title: Redox potential driven aeration during very-high-gravity ethanol fermentation by using flocculating yeast.
abstract: Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition. In this work, fermentation redox potential (ORP) was applied to drive the aeration process at low dissolved oxygen (DO) levels, which is infeasible to be regulated by a DO sensor. The performance and characteristics of flocculating yeast grown under 300 and 260 g glucose/L conditions were subjected to various aeration strategies including: no aeration; controlled aeration at -150, -100 and -50 mV levels; and constant aeration at 0.05 and 0.2 vvm. The results showed that anaerobic fermentation produced the least ethanol and had the highest residual glucose after 72 h of fermentation. Controlled aerations, depending on the real-time oxygen demand, led to higher cell viability than the no-aeration counterpart. Constant aeration triggered a quick biomass formation, and fast glucose utilization. However, over aeration at 0.2 vvm caused a reduction of final ethanol concentration. The controlled aeration driven by ORP under VHG conditions resulted in the best fermentation performance. Moreover, the controlled aeration could enhance yeast flocculating activity, promote an increase of flocs size, and accelerate yeast separation near the end of fermentation.
authors.affiliation: School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China.|School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116023, China.
authors.forename: Chen-Guang
authors.initials: CG
authors.lastname: Liu
authors.affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116023, China.
authors.forename: Xue-Mi
authors.initials: XM
authors.lastname: Hao
authors.affiliation: Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon SK S7N 5A9, Canada.
authors.forename: Yen-Han
authors.initials: YH
authors.lastname: Lin
authors.affiliation: School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China.|School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116023, China.
authors.forename: Feng-Wu
authors.initials: FW
authors.lastname: Bai
mesh_terms: D000332:Aerobiosis; D018533:Biomass; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005427:Flocculation; D005947:Glucose / Q000378:metabolism; D018471:Hypergravity; D050296:Microbial Viability; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism*
chemical_list: D000431:Ethanol; D005947:Glucose; D010100:Oxygen