Which of the following is NOT involved in imparting rancidity to Fats?
Ans. c (Reduction) (Ref. Vasudevan DM, Biochemistry 5th/pg. 76, Harper's 27th/Chapter 15)RANCIDITY OF FATSFats and oils have tendency to become rancid.Rancidity refers to appearance of an unpleasant smell and taste for fats and oilsThere are three mechanisms causing rancidity:# Hydrolytic rancidity# Oxidative rancidity# Polymerization of cyclic hydrocarbonsTypeCommentsHydrolytic rancidity Oxidative rancidity# Occurs due to partial hydrolysis of triacyl glycerol molecules due to traces of hydrolytic enzymes in naturally occurring fats and oils.# Occurs due to partial oxidation of Unsaturated Fatty Acids with resistant forms of epoxides and peroxidation of small molecular weight fatty acids by the peroxides and free radicals.# The same process if occurs in vivo will affect integrity of biomembrane, leading to cell death.# Many naturaly occurring fat cell oils may contain antioxidant (like Vitamin E) which prevents occurance of oxidative rancidity.# PUFA more easily oxidized, so vegetable oils with high PUFA are preserved by adding antioxidants.Polymerization of cyclic hydrocarbons# Fats and oils are preferred cooking media.# Overheating and repeated heating would lead to formation and polymerization of cyclic hydrocarbons, which imparts unpleasant taste and colour to the oil.# Coconut oil typically withstands this.Educational Points:# Naturally occurring antioxidants:- Vitamin E (tocopherol), which is lipid-soluble - prevents rancidity- Urate and vitamin C, which are water-soluble.- Beta-carotene is an antioxidant at low P02.# Antioxidants used as food additives:- Propyl gallate, butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)ANTIOXIDANTS FALL INTO TWO CLASSES# Preventive antioxidants, which reduce the rate of chain initiation- Catalase- Peroxidases such as glutathione peroxidase that react with ROOM;- Selenium, which is an essential component of glutathione peroxidase and regulates its activity and- Chelators of metal ions such asEDTA and DTPA.# chain-breaking antioxidants, which interfere with chain propagation.- Superoxide dismutase, which acts in the aqueous phase to trap superoxide free radicals (O2);- Urate; and- Vitamin E, which acts in the lipid phase to trap ROO radicals - prevents rancidity.
Oxidation
Hydrolysis
Reduction
Cyclization of hydrocarbons
Lipids