Flavanol-anthocyanin adduct
From Infogalactic: the planetary knowledge core
Flavanol-anthocyanin adducts are formed during wine ageing through reactions between anthocyanins and tannins present in grape, with yeast metabolites such as acetaldehyde. Acetaldehyde-induced reactions yield ethyl-linked species such as malvidin glucoside-ethyl-catechin.[1][2]
This type of compound has a better color stability at pH 5.5 than normal anthocyanins. When the pH was increased from 2.2 to 5.5, the solution of the pigment became progressively more violet (λmax = 560 nm at pH 5.5), whereas similar solutions of the anthocyanin were almost colorless at pH 4.0.[3]
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