STABILITY OF
FAT
The general resistance of Fat/oil to auto, photo, thermal and radiolytic
oxidation stress conditions
Rancidity
The Oxidation of fat in presence of
oxygen, moisture, heat and light results in disagreeable odor or flavor and is known as
rancidity, a leading cause of quality deterioration
Oxidative rancidity
Addition of oxygen to point of Unsaturation (double bond).
Oxygen
H
H H H
H H H
- C - C - C - C - C - C = C -
H
H H H H
The end products are peroxides and Hydro peroxides etc. detected by
Peroxide Value (POV).
Hydrolytic
rancidity
Liberation of fatty acids from glycerol by action of water in the presence of lipase.
The end products are Free Fatty Acids (FFA)
Detect by Acid value
Types of
oxidation
Lipid oxidation is the major cause of alteration in foods nutrition and sensorial
characteristics.
Auto-oxidation
Photo-oxidation
Radiolytic oxidation
Thermal oxidation
Photo-Oxidation
Fats and oils sold in markets placed in direct / indirect sunlight or to
intensive artificial lights for longer period of time, making fat rancid and
unfit for consumption.
Fat+ Light Free Radicals +O2 
Peroxide, Hydroperoxde
Organic compounds ( aldehyde, Ketone, alcohol, polymerized fat)
Radiolytic
oxidation
The ionizing radiation affect the quality of oil by increasing its
oxidation rate
•
Produce
Active Species Like Free Radicals
•
React With
Oxygen
•
Initiate
Certain Chemical Reactions
•
Leading To
The Formation Of Carbonyls
Result in rancidity
Thermal
oxidation
Deep fat frying is a traditional method of cooking.
Oil is exposed continuously or repeatedly to
elevated temperature in presence of air, moisture, and food.
Oxidation hydrolysis and thermal decomposition of
frying oil takes place resulting in degradation of oil.
Physico-Chemical
Changes during Frying
Physical changes
v Viscosity Increase
v Thickening of oil
v Increase of density
Chemical changes
•
Hydrolysis
•
Oxidation
•
Polymerization
•
Pyrolysis
•
Production
of volatiles
About 220 injurious volatile
compounds have been identified
Biological Effects of Abused Fried Oil
•
Depression in growth
•
Diminished
feed efficiency
•
Increased
liver, kidney and heart sizes
•
Fatty
tissues of liver, kidney and heart organs
•
Liver
enzymes had lower activity
•
Carcinogenicity (in highly abused frying oil)
Antioxidants
Preventing First Chain Initiation By Scavenging free
radicals
It Provide Protection Against Oxidative Attack By
Intercepting Singlet Oxygen
Antioxidants Are The Principle Ingredients, Which
Protect Food Quality By Retarding Oxidative Breakdown
Decreasing The Oxygen Concentration
Guideline
for avoiding rancidity
@ Use of the lowest storage
and process temperature
@ Reduce excess of air
@ Minimize interaction with
metals
@ Use of proper packing
@ Retention of Natural
antioxidants
( Essential oil,
vitamin E,C,ß-Carotene etc)
@ Use permitted levels of
Synthetic antioxidants
(BHA,BHT,TBHQ)
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