Optimization of pile-fermentation process, quality and microbial diversity analysis of dark hawk tea (Machilus rehderi)

Dark hawk tea, produced through pile-fermentation of Lauraceae family leaves, which is rich in various beneficial ingredients and health functions, relies heavily on microbial activity for its unique characteristics. However, the processing technology of dark hawk tea and the microorganisms' dynamic changes during its pile-fermentation remain largely unknown. In this study, based on the previous work, we optimized pile-fermentation parameters for analyzing changes in dark hawk tea's chemical components, volatile substances, and microbial diversity. The tea exhibited superior sensory scores and biochemical qualities under optimal conditions (35 °C, 62% water, 24 h), measuring 5.7 mg/g amino acid content. Gas chromatography-mass spectrometry (GC-MS) identified 108 volatile compounds, notably terpenes, ketones, and esters. Microbial analysis revealed Bacteroides and Faecalibacterium as dominant bacteria and Cladosporium and Mortierella as dominant fungi. Cladosporium prevailed in early fermentation, shifting to Mortierella later. Predicted metabolic pathways highlighted microbial functional genes predominantly participated in carbohydrate, amino acid, and energy metabolism during the pile-fermentation. These results hold important implications for expanding the variety of hawk tea products and deepening our understanding of microbial community dynamics through the pile-fermentation of dark hawk tea.