Microbial dynamics-linked properties and functional metabolites during Miang fermentation using the filamentous fungi growth-based process

Abstract

The microbial community in ethnic fermented tea, “Miang” prepared from Camellia sinensis var. assamica in northern Thailand was investigated during the 10 days of a filamentous fungi growth-based process (FFP) using both culture-dependent and culture-independent techniques. During the aerobic phase (days 1–3), filamentous fungi were visually observed growing on steamed tea leaves during which yeast and lactic acid bacteria (LAB) viable cell numbers substantially increased up to 108 and 109 CFU/g Miang, respectively, and became the main microbial population both in semi-submerged fermentation (SSF) and submerged fermentation (SMF) processes. Next generation sequencing indicated the high diversity of the filamentous fungal population in the initial stage of aerobic fermentation. Aspergillus niger was the predominant fungus on day 3 and was the most important microbe in association with yeast, LAB and Bacillus sp. in both the SSF and SMF processes. Pectinases, β-mannanase and cellulases were mainly found during the aerobic fermentation phase, suggesting they were important during fermentation. The organic acids found in Miang were acetic, gallic, glucuronic, lactic, oxalic and succinic acids, while FFP Miang showed similar bioactive compounds including total tannin, total flavonoids and total polyphenols with both SSF and SMF processes. However, SMF resulted in higher antioxidant activity than SSF, while the hardness of both was similar. This study showed an important product processing platform for assessing the relationship between microbes, biotransformation and also functional metabolites accumulated in Miang fermented using the FFP.