Characterization of Pinus brutia bark tannin by MALDI-TOF MS and C-13 NMR

Abstract

The structures of condensed tannin from Pinus brutia bark were characterized by means of GC-MS, solid and liquid state C-13 NMR and MALDI-TOF MS analyses. The results indicated that the monomeric units building up the condensed tannin of brutia pine bark are mainly composed of catechin/epicatechin, gallocatechin/epigallocatechin units accompanied by possibly tri- or tetra hydroxyl-flavanols. Some oligomers appear to present p-hydroxy- or 3,4-dihydroxy benzoic acid residues or glucose at their terminal unit. Apart from oligomers, monomeric flavanoids were also present in the brutia bark extract. Taxifolin was especially found in appreciable amounts. Additionally, in this tannin procyanidin oligomers predominated while prodelphinidin units were present to a lesser extent. The NMR results showed that the oligomers in brutia pine bark tannin Exhibit 2,3-cis stereochemistry and C4-C6 bonds with a noticeable portion of C4-C8 interflavonoid links being present. The MALDI-TOF MS showed a series of peaks corresponding to flavonoid hexamers of the condensed tannin (1750 Da). (C) 2013 Elsevier B.V. All rights reserved.