Research Progress on Microbial Diversity and Its Functional Activities during Pile Fermentation of Dark Tea

Dark tea is a type of post-fermented tea with unique sensory characteristics. The tea product is usually obtained in the four steps, namely fixation, rolling, pile fermentation, and drying. Pile fermentation, a key stage in dark tea processing, utilizes microbial metabolism to produce extracellular enzymes under the stimulation of moist heat. The enzyme activities modify the chemical components of the tea, thereby producing a dark tea with a distinct flavor. The present paper summarizes the types of microbes primarily involved in dark tea fermentation and their influences on polyphenols, free amino acids, alkaloids, theabrownins, and volatile components present in the dark tea. Besides, the functional activities of dark tea, including its antioxidant, gastroprotective, hypoglycemic, and hypolipidemic activities are also investigated. The results can aid in the optimization of dark tea processing and production and promote better utilization of the active components of dark tea.