초록
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 18.66g/l, NaCl 1.04g/l, speed of agitation 176rpm and cultivation time 34.08h. Under these conditions, the xylanase experimental yield (7.45U/ml) closely matched the yield predicted by the statistical model (7.23U/ml) with R<SUP>2</SUP>=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<SUP>o</SUP>C and at pH 8.0. The enzyme retained more 96% of its activity after 24h at pH ranges from 7.0 to 90.0. The enzyme preserved more 80% of its initial activity after 60min of pre-incubation from 30<SUP>o</SUP>C to 60<SUP>o</SUP>C. The main hydrolysis products yielded from corncob extracted xylan were xylobiose and xylotriose, suggesting the good potential of strain A21 in xylooligosaccharides production.