The Effects of Dilution, Aeration, and Agitation on Fungal Cellulase and Xylanase Production in the Fermentation Media Based on Distillers Dried Grains with Solubles Using Stirred Tank Bioreactors

Fungal cellulases and xylanases are commonly used for the biological hydrolysis of lignocellulosic biomass into simpler sugars, which can then be converted into various value-added products like bioethanol. However, these enzymes may be costly upon production strategy. Therefore, the enzyme production process should be more efficient by utilizing economical and highly fibrous feedstocks and other nutrients. Distillers dried grains with solubles (DDGS) is a coproduct of corn ethanol generation and can be considered an appropriate feedstock. Regarding the widely used submerged fungal enzyme production process, low activity is the most prominent challenge. Therefore, this study is undertaken to improve further the submerged fungal fermentation process to lead to higher fungal cellulases and xylanases. Dilute acid-hydrolyzed DDGS medium with solid DDGS particles (i.e., mostly cellulosic fraction) was used at varying dilutions to evaluate the effect of fermentation system parameters on enzyme productions in 2-L bench-top bioreactors by Aspergillus niger (NRRL 330). Namely, the effects of aeration and agitation were explored for each dilution factor for both cellulase and xylanase productions. A sharp increase in cellulase and xylanase was observed with higher agitation and aeration rates. The highest cellulase activity (0.76 IU/mL) was obtained on Day 7 when low dilution (2X) and higher agitation (500 rpm) and aeration rates (1 vvm) were used. On Day 7, the xylanase activity was 28.10 IU/mL implying simultaneous production of both enzymes. A higher xylanase activity of 29.04 IU/mL was achieved at the same reactor conditions on day 8 of fermentation. In conclusion, this study confirms that dilution, aeration, and agitation rates enhance enzyme production in the early phases of fungal fermentation. This study is certainly a step forward for the production of fungal cellulase and xylanase enzymes using DDGS as feedstock.