Food Lipids: Chemistry, Nutrition, and Biotechnology

11
Lipid Oxidation of Edible Oil
DAVID B. MIN and JEFFREY M. BOFF
The Ohio State University, Columbus, Ohio
I. INTRODUCTION
Oxidation can alter the flavor and nutritional quality of foods and produce toxic
compounds, all of which can make the foods less acceptable or unacceptable to
consumers [1]. Oxidation products typically include low molecular weight compounds
that are volatile as well as undesirable off-flavor compounds [2,3]. Triplet
oxygen lipid oxidation of foods has been extensively studied during the last 70 years
as part of the effort to improve the oxidative stability of foods [4,5]. However, triplet
oxygen oxidation does not fully explain the initiation step of lipid oxidation [6,7].
Rawls and VanSanten [8] suggested that singlet oxygen is involved in the initiation
of triplet oxygen lipid oxidation because singlet oxygen can directly react with double
bonds without the formation of free radicals. Singlet oxygen oxidation can be
very rapid in foods due to the low activation energy required for the chemical reaction.
The reaction rates of singlet oxygen and triplet oxygen with linoleic acid are
1.3 � 10 5 M �1 s �1 and 8.9 � 10 1 M �1 s �1 , respectively [8,9]. For many foods
containing lipids, special measures are taken to reduce or prevent oxidation, such as
removal of oxygen, addition of antioxidants, and use of gas barrier packaging
materials.
Rate of oxidation is dependent on several factors, including temperature, presence
of inhibitors or catalysts, and nature of the substrates [10]. Unsaturated fatty
acids are more susceptible to oxidation than saturated fatty acids, a property that is
primarily due to the lowered activation energy in the initiation of free radical formation
for triplet oxygen autoxidation [11,12]. During the last 30 years, increased
attention has been given to singlet oxygen oxidation of foods. The significance of
singlet oxygen oxidation in foods can be summarized in two statements. (a) The rate
of singlet oxygen oxidation is much greater than that of triplet oxygen oxidation,
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.