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58.5 PROPERTIES OF OILS AND FATS

PHYSICAL PROPERTIES

  1. Oils and fats are liquids or solids having a greasy feel. When pure, they are colourless, odourless and tasteless.
  2. They are insoluble in water but soluble in organic solvents such as ether, chloroform and benzene.
  3. They have a lower density than water and consequently float on the surface when mixed with water.

 CHEMICAL PROPERTIES

Fats and oils are triesters of glycerol with saturated arid unsaturated fatty acids. Their reactions are those of ester groups in triplicate and carbon-carbon double bonds.

1.      Hydrolysis. They are readily hydrolysed by heating with acids or alkalies or superheated steam. When boiled with sodium or potassium hydroxide solution, the hydrolysis products are glycerol and sodium or potassium salts of long-chain fatty acids. The latter are called soaps and alkaline hydrolysis is known as saponification.

2.      Hydrogenation. On catalytic hydrogenation, hydrogen adds across the carbon-carbon double bonds of the acid components of the triglycerides. This results in the formation of saturated glycerides which are solid fats at room temperature. This hydrogenation process is called hardening of oils. For example,


 

Partial hydrogenation of vegetable oils is used for the manufacture of margarine and other hardened oils.

 Add To Your Knowledge

For the manufacture of margarine, oils such as groundnut oil and palm oil are treated to remove undesirable material, bleached and heated. Hydrogen gas at a pressure of about 4 atmospheres is passed through the hot oil in the presence of nickel as catalyst. By controlling the extent of hydrogenation the oil is hardened to the desired level. The hardened oil is deodorized and then blended with milk. The product is then mixed with salt, vitamins, flavouring agents and
preservatives to obtain margarine. Margarine is used as a substitute for butter.