Xylanase production from Bacillus aerophilus KGJ2 and its application in xylooligosaccharides preparation

Xylanolytic enzyme was produced using a newly isolated Bacillus aerophilus KGJ2 and low cost lignocellulosic sources in solid state fermentation. Seven different agricultural residues (wheat bran, tea dust, saw dust, paper waste, cassava bagasse, rice straw and rice husk) and six nitrogen source namely yeast extract, beef extract, peptone, ammonium nitrate, ammonium sulphate, and ammonium chloride were examined for xylanase production. Upon initial screening, wheat bran and ammonium chloride were chosen as suitable carbon source and nitrogen source respectively. Plackett–Burman fractional factorial design was employed to screen the important process variables affecting enzyme production. Substrate concentration, nitrogen source, moisture content and MgSO4·7H2O were identified as statistically significant variables. Subsequently Box–Behnken method was used to optimize the process conditions to achieve maximum xylanase yield. Under optimized conditions xylanase yield was 45.9 U/gds. Best xylanase activity was obtained at 70 °C and pH 4.0. It retained more than 90% activity after incubation at 80–90 °C for 60 min. The hydrolytic efficiency of xylanase on xylan was examined and xylobiose, xylotriose and xylotetrose were obtained as hydrolytic products.