Simple Lipids
- Lipids containing only fatty acids and glycerol or long chain alcohols (monohydric) are called as simple lipids which include fats, oils and waxes.
Fats and oils
- Triacylglycerols are the simplest lipids constructed from fatty acids and glycerol. They are also referred as triglycerides, fats or neutral fats. Triacylglycerols are composed of three fatty acids esterified to the three hydroxyl groups of glycerol. When all the 3 fatty acid molecules are of the same kind the triacylglycerol is said to be simple triacylglycerol. Mixed triacylglycerol possesses two or more different fatty acids.
- Triacylglycerol that are solid at room temperature are called as fats. Liquid triacylglycerols are called as oils. Neutral fats or oils are mostly composed of mixed triacyl glycerol. Fats are usually rich in saturated fatty acids and the unsaturated fatty acids predominate in oils. Most oil-producing plants store their lipids in the form of triacylglycerols
Storage fats or oils
- Triacylglycerols are widely distributed in the plant kingdom. They are found both in vegetative as well as reproductive tissues.
- Triacylglycerols are normally stored in the endosperm of the seed although some plants store appreciable quantities of fat in the fleshy fruit mesocarp, for example, avocado. Some plants like the oil palm, store oils in both the mesocarp (Palm oil) and the endosperm (Palm kernel oil).
- The oil present as droplets in the cytoplasm of the seed cells. These droplets are called as oil bodies and are surrounded by a membrane composed of phospholipids and protein.Most of the common edible oils (groundnut, sunflower, gingelly, soybean, safflower, rice bran) contain limited number of the common fatty acids such as palmitic, stearic, oleic, linoleic and linolenic acidsPalm kernel and coconut oils contain higher amount of medium chain saturated fatty acids. Seed oils contain small amount of phospholipids, carotenoids, tocopherols, tocotrienols and plant sterols depending on the species of plant and degree of processing.
Structural or hidden fats in plants
- The leaves of higher plants contain upto 7% of their dry weight as fats. Some of them are present as surface lipids, the others as components of leaf cells, especially in the chloroplast membrane. The fatty acid composition of plant membrane lipids is very simple. Six fatty acids- palmitic, palmitoleic, stearic, oleic,linoleic and γ-linolenic generally account for over 90% of the total fatty acids.
Waxes
- Waxes are esters of long-chain saturated and unsaturated fatty acids with long chain alcohol. The carbon number of fatty acids vary from 14 to 34 and that alcohol from 16 to 30. For example, beeswax is an ester of palmitic acid with a 30 carbon alcohol,triacontanol. Waxes are the chief storage form of metabolic fuel in marine phytoplanktons. Biological waxes find a variety of applications in the pharmaceutical, cosmetic and other industries. Lanolin from lamb's wool, beeswax, carnauba wax, spermaceti oil from whales are widely used in the manufacture of lotions, ointments and polishes. Waxes are not easily hydrolysed like fats or digested by lipases.
Liquid wax - Jojoba oil
- About 50% of the seed dry weight of jojoba consists of a liquid wax which is unique in the plant kingdom and is similar to sperm whale oil. The wax is made up of straight chain esters with an average total chain length of 42 carbons. Jojoba wax has a wide range of industrial uses including cosmetics, pharmaceuticals, extenders for plastics, printers ink, gear oil additives and various lubricants. The oil is highly stable and can be stored for years without becoming rancid
Cuticular wax
- The outermost surface of the cell walls of epidermal cells are covered. with a hydrophobic cuticle which contains wax called cuticular wax. The main components of cuticular waxes are hydrocarbon (odd chain alkanes) and its derivatives, wax esters, free aldehydes, free acids, free alcohols and other components like mono esters of phenolic acids and aliphatic alcohols. The main function of the cuticular wax is to reduce the excessive losses and gains of water by the underlying tissue. It also helps in protecting the tissues from chemical, physical and biological attack
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