Enhancement of the release of phenolic compounds from white and black Qingke bran by autoclaving and fermentation treatments

Qingke (highland barley) is a functional food with health-promoting properties, but its by-product, Qingke bran, remains under-exploited. This study aimed to characterize the phenolic compounds (PCs) in Qingke bran and to improve the release of bound PCs by autoclaving and fermentation treatment, based on a comparative study between white and black Qingke bran. In this study, HPLC-ESI-QTOF-MS/MS was used to identify the diversity and composition of PCs in Qingke bran, and the antioxidant capacities of PCs were determined by ABTS, DPPH and FRAP assays. The results showed that both white and black Qingke bran contained a high content of PCs (647.82 and 931.42 mg GAE/100 g) and flavonoids (383.96 and 392.95 μg RE/100 g), and a wide diversity of PCs consisting of flavonoid glycosides, flavonoid aglycones, phenolic glycosides, phenolic acid aglycones, phenolic acid esters and other PCs. Ferulic acid and vitexin were the major phenolic acids and flavonoids in Qingke bran, and most PCs predominated in the bound form. The autoclaving and fermentation treatment could change the diversity and composition of PCs, enhancing the release of free PCs, especially ferulic acid. The enhancement of the release of PCs contributed to the increase in the antioxidant capacities. In summary, fermentation was proved to be an effective treatment to enhance the release of PCs and to improve the antioxidant capacity of Qingke bran. This study provides important insights into the potential health benefits of Qingke bran and suggests a promising approach for the development of functional food products.