A study of variability of suberin composition in cork from Quercus suber L. using thermally assisted transmethylation GC-MS

The chemical composition of suberin in cork from Quercus suber L. was determined on virgin and reproduction cork from different sites and trees in Portugal. Extractive-free samples were analyzed by pyrolysis-gas chromatography/mass spectrometry in the presence of tetramethylammonium hydroxide (TMAH), which provides in situ hydrolysis and (trans)methylation of hydroxyl and carboxyl groups of the suberin monomers. The average chemical monomeric composition of suberin on virgin and reproduction cork is, respectively, alkanoic acids 5.1, 3.3%; a,w-diacids 11.2, 10.1%; w-hydroxyacids 45.0, 48.1%; alkanols 1.9, 1.8%; 9,10-epoxy-18 hydroxyoctadecanoic acid 5.9, 5.8%; 9,10-epoxyoctadecanodioic acid 4.8, 3.6%; 9,10,18-trihydroxyoctadecanoic acid 7.5, 10.4%; 9,10-dihydroxyoctadecanedioic 6.1, 6.8%; ferulic acid 5.8, 4.5% and glycerol 4.3, 4.3%. In general, larger variability was found for the suberin monomers in virgin cork. Total content of w-hydroxyacids or of C18 or C22 compounds is however similar for all samples.