Flavor improvement of fermented soybean foods by co-fermentation with Bacillus velezensis and Lactiplantibacillus plantarum

This study aimed to improve the flavor of fermented soybean foods and to investigate the molecular mechanisms of this flavor improvement phenomenon. Three fermented soybean foods (Bv, BvLp and Lp) were obtained using Bacillus velezensis SDL1 and Lactiplantibacillus plantarum Ly8 as starter cultures. Organoleptic evaluation showed that BvLp had the best flavor, followed by Bv and Lp. Next, some flavor-related physicochemical properties were investigated. Acid production level was ranked as Lp > BvLp > Bv, in which acetic acid and lactic acid were the main contributors to the variation in sample acid content, and BvLp contained the most lactic acid and isovaleric acid, 3.72-49.62 and 3.61-37.75 times those of Lp and Bv, respectively. Free amino acid analysis showed that the concentration trends of branched-chain amino acids and threonine were consistent with the sensory evaluation. Volatile metabolomics analysis indicated that acetoin and pyrazines were the key compounds for the superior flavor of BvLp. Finally, transcriptomic analysis, combined with the above data, revealed that under a parasitic-like interaction in microbial mixed culture, BvLp had significantly more flavor than Bv and Lp by reducing the acid content and increasing the concentration of some esters, acetoin and pyrazines.