Pile-fermentation mechanism of ripened Pu-erh tea: Omics approach, chemical variation and microbial effect

As the critical process for quality formation of ripened Pu-erh tea (RpPT), pile-fermentation mechanism has been widely studied by using omics approach, chemical analysis, microbial distribution and their inoculated fermentation tests. Despite several reviews about chemical compositions and health benefits in RpPT and other dark teas, more comprehensive study is requisite to summarize the pile-fermentation mechanism of RpPT and application prospects of relevant microbes. This paper aims to elaborate dominant microbes, recent advances in single- and multi-omics approaches, and pathways of characteristic components during the pile-fermentation. Microbial effects are summarized and compared, which would enhance their application potential in RpPT production. At least 93 fungi and 53 bacteria have been isolated from RpPT related to the pile-fermentation. Aspergillus niger is regarded as dominant microorganism in pile-fermentation for its higher detection frequency and relative abundance. Aspergillus, Penicillium, Rasamsoni, Rhizomucor and Bacillus genera promote RpPT quality formation. The low mycotoxins contamination risk in pile-fermentation and inoculated fermentation indicates microbial application potential in RpPT production. Several microbes are confirmed to promote formation of characteristic components including theabrownins, puerins, teadenol A, gallic acid, lovastatin, gamma-aminobutyric acid and several flavonols such as quercetin. Future studies focusing on superiority and application potential of relevant microbes in RpPT production through exogenous inoculation in the pile-fermentation are guaranteed, which could improve sensory quality and health benefits of RpPT, and shorten fermentation cycle.