| Co-products from soybean and corn processing were used as substrates for both solid-state fermentation (SSF) and submerged fermentation (SmF) to enrich their values as animal feed. In the first study, we found synergistic effect among the three fungi, Aspergillus oryzae, Trichoderma reesei, and Phanerochaete chrysosporium, when they were inoculated in the soybean cotyledon fiber and distiller's dried grains with soluble (DDGS) in SSF. The inoculation sequence of different fungi was identified as an important factor to allow the best interaction among the fungi to achive vigorous growth and high enzyme production. Combination of fungi with the inoculation of T. reesei and P. chrysosporium for 36 hours, followed by A. oryzae for additional 108 hours was shown to be the best for both soybean cotyledon fiber and DDGS SSF. Large scale SSF with the same inoculation sequence of fungi was conducted and the fermented materials had 3.5--15.1% lower fiber and 1.3--4.2% higher protein content after SSF, demonstrating the potential for non-ruminant feed improvement. In the second study, arachidonic acid (ARA) and eicosapentaenoic acid (EPA) were produced by Pythium irregulare fungus using soybean cotyledon fiber and soy skim from aqueous soybean processing as substrates in different fermentation systems. Parameters such as moisture content, substrate glucose addition, incubation time, and vegetable oil supplementation were found to be crucial in SSF of soybean fiber, which is to be used as animal feed with enriched long chain polyunsaturated fatty acids (PUFA). Soybean fiber with 8% (dwb) glucose supplementation for 7-day SSF produced 1.3 mg of ARA and 1.6 mg of EPA in one gram of dried substrate. When soy skim was used as substrate for SmF, total ARA yield of 125.7 mg/L and EPA yield of 92.4 mg/L were achieved with the supplementation of 7% (w/v) soybean oil. This study demonstrated that the values of soybean fiber and soy skim could be enhanced through the long chain PUFA production by fermentations. |
