Abstract
Chinese red sour soup is a traditional fermented product famous in the southwestern part of China owing to its distinguished sour and spicy flavor. In the present study, the effect of inoculation of lactic acid bacteria (LAB) on the microbial communities and metabolite contents of the Chinese red sour soup was investigated. Traditional red sour soup was made with tomato and red chilli pepper and a live count (108 CFU/mL) of five bacterial strains (including Clostridium intestinalis: Lacticaseibacillus rhamnosus: Lactiplantibacillus plantarum: Lacticaseibacillus casei: Lactobacillus paracei) was added and fermented for 30 days in an incubator at 37 °C. Three replicates were randomly taken at 0 d, 5 d, 10 d, 15 d, 20 d, 25 d and 30 d of fermentation, with a total of 21 sour soup samples. Metabolomic analysis and 16S-rDNA amplicon sequencing of soup samples were performed to determine microbial diversity and metabolite contents. Results revealed that fermentation resulted in the depletion of native bacterial strains as LAB dominated over other microbes, resulting in differences in the relative abundance of bacteria, and types or contents of metabolites. A decrease (p < 0.01) in Shannon and Simpson indices was observed at different fermentation times. The metabolomic analyses revealed a significant increase in the relative content of 10 metabolites (particularly lactic acid, thymine, and ascorbic acid) in fermented samples as compared to the control. The correlation network revealed a positive association of Lacticaseibacillus rhamnosus with differentially enriched metabolites including lactic acid, ascorbic acid, and chlorogenic acid, which can desirably contribute to the flavor and quality of the red sour soup.
Highlights
Red sour soup is a traditional semisolid or liquid condiment product similar to ketchup but using different processing technology [1]
A slight increase in the abundance of Proteobacteria 5aonfd17 Bacteroidetes was observed only at 15 days after fermentation (T-III) but afterward, the Firmicutes dominated over other phyla comprehensively from T-IV to T-VI (Figure S1)
The present study indicated that Lactobacillus was the most predominant and significant bacterial taxa during the fermentation of red sour soup
Summary
Red sour soup is a traditional semisolid or liquid condiment product similar to ketchup but using different processing technology [1] It is mainly famous in two of the major ethnic groups Miao and Dong living in the southwestern part of Guizhou Province in China. It has been a very popular traditional fermented soup in southwest China for thousands of years owing to its fascinating sour and spicy flavor [2]. It is generally made by fermenting nutritious raw materials including tomatoes, red chilli pepper, white wine, glutinous rice flour, bacterial species, and other ingredients [3]. Traditional fermentation methods of producing red sour soup have some limitations which can be overcome by utilizing LAB inoculation and fermentation
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