The chemistry of Kielmeyera coriacea outer bark: a potential source for cork

Abstract

Cork is a material with a wide array of properties that make it uniquely suitable for many technological applications. All industrial cork comes from a single tree species, the cork-oak (Quercus suber L.), which is limited to the western Mediterranean region. A number of other trees and shrubs with “corky barks” are found in savannah-type ecosystems, namely in the Brazilian “Cerrado”, of which Kielmeyera coriacea Mart. and Zucc. (Pau-santo) is a conspicuous example. In this work, the chemical composition of K. coriacea outer bark as well as its extractives and suberin composition were analysed from the perspective of its potential use as an industrial cork source. K. coriacea outer bark showed a fairly high extractives content, ~15–20 %, with a significant proportion (6–10 %) of non-polar compounds, including very long chain (>C₂₈) fatty acids (28 % of the dichloromethane extract) and xanthones (19 %). The suberin content varied from 17 to 30 %, total lignin from 44 to 55 % and the polysaccharides from 11 to 17 %, showing less suberin and polysaccharides and more lignin than the reference Q. suber cork. K. coriacea cork suberin composition was dominated by C₁₈ mid-chain substituted ω-hydroxyacids and α,ω-diacids, with a noticeable absence of saturated chain monomers. Taking into account its cork content together with its cellular structure and chemical composition, K. coriacea outer bark is a potential source for cork. Although it might not be appropriate for solid cork products, it can be used to produce granulated cork for composite materials, or as a source of suberin-derived bio-based chemicals.