Production of β‐glucosidase by Aspergillus niger CDBB‐H‐175 on submerged fermentation

Abstract The production of high‐activity β‐glucosidase at low cost is essential to increase the efficiency of cellulose hydrolysis, necessary for the economically feasible production of biofuels from the conversion of renewable lignocellulosic resources, specifically agricultural waste. In this work, the Aspergillus niger CDBB‐H‐175 strain was used for the production of extracellular β‐glucosidase. In the first stage of this work, the production of β‐glucosidase was carried out in a shake flask, using different carbon sources in order to evaluate the effect of the substrate on enzyme activity; in this way, it was determined that the best substrate is maltose, obtaining 2954 U/ml of β‐glucosidase activity at 31 days of culture. In the second stage, a laboratory‐scale study was done using two discontinuous bioreactor systems for submerged fermentation, stirred tank and airlift, using maltose, sucrose, and glucose as a carbon source. The results showed that β‐glucosidase with the highest enzymatic activity (3122 U/ml at 192 h of fermentation) was produced at uncontrolled pH conditions in an airlift bioreactor with maltose. In a third stage, using an airlift bioreactor with maltose, an orthogonal experimental design L 4 with three factors was applied: pH, aeration, and maltose concentration. The aeration was of utmost importance to guarantee a better enzymatic expression, and acidification of the culture medium during the fermentation process was another necessary condition for a greater enzymatic production.