A carbohydrate-degrading microbial consortium named WS3 was obtained through enrichment, domestication, and functional screening. WS3 was primarily composed of Aspergillus, Candida, Glutamicibacter, and Ochrobactrum. After 30-day fermentation with WS3, the dominant bacterial genera shifted to Brachybacterium (66.97%), Brevibacterium (18.60%), and Enterococcus (7.45%), while the dominant fungal genera became Candida (70.52%), Aspergillus (19.43%), and Blastobotrys (10.03%). The tea infusion exhibited a milder and mellower taste with a marked reduction in bitterness and astringency and its aroma characteristics were spicy, woody, floral, and fruity. The content of pectin decreased by 49.83%–89.91%, cellulose by 14.92%, and hemicellulose by 35.22%, and monosaccharides by 70.17%, while the content of oligosaccharides increased by 58.69%. In addition, WS3 exhibited high activities of pectate lyase, xylanase, and β-glucosidase. Correlation analysis revealed significant associations between the dominant microbial taxa and enzyme activities, tea quality attributes, and the degradation of cell wall polysaccharides. This study elucidates the mechanism by which WS3 degrades cell wall components during Liupao tea fermentation, thereby providing a theoretical basis for developing functional starter cultures.

The microbial community structure in Liupao tea at different stages of pile fermentation was studied by traditional microbial isolation and molecular identification. A total of 27 bacteria belonging to 13 genus, 8 actinomycetes species belonging to 7 genus, and 23 fungal species belonging to 11 genera were identified. Aspergillus niger, Aspergillus tubingensis, Blastobotrys adeninivorans and Bacillus spp. were found at all stages of the fermentation process. Totally 22 species of bacteria, 7 species of actinomycetes and 9 species of fungi were reported first in Liupao tea. These findings are helpful to understand the microbial role in the pile fermentation of Liupao tea, and provide a theoretical basis for the pure culture fermentation and microbial safety analysis of Liupao tea.

In order to explore the source and activity of polyphenol oxidase (PPO) in the fermentation process of Liupao tea, PPO from unfermented and fermented Liupao tea was extracted by using buffer solutions at different pHs and different types and amounts of protective agents at different liquid-to-solid ratios, and was purified through sequential (NH₄)₂SO₄ precipitation, dialysis, and Sephadex G-100 gel filtration chromatography. The results showed that two PPO isozymes with molecular masses of 59 (PPO1) and 70 kDa (PPO2) were purified from Liupao tea. PPO1 may be derived from tea leaves, and PPO2 may be produced by microbial fermentation. When catechol was used as the substrate, the optimum pHs of PPO1 and PPO2 were 6.5 and 6.0, and the optimum temperatures were 40 and 35 ℃, respectively. The thermal stability of PPO1 was better than that of PPO2, although both were almost completely inactivated after heating at 90 ℃ for 5 min. Our data indicated that new isozymes produced during the fermentation of Liubao tea can synergistically improve the quality of dark tea, which will provide a theoretical basis for the control of dark tea processing conditions and the study of polyphenol oxidase of dark tea.