title: Identification and characterization of fermentation inhibitors formed during hydrothermal treatment and following SSF of wheat straw.
abstract: A pilot plant for hydrothermal treatment of wheat straw was compared in reactor systems of two steps (first, 80 degrees C; second, 190-205 degrees C) and of three steps (first, 80 degrees C; second, 170-180 degrees C; third, 195 degrees C). Fermentation (SSF) with Sacharomyces cerevisiae of the pretreated fibers and hydrolysate from the two-step system gave higher ethanol yield (64-75%) than that obtained from the three-step system (61-65%), due to higher enzymatic cellulose convertibility. At the optimal conditions (two steps, 195 degrees C for 6 min), 69% of available C6-sugar could be fermented into ethanol with a high hemicellulose recovery (65%). The concentration of furfural obtained during the pretreatment process increased versus temperature from 50 mg/l at 190 degrees C to 1,200 mg/l at 205 degrees C as a result of xylose degradation. S. cerevisiae detoxified the hydrolysates by degradation of several toxic compounds such as 90-99% furfural and 80-100% phenolic aldehydes, which extended the lag phase to 5 h. Acetic acid concentration increased by 0.2-1 g/l during enzymatic hydrolysis and 0-3.4 g/l during fermentation due to hydrolysis of acetyl groups and minor xylose degradation. Formic acid concentration increased by 0.5-1.5 g/l probably due to degradation of furfural. Phenolic aldehydes were oxidized to the corresponding acids during fermentation reducing the inhibition level.
authors.affiliation: Biosystems Division, Risø DTU, Technical University of Denmark, POB 49, DK-4000 Roskilde, Denmark. mette.hedegaard.thomsen@risoe.dk
authors.forename: Mette Hedegaard
authors.initials: MH
authors.lastname: Thomsen
authors.forename: Anders
authors.initials: A
authors.lastname: Thygesen
authors.forename: Anne Belinda
authors.initials: AB
authors.lastname: Thomsen
mesh_terms: D002482:Cellulose / Q000737:chemistry* / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D006868:Hydrolysis; D007218:Industrial Microbiology; D009930:Organic Chemicals / Q000737:chemistry* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature; D014908:Triticum / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009930:Organic Chemicals; D000431:Ethanol; D002482:Cellulose