Ferulates and lignin structural composition in cork

15 páginas.-- 4 figuras.-- 4 tablas.-- 63 referenciasThe structure of lignin and suberin, and ferulic acid (FA) content in cork from Quercus suber L. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Corksap), and milled-cork lignins (MCL) from Cork and Corksap were isolated. Suberin composition was determined by GC-MS/FID, whereas the polymers structure in Cork, Corksap, and MCL was studied by Py-TMAH and 2D-HSQC-NMR. Suberin contained 94.4% of aliphatics and 3.2% of phenolics, with 90% of ω-hydroxyacids and α,ω-diacids. FA represented 2.7% of the suberin monomers, overwhelmingly esterified to the cork matrix. Py-TMAH revealed significant FA amounts in all samples, with about 3% and 6% in cork and cork lignins, respectively. Py-TMAH and 2D-HSQC-NMR demonstrated that cork lignin is a G-lignin (>96% G units), with a structure dominated by β-O-4′ alkyl-aryl ether linkages (80% and 77% of all linkages in MCL and MCLsap, respectively), followed by phenylcoumarans (18% and 20% in MCL and MCLsap, respectively), and smaller amounts of resinols (ca. 2%) and dibenzodioxocins (1%). HSQC also revealed that cork lignin is heavily acylated (ca. 50%) exclusively at the side-chain γ-position. Ferulates possibly have an important function in the chemical assembly of cork cell walls with a cross-linking role between suberin, lignin and carbohydrates.We acknowledge partial financial support from Instituto Politécnico de Lisboa, Portugal (Research Project IPL 19/2003) and base funding from Fundação para a Ciência e Tecnologia, Portugal (FCT research Unit 702) to Centro de Estudos Florestais (PEstOE/AGR/UI0239/2014). This study was also partially funded by the LIGNOCELL project (AGL2011-25379) from the Spanish MICINN (co-financed by FEDER funds). JR acknowledges the CSIC JAE-Doc contract of the program “Junta para la Ampliaciôn de Estudios” co-financed by the European Social Fund (ESF). We also thank Dr. Manuel Angulo (CITIUS, University of Seville) for performing the NMR analysesPeer reviewe