Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 12 : Composition, Nutritive Value and Processing of Nuts and Oil Seeds

Spoilage of fats and oils

1. Flavor reversion
1. An objectionable flavour found before the onset of rancidity in refined oils when exposed to UV light, visible light or heating.
2. The reaction is catalysed by O2 and small amounts of metals such as iron and copper
3. Fats containing nucleic acid are most susceptible to reversion.
4. Soya bean oil is mostly subjected to flavor reversion.

Prevention of reversion
1. Hydrogenation
2. Small amount of linolenic acid prevents reversion.
3. Metallic activators or sequestrants tie up to iron and copper and prevents revertion in soya oil.


2. Rancidity
1. Occurs mostly in fats containing unsaturated fatty acids.

Hydrolytic rancidity
1. Occurs due to enzymes that decomposes fat in to free fatty acids (FFA) and glycerol.
2. Butyric acid and caproic acids are the volatile fatty acids, predominately present in butter are responsible for rancid flavour or odour in butter and makes butter inedible.
3. Long chain fatty acids such as stearic, palmitic and oleic acids do not produce rancidity unless oxidation occurs.
4. Heating thoroughly to destroy lipase catalyses hydrolysis of trans fats and prevents hydrolytic rancidity.
5. Certain microorganisms also produces lipase.

Oxidation
1. Unsaturated fats have lipoxygenase and are susceptible to oxidative changes.
2. Highly hydrogenated saturated fatty acids are resistant to oxidation.
3. Hydro peroxides that are formed readily producing smaller volatile substances will give characteristic odours of rancid fat.

Characteristics of Rancidity
1. Undesirable changes in odour, flavour, colour and consistency
2. Inactivates vitamin A & E
3. Oxidative rancidity may be a problem in dry foods containing only small quantities of fat such as prepared cereals.

Prevention of rancidity
1. Storage at refrigerator temperature prevents rancidity.
2. Light coloured glass containers absorb active rays and gives protection against spoilage.
3. Certain shades of green bottles, cora papers, yellow transparent cellophane etc. prevents rancidity.
4. Vacuum packaging
5. Anti-oxidants naturally present in food such as vitamin ‘C’, β-carotene and vitamin E.
6. Added antioxidants such as
1. Butylated hydrogen anisole (BHA)
2. Tertiary butly hydro quivous (TBHQ)
3. Propyl gallate
7. synergists or sequestering agents – citric acid – bind or chelate the metals and prevents oxidation process.