Effect of Salt Concentration on Microbial Communities and Flavor Profiles in Fermented Cowpea

Fermented cowpea is an important traditional fermented vegetable in China, widely consumed, particularly in southern regions. However, few studies have investigated the bacterial communities and flavor compounds in fermented cowpea, especially regarding the influence of salt concentration on microbial structure and metabolite dynamics. Therefore, this study investigated the effects of four salt concentrations (0%, 3%, 6%, and 9%) on microbial composition and metabolites in fermented cowpea. The results showed that 1-octen-3-ol, linalool, phenylethyl alcohol, 3-methyl-1-butanol acetate, 2-octanone, propanoic acid, 3-methyl-butanoic acid, benzeneacetaldehyde, and indole significantly contributed to the flavor of fermented cowpea. Lactobacillus, Acinetobacter, Pseudomonas, Muribaculaceae, and Bacteroides were the dominant bacterial genera. Furthermore, two-way orthogonal partial least squares (O2PLS) analysis revealed potential correlations between eight bacterial genera (Lactobacillus, Clostridium_sensu_stricto_1, Prevotella_9, Caproiciproducens, Bacillus, Lysinibacillus, Burkholderia-Caballeronia-Paraburkholderia, Pseudomonas, Acinetobacter, and Terribacillus) and nine characteristic flavor compounds, suggesting their significant impact on flavor profiles. Salt concentration was shown to influence both microbial composition and flavor characteristics. Additionally, the chemical profiles and bacterial communities of cowpea fermented with 3% salt were similar to those fermented with 6% salt. Fermentation at 3% salt concentration not only reduces production costs but also lowers health risks associated with high salt intake, providing an improved option for large-scale production.