Effect of inhibitors released during steam-explosion treatment of poplar wood on subsequent enzymatic hydrolysis and SSF.
Steam-exploded (SE) poplar wood biomass was hydrolyzed by means of a blend of Celluclast and Novozym cellulase complexes in the presence of the inhibiting compounds produced during the preceding steam-explosion pretreatment process. The SE temperature and time conditions were 214 degrees C and 6 min, resulting in a log R(0) of 4.13. In enzymatic hydrolysis tests at 45 degrees C, the biomass loading in the bioreactor was 100 g(DW)/L (dry weight) and the enzyme-to-biomass ratio 0.06 g/g(DW). The enzyme activities for endo-glucanase, exo-glucanase, and beta-glucosidase were 5.76, 0.55, and 5.98 U/mg, respectively. The inhibiting effects of components released during SE (formic, acetic, and levulinic acids, furfural, 5-hydroxymethyl furfural (5-HMF), syringaldehyde, 4-hydroxy benzaldehyde, and vanillin) were studied at different concentrations in hydrolysis runs performed with rinsed SE biomass as model substrate. Acetic acid (2 g/L), furfural, 5-HMF, syringaldehyde, 4-hydroxybenzaldehyde, and vanillin (0.5 g/L) did not significantly effect the enzyme activity, whereas formic acid (11.5 g/L) inactivated the enzymes and levulinic acid (29.0 g/L) partially affected the cellulase. Synergism and cumulative concentration effects of these compounds were not detected. SSF experiments show that untreated SE biomass during the enzymatic attack gives rise to a nonfermentable hydrolysate, which becomes fermentable when rinsed SE biomass is used. The presence of acetic acid, vanillin, and 5-HMF (0.5 g/L) in SSF of 100 g(DW) /L biomass gave rise to ethanol yields of 84.0%, 73.5%, and 91.0% respectively, with respective lag phases of 42, 39, and 58 h.
Cantarella
Maria
M
Department of Chemistry, Chemical Engineering and Materials, University of L'Aquila, Monteluco di Roio, 67040 L'Aquila, Italy. cantarel@ing.univaq.it
Cantarella
Laura
L
Gallifuoco
Alberto
A
Spera
Agata
A
Alfani
Francesco
F
D019149:Bioreactors / Q000382:microbiology; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005959:Glucosidases / Q000378:metabolism; D006867:Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D010936:Plant Extracts / Q000737:chemistry / Q000378:metabolism; D032107:Populus / Q000737:chemistry* / Q000382:microbiology*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013227:Steam; D014934:Wood
D004791:Enzyme Inhibitors; D010936:Plant Extracts; D013227:Steam; D000431:Ethanol; D006867:Hydrolases; D005959:Glucosidases; D005947:Glucose