Intrinsic Growth and Fermentation Rates of Alginate‐Entrapped Saccharomyces cerevisiae

Abstract

AbstractExperiments were conducted under anaerobic conditions to determine the intrinsic specific rates of growth, glucose uptake, and ethanol production for Saccharomyces cerevisiae immobilized in calcium alginate. The simultaneous processes of diffusion and reaction in an alginate membrane were analyzed to determine the intrinsic specific growth and reaction rates from glucose and ethanol concentration measurements made outside the alginate phase. Under anaerobic conditions, the specific growth rate of immobilized S. cerevisiae decreased by 20% compared to the growth rate for suspended cells. The specific glucose uptake rate and specific ethanol production rate increased by a factor of 4 compared to those for suspended cells. The ethanol yield remained the same, and the biomass yield decreased to one‐fifth the yield for suspended cells. Further experiments were conducted under aerobic conditions to investigate the effects of dissolved oxygen concentration on the specific rates of growth, glucose uptake, and ethanol production of immobilized S. cerevisiae. Although the obtained results cannot be interpreted unambiguously, oxygen appears to affect immobilized cells in a way similar to the way it affects suspended cells, while the observed differences between immobilized and suspended cells under anaerobic conditions remain the same in the presence of oxygen. Due to rate variability with oxygen, the obtained results are representative of average rate values. Experimental data and simulations indicate that glucose mitigates oxygen effects, yielding relatively small rate variations with aeration rates and relatively constant ethanol yields.