Microbial community in Chinese traditional fermented acid rice soup (rice-acid) and its correlations with key organic acids and volatile compounds

Rice-acid is a unique Chinese traditional fermented acid rice soup and its microbial community plays an important role in the formation of flavour compounds. In the study, rice-acid products from high-temperature and low-temperature fermentation methods were selected to analyze the microbial community, organic acids, and volatile flavour compounds (VFCs). The main bacterial and fungal phyla in Chinese traditional fermented rice-acid were determined to be Firmicutes and Ascomycota, including 62 bacterial genera and 57 fungal genera. The dominant bacterial genera were Lactobacillus, Acetobacter, and Prevotella and the dominant fungal genera were Naumovia, Pichia, Candida, and Saccharomyces. Among organic acids in rice-acid, L-lactic acid had the highest concentration, followed by malic acid, acetic acid, citric acid, oxalic acid, and tartaric acid. Volatile flavour compounds had a high contribution to the flavour, including ethyl acetate, ethanol, acetic acid, propanoic acid, 1-octen-3-ol, 2-nonanol, 2-undecanol, propyl propionate, ethyl propanoate, propyl propionate, and 2,3-butanedione. The microorganisms which were closely correlated with key organic acids in rice-acid included Lactobacillus, Acetobacter, Pichia, Candida, Kluyveromyces and Meyerozyma. The microorganisms which were correlated with VFCs included Acetobacter, Prevotella, Kluyveromyces and Saccharomyces. In particular, Lactobacillus, Pichia, Malassezia, Clavispora, Rhizopus and Cystofilobasidium were significantly positively correlated with lactic acid in rice-acid. Kluyveromyces, Saccharomyces and Emericella were significantly positively correlated with ethanol and ethyl acetate. The study provides the basis for improving the quality of rice-acid.