XYLITOL BIOPRODUCTION FROM SUGARCANE BAGASSE: DETOXIFICATION AND FERMENTATION STRATEGIES

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

Concepción

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

CIADEB-RIADICYP-PROVALOR-BIOREN- Centro de Biotecnología UdeC- Unidad de Desarrollo Tecnológico (UDT)- VTT

Hemicellulosesfrom bagasse are mainly pentosans (xylans) which can be depolymerized intosugar (xylose) as primary carbon source for the bioproduction of xylitol,ethanol, and others. Xylitol is used as a food additive and sweetening agent,and is industrially produced by expensive chemical processes. It can also beproduced by the fermentation of xylose extracted from hemicelluloses. Improvementsin biomass treatment, detoxification and fermentation processes are needed tomake xylitol production cost-effective, opening new markets and creating newapplications for it. The aim of this study was to evaluate detoxification and fermentationstrategies for spent liquors from the autohydrolysis of sugarcane bagasse, forxylitol biotechnological production. Hemicelluloses were removed from bagasseby autohydrolysis treatment. Different sequences of treatment for spent liquor detoxificationwere accomplished, and their effect on sugars loss, inhibitors removal, andxylitol production were evaluated. Spent liquor was concentrated under vacuumbefore and after posthydrolysis, and previous to activated charcoal treatment.The xylans were converted to xylose by posthydrolysis of the spent liquor in 1%H2SO4, and the acid was removed by precipitation with Ca(OH)2 to pH 10 (gypsum formation).Two methods were applied to adjust spent liquor to pH 5: (i) phosphoric acid,and (ii) anionic and cationic exchange resins. Spent liquor was subsequentlytreated with activated charcoal (3%, 100 rpm, 60°C for 1 h) to remove maininhibitors compounds. Acetic acid was removed by anionic exchange resins(Figure 1). Various experiences of fermentation were performed with commercialxylose to select the yeast (C. guilliermondii, C. tropicalis), and thefermentation conditions (nutrients, concentration of yeast cells). Conditionsof detoxified spent liquors fermentations were obtained from these experiences.Sugars and organics acids were quantified by HPLC chromatography. Totalphenolic content was determined by the Folin-Ciocalteu method, and maindegradation products of lignin were identified by HPLC chromatography. Yeast cellsconcentrations were measured by turbidimetry. HMF and furfural were completelyremoved by evaporation under vacuum. Total HMF, furfural, and phenolic contentsdecreased more than 95% after activated charcoal treatment. Acetic acid wasalmost completely removed by anionic and cationic exchange resins. Evaporationafter posthydrolisys of spent liquor produced the highest loss of sugars (50%),due to entrainment of liquor produced by gypsum precipitation after theaddition of Ca(OH)2. C.tropicalis behaved best in all fermentations. Samples ofliquor rich in xylose from each detoxification stage were used as culturemedium for xylitol 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-1of 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.