Enzyme characterization for hydrolysis of AFEX and liquid hot-water pretreated distillers' grains and their conversion to ethanol

Dried distillers' grains with solubles (DDGS), a co-product of corn ethanol production, was investigated as a feedstock for additional ethanol production. DDGS was pretreated with liquid hot-water (LHW) and ammonia fiber explosion (AFEX) processes. Cellulose was readily converted to glucose from both LHW and AFEX treated DDGS using a mixture of commercial cellulase and beta-glucosidase; however, these enzymes were ineffective at saccharifying the xylan present in the pretreated DDGS. Several commercial enzyme preparations were evaluated in combination with cellulase to saccharify pretreated DDGS xylan and it was found that adding commercial grade (e.g. impure) pectinase and feruloyl esterase (FAE) preparations were effective at releasing arabinose and xylose. The response of sugar yields for pretreated AFEX and LHW DDGS (6wt%/solids) were determined for different enzyme loadings of FAE and pectinase and modeled as a response surfaces. Arabinose and xylose yields rose with increasing FAE and pectinase enzyme dosages for both pretreated materials. When hydrolyzed at 20wt%/solids with the same blend of commercial enzymes, the yields were 278 and 261g sugars (i.e. total of arabinose, xylose, and glucose) per kg of DDGS (dry basis, db) for AFEX and LHW pretreated DDGS, respectively. The pretreated DDGS's were also evaluated for fermentation using Saccharomyces cerevisiae at 15wt%/solids. Pretreated DDGS were readily fermented and were converted to ethanol at 89-90% efficiency based upon total glucans; S. cerevisiae does not ferment arabinose or xylose.