Effects of tocopherols and tocotrienols on the inhibition of autoxidation of conjugated linoleic acid

Abstract

The effect of eight vitamin E homologues, i.e. alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma, and delta-tocotrienol, on the inhibition of autoxidation of conjugated linoleic acid (CLA) were investigated. The oxidation was carried out in the dark for 21 days at 50 degrees C and monitored by peroxide values (PV) and TBA values. The levels of the individual vitamin E homologues in CIA during storage were determined by HPLC. gamma-Tocopherol exhibited the highest antioxidant activity among the homologues tested in this study when the antioxidant activities of the individual homologues in CLA were compared by PV. The order of antioxidant activity of eight homologues was gamma-tocopherol > delta-tocopherol = delta-tocotrienol >= gamma-tocotrienol > beta-tocopherol = beta-tocotrienol > alpha-tocopherol = alpha-tocotrienol. The degradation rates of alpha-tocopherol and alpha-tocotrienol were faster than those of the other homologues, whereas delta-tocopherol had the highest stability in CLA during storage. All homologues exhibited an antioxidant activity by inhibiting the formation of secondary oxidation products. It appears that alpha-tocotrienol and beta-tocotrienol have significantly higher antioxidant activities for secondary oxidation in CIA than alpha-tocopherol and beta-tocopherol. Meanwhile, the other homologues, namely gamma-tocopherol, gamma-tocotrienol, delta-tocopherol, and delta-tocotrienol, exhibited similar antioxidant activity for secondary oxidation in CIA.