Bioethanol production by recycled Scheffersomyces stipitis in sequential batch fermentations with high cell density using xylose and glucose mixture

Abstract

Here, it is shown three-step investigative procedures aiming to improve pentose-rich fermentations performance, involving a simple system for elevated mass production by Scheffersomyces stipitis (I), cellular recycle batch fermentations (CRBFs) at high cell density using two temperature strategies (fixed at 30°C; decreasing from 30 to 26°C) (II), and a short-term adaptation action seeking to acclimatize the microorganism in xylose rich-media (III). Cellular propagation provided 0.52gdrycellweightgRS(-1), resulting in an expressive value of 45.9gdrycellweightL(-1). The yeast robustness in CRBF was proven by effective ethanol production, reaching high xylose consumption (81%) and EtOH productivity (1.53gL(-1)h(-1)). Regarding the short-term adaptation, S. stipitis strengthened its robustness, as shown by a 6-fold increase in xylose reductase (XR) activity. The short fermentation time (20h for each batch) and the fermentation kinetics for ethanol production from xylose are quite promising.

Fermentation strategy for second generation ethanol production from sugarcane bagasse hydrolyzate by Spathaspora passalidarum and Scheffersomyces stipitis

“…However, the temperature decrease along sequential fed batches and the sequential fed batches (recycle), together, promoted high xylose consumption, and all xylose content was consumed in third and fourth fed batches. This observation agrees with Santos et al (), which investigated the consumption of glucose and xylose by S. stipitis in sequential batches with temperature decrease concluding that it improves xylose consumption rate. An explanation for why recycling cells or decreasing temperature process can improve xylose consumption is presented by Slininger et al (, ).…”

“…The present study showed ethanol titer of 18.5 g L −1 , productivity of 0.36 g L −1 h −1 and sugar (glucose and xylose) conversion into ethanol of 0.32 g g −1 . These results are lower than that obtained for Santos et al (), Farias et al (), and Slininger et al (), however, it is important highlight that these works were performed in xylose (Analytical grade) and the present work have used sugarcane bagasse hydrolyzate. When the present work is compared with Dussán et al () results it is possible to observe that ethanol titer (7.34 g L −1 ), productivity (0.1 g L −1 h −1 ), and conversion yield (0.16 g g −1 ) attained by using detoxified sugarcane bagasse hydrolyzate in a batch system carried out in bioreactor were lower than results obtained by the present work (please see Table ).…”

“…It is believed that the two effects may influence the fermentation efficiency, but the effect of temperature appears to be more remarkable. In a previous report published by our group (Santos et al, 2016) we have demonstrated that the concentrations of the enzymes ADH, XDH, and XR were higher during recycles with temperature decrease for S. stipitis. Further experiments are necessary to evaluate the effect of recycle and temperature decrease separately for both microrganisms and its influence on enzymes production for S. passalidarum.…”

“…Xylose consumption rates for S. passalidarum were higher than xylose consumption rates for S. stipitis. Santos et al (2016) stated that decreasing 1 C at the fermentation temperature in cell recycle strategy contributes to xylose uptake by S. stipitis. This strategy seems to be effective for S. passalidarum ( Fig.…”

The Coptotermes gestroi aldo–keto reductase: a multipurpose enzyme for biorefinery applications

“…Glucose, xylose, acetic acid, glycerol, xylitol, furfural, and ethanol were measured during the fermentation according to the analytical measurements described below. Yeast concentrations (g/L) and kinetic parameter calculations (Yp/s: xylose conversion factor in ethanol; Y: percentage of ethanol production) were measured and calculated as described by Santos et al [82]. …”