title: Characterization of a recombinant flocculent Saccharomyces cerevisiae strain that co-ferments glucose and xylose: I. Influence of the ratio of glucose/xylose on ethanol production.
abstract: Glucose/xylose mixtures (90 g/L total sugar) were evaluated for their effect on ethanol fermentation by a recombinant flocculent Saccharomyces cerevisiae, MA-R4. Glucose was utilized faster than xylose at any ratio of glucose/xylose, although MA-R4 can simultaneously co-ferment both sugars. A high percentage of glucose can increase cell biomass production and therefore increase the rate of glucose utilization (1.224 g glucose/g biomass/h maximum) and ethanol formation (0.493 g ethanol/g biomass/h maximum). However, the best ratio of glucose/xylose for the highest xylose consumption rate (0.209 g xylose/g biomass/h) was 2:3. Ethanol concentration and yield increased and by-product (xylitol, glycerol, and acetic acid) concentration decreased as the proportion of glucose increased. The maximum ethanol concentration was 41.6 and 21.9 g/L after 72 h of fermentation with 90 g/L glucose and 90 g/L xylose, respectively, while the ethanol yield was 0.454 and 0.335 g/g in 90 g/L glucose and 90 g/L xylose media, respectively. High ethanol yield when a high percentage of glucose is available is likely due to decreased production of by-products, such as glycerol and acetic acid. These results suggest that ethanol selectivity is increased when a higher proportion of glucose is available and reduced when a higher proportion of xylose is available.
authors.affiliation: Biomass Refinery Research Center-BRRC, National Institute of Advanced Industrial Science and Technology-AIST, 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan. a-matsushika@aist.go.jp
authors.forename: Akinori
authors.initials: A
authors.lastname: Matsushika
authors.forename: Shigeki
authors.initials: S
authors.lastname: Sawayama
mesh_terms: D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
chemical_list: D000431:Ethanol; D014994:Xylose; D005947:Glucose