Four proanthocyanidin fractions were obtained from Pinot blanc pomace. All yielded cyanidin on heating with concentrated acid, but yielded a variety of phenolics on heating with dilute acid. The proanthocyanidins isolated apparently were compounds of catechin and leucocyanidin-like flavans. These proanthocyanidins were present at lower levels of concentrations that catechins. One of the proanthocyanidin isolated from grape skins apparently was a diglucoside, but none of those isolated from grape seeds were glucosides.
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Joslyn et al. (1967) studied this question.