Effect of different fermentation parameters on bioethanol production from corn meal hydrolyzates by free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus

摘要

BACKGROUND: Bioethanol produced from renewable biomass, such as corn meal, is a biofuel that is both renewable andenvironmentally friendly. Significant scientific and technological investments will be needed to achieve substitution ofconventional fossil fuels with alternative fuels. The ethanol fermentation of enzymatically obtained corn meal hydrolyzatesby free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus yeast in a batch system was studied. The initialglucose and inoculum concentration and the time required for the efficient ethanol production were optimized taking intoaccount parameters such as ethanol concentration, ethanol yield, percentage of the theoretical yield of ethanol and volumetricproductivity in both immobilized and free cell systems. RESULTS: The yeast cells were immobilized in Ca-alginate by an electrostatic droplet generation method. An optimal initialinoculum concentration of 2% (v/v) and optimal fermentation time of 38 h for both immobilized and free yeasts were determined.An optimal initial glucose concentration of 150 g L~(-1)for free system was achieved. At the initial glucose concentration of 176 g Lno substrate or product inhibition were achieved with immobilized yeast. CONCLUSION: By immobilization of the yeast into Ca -alginate using the method of electrostatic droplet generation a superiorsystem was realized, which exhibited lower substrate inhibition and higher tolerance to ethanol. The cells of S. cerevisiaevar. ellipsoideus yeast entrapped in Ca-alginate showed good physical and chemical stability, and no substrate and productdiffusion restrictions were noticed.