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Food Lipids: Chemistry, Nutrition, and Biotechnology

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14<br />

Methods for Measuring Oxidative<br />

Rancidity in Fats <strong>and</strong> Oils<br />

FEREIDOON SHAHIDI<br />

Memorial University of Newfoundl<strong>and</strong>, St. John’s, Newfoundl<strong>and</strong>, Canada<br />

UDAYA N. WANASUNDARA<br />

Pilot Plant Corporation, Saskatoon, Saskatchewan, Canada<br />

I. INTRODUCTION<br />

Autoxidation is a natural process that takes place between molecular oxygen <strong>and</strong><br />

unsaturated fatty acids. Autoxidation of unsaturated fatty acids occurs via a free<br />

radical chain mechanism consisting of basic steps of initiation [Eq. (1)], propagation<br />

[Eqs. (2) to (3)], <strong>and</strong> termination [Eqs. (4) to (6)]. Initiation starts with the abstraction<br />

of a hydrogen atom adjacent to a double bond in a fatty acid (RH) molecule/moiety,<br />

<strong>and</strong> this may be catalyzed by light, heat, or metal ions to form a free radical. The<br />

resultant alkyl free radical (R • ) reacts with atmospheric oxygen to form an unstable<br />

peroxy free radical, which may in turn abstract a hydrogen atom from another unsaturated<br />

fatty acid to form a hydroperoxide (ROOH) <strong>and</strong> a new alkyl free radical.<br />

The new alkyl free radical initiates further oxidation <strong>and</strong> contributes to the chain<br />

reaction. the chain reaction (or propagation) may be terminated by formation of<br />

nonradical products resulting from combination of two radical species.<br />

Initiation:<br />

initiator • •<br />

RH ⎯⎯⎯→ R � H (1)<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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