Expression and characterization of β‐1,3‐1,4‐glucanase of Aspergillus usamii in Escherichia coli and its application in sourdough bread making

Abstract A β‐1,3‐1,4‐glucanase gene ( Auglu 12A) from Aspergillus usamii was successfully expressed in Escherichia coli BL21(DE3). The recombinant enzyme, re Au glu12A was efficiently purified using the one‐step nickel‐nitrilotriacetic acid affinity chromatography. The specific activity of re Au glu12A was 694.8 U/mg, with an optimal temperature of 55°C and pH of 5.0. The re Au glu12A exhibited stability at temperatures up to 60°C and within the pH range of 4.0–5.5. The re Au glu12A hydrolytic activity was increased in the presence of metal ions, especially K + and Na + , whereas it exhibited a K m and V max of 8.35 mg/mL and 1254.02 µmol/min/mg, respectively, toward barley β‐glucan at pH 5.0 and 55°C. The addition of re Au glu12A significantly increased the specific volume ( p < 0.05) and reduced crumb firmness and chewiness ( p < 0.05) of wheat–barley sourdough bread during a 7‐day storage period compared to the control. Overall, the quality of wheat–barley sourdough bread was improved after incorporation of re Au glu12A (especially at 3000 U/300 g). These changes were attributed to the synergistic effect of acidification by sourdough and its metabolites which provided a conducive environment for the optimal action of re Au glu12A in the degradation of β‐glucans of barley flour in sourdough. This stabilized the dough structure, thereby enhancing the quality, texture, and shelf life of the bread. These findings suggest that re Au glu12A holds promise as a candidate for β‐glucanase application in the baking industry.