Antioxidant Activity of γ-Oryzanol and Synthetic Phenolic Compounds in an Oil/Water (O/W) Emulsion System

γ-Oryzanol is one of the chain breaking antioxidants. Both sterol (triterpene) and phenolic hydroxyl groups in the structure of γ-oryzanol may be responsible for its antioxidative function. We hypothesize that γ-oryzanol is more effective in preventing the autoxidation of polyunsaturated fatty acid (PUFA) than the synthetic phenolic compounds in an oil/water (O/W) emulsion system. The antioxidative effectiveness of different concentrations of γ-oryzanol and synthetic antioxidants was evaluated at different incubation times (0, 4, 8, 16, and 32 h) by measuring both the formation of hydroperoxides and the decomposition product of hydroperoxides (hexanal) in each emulsion system. Overall, the order of effectiveness of various antioxidants for inhibiting the formation of hydroperoxide in the O/W emulsion was: γ-oryzanol＞ tert-butylhydroquinone (TBHQ)＞ butylated hydroxytoluene (BHT)＞ butylated hydroxyanisole (BHA). O/W emulsion with selective lower concentrations of γ-oryzanol showed better effectiveness than that with higher concentration of synthetic antioxidants. However, the ability of both γ-oryzanol and synthetic antioxidants to decompose hydroperoxide was similar. γ-Oryzanol was more effective antioxidant than the synthetic phenolic compounds in preventing the formation of hydroperoxide in the O/W emulsion system.