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The present study concerns the recovery of proteins from soybean hulls, mainly as oligopeptides, and the production of ethanol from the remaining lignocellulosic fraction. These goals were achieved using the following steps: hydrolysis of the soybean hulls by endoprotease Novo-ProD®, acid hydrolysis of the lignocellulosic residue to remove hemicellulose, hydrolysis of cellulose by cellulolytic enzymes (Accellerase 1500®), and alcoholic fermentation of the saccharified liquor. The proteolysis of the soybean hulls resulted in recovery of around 60% of the proteins as small peptides (86% with molar mass less than 6.5 kDa). The acid pretreatment removed more than 60% of the hemicelluloses, allowing conversion of around 55% of the cellulose to glucose in the enzymatic hydrolysis. In the fermentation with Saccharomyces cerevisiae, a yield of around 90% was achieved, relative to the theoretical yield, representing an ethanol productivity of around 0.20 g/L/h for the integrated process. The results of this work indicate that soybean hulls might be a promising feedstock for the production of cellulosic ethanol and a high-value protein hydrolysate composed mainly of low molecular weight oligopeptides. |
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