The effect of thermal inactivation of lipoxygenase on the stability of vitamin E in wheat

Abstract

Less than 10% of the vitamin E in wholemeal and white wheat flours was retained after drum-drying. This extensive destruction of vitamin E may be due to lipid degradation. It is known that tocopherols are oxidized by the co-oxidation reaction of lipoxygenase. The study showed that the loss of vitamin E started immediately on mixing the flour with water, which is the first stage in the drum-drying process. The loss increased as the storage time of the flours increased. It also increased as the temperature of the flour-water slurry increased, even though lipoxygenase activity was inactivated in the hot slurries. When lipoxygenase was heat-inactivated by low moisture processes, such as steam flaking and microwave-treatment, vitamin E retention was improved. To what extent the vitamin E losses can be ascribed to enzymic or non-enzymic oxidation is not known. Both mechanisms seems to be important. Non-enzymic lipid oxidation was favoured by a two- to five-fold increase in pro-oxidative substances, such as iron and copper, during the drum-drying process.