Alkaline xylanases from Bacillus mojavensis A21: production and generation of xylooligosaccharides

Medium composition and culture conditions for the xylanases production by Bacillus mojavensis A21 were optimized using two statistical methods: Plackett-Burman design applied to find the key ingredients and conditions for the best yield of enzyme production and Box-Behnken design used to optimize the value of the four significant variables: barley bran, NaCl, agitation, and cultivation time. The optimal conditions for higher production of xylanases were barley bran 18.66 g/l, NaCl 1.04 g/l, speed of agitation 176 rpm and cultivation time 34.08 h. Under these conditions, the xylanase experimental yield (7.45 U/ml) closely matched the yield predicted by the statistical model (7.23 U/ml) with R² = 0.98. The medium optimization resulted in a 6.83-fold increase in xylanase production compared to that of the initial medium. Best xylanase activity was observed at the temperature of 50 °C and at pH 8.0. The enzyme retained more 96% of its activity after 24 h at pH ranges from 7.0 to 90.0. The enzyme preserved more 80% of its initial activity after 60 min of pre-incubation from 30 °C to 60 °C. The main hydrolysis products yielded from corncob extracted xylan were xylobiose and xylotriose, suggesting the good potential of strain A21 in xylooligosaccharides production.