Determination of proanthocyanidin–anthocyanin adducts in red wine and red wine inspired hemisynthesis of procyanidin analogs

Abstract

The chemical diversity of red wine is caused by the natural compounds that originate from grapes, and the further derivatives or adducts of the natural compounds that are formed during wine making and storage. Grapes are rich in natural pigments called anthocyanins, and in proanthocyanidins, which are the primary tannins of red wine. Both compound groups and their adducts have an impact on the valuable sensorial properties of red wine, such as colour and astringency. The oligomeric and polymeric proanthocyanidin–anthocyanin adducts pose an analytical challenge because there are several structural subgroups, and each subgroup consists of dozens of individual compounds. One consequence of this analytical challenge is that the studies about the properties and composition of proanthocyanidin–anthocyanin adducts in red wine have focused on the analysis of some individual and mainly dimeric model compounds. This might not accurately reflect the properties and functions of the compound groups as a whole.

A new analytical method based on liquid chromatography and tandem mass spectrometry was developed in this thesis for the analysis of proantocyanidin–anthocyanin adducts and other pigments in red wine. The method was utilized in the analysis of over 300 commercial red wines. The comprehensive wine set was used for studying how the composition of proanthocyanidin–anthocyanin adducts differs between wine types, how the age of the wines affects the composition of the adducts and how the oligomeric adducts contribute to the colour of red wines, for instance.

The chemical reactions occurring in red wine demonstrate how proantocyanidins and their constituting units are reactive in right conditions. This reactivity was utilized in the hemisynthesis of procyanidin analogs, which was inspired by the reactions taking place in red wine. The hypothesis was that the small structural differences in the synthetic procyanidin analogs in comparison to the natural procyanidins would have a positive effect on the important biological properties, such as interactions with proteins. Indeed, the protein precipitation capacity of procyanidin analogs was greatly improved in comparison to similar naturally occurring procyanidins, and other biological properties were affected as well.