Dynamic changes, flavor contributions, and enzymatic transformation mechanisms of phenolic acids during black tea...

The characteristic flavor of black tea originates from the oxidative transformation of phenolic compounds during processing. Despite their low abundance, phenolic acids are important contributors to flavor quality; however, their roles and transformation pathways during black tea manufacture remain unclear. Here, untargeted and targeted metabolomics were used to characterize phenolic acid dynamics. Fermentation was identified as the critical stage, marked by the degradation of hydroxycinnamic acids and the accumulation of hydroxybenzoic acids, particularly gallic acid. Sensory evaluation suggested that cryptochlorogenic acid, neochlorogenic acid, and 5-O-caffeoylshikimic acid were major contributors to astringency and sourness. In vitro enzyme assays indicated that polyphenol oxidase and peroxidase could synergistically drive phenolic acid transformation. In addition to self-oxidation, phenolic acids potentially participated in catechin oxidation, forming putative aryl adducts. These findings provide new insights into the enzymatic mechanisms of phenolic acid transformation and their potential impact on black tea quality.