Xylitol bioproduction from sugarcane bagasse: Detoxification and fermentation strategies

VALLEJOS, M.E.; CHADE, M.; MERELESE.B.; BENGOECHEA, D.I.; BRIZUELA, J.G.; FELISSIA, F.E.; AREA, M.C.

Concepción

Congreso; 3er Congreso Iberoamericano sobre Biorrefinerías (CIAB), 4to Congreso Latinoamericano sobre Biorrefinerías y 2do Simposio Internacional sobre Materiales Lignocelulósicos l; 2015

Unidad de Desarrollo Tecnológico - Universidad de Concepción

Hemicelluloses frombagasse are mainly pentosans (xylans) which can be depolymerized into sugar(xylose) as primary carbon source for the bioproduction of xylitol, ethanol,and others. Xylitol is used as a food additive and sweetening agent, and isindustrially produced by expensive chemical processes. It can also be producedby the fermentation of xylose extracted from hemicelluloses. Improvements inbiomass treatment, detoxification and fermentation processes are needed to makexylitol production cost-effective, opening new markets and creating newapplications for it. The aim of this study was to evaluate detoxification andfermentation strategies for spent liquors from the autohydrolysis of sugarcanebagasse, for xylitol biotechnological production. Hemicelluloses were removedfrom bagasse by autohydrolysis treatment. Different sequences of treatment forspent liquor detoxification were accomplished, and their effect on sugars loss,inhibitors removal, and xylitol production were evaluated. Spent liquor wasconcentrated under vacuum before and after posthydrolysis, and previous toactivated charcoal treatment. The xylans were converted to xylose byposthydrolysis of the spent liquor in 1% H2SO4, and the acid was removed byprecipitation with Ca(OH)2 to pH 10 (gypsum formation). Two methods wereapplied to adjust spent liquor to pH 5: (i) phosphoric acid, and (ii) anionicand cationic exchange resins. Spent liquor was subsequently treated withactivated charcoal (3%, 100 rpm, 60°C for 1 h) to remove main inhibitorscompounds. Acetic acid was removed by anionic exchange resins (Figure 1).Various experiences of fermentation were performed with commercial xylose toselect the yeast (C. guilliermondii, C. tropicalis), and the fermentationconditions (nutrients, concentration of yeast cells). Conditions of detoxifiedspent liquors fermentations were obtained from these experiences. Sugars andorganics acids were quantified by HPLC chromatography. Total phenolic contentwas determined by the Folin-Ciocalteu method, and main degradation products oflignin were identified by HPLC chromatography. Yeast cells concentrations weremeasured by turbidimetry. HMF and furfural were completely removed byevaporation under vacuum. Total HMF, furfural, and phenolic contents decreasedmore than 95% after activated charcoal treatment. Acetic acid was almostcompletely removed by anionic and cationic exchange resins. Evaporation afterposthydrolisys of spent liquor produced the highest loss of sugars (50%), dueto entrainment of liquor produced by gypsum precipitation after the addition ofCa(OH)2. C.tropicalis behaved best in all fermentations. Samples of liquor richin xylose from each detoxification stage were used as culture medium forxylitol production, and the results were compared with a sample of commercialxylose. Xylitol concentration of 12.5 gL-1 (fermentation efficiency of 36%) wasachieved with the following fermentation conditions: 40 gL-1 of initial xylose,2.4 gL-1 of yeast cells, 30°C, and 120 rpm. This concentration was 27% lowerthan that obtained from the sample of commercial xylose, fermented in the sameconditions. Other fermentation experiences at high initial xylose concentrationwere performed, increasing fermentation efficiency.