Abstract: The effects of salt concentration on the microbial load and community structure in Pixian broad bean paste mash and its quality during fermentation were studied in this paper. The results showed that the total number of molds decreased continuously during the fermentation process. The lower the salt concentration was, the faster the decline rate was. For each salt concentration, the total amount of bacteria decreased at first, then increased slowly, and finally remained at around 7.3 (lg(CFU/g)). Lactic acid bacteria were detected only at the early stage of fermentation for low-salt broad bean paste mash (6% and 9%), which resulted in significant differences in the total bacterial quantity at the early stage of fermentation among broad bean paste mashes with different salt concentrations. High-throughput sequencing indicated that Aspergillus was the dominant fungus in the fermentation process of broad bean paste mash for all salt concentrations. However, there were significant changes in the bacterial composition in broad bean paste mash with salt concentration. The dominant bacteria in low-salt broad bean paste mash (6% and 9%) were Lactobacillus, Staphylococcus and Weissella, while in high-salt broad bean paste mash (12% and 15%), the dominant bacteria were Staphylococcus, Tetragenococcus and Bacillus. There was a significant influence of salt concentration on the contents of total acids, amino nitrogen and reducing sugars. The total acid and amino nitrogen contents increased, while the reducing sugar content decreased with decreasing salt concentration. Sensory evaluation showed that broad bean paste mash with 12% salt was the best in sensory quality, followed by that with 15% salt concentration, and the samples with 6% and 9% salt was the worst. Low-salt broad bean paste mash (6% and 9%) scored lower in sensory evaluation, mainly because it had a very high acidity and was too soft and out of shape. All the results indicated that the fermentation of broad bean paste mash should not blindly pursue low salt, and the salt concentration should be controlled at above 12%.

Key words: Pixian broad bean paste mash; salt concentration; microbial community diversity; quality