Discovering the corky bark of Eucalyptus suberea from anatomical and chemical perspectives – a case study

Abstract

This paper presents the first scientific investigation of the corky bark of Eucalyptus suberea (cork mallee). The study involved two trees with diameters of 23 cm (A) and 47 cm (B), collected from a plantation in Portugal. Anatomical analysis, performed by scanning electron microscopy, revealed the presence of cork cells'. The chemical characterization included summative chemical analysis, FTIR, GC-MS/FID for suberin composition and Py-GC-MS for lignin composition. E. suberea extractive-free barks A and B contained 29 % and 25 % suberin, 30 % and 37 % lignin, and 39 % and 38 % polysaccharides, respectively. The bark A exhibited a higher extractives content (49 %) than just 14 % for bark B. Dichloromethane extract from bark A was notably rich in alkanol ferulates. The main components of E. suberea A and B suberins were glycerol, with 15 % and 11 %, ω-hydroxyacids, with 45 % and 50 %, and α,ω-diacids, with 30 % and 17 %, representing a total of ca. 90 % and 78 % of E. suberea A and B suberins mass, respectively. Both suberins showed low contents of epoxides and vic-diols; also, both presented the particularity of having high contents of free acid groups, especially the suberin of bark B, suggesting a polyester structure with a smaller than usual degree of polymerization. E. suberea corky bark presents a lignin composition that differentiates from the cork G-lignins analyzed until now with a monomer composition exhibiting a GS character, with more G- (53–56 %) than S-units (34–37 %) with an S/G ratio between 0.64 and 0.66, for A and B lignins, respectively.