Enhanced production of bioethanol and ultrastructural characteristics of reused Saccharomyces cerevisiae immobilized calcium alginate beads

• Published in: Bioresource technology 2011-09, Vol.102 (17), p.8191-8198
• Main Authors: Lee, Kwang Ho, Choi, In Seong, Kim, Young-Gyu, Yang, Duck-Joo, Bae, Hyeun-Jong
• Format: Article
• Language: English
• Subjects: Alginates; Alginates - ultrastructure; Beads; Biofuel production; Biological and medical sciences; Biotechnology; Calcium alginate; Calcium alginate beads; Egg-box model; Energy; Ethanol; Ethanol - metabolism; Ethanol fermentation; Ethyl alcohol; Fermentation; Fundamental and applied biological sciences. Psychology; Glucose - metabolism; Glucuronic Acid; Hexuronic Acids; Hydrogen-Ion Concentration; Industrial applications and implications. Economical aspects; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology; Microscopy, Electron, Transmission; Reused beads; Saccharomyces cerevisiae; Saccharomyces cerevisiae - metabolism; Temperature; Transmission electron microscopy; Ultrastructural characteristics; Yeast
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2011.06.063

► We examine optimal batch fermentation condition of immobilized yeast with Ca-alginate beads. ► Reused yeast immobilized beads give excellent results in converting glucose to ethanol. ► Short fermentation time and the high ethanol yield with the reused beads are due to a higher yeast population and porosity. ► We explain and confirm “egg-box” model of alginate matrix structure using TEM observation. Yeast immobilized on alginate beads produced a higher ethanol yield more rapidly than did free yeast cells under the same batch-fermentation conditions. The optimal fermentation conditions were 30°C, pH 5.0, and 10% initial glucose concentration with 2% sodium alginate beads. The fermentation time using reused alginate beads was 10–14h, whereas fresh beads took 24h, and free cells took 36h. All bead samples resulted in nearly a 100% ethanol yield, whereas the free cells resulted in an 88% yield. Transmission electron microscopy (TEM) showed that the shortened time and higher yield with the reused beads was due to a higher yeast population per bead as well as a higher porosity. The ultrastructure of calcium alginate beads and the alginate matrix structure known as the “egg-box” model were observed using TEM.