A Novel simultaneous-Saccharification-Fermentation Strategy for Efficient Co-fermentation of C5 and C6 Sugars Using Native, Non-GMO Yeasts

Varanasi, Sasidhar¹  Relue, Patricia¹ 

[1] Univ. of Toledo, OH (United States)

关键词: cellulosic ethanol;    biomass hydrolysate;    fermentation;    native yeasts;    glucose and xylose;   

DOI  :  10.2172/1252730
RP-ID  :  DOE-UTOLEDO--GO18163
PID  :  OSTI ID: 1252730

学科分类：燃料技术

美国|英语

来源: SciTech Connect

【 摘 要 】

Economic bioethanol production is critically dependent upon the ability to convert both the hexose (C6) and pentose (C5) sugars resulting from cellulose and hemicellulose. C5 sugars are not readily fermentable by native Saccharomyces cerevisiae. Genetically Modified Organisms (GMOs) are designed to ferment xylose, but their stability, ethanol yield, environmental impact, and survival under conditions of industrial fermentation are unproven. In this project, we developed a novel approach for efficient fermentation of both C5 and C6 sugars using native S. Cerevisiae by exploiting its ability to produce ethanol from xylulose - the keto-isomer of xylose. While the isomerization of xylose to xylulose can be accomplished via commercially (and cheaply) available Xylose Isomerase (XI) (Sweetzyme???), this conversion has an extremely unfavorable equilibrium (xylose:xylose is about 5:1). To address this, we developed two alternate strategies. In the first, the two enzymes XI and urease are coimmobilized on solid support particles to enable complete isomerization of xylose to xylulose under pH conditions suitable for fermentation, in a simultaneous-isomerization-fermentation (SIF) mode. The ability of our technology to conduct isomerization of xylose under pH conditions suitable for both saccharification and fermentation opens the possibility of SSF with native yeasts for the first time. Herein, we performed specific research tasks for implementation of our technology in several modes of operation, including simultaneous-isomerization-and-fermentation (SIF), simultaneous-saccharification-and-isomerization (SSI) followed by fermentation, and SSF mode with the biomass feedstock poplar. The projected economics of our process are very favorable in comparison to the costs associated with engineering, licensing and propagating GMOs. This novel fermentation technology is readily accessible to rural farming economies for implementation in cellulosic ethanol production facilities.