Effects of Combined Microwaving/Atmospheric Steaming with Xylanase Enzymolysis on Endogenous Enzyme Activity and Antioxidant Activity in Wheat Bran-Germ

Oxidative rancidity plays a crucial role on the quality of wheat processing by-products—wheat bran-germ, and in order to attenuate its adverse effects on wheat bran-germ products. This study aimed to investigate the effect of six wheat bran-germ modification treatments (microwaving, atmospheric steaming, enzymolysis, microwaving combined atmospheric steaming, microwaving combined enzymolysis, atmospheric steaming combined enzymolysis) on endogenous enzyme activity and antioxidant activity of wheat bran-germ. All the single treatment techniques significantly reduced the activities of lipase, lipoxidase and peroxidase in wheat bran-germ under optimal conditions (P<0.05), especially atmospheric steaming and enzymatic hydrolysis. Atmospheric steaming treatment group achieved over 95% inactivation of lipase and completely inactivated peroxidase. Meanwhile, enzymolysis treatment group resulted in a lipase inactivation rate of over 97%. Compared with the single treatment, the combined treatment exhibited enhanced efficacy, resulting in inactivation rates exceeding 90% for the three endogenous enzymes in wheat bran-germ. The total phenolic contents increased in all treatment groups, especially it significantly increased by 1.4-fold in microwaving combined enzymolysis treatment group. This was followed by the atmospheric steam combined enzymatic hydrolysis group, showing a 1.05-fold elevation in total phenolic contents. Furthermore, microwaving resulted in the highest free-radical-scavenging rate towards DPPH and ABTS⁺ radicals in wheat bran-germ, reaching 91.73% and 91.79%, respectively. Given the high efficiency and eco-friendliness of microwaving combined enzymolysis technology, this approach could be a potential approach to deactivate endogenous enzyme activity and enhance the antioxidant properties of wheat bran-germ. These findings will aid future optimization of industrial wheat bran-germ modification.