Challenges in Elucidating Lipid Oxidation Mechanisms: When, Where, and How Do Products Arise?

Publisher Summary This chapter highlights that the intention of the chapter is to challenge anyone concerned with lipid oxidation—whether in fundamental chemical research, food quality deterioration, pathology or toxicology, cell signaling, or any other application—to think beyond hydrogen abstraction in established free-radical chain reactions and to consider other mechanisms that may alter the course, kinetics, and product distribution of lipid oxidation. It introduces the chemistry of alternate reactions to show that lipid oxidation is much more complex than the simplistic radical chain reactions normally presented and to encourage more detailed thinking about how and when products are generated in oxidizing lipids and where these products have important effects in foods, emphasizing on the propagation processes. Hydrogen abstraction by lipid radicals to propagate radical chains and generate stable lipid hydro peroxides has long been considered the anchoring process in lipid oxidation. However, β-scission of oxygen, internal rearrangement to epidioxides, addition and disproportionation of lipid peroxyl radicals, as well as internal rearrangement to epoxides, addition, and α- or β-scissions of alkoxyl radicals, are also active and compete with hydrogen abstraction in propagation to alter the kinetics, course, and products of lipid oxidation. The chapter describes these alternate reactions, provides basic information about how their kinetics and balance change with reaction environment, notes data supporting the existence of these pathways, and discusses the consequences of alternate pathways on the progress and effects of lipid oxidation as starting points for rethinking the chemistry of lipid oxidation.