Cellulase adsorption and an evaluation of enzyme recycle during hydrolysis of steam-exploded softwood residues

The sugar yield and enzyme adsorption profile obtained during the hydrol-ysis of SO2-catalyzed steam-exploded Douglas-fir and posttreated steam-exploded Douglas-fir substrates were determined. After hot alkali peroxide posttreatment, the rates and yield of hydrolysis attained from the posttreated Douglas-fir were significantly higher, even at lower enzyme loadings, than those obtained with the corresponding steam-exploded Douglas-fir. The enzymatic adsorption profiles observed during hydrolysis of the two sub-strates were significantly different. Ultrafiltration was employed to recover enzyme in solution (supernatant) and reused in subsequent hydrolysis reactions with added, fresh substrate. These recycle findings suggested that the enzyme remained relatively active for three rounds of recycle. It is likely that enzyme recovery and reuse during the hydrolysis of posttreated soft-wood substrates could lead to reductions in the need for the addition of fresh enzyme during softwood-based bioconversion processes. Index Entries: Cellulases; Douglas-fir; ultrafiltration; adsorption; enzyme recycle; hydrolysis; bioconversion