Enzymatic solubilization of hemicelluloses in industrial softwood kraft pulps

Industrial softwood kraft pulps produced by different methods were studied with respect to chemical composition and enzymatic accessibility. The main differences in the carbohydrate compositions of the pulps were in xylose and arabinose contents. A moderate cooking and oxygen delignification lead to pulps with a relatively higher content of low-arabinose substituted xylan than the extended cooking. However, the xylan in extended cooking pulps was more accessible to a xylanase isolated from Trichoderma reesei. The ratio of arabinose to xylose was equal in the hydrolysates of all xylanase treated pulps although the original amount of arabinose in pulps varied considerably. The xylanase was more effective than the mannanase of T reesei in solubilizing the corresponding carbohydrates, probably due to the more accessible location of xylan on the layers of the fibre. The decreased kappa number did not render the hemicelluloses more accessible to enzymatic action, and the degree of hydrolysis was related to the original hemicellulose content of the pulps.