[Determination of the activities of lipase, lipoxygenase and peroxidase in native and extruded cereal brans].

To avoid fat deterioration in grain products during storage the cereal inherent enzymes lipase, lipoxygenase and peroxidase have to be inactivated. Known methods for the determination of the enzymes activity are tested and their applicability evaluated. Own optimized methods are presented. In laboratory and semiindustrial extrusion tests (laboratory single screw extruder, twin screw extruder, short screw extruder) the degree of enzyme inactivation of wheat bran, rye and maize bran, and oat bran is determined in dependence on the extrusion parameters. The enzymes mentioned already had been inactivated at mild extrusion conditions (temperature < 120 degrees C, moisture 20%, low mechanical stress). Only in brans of high fat content (10-14%) or high moisture (> 25%) minor residual activities of peroxidase and lipase were observed.