*Saponifiable lipids - contain esters, which can undergo saponification
*Nonsaponifiable lipids - — do not contain ester groups, and cannot be saponified
Saponifiable lipids can also be divided into groups:
*Simple lipids — contain two types of components (a fatty acid and an alcohol)
*Complex lipids — contain more than two components (fatty acids, an alcohol, and other components)
The main simple lipids are triglycerides (also known as triacylglycerols), steryl esters, and wax esters.
Waxes are simple lipids. Structurally, they are considered as esters of long-chain (C14-C36) saturated and unsaturated fatty acids with long-chain (C16-C30) alcohols.
Waxes are insoluble in water, and not as easily hydrolyzed as fats and oils. They are solid at room temperature. The most important waxes in human body are cholesterol esters, which are present in blood and other tissues. They often occur in nature as protective coatings on feathers, fur, skin, leaves, and fruits.
The leaves of plants like rhododendrons, poison ivy and several tropical plants are shiny in appearance due to wax coating on them. This prevents excess evaporation of water and provides protection from the parasites.
Sebum, secreted by the sebaceous glands of the skin, contains waxes that help to keep skin soft and prevent dehydration.
Wax esters may accumulate in considerable amounts in some biological tissues and this class comprises the main constituent of beeswax and jojoba oil.
Simple lipids: Waxes
