Analysis of lignin and proanthocyanidin polymers the most abundant polyphenols in the biosphere, heavily relies on chemical degradation methods. The most recent development of acid-catalysed degradations in the presence of cn nucleophilic thiol are presented: identification of novel monomeric units, determination of frequency and nature of monomer units and intermonomeric linkages, determination of polymer refit;ent in plant materials.
Depolymerization of proanthocyanidins in the presence of phloroglucinol or benzyl mercaptan nucleophiles was studied to develop a method for their quantitative determination. Degradation products were separated and quantified by either GC or HPLC and the reaction conditions optimized. The high depolymerization yields obtained with benzyl mercaptan make the method suitable for proanthocyanidin determination. The method is more specific and sensitive than the colorimetric methods classically used. It is particularly well suited for the analysis of samples containing either low amounts of proanthocyanidins or insoluble proanthocyanidins.
Analysis of lignin and proanthocyanidin polymers, the most abundant polyphenols in the biosphere, heavily relies on chemical degradation methods. The most recent developments of acid-catalyse degradations in the presence of a nucleophilic thiol are presented: identification of novel monomeric units, determination of frequency and nature of monomer units and intermonomeric linkages, determination of polymer content in plant materials.
Proanthocyanidins were analysed in the bark of several European conifer and broad-leaved tree species by thiolysis and gel permeation chromatography. They are largely procyanidins with varying proportions of catechin/epicatechin units and average degrees of polymerization ranging from 3 to 8. Some were not extracted by methanol-water and were directly analysed in the residue of extraction by thiolysis. These non-extractable proanthocyanidins represent up to 97% of the total proanthocyanidins in the outer bark exposed to rainwater. Their contribution to tree defence is discussed.
