Fats and oils undergo certain undesirable changes during storage which result in spoilage. The major spoilage of fats and oils is rancidity.
Rancidity refers to the development of disagreeable odour and flavour in fats and oils owing to specified chemical reaction such as oxidation and hydrolysis.
Hydrolysis is the decomposition of fats into free fatty acid and glycerol by enzymes in the presence of moisture. These free fatty acids released are responsible for the unpleasant flavour and odour.
During oxidation, oxygen is added to the unsaturated linkage and this results in the formation of peroxides. These peroxides decompose to yield aldehyde and ketones which are responsible for the pronounced off flavour. Rancidity may also be caused by the absorption of odour and action of micro organism and enzymes.
Prevention of rancidity :
1. Storage in coloured glass containers prevent oxidation of fats by rays of light.
2. Vacuum packaging retards rancidity by excluding oxygen.
3. Naturally occurring antioxidants like vitamin C, b carotene and vitamin E protect against rancidity.
4. Synthetic antioxidants like butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT) and propylgallate can also be added to prevent rancidity.
Fats And Oils
Fats are an important component of the diet and is present naturally in many foods. Fats are solid at room temperature while oils are liquid. Fats in the diet can be of two kinds viz., the visible and the invisible fat.
Invisible fats are those present inherently in foods. Example of food containing appreciable quantities of invisible fat include meat, poultry, fish, dairy products, eggs, nuts and seeds.
Visible fats are those fats that are made from these products. They are cooking oils, salad oils, butter, ghee and margarine.