolysis of all ester bonds. In metabolic processes this reaction is catalyzed by the lipase enzymes, for example the process of digestion by pancreatic juice in the body.

Uses of lipids

Lipids

Fixed oils and fats

Wax

Sterols

Phospholipids

Properties of lipids. Functions, importance.