The physiochemical characteristics and metabolic components of Paeonia ostii petal tea produced through Eurotium cristatum-mediated liquid fermentation

Fermentation can change tea flavour. This study aimed to improve the quality of tree peony flower tea through fermentation and investigate the underlying metabolomic changes. <i>Eurotium cristatum</i> were identified from three commercial Fu brick teas and ten strains were subsequently used for fermentation to produce instant peony dark tea (IPDT). It found that fermentation significantly improved the quality of IPDT by reducing astringency, improving the taste, and enhancing the antioxidant and antibacterial activity. Moreover, total sugar content and free amino acids content were reduced in IPDT, while total polyphenols and total flavonoids content were increased. A total of 84 metabolites were identified, which were mainly enriched in carbon metabolism and amino acid metabolism. The improvement of tea flavour after fermentation was clearly explained through "metabolic pathways - metabolic substance concentration - sensory evaluation" model. This study provides technical guidance for IPDT production and enhances comprehensive utilization of peony petals.