Glycerol vs fatty acids: the connection and difference between the two

Glycerol is an organic alcohol with three hydroxyl (OH) groups that has good moisturizing properties and can be used as a humectant, solvent, sweetener, and drug. A 70% glycerol solution freezes at -37.8°C, so it can act as an antifreeze compound like ethylene glycol.

Fatty acids consist of an acyl (hydrocarbon) chain with a methyl group and a carboxyl group at each end. It is a building block of larger lipid compounds or serves as a substrate for biologically active molecules. Most fatty acids have an even number of carbons. Typical fatty acids contain 12-18 carbons, but some may have as few as 4 or as many as 36.

Glycerol and fatty acids are the basic components of fats or lipids. When glycerol is replaced by one fatty acid, it is called a monoglyceride; two fatty acids are diglycerides, and three fatty acids are triglycerides. The specific structure is shown below:

In addition, adult diabetic patients have abnormally high concentrations of free fatty acids and glycerol in their serum, accompanied by altered creatine kinase isoenzyme MM patterns in such patients. Serum samples with increased free fatty acids also showed increased electrophoretic mobility of the MM isozymes on cellulose acetate membranes. The fatty acid concentration in these samples averaged 9.88 +/- 5.65 (SD) meq/L and the average glycerol concentration was 153 +/- 115 (SD) mg/L. Serum glycerol concentration correlated with free fatty acid concentration.

The rates of esterification of eight common fatty acids were studied at 180°C using equimolar and equimolar amounts of glycerol (with and without a cosolvent). The results showed that esterification using equimolar amounts of glycerol followed second order kinetics and that the rates of esterification were similar for all acids tested. The kinetics of esterification using equimolar amounts of glycerol were complex, with rates dependent on the solubility of glycerol in the individual fatty acids.

References:

[1] H A SCHWERTNER  E L A  R C McLaren. Increased concentrations of free fatty acids and glycerol and altered creatine kinase MM isoenzyme patterns in certain diabetic patients.[J]. Clinical chemistry, 1979, 25 4: 520-522.

[2] HARTMAN L. Esterification rates of some saturated and unsaturated fatty acids with glycerol[J]. Journal of the American Oil Chemists Society, 1966, 43 9: 536-538. DOI:10.1007/BF02679867.

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