Processing-induced changes in sensory quality, anthocyanins and non-volatile metabolites of bud green tea from the purple-leaf cultivar 'Zijuan'.

We investigated how processing modulates bud green tea quality in the purple-leaf cultivar 'Zijuan' using sensory evaluation with targeted and untargeted metabolomics. Liquor color shifted from pale yellow-green to purplish yellow by final drying (JFT), while taste profiling indicated a fuller body and reduced bitterness. These changes paralleled the chemistry, with total polyphenols and pigments declining during heating, galloyl hydrolysis increasing gallic acid and implying reduced catechin galloylation, and several free amino acids peaking around fixation. Untargeted metabolomics identified fixation as a metabolic turning point, with KEGG enrichment of phenylalanine-flavonoid-anthocyanin pathways. Targeted profiling of anthocyanin and proanthocyanidin showed dominance of procyanidins and delphinidin and cyanidin series, with delphinidin conjugates stable, cyanidin declining, and total anthocyanin and proanthocyanidin lowest at JFT. Overall, fixation acts as a metabolic inflection point and drying consolidates quality, with reduced bitterness and color development associated with flavonoid-pathway rebalancing and selective anthocyanin and proanthocyanidin degradation.