Revealing the microbial diversity and volatile flavor formation in finger citron kombucha by metagenomic and GC-MS analysis

Kombucha is a kind of health drink formed by the metabolism of Symbiotic Culture of Bacteria and Yeast (SCOBY) composed of yeast, acetic acid bacteria and lactic acid bacteria, which is popular among researchers and fond of consumers because of its antioxidant and hypoglycemic effects. In this study, the finger citron kombucha with different fermentation time (2, 4, 6, 8 day) were analyzed by headspace solid phase micro-extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and metagenomic sequencing. The results showed that a total of 76 volatiles were identified, including 15 key volatiles, such as linalool, geraniol, α-terpinene, and limonene, which had a great influence on the flavor of kombucha. Metagenomic analysis showed that unclassified-g-Gluconobacter, Komagataeibacter saccharivorans, Gluconobacter-sp.-R71656 and other microorganisms were the dominant species in finger citron kombucha. Through the correlation heat map analysis of volatiles and microbial composition, it was found that Gluconobacter had a positive effect on the formation of most volatiles of kombucha. In addition, Novacetimonas hansenii, Brettanomyces bruxellensis and Wickerhamiella sorbophila were also closely related to the flavor formation of kombucha. This study provided a theoretical basis for finding the key aroma-producing microorganisms in the fermentation process of finger citron kombucha and the subsequent construction of SCOBY.