Optimization of Cellulase Production by Aspergillus niger ITV 02 from Sweet Sorghum Bagasse in Submerged Culture Using a Box–Behnken Design

Abstract

The objective of this study was to evaluate the effects of nitrogen and carbon source on cellulase activity of Aspergillus niger ITV 02. The results obtained showed that nitrogen had an influence on the increase in cellulase activity by A. niger ITV 02 during submerged fermentation. Optimal concentrations obtained from nitrogen sources, using a Box–Behnken design were 0.9 g/L urea, 2.4 g/L ammonium sulfate and 1.5 g/L yeast extract, obtaining endoglucanase and β-glucosidase specific activities of 24.63 U/mg and 72.66 U/mg, respectively, at 50 h of fermentation. Subsequently, the effect of three carbon sources was evaluated: carboxymethylcellulose, delignified sweet sorghum bagasse (DSSB) and sweet sorghum bagasse cellulose (SSBC). Maximum cellulase specific activity was obtained when using DSSB, increasing endoglucanase activity fivefold and β-glucosidase activity 1.25-fold (126.72 and 85 U/mg) respectively. SSBC hydrolysis using enzymatic extract produced 18 g/L reducing sugars, equivalent to a 25% residue conversion. These results showed that it is possible to obtain an extract with cellulase activity from A. niger ITV 02 to be used in SSBC hydrolysis using low-cost substrates such as DSSB, which would contribute to a reduction in second-generation ethanol process production costs and an increase in the availability of enzymes for this use.