FUNDAMENTALS OF FOOD TECHNOLOGY (1+1)

Properties of fat

Properties of fats

Solubility

• Fats are soluble in ethyl ether, petroleum ether, acetone, hot alcohol and enzyme. The quantity of fat present in food materials is usually determined by extraction with ethyl ether or petroleum ether.

Hydrogenation

• Unsaturated fats have a tendency to combine with hydrogen at the site of its double bonds. Vegetable fats are exposed to hydrogen at high temperature in the presence of an alkali. Nickel or cobalt is used as a catalyst e.g. Vanaspati

Emulsification

• Fat forms a homogeneous mixture with water it is called emulsification. This property is made use of in the preparation of ice cream, mayonnaise.

Saponification

• The ester linkage of fatty acids with glycerol brings this process of saponification. Neutral fats are rich in ester linkage. When neutral fats are heated with sodium or potassium hydroxide the fat molecules may readily rupture at the ester linkage. It is thus hydrolyzed into glycerol and sodium or potassium salts of fatty acids and this is known as soap. Thus, the formation of soap from the hydrolysis of fat with heat and alkali is termed as saponification

Iodine value / number

• This is the measure of the extent of unsaturated fatty acids present in fats and oils. It is defined as the number of grams of iodine absorbed by 100 g of fat. 2 atoms of iodine are added to each unsaturation linkage.

Rancidity

• The development of off-flavours in fats is known as rancidity. There are three main types of rancidity.
1. Hydrolytic
2. Oxidative
3. Ketonic

Hydrolytic rancidity

• When fat is hydrolysed by lipase, free fatty acids are formed. The odours of low molecular weight fatty acids contribute to the rancidity.

Oxidative rancidity

• The oxidation takes place at the unsaturated linkage (double bond). The addition of oxygen to the unsaturated linkage results in the formation of peroxide which on decomposition yields aldehydes and ketones having pronounced off odour.

Ketonic rancidity

• It occurs in action of fungi aspergillus, blue green mould, pencillium on coconut and oil seeds. It produces tallowy odour.