chapter  14
Methods for Measuring Oxidative Rancidity in Fats and Oils
ByFereidoon Shahidi, Udaya N. Wanasundara
Pages 24

I. INTRODUCTION Autoxidation is a natural process that takes place between molecular oxygen and unsaturated fatty acids. Autoxidation of unsaturated fatty acids occurs via a free radical chain mechanism consisting of basic steps of initiation [Eq. (1)], propagation [Eqs. (2) to (3)], and termination [Eqs. (4) to (6)]. Initiation starts with the abstraction of a hydrogen atom adjacent to a double bond in a fatty acid (RH) molecule/moiety, and this may be catalyzed by light, heat, or metal ions to form a free radical. The resultant alkyl free radical (R•) reacts with atmospheric oxygen to form an unstable peroxy free radical, which may in turn abstract a hydrogen atom from another unsaturated fatty acid to form a hydroperoxide (ROOH) and a new alkyl free radical. The new alkyl free radical initiates further oxidation and contributes to the chain reaction. the chain reaction (or propagation) may be terminated by formation of nonradical products resulting from combination of two radical species.