Abstract

BackgroundSimultaneous saccharification and co-fermentation (SSCF) has been recognized as a feasible option for ethanol production from xylose-rich lignocellulosic materials. To reach high ethanol concentration in the broth, a high content of water-insoluble solids (WIS) is needed, which creates mixing problems and, furthermore, may decrease xylose uptake. Feeding of substrate has already been proven to give a higher xylose conversion than a batch SSCF. In the current work, enzyme feeding, in addition to substrate feeding, was investigated as a means of enabling a higher WIS content with a high xylose conversion in SSCF of a xylose-rich material. A recombinant xylose-fermenting strain of Saccharomyces cerevisiae (TMB3400) was used for this purpose in fed-batch SSCF experiments of steam-pretreated wheat straw.ResultsBy using both enzyme and substrate feeding, the xylose conversion in SSCF could be increased from 40% to 50% in comparison to substrate feeding only. In addition, by this design of the feeding strategy, it was possible to process a WIS content corresponding to 11% in SSCF and obtain an ethanol yield on fermentable sugars of 0.35 g g-1.ConclusionA combination of enzyme and substrate feeding was shown to enhance xylose uptake by yeast and increase overall ethanol yield in SSCF. This is conceptually important for the design of novel SSCF processes aiming at high-ethanol titers. Substrate feeding prevents viscosity from becoming too high and thereby allows a higher total amount of WIS to be added in the process. The enzyme feeding, furthermore, enables keeping the glucose concentration low, which kinetically favors xylose uptake and results in a higher xylose conversion.

Highlights

  • Simultaneous saccharification and co-fermentation (SSCF) has been recognized as a feasible option for ethanol production from xylose-rich lignocellulosic materials

  • The aim of the current study was to investigate dual feeding, i.e., a combination of both substrate and enzyme feeding as a means to improve xylose utilization in SSCF of pretreated wheat straw

  • A standard fed-batch SSCF was carried out as a reference (Figure 1)

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Summary

Introduction

Simultaneous saccharification and co-fermentation (SSCF) has been recognized as a feasible option for ethanol production from xylose-rich lignocellulosic materials. To reach high ethanol concentration in the broth, a high content of water-insoluble solids (WIS) is needed, which creates mixing problems and, may decrease xylose uptake. A recombinant xylose-fermenting strain of Saccharomyces cerevisiae (TMB3400) was used for this purpose in fed-batch SSCF experiments of steam-pretreated wheat straw. Biomass residues from both forest industry and agriculture, or dedicated perennial (energy) crops, are potential feedstocks for fermentative ethanol production. Simultaneous saccharification and fermentation (SSF) [4] has been established as a promising option for ethanol production from lignocellulosic materials [5] In this process, the enzymatic hydrolysis of the pretreated material takes place together with the fermentation. A high WIS content gives a high concentration of these inhibitors

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