Fermentação de licor de hemicelulose advindo do pré-tratamento hidrotérmico do bagaço de malte com as leveduras Scheffersomyces stipitis e Pachysolen tannophilus para produção de etanol 2G

• Autor(a) principal: Silva, Elizabeth Gonçalves da
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• dARK ID: ark:/38995/0013000007s9z
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/10043
• topic: Etanol 2G; Hemicelulose; Scheffersomyces stipitis; Pachysolen tannophilus; Xilose; 2G ethanol; Hemicellulose; Scheffersomyces stipitis; Pachysolen tannophilus; Xylose; ENGENHARIAS::ENGENHARIA QUIMICA

Ethanol is considered an important alternative energy source that contributes to alleviate energy problems and global warming caused by the accumulation of CO2 from burning fossil fuels. In this sense, the production of ethanol from lignocellulosic materials, known as second generation ethanol (2G), has stood out for presenting environmental advantages and economical. However, the economic viability of this process depends on the utilization of all fermentable fractions present in the different lignocellulosic materials under study, allowing the conversion of both cellulose (C6) and hemicellulose (C5) into ethanol. After the hydrolysis step of these materials is generated as main sugars, glucose and xylose, respectively. Xylose is not fermented by Saccharomyces cerevisiae (yeast widely used in 1G ethanol production), however Scheffersomyces stipitis and Pachysolen tannophilus are considered good biocatalysts for 2G fuel. This work evaluated xylose consumption and metabolites produced in different types of fermentation media. (YPX, MMX and hydrothermal pretreatment liquor from brewer’s spent grain supplemented) in aerobic system and with oxygen limitation. Using two pentose fermenting yeasts, S. stipitis and P. tannophilus, as an industrially viable alternative for the production of bioethanol in brewer’s spent grain hemicellulosic liquor, in order to determine between the two strains cited, a yeast with high ethanol/xylitol selectivity from the fermentation of this liquor through the conversion of xylose. The crops were performed in shaken flasks 500 mL volume filled with 200 mL of inoculated media at 200 rpm with a temperature of 30 ° C; and in 2 mL eppendorfs containing 1.5 mL of the inoculated media at 100 rpm and 30 °C. In cultures with aerobic conditions cell concentrations up to 10.64 g/L were achieved with the P. tannophilus strain in YPX media compared with the cell concentration of 5.42 g/L of the S. stipitis strain in YPX media but in oxygen limitation. At the end of the process were evaluated the kinetic parameters of each yeast in the different culture media and the values for maximum specific speed, xylose conversion factor in cells, xylose conversion factor in ethanol and xylitol were μmax = 0,21 h-1 to S. stipitis in the YPX media under aerobic conditions, Yx/s = 0,56 to P. tannophilus in the YPX media under aerobic conditions, YP/S(etanol) = 0,26 to S. stipitis in the YPX media under oxygen limitation, YP/S(xylitol) = 0,55 to S. stipitis in the MMX media under oxygen limitation. But for the researched environment, hemicellulose liquor from brewer’s spent grain supplemented with MMX components with 1.5 g/L urea obtained better responses for S. stipitis in relation to cell growth and ethanol production under aerobic conditions, already for ethanol production under conditions of oxygen limitation obtained better yield to P. tannophilus, as well as to the production factor of xylitol in the two oxygenation conditions studied. Therefore for better ethanol production the S. stipitis yeast had the highest YP/S(ethanol) = 0,1 under aerobic conditions, and for xylitol production the P. tannophilus strain is the most effective reaching YP/S(xylitol) = 0,46 under conditions of oxygen limitation. With the use of LHBMS media with urea at 6 g/L S. stipitis presented similarity with the conversion factors of urea (1.5 g/L) in the studied oxygen conditions, increasing only the accumulation of ethanol mainly in limitation of oxygen, reaching 3.9 g/L. In this media for P. tannophilus the yield was not plausible, prevailing the media with lower concentration of nitrogen source, because it favored the production of acetic acid, inhibiting the cellular metabolism of this yeast.