MALDI-TOF and 13C NMR analysis of Tunisian Zizyphus jujuba root bark tannins

Matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry was used to examine the oligomer types and their distribution of jubjube (Zyziphus jujuba Mill.) root bark tannin extract. The flavonoid oligomers, up to hexamers, of lower degree of polymerization than that of commercial tannins, are very frequently covalently linked to carbohydrate monomers and dimers. The site of carbohydrate linkage to the flavonoid has been identified by 13C NMR spectroscopy. Fisetinidin, robinetinidin, catechin and gallocatechin flavonoid units are all present in this tannin, all entering to form mixed oligomers based on these four units. This forbids the classification of this extract as just a simple procyanidin, prorobinetinidin, profisetinidin or prodelphinidin.