Enzymatic prebleaching of sulphite pulps

The ability of a crude enzyme preparation of Aureobasidium pullulans containing xylanase [61 units (U)/ml] and xylosidase (3 U/ml) activity to remove pentosans from unbleached sulphite pulps was investigated. Greater amounts of pentosans and reducing sugars were released from the pulp when the enzyme dosages and incubation times were increased. A combination of enzyme hydrolysis and alkali extraction resulted in a greater removal of pentosans than using the enzyme preparation alone. By treatment with a xylanase loading of 450 U/g pulp for 24 h followed by alkaline extraction, 35% of the pentosans were removed. The kappa number decreased up to 30% whereas viscosity was only slightly affected by these treatments. Enzymatic hydrolysis released mainly xylose whereas xylobiose was the main product liberated by alkaline extraction. Scanning electron micrographs indicated improved fibrillation and flexibility of the fibre structure by enzyme treatment.