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
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2019-08-30
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Universidade Federal de Goiás
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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.
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SILVA, E. G. 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. 2019. 116 f. Dissertação (Mestrado em Engenharia Química) - Universidade Federal de Goiás, Goiânia, 2019.