Effect of Salt Concentration on Physicochemical Properties and Bacterial Diversity of Shrimp Paste

In order to investigate the effect of salt addition on the fermentation of shrimp paste, the physicochemical indexes, sensory attributes and bacterial communities of shrimp paste (noted as C10, C15, C20 and C25, respectively) with four salt concentrations (10%, 15%, 20% and 25%) were analyzed. The results showed that C15 had the highest sensory scores for smell, taste and overall acceptability. As fermentation proceeded, the increasing trend of total volatile basic nitrogen (TVB-N) and amino acid nitrogen (AAN) contents in shrimp paste was negatively correlated with salt addition. Malondialdehyde (MDA) content showed a fluctuating upward trend, and at the end of fermentation, C15 had the lowest MDA value. The pH of shrimp paste did not change significantly during the fermentation process, and no significant difference was observed among the four shrimp pastes (P > 0.05). Bacterial diversity and abundance were significantly lower in C10 and C15 than in C20 and C25 (P < 0.05). The dominant bacterial genera in C10 were Tetragenococcus and Staphylococcus. Tetragenococcus was the dominant genus in C15. Unclassified_f__Rhodobacteraceae, Planktotalea and Pandoraea were the dominant genera in unfermented shrimp paste, C20, and C25. Using Kruskal-Wallis H Test, 10 significant differential bacterial genera were selected among unfermented shrimp paste and the four fermented samples. Pearson correlation analysis showed that in C10, the relative abundance of Acinetobacter, Virgibacillus and unclassified_f__Bacillaceae was positively correlated with TVB-N. In C15, the relative abundance of Persicirhabdus showed a significant negative and positive correlation with TVB-N and AAN, respectively. In C20, the relative abundance of Sulfitobacter, Rubritalea, Ruegeria and Planktotalea showed a positive correlation with both TVB-N and MDA. In C25, the relative abundance of Sulfitobacter, Ruegeria, Ruegeria, Ascidiaceihabitans and Planktotalea was positively correlated with all AAN, TVB-N, and MDA. Overall, the key microorganisms responsible for the differences in physicochemical properties between low- (C10 and C15) and high-salt (C20 and C25) shrimp pastes were Acinetobacter, Mycobacterium, Rubritalea, Planktotalea, Sulfitobacter and Ascidiaceihabitans. This study provides a theoretical basis for the development and industrial production of salt-reduced shrimp paste.