Abstract
To try to improve hydrolysis yields at elevated solids loadings, a comparison was made between batch and fedβbatch addition of fresh substrate at the initial and later phases of hydrolysis. Both ethanol (EPCS) and steamβpretreated corn stover (SPCS) substrates were tested at low (5 FPU) and high (60 FPU) loadings of cellulase per gram of cellulose. The fedβbatch addition of fresh substrate resulted in a slight decrease in hydrolysis yields when compared with the corresponding batch reactions. A 72βh hydrolysis of the SPCS substrate resulted in a hydrolysis yield of 66% compared with 51% for the EPCS substrate. When the enzyme adsorption and substrate characteristics were assessed during batch and fedβbatch hydrolysis, it appeared that the irreversible binding of cellulases to the more recalcitrant original substrate limited their access to the freshly added substrate. After 72βh hydrolysis of the SPCS substrate at low enzyme loadings, βΌ40β50% of the added cellulases were desorbed into solution, whereas only 20% of the added enzyme was released from the EPCS substrate. Both simultaneous and sequential treatments with xylanases and cellulases resulted in an up to a 20% increase in hydrolysis yields for both substrates at low enzyme loading. Simons' stain measurements indicated that xylanase treatment increased cellulose access, thus facilitating cellulose hydrolysis. Β© 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2011