Antioxidants are defined as “any substance which significantly delays or inhibits oxidation of a substrate when present at low concentrations compared to that of an oxidizable substrate” (Jun, Park, Jung, & Kim, 2004). Antioxidants are commonly used in the food industry to prevent lipid oxidation which can lead to product degradation and production of off-flavours, but they also have applications in other fields where oxidation will degrade the product quality (Gao, Miller, & Han, 2004).
Compounds such as polyphenols and carotenoids found in brightly coloured fruits and vegetables have been shown to possess beneficial health properties such as preventing cancer, diabetes, arthritis, atherosclerosis, and other age-related diseases (Kaur & Kapoor, 2001). The primary focus has been on the antioxidant properties of molecules such as flavonoids, polyphenols, and carotenoids derived from fruit and vegetable sources (Fukumoto & Mazza, 2000, Pulido, Bravo, & Saura-Calixto, 2000, Kaur et al., 2001, Sanchez-Moreno, 2002) but some groups are also investigating the antioxidant properties of proteins and peptides derived from both animal and non-animal sources (Chen, Muramoto, Yamauchi, Fujimoto, & Nokihara, 1998, Jao & Do, 2002, Saito et al., 2003). Wayner and co-workers recognized that 10-50% of the antioxidant properties found in human blood plasma could not be explained by known antioxidants such as vitamin E, urate, or ascorbate and theorized that a number of essential amino acids possessing labile hydrogen atoms could allow amino acids and peptides to behave as antioxidants (Wayner, Burton, Ingold, Barclay, & Locke, 1987). Research currently underway covers a wide range of potential antioxidant peptide sources such as rice, soybean, fish, skeletal muscle tissue, chicken eggs, and bovine milk.