Effects of Different Methods of Inactivating Enzyme on Grain Structure, Nutrient Composition and Antioxidant Activity of Black Highland Barley

In order to prevent the oxidative rancidity of highland barley, three common treatment methods of microwave, roasting and superheated steam were used to inactivate the enzyme of black highland barley. Then the changes of microstructure, nutrient composition, phenolic compounds and antioxidant capacity before and after inactivation of enzymes treatment were evaluated when the same enzyme inactivation effect was achieved. The experimental results showed that different methods of inactivating enzyme resulted in different degrees of expansion and browning of highland barley. The color change and equivalent radius of highland barley roasted at 175 ℃ for 20 min was the largest, the equivalent radius of highland barley grain was similar after microwave and superheated steam treatment. By observing the electron microscope of highland barley treated with different methods of inactivating enzyme, it could be found that there were gaps and pores in the cross section of grain, and even large holes in vascular bundles. In addition, total phenols (decreased by 14.71%~20.52%) and total flavonoids (decreased by 11.39%~45.15%) decreased significantly after three treatments, and the content of flavonoids and phenols in highland barley roasted at 150 ℃ for 20 min was the lowest. While the effect of microwave treatment on the content of total phenols was lower than the other two treatments, and the effect of superheated steam treatment on the content of total flavonoids was the least. But DPPH free radical scavenging rate, ABTS⁺ scavenging rate and antioxidant activity increased except microwave treatment. However, the change trend of antioxidant capacity of highland barley after different enzyme inactivation treatments was not completely consistent with the change trend of total phenol and total flavonoids. Under the treatment conditions of enzyme inactivation rate of 50% and 60%, the antioxidant capacity of highland barley treated with superheated steam was the highest, followed by roasting treatment, and the antioxidant capacity of microwave treatment was the lowest. In summary, it can be concluded that the three treatments can be used to inactivate enzyme and can effectively improve the nutritional quality of highland barley. However, the comprehensive evaluation shows that superheated steam treatment is the best choice among the three treatments.