Triacylglycerols or Triglycerides

Triacylglycerols or Triglycerides

Triacylglycerols are simple lipids synthesized by esterification of glycerol with three molecules fatty acids. It is the storage form of fat, stored in adipose tissue. They are hydrolyzed in the gut by lipases to free fatty acids and monoglycerides.

If the three hydroxyl groups of glycerol molecule are esterified with the same type of fatty acid then the lipid is called simple triacyl glycerol eg: tripalmitin. If esterification is with different fatty acids, it is called as mixed glycerides eg: dioleopalmitin.

Properties

Physical properties

·     They are non-polar, hydrophobic, insoluble in water and soluble in organic solvents.

·     Specific gravity is less than water. Therefore fats and oil float on water.

·     They serve as solvent for other fats. Example: Fat soluble vitamins A, D, E and K

·     The saturated fatty acids have higher melting points than unsaturated fatty acids of corresponding length.

Chemical properties

i. Hydrolysis:

Triglycerides (fats) can be hydrolyzed to produce glycerol and fatty acids in the presence of acid and heat or with a suitable lipase enzyme under biological conditions.

ii. Hydrogenation:

Hydrogenation is a process of adding hydrogen atoms to unsaturated fats until they become saturated. Hydrogenation of fat is a process used in industries, food manufacturers, to synthesize modified plant fats called hydrogenated fats that share similar texture and taste characteristics with saturated animal fats.

iii. Saponification:

The process of hydrolysis of fat by aqueous alkali (NaOH or KOH) to yield glycerol and the salt of fatty acid (soap) is called saponification or alkaline hydrolysis of esters. Soaps are sodium or potassium salts of long chain fatty acids.

iv. Halogenation:

Unsaturated fatty acids have the ability to bind halogens like Cl₂, Br₂ and I₂ to their double bonds. It is a very important property which determines the degree of unsaturation of the fat or oil that determines its biological value.

v. Rancidity:

Rancidity is a term generally used to denote unpleasant odours and flavours in foods resulting from deterioration in the fat or oil portion of a food. The triacylglycerols in fats with low molecular mass carboxylic acids undergo oxidation very quikly when exposed to air, moisture and light or hydrolysed in the presence of bacterial lipases.