Enhanced Fermentation of Pu-Erh Tea with Aspergillus niger: Quality and Microbial Community Analysis

Post-fermented Pu-erh tea (PFPT) is a microbial fermented tea characterized by unique sensory attributes and multiple health benefits. <i>Aspergillus niger</i> is the dominant fungus involved in the fermentation process and plays a significant role in imparting the distinct characteristics of PFPT. To investigate the role of <i>Aspergillus niger</i> in the fermentation of Pu-erh tea, this study inoculated unsterilized sun-dried green tea with <i>Aspergillus niger</i> isolated from Pu-erh tea to enhance the fermentation process. Metabolites and microbial communities in sun-dried green tea (CK), fortified fermented tea (TF), and naturally fermented tea (NF) were analyzed using non-targeted metabolomics, 16S rDNA, and internal transcribed spacer sequencing. Non-targeted metabolomics revealed that <i>Aspergillus niger</i> significantly altered the metabolite profile of the tea samples, identifying a total of 200 different metabolites, with 95 showing significant increases and 105 significant decreases, predominantly enriched in metabolic pathways associated with amino acid biosynthesis and degradation. High-throughput sequencing revealed that although the relative abundance of the fungal community remained largely unchanged, the inoculation of <i>Aspergillus niger</i> significantly increased the abundance of <i>Bacillales</i> and <i>Pseudomonas</i> within the bacterial community, thereby influencing the dynamic balance of the microbial ecosystem. Collectively, the inoculation of <i>Aspergillus niger</i> altered the composition of the microbial community and metabolic activities, resulting in changes to the content of amino acid-dominated metabolites, thereby enhancing the flavor profile and overall quality of Pu-erh tea. These findings provide important insights for optimizing the production processes of Pu-erh tea and the application of microorganisms in other fermented foods.