Determination of Molecular Structures of Condensed Tannins from Plant Tissues Using HPLC-UV Combined with Thiolysis and MALDI-TOF Mass Spectrometry

Abstract

Condensed tannins extracted from plant tissues are suitable substitutes for phenolic resins. Their molecular structure, which might influence their chemical reactivity, can be assessed by the use of both HPLC-UV after acid thiolysis and MALDI-TOF mass spectrometry. Thiolysis of plant extracts in acidic methanol with cysteamine hydrochloride results in the release of the monomeric units of the condensed tannin oligomers that can be further quantified by reversed-phase HPLC-UV by comparison with analytical standards. MALDI-TOF mass spectrometry using 2,5-dihydroxybenzoic acid as matrix and K+ as cationization agent highlights the molecular structural characteristics (e.g., monomeric unit sequence) of the tannin oligomers. The methodologies permit the estimation of the mean and the maximum (observable) degree of polymerization, the type of monomeric units and the presence of glycosylation and/or esterification of the tannin oligomers.