Effect of additives on the digestibility of corn stover solids following pretreatment by leading technologies

Bovine serum albumin (BSA), Tween-20, and polyethylene glycol (PEG6000) were added to washed corn stover solids produced by ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), dilute sulfuric acid (DA), lime, controlled pH, and sulfur dioxide (SO(2)) pretreatments and to untreated corn stover (UT) and pure Avicel glucan prior to adding cellulase supplemented with beta-glucosidase at an activity ratio of 1:2/g and a moderate enzyme loading of 16.1 mg/g glucan in the raw corn stover. The additives were applied individually at 150, 300, and 600 mg/g glucan in the pretreated solids and in combinations of equal amounts of each that totaled 600 mg/g. The greatest increase in total sugar release was by Tween-20 with SO(2) pretreated solids followed by PEG6000 with ARP solids and Tween-20 with lime solids. The effectiveness of the additives was observed to depend on the type of sugars left in the solids, suggesting that it may be more beneficial to use the mixture of these additives to realize a high total sugar yield. In addition, little enhancement in sugar release was possible beyond a loading of 150 mg additives/g glucan for most pretreatments, and combinations did not improve sugar release much over use of additives alone for all except SO(2). Additives were also found to significantly increase concentrations of cellobiose and cellooligomers after 72 h of Avicel hydrolysis.