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 (108CFU/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.

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The technological applications utilized for tofu processing are diverse and complex, resulting in different yields and quality characteristics of tofu. The current study investigated the gel‐forming principle of soybean protein coagulated using fermented yellow whey (FYW) to produce tofu. The effects of several processing parameters (soybean‐to‐water ratio, boiling temperature, boiling time, and FYW content) on the yield and protein content of tofu produced by the boiling‐to‐filtering method (BFM) were studied and optimized using response surface methodology. Results indicated significant differences in yield and protein content of tofu using different processing parameters, with FYW content being the most significant (p < .05). Optimum processing parameters of the BFM were found to be: soybean‐to‐water ratio of 1:5 (kg:kg), boiling time 6.1 min, boiling temperature 105°C, and FYW content of 26%. Under optimum conditions, tofu's yield and protein content were 235.17 g/100 g and 10.60%, respectively, and these were 47.93 g/100 g and 4.16% higher than those before optimization. This study provides practical technical support and a theoretical basis for the standardized industrial production of high‐yield and high‐protein tofu.