Analysis of carbohydrates in wood and pulps employing enzymatic hydrolysisand subsequent capillary zone electrophoresis

An efficient method for determining the carbohydrate composition of extract ive-free delignified wood and pulp is described here. The polysaccharides i n the sample are first hydrolyzed using a mixture of commercially available preparations of cellulase and hemicellulase. The reducing saccharides in t he hydrolysate thus obtained are subsequently derivatized with 4-aminobenzo ic acid ethyl ester and thereafter quantitated by capillary zone electropho resis (CZE) in an alkaline berate buffer with monitoring of the absorption at 306 nm. All reducing sugars (i.e., neutral monosaccharides and uronic ac ids) which occur as structural elements in the polysaccharides of wood and pulp can be quantitated in a single such analytical run, which can also det ermine the contents of 4-deoxy-beta-L-threo-hex-4-enopyranosyluronic acid ( HexA) residues present in pulps obtained from alkaline processes. CZE analy ses were performed using linear regression of standard curves over a concen tration range spanning approximately three orders of magnitude. Carbohydrat e constituents constituting approximately 0.1% of the dry mass of the sampl e could be quantitated. The overall precision of this analytical procedure involving enzymatic hydrolysis, derivatization and CZE - was good (RSD=2.2- 7.5%), especially considering the heterogeneity of the wood and pulp sample s. The total yield of carbohydrates (93-97%) obtained employing the procedu re developed here was consistently higher than that obtained upon applying the traditional procedure for carbohydrate analysis (85-93%) (involving aci d hydrolysis and gas chromatographic analysis) to the same pulps. The trisa ccharide HexA-xylobiose was the only HexA-containing saccharide detected us ing the conditions for enzymatic hydrolysis developed here (i.e., 30 h incu bation at pH 4 and 40 degrees C); whereas mixtures of HexA-xylobiose and He xA-xylotriose were obtained when the incubation was performed at pH 5 or 6. (C) 2000 Elsevier Science B.V. All rights reserved.