Insights into major pigment accumulation and (non)enzymatic degradations and conjugations to characterized flavors during intelligent black tea processing

Intelligently processed black teas (BT) possess premium quality but there is a lack in comprehensive understanding of flavor formation mechanism. In this study, the accumulation of carotenoids, flavonoids, and Maillard products and (non)enzymatic degradations and conjugations to characterized flavors were comprehensively studied. Significant decrease was observed that flava-3-ols were heavily oxidised from > 240 mg·g^-1 in fresh leaves (FL) to < 30 mg·g^-1, while other 21 flavonoids decreased by < 30% in BT, accompanied by a sweet aftertaste. Carotenes and xanthophylls, significantly accumulated during withering compared to FL (from 641 ± 39.7 μg·g^-1 to 728 ± 44.9 μg·g^-1) but decreased in BT. Strong correlations were confirmed between the 218 primary metabolites, carotenoids, and flavonoids, and their contributions to BT sweet tastes were elucidated. Furthermore, 45 floral/sweet volatiles with VIP > 1 originating from carotenoids, lipids, and amino acids were screened. An integrated illustration of pigments thermal- and enzymatic-dominated contributions to BT flavour was comprehensively conducted.