Underlying mechanisms of synergistic antioxidant interactions during lipid oxidation

Unsaturated lipids undergo radical-initiated oxidative deterioration during lipid oxidation, which is one of the most significant food quality and waste issues. Lipid oxidation results in off-flavors, toxic aldehydes, and the co-oxidation of proteins and color compounds. Various antioxidant strategies are utilized by the food industry to reduce lipid oxidation and increase shelf-life. Combining antioxidants to achieve synergistic interactions has been practiced for decades to improve oxidative stability. Nevertheless, underlying mechanisms of synergistic interactions between antioxidants are poorly understood and rarely studied. This review examines the main hypothesized mechanisms of antioxidant synergism, which include: 1) Regeneration of an oxidized antioxidant by another compound, 2) Differences in antioxidant partitioning in homogeneous and heterogeneous systems, 3) Combination of free radical scavenging and metal chelating activities to provide two distinct protection pathways, and 4) Formation of additional antioxidant compounds, such as phenolics, dimers, or adducts, upon oxidation which can further inhibit lipid oxidation. In complex food systems, it is often difficult to predict which antioxidant combinations will work synergistically. Understanding the mechanisms of synergism will aid the food industry in the production of effective antioxidant mixtures to improve oxidative stability and shelf-life, as well as in the development of simple, rapid, and reliable methods for determining and evaluating synergism.