Effects of Streptococcus thermophilus Fermentation on the Flavors and Antioxidant Properties of Barley Juice

Lactic fermentation can improve the metabolic profile and functionality of juice, which is beneficial to human health. This study aimed to investigate the effect of Streptococcus thermophilus fermentation on the metabolic profiles and antioxidant activity of barley juice. The results demonstrated that S. thermophilus 7G10 dramatically increased the total titratable acidity and total phenolic and flavonoid contents in the barley juice after 24 h of fermentation. Only sixteen volatile compounds were detected in the fermented barley juice, including six acids, four ketones, three alcohols, and one aldehyde. In addition, based on non-targeted metabolomics, 30 important differential metabolites were screened among the 1460 non-volatile compounds. Notably, the barley juice fermented with S. thermophilus 7G10 had increased free radical (ABTS, DPPH, and O-2(-)) scavenging activities. Furthermore, sensory evaluation showed that the barley juice fermented with S. thermophilus 7G10 was most attractive to consumers. These results show that LAB fermentation promotes the formation of volatile compounds and potentially enhances the antioxidant properties of barley juice.