The Role of the Bacterial Community in Producing a Peculiar Smell in Chinese Fermented Sour Soup

Abstract

In this paper, the volatile flavour constituents and the bacterial diversity in characteristic Chinese fermented sour soup were analysed, and the dynamics of bacteria associated with the odour were characterized. The bacterial diversity of sour soup was studied by high-throughput sequencing. A total of 10 phyla and 89 genera were detected. Firmicutes was the dominant phylum of sour soup, accounting for 87.14–98.57%. The genus structure of normal sour soup was relatively simple, and Lactobacillus (78.05–90.26%) was the dominant genus. In addition to Lactobacillus, the foul-smelling sour soup contained more Pediococcus spp., Caproiciproducens spp., and Clostridium-sensu-stricto12 spp. (relative abundance >1%) than the normal sour soup. A total of 51 aroma compounds were detected by gas chromatography-mass spectrometry(GC-IMS), including 25 esters, 8 terpenes, 8 alcohols, 3 sulfur compounds, 2 acids, 2 ketones, 1 pyrazine, 1 monoterpene and 1 aldehyde. According to the relative odour active value (ROAV) calculation, 51 important flavour-contributing substances and 7 flavour-coordinating substances were determined. The esters with the highest relative percentages and ROAV values provided the pleasant flavour of the sour soup. In the foul-smelling sour soup, the ROAV values of 1,8-cineole, isobutyl acetate, ethyl butanoate, ethyl octanoate-M, and ethyl hexanoate-M decreased, while those of diallyl disulfide-M and diallyl disulfide-D, which were probably responsible for the foul flavour, increased. Through Pearson correlation analysis, the odour production of the foul-smelling soup was determined to be related to Pediococcus spp., Caproiciproducens spp., Clostridiumsensu_stricto_12 spp., Oscillibacter spp., Bacteroides spp., Fibaculaceae_unclassified spp., Acinetobacter spp. and Halomonas spp.

The Correlation Mechanism between Dominant Bacteria and Primary Metabolites during Fermentation of Red Sour Soup

“…These bacteriocins serve as natural antimicrobial agents and increase the safety of food products. Apart from bacteriocins, LAB also produces metabolites that contribute to the flavor, taste, and odor of sour soup [8]. A recent study reported the presence of aldehydes and butyric acid as the causative agents of foul odor in sour soup [9].…”

“…A recent study reported the presence of aldehydes and butyric acid as the causative agents of foul odor in sour soup [9]. Metagenomic (Illumina MiSeq) sequencing and metabolomic investigation of fermented Chinese sour soup detected 89 bacterial genera and 51 aromatic compounds (including 25 esters, eight alcohols, eight terpenes, three sulfur compounds, two acids, two ketones, one aldehyde, one pyrazine, and one monoterpene) in sour soup [8]. Metagenomic sequencing can be used to analyze millions of DNA sequences at the same time for the dissection of the genetic makeup of the microbial community to predict their functions [10].…”

“…Through metabolomic techniques, the metabolic contents of a biological sample could be thoroughly characterized, and metabolite profiles can be compared between samples [13]. Previous studies have determined the role of bacterial diversity in producing certain metabolites that were involved in producing a peculiar smell in the sour soup [8]. Microbial diversity of different Chinese fermented foods has been reported in different studies, however, the correlation between dominant bacterial species and primary metabolites in fermented red sour soup, is still unclear.…”

Comparison of Fermentation Behaviors and Characteristics of Tomato Sour Soup between Natural Fermentation and Dominant Bacteria-Enhanced Fermentation

“…Therefore, selecting suitable microbial strains to standardize the fermentation process, shorten the fermentation cycle, and stabilize the flavor quality of the product is necessary. Although there have been studies on the flavor and microbial communities of sour soup, and the microbial flora [ 12 , 13 , 14 , 15 , 16 ], there are few studies on the VFCs of tomato sour soup that use the inoculation of dominant bacteria, or on the relationship between the change in microbial communities and VFC generation in the CTN fermentation process used to enhance fermentation. Therefore, improving the quality of CTN is necessary to study the succession of microbial communities, the change in VFCs, their relationship during CTN fermentation, and the influence of enhanced fermentation by dominant bacteria on the quality of tomato sour soup.…”

“…Recently, HTS was used to analyze bacteria in tomato sour soup, in which Lacticaseibacillus spp. was found to be the dominant bacteria [ 16 ]. The microbial structure of fermented foods often has an effect on flavor substances; however, the relationship between these microbiota and flavor is still poorly understood.…”