Flavanyl-pyranoanthocyanins

A.2.4.2 Anthocyanin-Vinylflavanol Condensation Reactions Flavanyl-Pyranoanthocyanins... 

Mechanism of reaction. The mechanism proposed for the formation of flavanyl-pyranoanthocyanins (Francia-Aricha et al. 1997 Mateus et al. 2003a,b) (Fig. 9A.3g), is similar to that described above by Fulcrand et al. (1996) for the formation of hydroxyphenyl-pyranoanthocyanins (Sect. 9A.2.4.1 Fig. 9A.3f). 

Formation of pyranoanthocyanins is faster at lower pH values since the mechanism requires anthocyanins to be under the flavylium cation form and ketones to be in the enol form, both of which are favoured in acidic media. Formation of flavanyl-pyranoanthocyanins should be further facilitated in acidic media due to enhanced cleavage of the ethyl bridges. However, even at higher pH values, pyranoanthocyanins are expected to accumulate progressively in wines because of their stability. 

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