Characterization of the mean degree of polymerization of proanthocyanidins in red wines using liquid chromatography-mass spectrometry (LC-MS)

An HPLC-MS method for the characterization of proanthocyanidins (PA) has been refined. Further application to red wines provided interesting conclusions about the composition of the flavanol fraction and PA extractability during winemaking. The yield in PA extraction increases with the length of the postfermentative maceration (PFM), as well as the mean degree of polymerization (mDP) of wine flavanols. In early winemaking events mostly monomers to trimers are extracted from grape solids, whereas PFM is required for the significant extraction of higher oligomers. Nevertheless, at the end of a regular process of elaboration the mDP is not very high and does not usually exceed a value of 2.3, dimers and trimers being the predominant flavanols in red wines. With regard to groups of compounds, gallocatechins and prodelphinidins (located in the skins) are extracted rapidly in the first stages of the winemaking. On the contrary, long postfermentative macerations are required for the extraction of galloyled derivatives from the seeds. PA extractability is also dependent on the grape variety used for winemaking. Thus, wines made with Graciano grapes were found to require a longer process of PFM than those made from Tempranillo grapes to obtain similar yields in the extraction of flavanols.