Study on the Functional, Physiological, and Sensory Properties of Coffee Leaf Dark Tea Processed Using the Pile...

Coffee leaves are a promising raw material for functional beverages due to their distinctive phytochemical profile. In this study, sun-dried Arabica coffee leaves were processed into coffee leaf dark tea using Pu-erh-style pile fermentation with three treatments: spontaneous pile fermentation (SPPF), Saccharomyces cerevisiae-inoculated fermentation (SIPF) and Aspergillus niger-inoculated fermentation (AIPF). Changes in basic components, tea pigments, key phytochemicals, antioxidant capacity, in vitro hypoglycemic and hypolipidemic activities, and sensory properties were evaluated over 25 days. Pile fermentation reduced water extract, free amino acids and several phenolic constituents, while promoting the formation of theabrownins, particularly in SIPF and AIPF. Total phenolics, flavonoids, and antioxidant activities increased initially and then declined, with higher bioactivities observed at intermediate fermentation times. Coffee leaf dark tea also exhibited in vitro α-amylase and α-glucosidase inhibition, glucose diffusion retardation, reduced starch digestibility, and pancreatic lipase inhibition, with SIPF and AIPF outperforming SPPF. Sensory evaluation showed that inoculated fermentations, especially AIPF at 15 days and SIPF at 10 days, produced teas with superior overall quality. These results suggest that Pu-erh-style pile fermentation with targeted microbial inoculation may be a feasible strategy to obtain coffee leaf dark tea with enhanced in vitro functional-related properties and desirable sensory characteristics.