Production of Xylan-Degrading Enzymes by Thermophilic Fungi, Aspergillus fumigatus and Humicola lanuginosa
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Thermophilic fungi, Aspergillus fumigatus as a β-xylosidase producer and Humicola lanuginosa as a xylanase producer, were selected as potent producers of thermophilic enzymes. In solid-state culture on wheat bran, the optimum culture conditions for β-xylosidase formation by A. funigatus were incubation at 40℃ with an initial moisture content of 54%, while for xylanase formation by H. lanuginosa, 45℃ with an initial moisture content of 65%. A small addition of crude xylan to the wheat bran medium increased the enzyme about 2-fold. The optimum reaction temperature for both enzymes was 65℃. The optimum reaction pH for β-xylosidase was between 4.5 and 5.5,and for xylanase, between 5.0 and 6.0. Both enzymes were thermo- and pH- stable : β-xylosidase activity was unchanged after heating at 60℃ for 15 min and after standing at 4℃ for 24 h in the range of pH 2-12; xylanase was stable at 65℃ and at pH between 4 and 12. The enzymes from A. fumigatus hydrolysed xylan mainly to xylose, whereas those from H. lanuginosa produced xylooligosaccharides from xylan. Crude xylan was hydrolysed at 55℃ for 20 h with the mixtuer of β-xylosidase and xylanase, and the results were compared those of hydrolysis by 0.8 N H_2SO_4 at 120℃ for 15 min. In the both cases, a similar final amount of xylose was produced, 14 g of xylose from 25 g of xylan.