Effect of initial cell concentration on ethanol production by flocculent Saccharomyces cerevisiae with xylose-fermenting ability.
Different initial cell concentrations of a recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated for their effects on xylose fermentation and glucose-xylose cofermentation. A high initial cell concentration greatly increased both the substrate utilization and ethanol production rates. During xylose fermentation, the highest rates of xylose consumption (2.58 g/L h) and ethanol production (0.83 g/L h) were obtained at an initial cell concentration of 13.1 g/L. During cofermentation, the highest rates of glucose consumption (14.4 g/L h), xylose consumption (2.79 g/L h), and ethanol production (6.68 g/L h) were obtained at an initial cell concentration of 12.7 g/L. However, a high initial cell density had no positive effect on the maximum ethanol concentration and ethanol yield mainly due to the increased amount of by-products including xylitol. The ethanol yield remained almost constant (0.34 g/g) throughout xylose fermentation (initial cell concentration range, 1.81-13.1 g/L), while it was slightly lower at high initial cell concentrations (9.87 and 12.7 g/L) during cofermentation. The determination of the appropriate initial cell concentration is necessary for the improvement of substrate utilization and ethanol yield.
Matsushika
Akinori
A
Biomass Technology Research Center, National Institute of Advanced Industrial Science and Technology, Higashi-Hiroshima, Japan. a-matsushika@aist.go.jp
Sawayama
Shigeki
S
D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D005427:Flocculation; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
D000431:Ethanol; D014994:Xylose