Effects of Weissella confusa and Bacillus subtilis Strains as Starter Cultures on the Flavor Profile of Broad Bean Paste

Broad bean paste (BBP), a traditional Chinese fermented condiment, often suffers from inconsistent quality during spontaneous fermentation. In this study, Weissella confusa KUST3424 and Bacillus subtilis KUST4527 were isolated from BBP and evaluated as starter cultures, either individually or in combination. Flavor characteristics were analyzed using an electronic nose, electronic tongue, and GC–MS combined with odor activity value (OAV) calculations. Results showed that 13 key flavor compounds with OAVs greater than 1 were identified as major contributors to the overall aroma of fermented BBP juice (FBPJ). Moreover, inoculated groups exhibited distinct flavor profiles compared with natural fermentation, with the co-culture producing the most pronounced improvements. The mixed fermentation markedly enhanced desirable alcohols and esters, including significant increases in isoamyl alcohol (125.87%), 2-furanmethanol (128.91%), phenethyl alcohol (354.06%), and 4-vinylguaiacol (150.99%). In addition, compounds such as acetoin, guaiacol, ethyl hexanoate, and ethyl benzoate were newly generated in the co-culture group, while the diversity and total content of esters increased significantly from 0.52% to 9.69%. These findings demonstrate that the combined use of W. confusa KUST3424 and B. subtilis KUST4527 as starter cultures can effectively enhance the complexity and overall quality of BBP flavor. This co-culture strategy shows promise for enhancing flavor control and consistency in industrial-scale BBP production.