Effect of pH on the solubilization of brewers' spent grain by microbial carbohydrases and proteases.

The potential for enzymatic solubilization of brewers' spent grain by carbohydrases and proteases was examined over a broad pH range (pH 3.2-11.2). Enzymes from Trichoderma (Depol 686) were most efficient at a lower pH, while enzymes from the Humicola preparation (Depol 740) were the best performer over the whole range. Profiling of key glycoside hydrolase, esterase and protease activities across the pH range demonstrated that solubilization of spent grain by the Trichoderma enzymes corresponded to the range of maximum activities. This was not the case with the Humicola enzymes, where maximum solubilization of the substrate occurred at pH 9.1, at which pH the determined activities were low. Protease activity in Depol 740 was associated with a high solubilization, but inhibition of proteolytic activity resulted in only a 5% decrease in spent grain solubilization. These results suggest that while enzymes can be used to exploit agro-industrials byproduct, the use of high pH increases the extent of hydrolysis and an unidentified factor produced by Humicola improves the enzyme-catalyzed solubilization of lignocellulosic material.