Chemical composition and cellular structure of cork from Agonandra brasiliensis from the Brazilian Cerrado

摘要

Agonandra brasiliensis, ivory wood, is a tree species from the Brazilian cerrado with a bark featuring a thick cork layer. The present study aimed to describe the cellular features and chemical composition of this cork. The cork was investigated regarding cellular structure and biometry, as well as summative chemical composition. The results were compared with those of corks from Quercus suber, as a reference commercial cork, and Kielmeyera coriacea and Plathymenia reticulata, which are native Cerrado cork species. The periderm of A. brasiliensis develops continuously around the stem with a thick cork layer. The cork has the typical characteristics of cork tissues with a compact structure of prismatic cells, stacked base to base in the radial direction without intercellular spaces. Cell walls were heavily corrugated and growth rings were present with a distinction of earlycork and latecork cells. A. brasiliensis cork cells are larger (49.1 mu m prism height and 5.5 x 10(-5) cm(2) base area) than those from the reference Quercus suber cork, the number of cells per unit volume is smaller as well as the fraction of solid volume (7.6%), contributing to a lower density of cork. Chemically A. brasiliensis cork is characterized by a low suberin content of 5.6%, and a high lignin content of 45.5%, and includes 13.6% extractives. The ethanol-water extracts have low phenolic content and weak antioxidant activity. The cork of A. brasiliensis differs considerably from those of Q. suber, P. reticulata and K. coriacea, namely regarding its suberization level, which will impact the mechanical properties and limit the range of commercial applications, that should be directed towards insulation and low-density products.