Bacterial community and functional prediction differences between white and red sour soup.

Sour soup is a traditional plant-based fermented food from Qiandongnan Prefecture, Guizhou Province, China. It is divided into two types: white sour soup and red sour soup. White sour soup is made by semi-anaerobic fermentation of oryza sativa var. glutinosa washing water in earthenware jars for 7-10 days. Red sour soup is prepared by crushing and mixing solanum lycopersicum, red capsicum annuum, and zingiber officinale with oryza sativa var. glutinosa washing water at a ratio of 3:1:0.5:5, followed by semi-anaerobic fermentation for 10-15 days. To date, no study has systematically compared the bacterial community and functional differences between the two types of sour soup. In this study, six samples of each type were analyzed by 16 S rRNA gene sequencing and PICRUSt2 functional prediction. The results showed that their community structures were significantly separated (p < 0.05). White sour soup was dominated by Proteobacteria (93.66%) and enriched with Lactobacillus (LDA = 3.63), Acetobacter (LDA = 5.67), and Clostridiales (LDA = 4.21). Red sour soup exhibited higher diversity, with Proteobacteria decreasing to 39.09% and co-existing with multiple other phyla including Chloroflexota (19.72%), and specifically enriched with Akkermansia (LDA = 4.26). Functionally, white sour soup showed higher predicted abundances in host circulatory system (FC = 3.26, p < 0.001) and host immune system (FC = 1.65, p < 0.01) pathways, whereas red sour soup showed higher abundance in the host digestive system pathway (FC = 0.46, p < 0.01). This study systematically reveals, for the first time, raw material-driven bacterial differentiation and provides a theoretical foundation for the functional development of traditional fermented foods.