Lactobacillus delbrueckii is the key functional microorganism of natural fermented tofu sour water involved in the traditional coagulation of Chinese Huizhou Mao-tofu

Abstract Mao-tofu is traditionally coagulated by natural fermented tofu sour water (NFTSW), which contains large numbers of microorganisms from the environment. Nonetheless, the microorganisms accountable for coagulation require further analysis and characterization. Our aim was to evaluate the bacteria in NFTSW that carry out the traditional fermentation process of Mao-tofu by using polymerase chain reaction-denaturing gradient gel electrophoresis. Results show that Lactobacillus ultunensis, Enterococcus bulliens, Lactobacillus graminis, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. lactis, and Lactobacillus mucosae are the primary bacteria involved in brewing. Furthermore, 6 types of lactic acid bacteria were sequestered from NFTSW by methodology dependent on culture and their acid-producing abilities were analyzed. The results indicated that strain L1, which was identified as Lactobacillus delbrueckii, produced the highest lactic acid content of 2.85 g/100 mL. Simulated coagulation further confirmed that strain L1 was preferable for Mao-tofu coagulation through the evaluation of textural properties, volatile flavour compounds, and sensory characteristics. The results suggested that Lactobacillus delbrueckii might be the core functional microorganism significantly contributing to flavor compound synthesis during the traditional production of Chinese Huizhou Mao-tofu. The research method we used in this investigation may encourage detection of the main microorganisms with different roles involved in other food fermentation processes.