21.2 Tea and Tea-Like Products 957(21.6)I: (−)-epicatechin, R^1 ,R^2 =H
II: (−)-epicatechin-3-gallate, R = H, R^1 = 3,4,5-trihydroxybenzoyl
III: (−)-epigallocatechin, R = OH, R^1 =H
IV: (−)-epigallocatechin-3-gallate, R = OH, R^1 = 3,4,5-trihydroxybenzoyl
V–VIII: o-quinones of compounds I–IV
IX: theaflavin, R, R^1 =H
X: theaflavin gallate A, R = H, R^1 = 3,4,5-trihydroxybenzoyl
XI: theaflavin gallate B, R = 3,4,5-trihydroxybenzoyl, R^1 =H
XII: theaflavin digallate, R, R^1 = 3,4,5-trihydroxybenzoyl
XIII: bisflavanol A, R = R^1 = 3,4,5-trihydroxybenzoyl
XIV: bisflavanol B, R = 3,4,5-trihydroxybenzoyl, R^1 =H
XV: bisflavanol C, R = R^1 =H
XVI: epitheaflavic acid, R = H
XVII: 3-galloyl epitheaflavic acid, R = 3,4,5-trihydroxybenzoyl
XVIII: thearubigins (proanthocyanidin-type), R = H, OH; R^1 = H, 3,4,5-trihydroxybenzoyl
XIX: thearubigins (polymeric catechins of unknown structure)
(21.7)and an acidic environment. The undesired brown
color is obtained at higher pH’s. The astringent
character of teas is decreased by the formation
of complexes between phenolic compounds and
proteins. The firing step also affects the balance of
aroma substances. On the one hand there is a loss
of volatile compounds, on the other hand, at high
temperatures, an enhancement of the build-up of
typical aroma constituents occurs, e. g., as a result
of sugar-amino acid interactions.