Food Lipids: Chemistry, Nutrition, and Biotechnology

15
Antioxidants
DAVID W. REISCHE
The Dannon Company, Inc., Forth Worth, Texas
DORRIS A. LILLARD and RONALD R. EITENMILLER
The University of Georgia, Athens, Georgia
I. INTRODUCTION
Lipid oxidation in foods is a serious problem, difficult to overcome often and
leads to loss of shelf life, palatability, functionality, and nutritional quality. Loss
of palatability is due to the generation of off-flavors that arise primarily from the
breakdown of unsaturated fatty acids during autoxidation. The high reactivity of the
carbon double bonds in unsaturated fatty acids makes these substances primary targets
for free radical reactions. Autoxidation is the oxidative deterioration of unsaturated
fatty acids via an autocatalytic process consisting of a free radical chain
mechanism [1]. The chain of reaction includes initiation, propagation, and termination.
Propagation reactions are primarily responsible for the autocatalytic nature of
autoxidation.
Autoxidation must be induced by preformed or primary hydroperoxides. The
source of preformed hydroperoxides is either photosynthesized oxidation or lipoxygenase
catalysis. Photosynthesized oxidation (photooxidation) involves direct reaction
of light-activated, singlet oxygen with unsaturated fatty acid and the subsequent
formation of hydroperoxides. Lipoxygenase catalysis involves enzymatic oxidation
of unsaturated fatty acids to their corresponding hydroperoxides. Formation of primary
hydroperoxides is catalyzed by either light, metals, singlet oxygen and sensitizers,
or preformed hydroperoxide decomposition products.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.