Symbiosis of acetic acid bacteria and yeast isolated from black tea fungus mimicking the kombucha environment in bacterial cellulose synthesis

The symbiotic effect of acetic acid bacteria and yeast on bacterial cellulose (BC) synthesis in kombucha was explored. Firstly, the optimal culture ratio of acetic acid bacteria and yeast was optimised through single factor and orthogonal test. The results showed that when Komagataeibacter intermedius:Brettanomyces bruxellensis:Zygosaccharomyces bisporus ratio was 1:10:10, and the inoculation amounts of K. intermedius, B. bruxellensis, and Z. bisporus were 104, 105, and 105 CFU/mL, respectively, the yield of BC was the highest, and the dry basis was 5.51 g/L. It was determined that the metabolites of B. bruxellensis and Z. bisporus could promote the synthesis of BC by K. intermedius. In addition, the composition of yeast filtrate was analysed by amino acid analyser, gas chromatography-mass spectrometry (GC-MS), and high performance liquid chromatograph (HPLC). Results showed that 16 amino acids were detected in yeast filtrate, and cysteine was only detected in yeast filtrate. The increase in isoleucine before and after fermentation was the highest, which was 11.64 times that of the control group. The increase in aspartic acid and glycine were second and third, accounting for 60.00 and 41.67%, respectively. The main volatile substances were alcohols, accounting for 84.89%, of which the relative content of ethanol was the highest at 77.35%. The relative contents of 3-methyl-1-butanol and phenylethanol were also high, accounting for 4.13 and 3.14%, respectively. Tartaric, citric, and succinic acids were detected in the yeast filtrate. The chemical species did not change before and after fermentation, but the content decreased. Vitamins B2 and B6 were detected in yeast filtrate, and the species and content did not change significantly before and after fermentation. A theoretical basis for kombucha fermentation and BC synthesis was provided.