1. AUTOXIDATION OF OILS AND FATS

2. OBJECTIVES
To explain the autoxidation of oils and fats via free radical mechanism.
To show clearly the role of trace metals in promoting the autoxidation.
To determine how to prevent or reduce autoxidation in oils and fats.

3. INTRO Process via free radical mechanism in the presence of O2.
As starting material (initiator).
Reactions can be divided into : chain initiation, propagation and termination.
Produce unstable hydroperoxide compounds.
Causes deterioration of oils and fats.

4. Mechanism of free radical of oils and fats

5. What is Free radical?
A free radical is a group with an odd number of unpaired electrons.
They are extremely unstable and immediately react with another molecule to form stable substances.

7. Fatty Acid Free Radical Autoxidation
The most accepted mechanism of autoxidation involves hydrogen abstraction on carbon -8 and carbon -11 with formation of two allylic radicals . These radicals intermediates react with oxygen at the end carbons to produce a mixture of 8-, 9-, 10-, and 11- allylic hydroperoxides.

8. Roles of Trace Metals in Autoxidation
Metals : eg.- Fe, Cu and Co
From impurities accompanying the plant material, packaging of oil, or from processing equipment.
Responsible for initiation reactions of free radical reaction with present of O2.

9. Initiation mechanisms-Metal Catalysis
Metal ions (e.g. Fe, Co, Cu) can also initiate reaction
found naturally in foods, from metal equipment
RH + M R• + H+ + M+

10. How autoxidation in oils and fats can be prevented or reduced?
Antioxidants - to delay the onset or slow the development of rancidity due to oxidation.
Anti-microbial agents - to prevent rancidification by inhibiting the growth of bacteria.
Chelating agents(citric acid) – treated fats and oils.

11. REFERENCE
N.J. Fox, G.W. Stachowiak, Vegetable oil-based lubricants—A review of oxidation.2006.
Frank Gunstone, Blackie Academic & Profesional : Chapman & Hall ; 1st ed – oxidative deterioration and oxidative stability , pg. 108
Michael R. Hoffmann Environ. Sci. Technol., 1980, 14 (9), pp 1061–1066