Effect of fermentation by lactic acid bacteria on the phenolic composition, antioxidant activity, and flavor substances of jujube–wolfberry composite juice

In this study, 11 strains of lactic acid bacteria (LAB) from 4 species were comprehensively characterized for their ability to improve the functional properties and flavor quality of jujube–wolfberry composite juice. The results revealed that the jujube–wolfberry fresh juice was a favorable substrate for LAB growth, and the total number of LAB colonies remained above 7.93 log CFU/mL after fermentation. Fermentation with Lactiplantibacillus plantarum 9-2 (LP9-2) increased the total phenolic content by 16.67% and reduced the total flavonoid content by 14.15%; correspondingly, the antioxidant capacity significantly increased (p < 0.05) and was positively correlated with the content of gallic acid and rutin. In total, 56 volatile compounds were identified and quantified from the fermented juice. In total, 11 volatile compounds with relative odor activity value ≥ 1 were identified. In particular, LP9-2 increased the levels of (E)-2-hexenal, hexanal, and benzaldehyde, which resulted in an enhanced “jujube and wolfberry” flavor in the final product.