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, atmospheric steaming combined microwaving, microwaving combined enzymolysis, atmospheric steaming combined enzymolysis) on endogenous enzyme activity, color, total phenolic contents, and antioxidant activity of wheat bran-germ. The results showed that all the single treatment techniques significantly reduced the activities of lipase, lipoxidase and peroxidase in wheat bran-germ under optimal conditions, especially atmospheric steam and enzymatic hydrolysis inactivated the three endogenous enzymes better than microwave. 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 treatm, the combined treatment exhibited enhanced efficacy, resulting in inactivation rates exceeding 90% for the three endogenous enzymes in wheat bran-germ.In terms of total phenolic content, microwave combined enzymatic digestion resulted in a maximum increase of 1.40-fold in total phenolic content compared to untreated wheat bran-germ. This was followed by the atmospheric steam combined enzymatic hydrolysis group, showing a 1.05-fold elevation in total phenolic contents. Furthermore, microwaving combined enzymolysis resulted in the highest free-radical-scavenging rate towards ABTS+ and DPPH radicals in wheat bran-germ, reaching 91.13% and 91.79%, respectively. Given the eco-friendliness, high efficiency, mature equipment, standardized operation, and significant long-term economic benefits 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.