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Triacylglycerols are esters of fatty acids. Fats or triglycerides are triacylglycerols. In a triacylglycerol, a glycerol molecule is linked with three fatty acids by ester linkages. The structure of glycerol is shown below:


The fatty acids that are present in fats are mostly straight-chain fatty acids (saturated and unsaturated), with even number of carbon atoms. According to the number of fatty acids esterifying the glycerol’s hydroxyl groups, the glyceride formed could be a monoglyceride, a diglyceride or a triglyceride. Glycerides with long chain fatty acids are insoluble in water.


A diagrammatic representation of a triglyceride (triacylglycerol) is shown in Figure 30-1. In the figure, the vertical bar represents glycerol and the horizontal bars represent the fatty acids. The fatty acids (1, 2, & 3) present in a triacylglycerol molecule can be the same three fatty acids, or can be different fatty acids.
Fats can be solid or liquid. This physical property is a direct effect of the fatty acid substituents that are present in them. When fats are in their liquid state they are commonly called oils. Broadly we can generalize that solid fats mainly contain saturated fatty acids, and liquid fats mainly contain unsaturated fatty acids. We should not confuse this generalization with the fact that the naturally occurring fats and oils contain many different types of fatty acids, both saturated and unsaturated. The physical properties of fats are mostly a function of the fatty acids that are present in them.
For example, human stored fat contains predominantly oleic acid (a saturated fatty acid) which constitutes about 47 % of the total fatty acid content. It also contains palmitic acid, linoleic acid, stearic acid, myristic acid, and other fatty acids in decreasing amounts respectively.

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