Classification of fats and oils:
|1.Saturated fatty acids (a) Short chain : Butyric acid C4:O Caproic acid C6:O Caprylic acid C8:O||Butter Butter & coconut oil Butter & coconut oil|
|(b) Medium chain : Capric acid C10:O Butyric acid C12:O Myristic acid C14:O||Butter & coconut oil Butter & coconut oil Butter & vegetable oil|
|(c) Long chain : Palmitic acid C16:0 Stearic acid C18:O Arachidic acid C20:O Behenic acid C22:O||Most vegetable & animal fat Most vegetable & animal fat Butter, lard, peanut oil Vegetable oil.|
|2. Unsaturated fatty acids (a) Monounsaturated fatty acids: Palmitoleic acid C16:1 Oleic acid C18:1 Erocic acid C22:1||Fish, olive oil, beef fat Olive oil, canola oil. Rape seed oil, canola oil.|
|(b) Polyunsaturated fatty acids : Linoleic acid C18:2 (n-6) Linoleic acid C18:3 (n-3)||Sunflower,Corn, soybean, cotton seed Vegetable oils, soybean oil|
Classification of fats and oils:
Spoilage of fats may occur on storage, particularly if the fats are highly unsaturated and the conditions of storage are conducive to chemical change in the fats .
The process of complete or incomplete oxidation or hydrolysis of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odour is known as rancidification.
Rancidity is of two types oxidative and hydrolytic rancidity.
- Oxidative rancidity :
Only saturated fats and foods which have lipo-oxygenase suspectable to oxidative changes. Highly hydrogenated and saturated fatty acids are relatively resistant to oxidation. H 202 there are formed, brake readily producing small volatile substances that gave the characteristic order of rancid fat. Oxidative rancidity may be a problem in dry food containing only small quantity of fat such as preparing cereals etc.
- Hydrolytic rancidity :
Fats may become rancid when the triglycerides react with water and free their fatty acid from glycerol. One molecule of water reacts with triglycerides, one fatty acid is liberated and diglycerides will remain.
To liberate glycerol, all three fatty acids must be removed from the molecule. Reaction is catalysed by lipases. Butter contains lipase, left on a warm day, characteristic rancid smell frequently develops due to liberation of the short chain butyric acid. And like long chain fatty acids, short chain fatty acids may form an unpleasant order and flavour.
hydrolytic rancidity is also a problem with deep fat frying (temperature is high and wet foods are often introduced into the hot fat ) the continued use of rancid oils results in additional breakdown of the oil.
Prevention of rancidity :
Fats can be protected against the rapid development of rancidity by controlling the condition of storage.
- Storage at refrigerator and freezing temperature
- Ray of light catalyse the oxidation of fats by the use of coloured glass containers that absorbs active rays certain shapes of green bottle and wraps and yellow transparent cellophane wraps are effective in preventing rancidity.
- Vacuum packaging also helps to retard the development of rancidity.
- Anti – oxidants naturally present in the food such as Vitamin – C, β – carotene and Vitamin – E.
- Certain antioxidant can also be added
- Butylated hydroxy Anisole (BHA), Propyl gallate.
- Butylated hydroxy Toulene (BHT)
- Tertiary butyl hydroxy quinone (TBHQ)