Chemical pretreatment and saccharification of corncob for poly-γ-glutamic acid production by Bacillus subtilis SCP010-1

Lignocellulosic biomass is an important raw material which has been extensively studied for biotechnological applications, but research on its use for the production of γ-polyglutamic acid (γ-PGA) is rarely reported. The present study aimed to improve the release of xylose and glucose from corncob for γ-PGA production using the strain Bacillus subtilis SCP010–1, which could metabolize xylose. The effectiveness of the three chemical reagents NaOH, NH3 and H2O2 pretreatments was investigated by the response surface methodology (RSM). The results showed that maximum glucose and xylose yields of 11.8 ± 0.3 and 17.36 ± 0.6 g/L, respectively, as determined by phloroglucinol-acid and enzymatic methods, were obtained when using 0.986% of NaOH for 2.07 h. Then, the pretreatment solution was subject to further optimize conditions of enzymatic hydrolysis, and the content of glucose and xylose in the corncob hydrolysate reached respectively 15.3 ± 0.3 and 22.34 ± 0.17 g/L under synergism of hemicellulase and cellulase. Finally, the fermentation conditions for γ-PGA production by B. subtilis SCP010–1 were also optimized, and after adding supplemental nutrients to the corncob hydrolysate, a maximum γ-PGA production of 30.035 ± 0.49 g/L was achieved by fed batch fermentation with feeding corncob hydrolysate. Considering the cost of the materials used in this study, nearly 85% of reduction in cost could be achieved, hence indicating that this production plan offers good prospects for industrial production of γ-PGA. More importantly, this process allows the use of environmental-friendly biological resources.