Integration of intelligent sensory evaluation, metabolomics, quantification, and enzyme activity analysis to elucidate the influence of first-drying methods on the flavor formation of congou black tea and its underlying mechanism

First-drying is a crucial step in black tea processing. Herein, the influence of different first-drying methods on black tea flavor formation was investigated, including box-hot air first-drying (BFD), roller first-drying, and microwave first-drying. Electronic tongue and color difference revealed distinct taste profiles (especially in bitter, astringency, sweet, umami) and liquor colors among three groups. Quantification and metabolomics analysis revealed that tea pigments (theaflavins, thearubigins), catechins, and other 34 metabolites including dimeric/trimeric catechins, amino acids and derivatives, flavonols and flavonol/flavone glycosides, phenolic acids, etc., were key differential components. The evolution of key metabolites, polyphenol oxidase (PPO) and peroxidase (POD) activities were tracked during drying. BFD exhibited significantly slower enzyme inactivation rate. Multiple conversions were possibly involved in drying, including catechins conversion (polymerization, degalloylation, epimerization), hydrolysis of flavonol- O -glycosides and phenolic acid esters, flavone- C -glycosides synthesis, etc., driven by the remaining PPO and POD activities and heat. Moreover, validation batch further verified the result.