The more -: The better?: Estimating the inhibitory activity of alpha-tocopherol towards lipid oxidation

Tocopherols are considered to be powerful antioxidants, but prooxidative effects are discussed for higher concentrations. The aim of this in vitro study was to investigate the dose-dependent inhibition of oxidation product formation caused by alpha-tocopherol, and to estimate the range of maximum antioxidant activity of alpha-tocopherol at different stages of lipid oxidation. Alpha-tocopherol was added to rapeseed oil triglycerides (ROTG, purified rapeseed oil) in concentrations ranging from 25 to 1500 mu mol/kg ROTG. The inhibitory activity of alpha-tocopherol increased up to a concentration of 100 mu mol/kg ROTG. A concentration of 125 mu mol alpha-tocopherol/kg ROTG did not result in an improved antioxidant effect. The formation of volatile secondary oxidation products followed the same trend, and the maximum inhibitory effect was also found for 100 mu mol alpha-tocopherol/kg. Further, concentrations between 250 and 1500 mu mol alpha-tocopherol/kg ROTG clearly caused increased formation of hydroperoxides during the induction period. However, compared to the control, all tested alpha-tocopherol concentrations resulted in a reduction of hydroperoxide formation and no prooxidative effects were observed. (c) 2005 Published by Elsevier GmbH.