Antioxidants and Functional Components in Aquatic Foods, First Edition. Edited by Hordur G. Kristinsson. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd. 1 1.1 Introduction Lipid oxidation in muscle food is one of the major deteriorative reactions causing a loss in quality during storage. Marine lipids are natural and good sources of polyunsaturated omega-3 fatty acids (PUFAs), which have been reported to have ben- eficial health effects. However, because of the high amount of PUFAs (Ackman 1980; Shewfelt 1981; Gandemer 1999), along with highly active pro-oxidants (Hultin 1994), marine lipids are highly vulnerable towards oxidation. Lipid oxidation is therefore one of the primary causes of deterioration of fish muscle during storage (Ackman 1980) and negatively affects color (Wasasundara and Shahidi 1994), odor and flavor (Bateman et al. 1953), protein functionality and conformation (Gutteridge 1988), and the overall nutritional content of fish muscle (Pearson et al. 1983; Gray 1987). Lipid oxidation can be divided into three types of initiation reactions, including non-enzymatic and enzymatic reactions. Non-enzymatic mechanisms include autoxidation (free radical mechanism) and photogenic oxidation (singlet oxygen mediated). Enzymatic mechanisms include actions by lipoxygenase and cyclooxyge- nase. Lipid oxidation most commonly occurs by a free radical mechanism involving the formation of a reactive peroxyl radical (Erickson 2002). The autoxidation mechanism occurs when the unsaturated fatty acids are exposed to oxygen and undergo an autocatalytic chain reaction (Figure 1.1). This mecha- nism is deemed to be the primary cause of lipid oxidation in post-mortem fish (Erickson 2002) and is historically referred to as lipid peroxidation (Mead 1976). The process has three main phases: initiation, propagation, and termination. Oxidation in aquatic foods and analysis methods Magnea G. Karlsdottir 1 , Holly T. Petty 2 , and Hordur G. Kristinsson 1,2 1 Division of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, Iceland 2 Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA