Extraction of acetylated glucuronoxylans and glucomannans from Okoume (Aucoumea klaineana Pierre) sapwood and heartwood by steam explosion

Abstract

Aucoumea klaineana Pierre (okoume) is a tropical hardwood of industrial importance, used for veneers and plywood production. Various conditions of Steam Explosion (SE) treatment (temperature, duration, pH) have been applied on okoume co-products, sapwood (SW) and heatwood (HW) for the extraction of polymeric hemicelluloses. Conventional extractions with alkali or dimethyl sulfoxide (DMSO) were also performed from delignified SW and HW for comparison. The hemicelluloses extracts have been characterized by HSQC-NMR, FTIR, size exclusion chromatography. The acetyl contents have been determined by chromatography after saponification and from HSQC spectra. Using basic impregnation prior to SE (NaOH-SE), high molecular mass glucuronoxylans (GX, Mw = 65–100 KDa) were recovered in 3–6 % % yields. A neutral impregnation (H2O-SE) produced O2 and/or O3 acetylated GX and glucomannans (GM), preserving the acetyl moieties in a greater extent compared to the mild DMSO extraction (% Ac ≈ 6.6–8.4 % and 1.0–4.1 % w/w respectively). This study provides insights on the composition of SW and HW okoume with a view to further innovative processing and valorization including the preparation of films with advanced properties for food packaging.