title: Carbon material and bioenergetic balances of xylitol production from corncobs by Debaryomyces hansenii.
abstract: The effect of oxygenation on xylitol production by the yeast Debaryomyces hansenii has been investigated in this work using the liquors from corncob hydrolysis as the fermentation medium. The concentrations of consumed substrates (glucose, xylose, arabinose, acetate and oxygen) and formed products (xylitol, arabitol, ethanol, biomass and carbon dioxide) have been used, together with those previously obtained varying the hydrolysis technique, the level of adaptation of the microorganism, the sterilization procedure and the initial substrate and biomass concentrations, in carbon material balances to evaluate the percentages of xylose consumed by the yeast for the reduction to xylitol, alcohol fermentation, respiration and cell growth. The highest xylitol concentration (71 g/L) and volumetric productivity (1.5 g/L.h) were obtained semiaerobically using detoxified hydrolyzate produced by autohydrolysis-posthydrolysis, at starting levels of xylose (S(0)) and biomass (X(0)) of about 100 g/L and 12 g(DM)/L, respectively. No less than 80% xylose was addressed to xylitol production under these conditions. The experimental data collected in this work at variable oxygen levels allowed estimating a P/O ratio of 1.16 mol(ATP)/mol(O). The overall ATP requirements for biomass production and maintenance demonstrated to remarkably increase with X(0) and for S(0) >or= 130 g/L and to reach minimum values (1.9-2.1 mol(ATP)/C-mol(DM)) just under semiaerobic conditions favoring xylitol accumulation.
authors.affiliation: Department of Chemical Engineering, University of Vigo (Campus Ourense), Faculty of Science, Polytechnical Building, As Lagoas, 32004 Ourense, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Rivas
authors.forename: Paolo
authors.initials: P
authors.lastname: Torre
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Domínguez
authors.forename: Patrizia
authors.initials: P
authors.lastname: Perego
authors.forename: Attilio
authors.initials: A
authors.lastname: Converti
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Parajó
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D019149:Bioreactors / Q000382:microbiology*; D002244:Carbon / Q000378:metabolism; D003198:Computer Simulation; D004734:Energy Metabolism / Q000502:physiology; D004735:Energy Transfer / Q000502:physiology; D006868:Hydrolysis; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology; D010936:Plant Extracts / Q000378:metabolism; D004718:Saccharomycetales / Q000254:growth & development* / Q000378:metabolism*; D014993:Xylitol / Q000096:biosynthesis*; D014994:Xylose / Q000378:metabolism*; D003313:Zea mays / Q000737:chemistry*
chemical_list: D010936:Plant Extracts; D002244:Carbon; D000255:Adenosine Triphosphate; D014994:Xylose; D014993:Xylitol