Chemical and cellular features of virgin and reproduction cork from Quercus variabilis

Abstract

Quercus variabilis (Chinese cork oak) has a substantial cork in the periderm that regenerates if removed, allowing a potential sustainable production. Samples of virgin and reproduction cork of Q. variabilis from China were characterized and compared with Q. suber cork. Virgin and reproduction cork are chemically very similar: on average 0.9% ash, 9.2% extractives, 37.8% suberin, and 28.5% lignin. The suberin composition of Q. variabilis cork is reported for the first time. It is composed mostly by saturated ω-hydroxyacids and substituted ω-hydroxyacids, including mainly 22-hydroxydocosanoic acid (20–23% of the total compounds) and 18-hydroxy-9-octadecenoic acid (17–22%). Comparison with Q. suber cork shows differences, stressing that suberin composition is species specific. The lipophilic extractives include mainly triterpenes (48.6–56.9%) especially friedelin and betulinic acid.Q. variabilis cork has the typical cellular characteristics of cork tissues with radially aligned cells without intercellular voids. Cell wall undulations were conspicuous, especially in virgin cork.Q. variabilis cork may be a complementary raw-material to Q. suber cork for agglomerated products. Despite similarities with the commercial cork, Q. variabilis cork has differences that impact unfavourably on properties e.g. higher density and compressive strength.