Unsaturated fatty acids are liquids at room temperature and are characterized by having on or more double bonds. Some unsaturated fatty acids possess several bonds and are called polyunsaturated.

Fats are generally insoluble in water but soluble in organic solvents. Oils are generally liquid at room temperature and some are solids possessing high melting points. They may be hydrolyzed by alkali treatment and yield glycerol and fatty acids.


Fats develop an unpleasant odour and taste when exposed to air. This is because the fats turn rancid , a term derived from butter when it turns rancid due to action of light, heat and bacterial action. Rancid fat is unsuitable for human consumption , because beside having an unpleasant smell and taste , it oxidizes essential dietary constituents and gives rise to peroxide linkage with double bonds.

Esterification   The carboxyl group of fatty acids is esterified when reacted with alcohol resulting in the formation of an ester and a molecule of water. The reaction is very slow but hastens up in the presence of enzyme.


Hydrogenation   The double bonds of unsaturated fatty acids can be readily oxidized or hydrogen or halogen may be added to them. Addition of hydrogen to double bonds proceeds in the presence of catalysts like platinum and nickel and the process is known as hydrogenation.