title: Effect of flocculation on performance of arming yeast in direct ethanol fermentation.
abstract: In the direct ethanol fermentation of raw starch by arming yeast with alpha-amylase and glucoamylase, it is preferable to use a flocculent yeast because it can be recovered without centrifugation. Three types of arming yeast system, I (nonflocculent), II (mildly flocculent), and III (heavily flocculent), were constructed and their fermentation performances were compared. With an increase in the degree of flocculation, specific ethanol production rate for soluble starch decreased (0.19, 0.17, and 0.12 g g-dry-cell(-1) h(-1) for systems I, II, and III, respectively), but that for raw starch did not decrease as much as expected (0.06, 0.06, and 0.04 g g-dry-cell(-1) h(-1) for systems I, II and III, respectively). Microscopic observation revealed that many starch granules were captured in the yeast flocs in system III during the direct ethanol fermentation of raw starch. It was suggested that the capture of starch granules increases apparent substrate concentration for amylolytic enzymes in arming yeast cell flocs; thus, the specific ethanol production rate of system III was kept at a level comparable to those of the other systems.
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan. shioya@bio.eng.osaka-u.ac.jp
authors.forename: Khaw Teik
authors.initials: KT
authors.lastname: Seong
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Katakura
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ninomiya
authors.forename: Yohei
authors.initials: Y
authors.lastname: Bito
authors.forename: Satoshi
authors.initials: S
authors.lastname: Katahira
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kondo
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Ueda
authors.forename: Suteaki
authors.initials: S
authors.lastname: Shioya
mesh_terms: D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005427:Flocculation; D008853:Microscopy; D008954:Models, Biological; D013213:Starch / Q000378:metabolism; D015003:Yeasts / Q000378:metabolism*
chemical_list: D000431:Ethanol; D013213:Starch