Effects of Salinity on Physicochemical Properties, Flavor Compounds, and Bacterial Communities in Broad Bean Paste-Meju Fermentation

Abstract

Broad bean paste (BBP) is a traditional fermented soy food, and its high salt content not only prolongs the fermentation time but also threatens human health. In this study, three BBP-meju with different salt concentrations were prepared, and the effects of varying salinity on fermentation were comprehensively compared. The results showed that salt-reduced fermentation contributed to the accumulation of amino acid nitrogen, reducing sugars, free amino acids, and organic acids. Alcohols, esters, aldehydes, and acids were the main volatile flavor compounds in BBP-meju, and the highest total volatile flavor compounds were found in medium-salt meju. Bacillus, Staphylococcus, Aspergillus, and Mortierella were the dominant microbial communities during fermentation, and there were also three opportunistic pathogens, Enterobacter, Pantoea, and Brevundimonas, respectively. According to Spearman correlation analysis, Wickerhamomyces, Bacillus, Staphylococcus, and Mortierella all showed highly significant positive correlations with ≥3 key flavor compounds, which may be the core functional flora. Furthermore, the dominant microbial genera worked synergistically to promote the formation of high-quality flavor compounds and inhibit the production of off-flavors during salt-reduced fermentation. This study provides a theoretical reference for the quality and safety control of low-salt fermented soy foods.

Keywords: broad bean paste; correlation; flavor compounds; microbial community; salinity.

Figure 1

Physicochemical properties during fermentation of BBP-meju with different salt concentrations: (a) moisture contents; (b) pH; (c) salinity; (d) total acid contents; (e) AAN contents; (f) reducing sugar contents.

Figure 2

FAAs during fermentation of BBP-meju with different salt concentrations: (a) content of amino acids; (b) relative abundance of amino acids; (c) average content of amino acids in BBP-meju samples. Asterisks indicate a statistically significant difference from the control group (* p ≤ 0.05, ** p ≤ 0.01).

Figure 3

OAs during fermentation of BBP-meju with different salt concentrations: (a) content of OAs; (b) relative abundance of OAs; (c) average content of OAs in BBP-meju samples with different salt concentrations. Where letters a, b, and c indicated the significant differences (p < 0.05).

Figure 4

The volatile compounds of BBP-meju with different salt concentrations based on E-nose data: (a) PCA scores and (b) radar chart.

Figure 5

Content distribution of volatile flavor compounds during fermentation of BBP-meju with different salt concentrations: (A) relative abundance of different types of volatile flavor compounds; (B) content of different types of volatile flavor compounds; (C) variation in the content of different types of volatile flavor compounds across samples.

Figure 6

The α-diversity of bacterial (a–e) and fungal (f–j) communities during fermentation of BBP-meju with different salt concentrations.

Figure 7

Structural analysis of bacterial and fungal communities in BBP-meju samples: (a,b) comparison of OTUs of bacteria (a) and fungi (b); (c,d) relative abundance of bacteria (c) and fungi (d) at the genus level.

Figure 8

Correlation clustering heat map (a) and correlation network diagram (b) between dominant microbial genera and key volatiles flavor compounds (VIP > 1) during BBP-meju fermentation with different salt concentrations. (a) The red and blue indicate positive and negative correlation, respectively, and the darker the color, the stronger the correlation; asterisks represent significance, * is p < 0.05, and ** is p < 0.01. (b): blue squares represent key volatile flavor compounds, red circles represent dominant microbial genera, and the yellow solid line and gray dotted line represent positive and negative correlation, respectively, and the thicker the lines, the stronger the correlation.