Effect of Natural and Pretreated Soybean Hulls on Enzyme Production by Trichoderma reesei

The enzyme induction utility of soybean hulls (SBH), consisting in excess of 50 wt% non-starch polysaccharides (NSP) cellulose, hemicellulose, and pectin, was studied through cultivation of the carbohydrase-producing fungus Trichoderma reesei Rut C-30. Shake flask systems of T. reesei were grown in a medium consisting of defatted soybean flour as a nitrogen source and SBH, some of which were untreated and others pretreated by liquid hot water, alkaline, and supercritical carbon dioxide, as carbon source. Cellulase, xylanase, and polygalacturonase activities were measured for the systems, and the natural hull systems were found to yield optimum enzyme production. Controlled batch fermentation experiments were carried out to compare enzyme production resulting from media with Avicel(A (R)) (FMC BioPolymer, Philadelphia, PA, USA) versus natural SBH with and without soybean flour as the nitrogen source. Soybean hull fermentations were also performed at several pH levels to observe the effects on enzyme production. Soybean hulls induced comparable levels of cellulase, and higher levels of xylanase and polygalacturonase, than Avicel(A (R)). With SBH, cellulase and xylanase production were enhanced at higher pH levels (6.0), and polygalacturonase was enhanced at lower pH levels (4.0-4.5). Enzyme production was largely unaffected by the presence of soybean flour as the nitrogen source.