ISOLASI DAN KARAKTERISASI XILANASE JAMUR TANAH SEBAGAI AGENSIA PEMUTIH BUBUR KERTAS

Utilizing of chlorine-based chemicals in pulp bleaching process causes environmental pollution. Utilization of biological agents, such as enzymes for bleaching process is a wise measure to reduce the pollution. One of the enzymes that play an important role in pulp bleaching process is xylanase. Xylanase facilitate bleaching by cleaves xylan that associated with lignin to release the lignin. The aims of this study are isolation and selection of soil fungus which have xylanolytic activity, identification selected isolate, optimation of xylanase production and its characterization. Isolation soil fungus from soil around the timber area and sawdust. The selection xylanolytic soil fungi based on the qualitative activity on solid medium and quantitave activity analyzing in liquid medium. Furthermore, selected fungi was identified based on the macroscopic and microscopic characteristics. Optimation of xylanase production included inoculums and xylan concentration, pH of medium and incubation time. Purification of xylanase was fractionated by ammonium sulfate precipitation and followed by gel filtration on sephadex G-75. Characterization of purified xylanase include molecular weight, investigate the effect of pH and temperature to their activity and measure of kinetic parameter (Michaelis constant (Km) and maximum velocity (vmax)). The result on the isolation step was obtained 108 fungal strain from soil. Of 108 isolates, 92 isolates were found positive for xylanase production which showed zone of hydrolysis on xylan-agar medium. Among these, 8 isolates were further selected for xylanase production by growing in liquid medium. The selection step resulted TKM-24 isolate as a selected strain which had highest xylanase activity (287,04 U/ml) and specific activity (3089,57 U/mg). TKM-24 isolate was identified as Aspergillus tamarii. Optimation of xylanase production was achieved using inoculums concentration 1 % (v/v), xylan concentration 1% (w/v), pH 5 and incubation time for 5 days. The specific activity increased after fractionation by ammonium sulfate and gel filtration chromathography, which achieved 23140,97 U/mg and 75671,88 U/mg, respectively. The molecular weight of the Aspergillus tamarii TKM-24 xylanase was estimated to be 25 kDa, showed optimal activity at 60 o C and pH 6. The Km and vmax were 24,4 mg/ml and 1520 µmol/ml/min for oat spelt xylan