Interactions between raw dark tea chemistry and dominant fungi shape Hei brick tea quality

Hei brick tea undergoes a unique "steam pressing-drying (SPD)" process, where the interactions between raw tea chemicals and microbial communities occur, shaping the sensory qualities. Current studies have revealed the sensory attributes and microbial succession process in dark tea, while the correlations and interaction mechanisms between raw tea and dominant fungi during the SPD process are hardly uncovered. In this study, raw dark teas of two cultivars (Jiukeng and Chunyu 2) were applied to the SPD process. The steam pressing and drying provide the same initial microbes and fermentation conditions, respectively. High-throughput sequencing revealed a reduction in microbial diversity and an increase in key fungi like Aspergillus. A strong correlation was found among 28 non-volatile components, 99 volatile flavor contributors and dominant fungi. For instance, gallic acid, caffeine, and GCG were positively associated with the most predominant fugus A. amstelodami, while valine, glutamic acid, γ-aminobutyric acid, alanine, isoleucine, GC, and leucine exhibited negative correlation with A. amstelodami. Simultaneously, A. amstelodami contributed to improving aroma formation through increasing volatile long-chain alcohols, ketones, and acids. The study provides basic data on microbial dynamics and chemical transformations during the SPD process, guiding fermentation optimization for enhanced tea quality.