Structural features of macromolecular components of cork from <i>Quercus suber</i> L.
Diana G. Branco, Joana R. Campos, Luís Cabrita, Dmitry V. Evtuguin
Abstract
Abstract The structural features of macromolecular components of cork (suberin, lignin, cellulose and hemicelluloses) from Quercus suber L. used for the production of stoppers were assessed after their isolation and purification. Suberin is the major component of cork (ca. 44%) and is constituted mainly by hydroxy fatty acids (C 14 –C 26 ). Cork lignin was found to be highly condensed (16.2%) and revealed a syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) ratio of 26:71:3 with predominant β- O -4′ (0.38%), β-5′, β-β and tetrahydrofuran (THF) type (totally ca. 27%) structures. Cork lignin also has a remarkable amount of ferulic acid structures, which are considered the binding point between lignin and suberin. The cellulose of cork cells (17.2%) is a typical cellulose I polymorph with a degree of crystallinity (DC) of 70.3% and an average crystallite width of 3.5 nm. The major hemicellulose of cork is glucuronoxylan (near 6.0%) possessing a molar Xyl p :MeGlc p A ratio of 14:1.