Oxidative stability of corn oil with elevated tocotrienols

Oxidation of tocotrienol enriched corn oil was measured for primary oxidative products, lipid hydroperoxides and quantified by peroxide value (PV). Oxidative Stability Index (OSI) was used to determine the induction period (hrs) by indirect measurement of volatile secondary oxidation products, mainly formic acid. Vitamin E stripped corn oil samples were spiked with individual tocotrienols or tocopherols (collectively, tocols) at concentrations between 100 and 5,000 ppm. A positive relationship was observed between the concentration of all tocols and inhibition of the formation of secondary products. Gamma tocotrienol (γ-T3) provided the most protection, with delta tocopherol (δ-T) and delta tocotrienol (δ-T3) providing similar protection. Alpha tocotrienol (α-T3) and alpha tocopherol (α-T) followed a similar trend but with diminishing capacity at concentrations higher than 700 ppm. The change in mean daily peroxide value increased as αtocopherol and αtocotrienol concentrations increased. When compared against the non-spiked, stripped control oil, both αtocopherol and αtocotrienol demonstrated better antioxidant effects at lower concentrations and actually promoted oxidation at concentrations at 700 ppm and above. These effects were not observed with the γand δtocols. Crude oils from corn kernels, both control and that expressing a homogentisate geranylgeranyl transferase (HGGT) gene, were tested for oxidative stability. No pro-oxidant effects were observed in the modified crude corn oil containing up to 5,000 ppm tocotrienols (6,200 ppm total tocotrienols and tocopherols) when compared to the control crude corn oil containing 300 ppm tocotrienols (1,500 ppm total tocols).