Enhancing the quality of dark tea through fermentation with Aspergillus niger :Unveiling aroma and taste characteristics

Amidst the increasing demand for premium dark tea, the utilization of Aspergillus niger-inoculated fermentation has emerged as a potential solution to address the challenges associated with extended processing cycles and inconsistent quality. This study comprehensively investigated the efficacy and mechanisms of A. niger PW-2 inoculation in enhancing dark tea quality compared to spontaneous fermentation, using metabolomics, electronic tongue, molecular docking, and high-throughput sequencing. A. niger PW-2 shaped the fungal community within 7 days, degrading terpene glycosides and lactones while generating terpenoids and unsaturated fatty acids, which enriched the floral aroma of PW-2-inoculated fermentation dark tea (AF). Flavonoid degradation and reduced theaflavins/thearubigins levels in AF decreased astringency, while increased bitter dipeptides and isoflavonoids enhanced bitterness, and the accumulation of umami dipeptides and theabrownins improved umami taste perception of AF. Molecular docking identified key compounds responsible for astringency (kaempferol glycosides), bitterness (6″-caffeoylisoorientin, kaempferol 4′-glucoside 7-rhamnoside, dihydrodaidzein 7-O-glucuronide), and umami (3-O-p-trans-coumaroylalphitolic acid, dihydrodaidzein 7-O-glucuronide, 1-methoxyphaseollidin). Overall, A. niger PW-2 inoculation accelerates fermentation process and enhances flavor characteristics of dark tea, offering a promising approach for high-quality dark tea production.