Oxidation of Corn Oils with Spiked Tocols

Abstract

Stripped corn oils with added tocopherols and tocotrienols, at concentrations between 100 and 5,000 ppm, were used to evaluate antioxidant activity of these tocol compounds. The formation of lipid hydroperoxides, measured as peroxide value (PV), was accelerated at 60 °C in the dark for 5 days. Resistance to oxidation as induction period (IP) was also measured using an oxidative stability instrument (OSI) at 100 °C. For PV inhibition, the oils containing α-tocols exhibited decreasing effectiveness with increasing concentration. At day five, samples with 100 ppm α-tocols had the lowest PVs of about 40 mequiv/kg and samples containing 5,000 ppm had the highest values, ranging from 150 to 200 mequiv/kg. At concentrations above 700 ppm of α-tocols, there was an inversion of antioxidative properties as α-tocols promoted lipid oxidation. The opposite concentration effect was observed with δ-tocols and γ-tocotrienol (T3) for which antioxidant effectiveness increased with concentration. OSI-IP hour at 100 °C increased with increasing tocol concentrations for all tocol homologs, although with diminishing effectiveness at greater than 700 ppm. The α-tocols were less effective in extending the IP (~9 h at 5,000 ppm) than the δ-tocols and γ-T3 (13–14 h at 5,000 ppm). Therefore, the antioxidant or prooxidant activities of different tocols are different and the outcomes are different depending on the evaluation methods used.