Evaluating fungal co-production of cellulase and xylanase enzymes at shake-flask scale using distillers dried grains with solubles (DDGS) and its validation in benchtop fermenters

Most of the corn ethanol plants use dry-mill process and generates large volume of distillers dried grains with solubles (DDGS) as the co-product in addition to ethanol and carbon dioxide. The DDGS is a promising feedstock for fermentation industry due to rich content of cellulose and xylan. Thus, the goal of this study was to optimize production of cellulase and xylanase enzymes by Trichoderma reesei (NRRL 6156) using DDGS as the carbon source at shake-flask scale and validate the shake-flask results at benchtop fermenters. The dilute-acid pretreated DDGS media containing varied levels of DDGS, yeast extract, and peptone were examined for maximal enzyme production at shake-flask at 30oC, initial pH of 5.0 and 180 rpm with 3% (v/v) inoculum size using the Box-Behnken response surface methodology. According to the analyses of results, co-production of xylanase and cellulase enzymes was not achieved in the same medium; higher solid load of DDGS favored cellulase enzyme only while lower solid load induced the xylanase enzyme. Maximal xylanase of 18.5 IU/mL was predicted with 5% DDGS load, 0.1 g/L yeast extract, and 2 g/L peptone, while maximal cellulase of 1.1 IU/mL was predicted with 20% DDGS load, 1 g/L yeast extract, and 0.5 g/L peptone. Of the two developed models obtained from shake-flasks, xylanase model predicted successfully the fermenter results with 1.5 L working volume compared to cellulase model, which needs further refinement.