Eucommia ulmoides leaf as an alternative substrate for kombucha fermentation: the role of microbial communities in...

Eucommia ulmoides leaf (EUL) was introduced as a novel fermentation substrate to replace traditional tea in kombucha. High-performance liquid chromatography, untargeted metabolomics, and high-throughput sequencing were applied to understand the potential relationships during fermentation. EUL kombucha exhibited slower sugar consumption rate and superior in vitro antioxidant activity compared with traditional kombucha. Total polyphenols, geniposidic acid, pinoresinol diglucoside, and rutin demonstrated an increasing trend, whereas total flavonoids and chlorogenic acid contents considerably decreased. Metabolite profiling revealed 211 positive and 165 negative ion components in samples fermented for 0, 4, and 8 days. Komagataeibacter and Gluconobacter were the dominant bacterial genera while Hanseniaspora, Dekkera, and Kregervanrija dominated the yeast community. The dominant microbial genera could have regulated nucleotide metabolism, pentose and glucuronic acid-related conversions, ascorbic acid and aldehyde metabolism, and flavonoid biosynthesis, leading to changes in the expression of differential metabolites of EUL kombucha. The findings support innovation in kombucha development.