Selective binding of potassium and calcium ions to novel cyclic proanthocyanidins in wine by HPLC-HRMS.

Rationale: Cyclic B-type (referred also as crown) proanthocyanidins were recently identified in wines. An HPLC-HRMS/MS method was applied to study the binding of cyclic and non-cyclic PAC to potassium and calcium ions, which affect the chemico-physical stability of wines. Different binding affinities suggest that cyclic and non-cyclic analogues, despite the equal number of monomer units, influence the colloidal stability of wine and are related to the grape variety or winemaking conditions.

Methods: Nineteen red and white wines were analysed by HPLC high resolution tandem mass spectrometry with positive electrospray ionization to investigate the distribution of novel cyclic proanthocyanidins and their calcium, potassium and sodium adducts. Principal Component Analysis was used to study the distribution of the wines and the relationships among proanthocyanidins with and without cation complexes.

Results: A dependence on specific isomers (and conformations) was found for the non-cyclic procyanidin (PC) trimer whereas the cyclic tetrameric PAC were shown to bind better to potassium than their non-cyclic analogues. The binding to these metals appeared to be influenced not only be the number of monomer units but also by the conformation assumed by the molecules. Statistical analysis evidenced that the adducts distribution in different wines is less influenced by the grape variety used for winemaking than their associated [M+H] species studied earlier.

Conclusions: Wines from 19 grape varieties were investigated in order to identify potassium and calcium complexes of non- and cyclic B-type proanthocyanidins that were recently discovered. The results showed a dependence of the distribution of metal complexes according to the cyclic or non cyclic geometry of proanthocyanidins. The multivariate analysis of the mass spectrometric results showed a relationship with the grape variety, however not so straightforward as evidenced for the non-complexed species.