Metabolic function and quality contribution of tea-derived microbes, and their safety risk in dark tea manufacture

Microbial fermentation, especially the microbes involved, plays a crucial role in the quality formation of dark tea. Over the last decade, numerous microbes have been isolated from dark tea and in turn, applied to dark tea manufacture through pure-strain, mixed-strain, and enhanced fermentation. This article systematically summarizes the specific metabolic function and quality contribution of tea-derived microbes, with special attention paid to their safety risk. Aspergillus niger converts catechins via hydrolysis, addition, oxidative polymerization, and B-ring fission, contributing greatly to the reddish-brown color and mellow taste of dark tea. Aspergillus sydowii and Penicillium simplicissimum are caffeine-degrading microbes, degrading caffeine mainly into theophylline. However, under adverse conditions, Aspergillus, Penicillium, and Fusarium species potentially produce aflatoxins, ochratoxin A, and citrinin, the mycotoxins occurring in dark tea. The in-depth knowledge of tea-derived microbes is important for improving the quality and safety of dark tea, providing a theoretical basis for its industrial modernization.