Solid-state fermentation of soybean and corn processing coproducts for potential feed improvement.

Two agro-industrial coproducts, soybean cotyledon fiber and distiller's dried grains with solubles (DDGS), were used as substrates to evaluate the effect of coculturing three different fungi, Aspergillus oryzae, Trichoderma reesei, and Phanerochaete chrysosporium, on enzyme production by solid-state fermentation (SSF). When soybean fiber was used as the substrate, a maximum xylanase activity of 757.4 IU/g and a cellulase activity of 3.2 IU/g were achieved with the inoculation and incubation of T. reesei and P. chrysosporium for 36 h, followed by A. oryzae for an additional 108 h. This inoculation scheme also resulted in the highest xylanase activity of 399.2 IU/g compared to other fungi combinations in the SSF of DDGS. A large-scale SSF by this fungus combination produced fermented products that had xylanase and cellulase activities of 35.9-57.0 and 0.4-1.2 IU/g, respectively. These products also had 3.5-15.1% lower fiber and 1.3-4.2% higher protein contents, suggesting a potential feed quality improvement.