State-of-the-art review of dark tea: From chemistry to health benefits

Dark tea is a post-fermented tea with unique organoleptic characteristics. A unique microbial fermentation procedure is involved in dark tea processing that is considered a major factor to manage the quality of dark tea. Dark tea is gaining increasing attention recently because it contains various bioactive compounds with diverse biological functions. This review summarizes the microbial fermentation process, main bioactive compounds, and important biological functions or health benefits of dark tea, emphasizing its protective effects against different diseases and relevant molecular mechanisms, and proposes the perspectives in research and application of dark tea. Functional core microorganism-mediated bioconversion is crucial for the formation of dark tea's main quality components during the fermentation period. Dark tea contains a variety of bioactive compounds, including alkaloids, free amino acids, peptides, polyphenols, pigments, polysaccharides, and volatile compounds. Consumption of dark teas has been linked to multiple health benefits, such as antioxidant, anti-obesity, anti-diabetic, anti-cancer, cardiovascular protective, gastrointestinal protective, hepatoprotective, neuroprotective, and photoprotective activities. Future studies focusing on the health mechanisms of dark teas and the potential applications of dark tea in the food, pharmaceutical, and medical industries are guaranteed.