The Formation of Phenol and Indole Flavor Substances in Stinky Tofu Brine Based on Metabolism of Aromatic Amino Acids

Understanding the formation mechanism of the flavor compounds in stinky tofu brine is crucial for controlling the flavor quality of Changsha stinky tofu. Dynamic changes in associated bacteria, enzymes, and differential metabolites in the metabolic pathway of aromatic amino acids in brine were investigated. Results showed that phenol (0.39-89.96 µg/mL), p-cresol (0.19-389.62 µg/mL), indole (1.14-242.97 µg/mL), 3-methylindole (0.14-3.00 µg/mL) were the key flavor substances of brine. The main associated bacteria Clostridiales bacterium SYSU GA17129, Aneurinibacillus aneurinilyticus, and Anaerosalibacter massiliensis were significantly positively correlated with key flavor substances (P < 0.05). The main associated enzymes were transaminase, decarboxylase, and lyase. In summary, phenol and p-cresol were formed by the metabolism of tyrosine and phenylalanine through five reaction chains, and indole and 3-methylindole were formed by the metabolism of tryptophan through one and three reaction chains, respectively.