2.  What is Rancidity ?

Ans: The moisture and oxygen cause deterioration of fats. The combine action of both moisture and oxygen causes rancidity which is characterised by bad smell, development of red colour, increase in acidity and increase in viscosity. During frying, cooking, baking etc, oil undergo hydrolytic and polymerization reaction. These reactions are undesirable in edible oils. Prolonged exposure to air yield undesirable resinous products causing rancidity.

3.  What is winterising ?

Ans: When oils are cooled slowly to a lower temperature, then less soluble glycerides rich in fatty acid crystallizes out. These crystals can be separated by centrifuge or by filter. This separation of solid fats by chilling is called winterising.

4.  What is saponification value ?

Ans: Alkaline hydrolysis of fats and oils is known as saponification. This forms the basis of soap making.

Saponification value indicates the average molecular weight of a fat or oil. This may also be defined as number of mg of caustic potash required to neutralize the fatty acid obtained by complete hydrolysis of 1gm of oil or fats.

5.  What is acid value ?

Ans: It indicates the proportion of free fatty acid present in oil or fats. Acid value is defined as number of mg of caustic potash required to neutralize the acid in 1gm of the sample. Generally acid value for most of samples lies within 0.5.

6.  What is Iodine value ?

Ans: Iodine value is a measure of extent of unsaturated fatty acid present in fats. It is defined as number of grams of iodine that combines with 100gms of oil and fats.

The iodine value of non-drying oil is less than 90, of semi-dryng oil is between 90 to 140.

 

References:

1. Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008

2. Shreve R. N. ,   Austin G. T., Shreve's Chemical process industries, McGraw – Hill, 1984