Optimization of Xylanase Production from Some Agro-lignocellulosic Wastes by Aspergillus niger Via Solid State Fermentation

Abstract

Extracellular xylanase production by A. niger was studied under solid-state fermentation using six agricultural wastes individually (wheat bran, rice husk, corn cobs, rice straw, clover straw and wheat straw) as well as fifteen treatment represent different combinations of the above agro-lignocellulosic wastes. The best substrate was the combination of wheat bran and clover straw. The initial moisture content, additive carbon source, additive nitrogen source, initial pH of the culture, incubation temperature and inoculum size affected the production of xylanase. The optimal fermentation medium was at 80% of initial moisture and composed of 5 g WB+CS (1:1 w/w) supplemented with 1% (w/w) of xylan and 1% (w/w) of (NH4)3PO4 and inoculated by adding 1 ml of spore suspension containing 2x105spores/ml. Xylanase production reached a peak of 1294.15 IU/gdw after 7 days of incubation at 35 °C under SSF. The produced enzyme has maximum activity at 70 oC and pH 5.5. Addition of 10 mM FeSO4 and 5mM of KCl, CaCl2 and MnCl2 to the reaction mixture enhanced xylanase activity to 127.46, 118.86, 115.76 and 111.15%, respectively. A. niger xylanase showed superior heat and pH tolerance, it remained 86.47 and 76% of its activity after 60 min of incubation at 70 oC with and without 10 mM CaCl2.The enzyme showed more stability in a pH ranged from 4 to 5 retaining more than 75% of its original activity, therefore it may have significant applications in biofuel and paper industries.