Yoshinobu Tsuchiya

Kinetic analysis for batch ethanol fermentation of Saccharomyces cerevisiae

Abstract Ethanol batch fermentation of Saccharomyces cerevisiae revealed that lower culture temperatures caused slower growth and slower ethanol production, however, the final cell mass and ethanol concentrations reached levels which were higher than those for higher culture temperatures. To explain these phenomena, a kinetic model was proposed on the basis of enzyme deactivation kinetics. In the model, growth and ethanol production were expressed as a function of the “integrated ethanol concentration” as follows: μ=μ0 exp (−k′∫ t 0 p n d t and v=aμ+β 0 exp (−k″∫ t 0 p n d t where μ is the specific growth rate; μ0, the initial value of μ; ν, specific ethanol production rate; α, growth associated constant; β0, non-growth associated constant; p, ethanol concentration; t, time; k′ and k″, decay constants and n, degree of inhibition. The proposed model simulated the temperature dependent ethanol fermentations, suggesting that the model might be applicable for the optimization of ethanol batch cultures by controlling the culture temperature as an operating variable.

Medium optimization for a methanol utilizing bacterium based on chemostat theory

SummaryIn the productions of biomass and vitamin B12 using methanol as the sole carbon source, it is necessary to use a medium in which methanol is the growth limiting substrate. Other inorganic salts should be in slight excess so that the yield of cells and the intracellular content of vitamin B12 do not vary. From basic principles of chemostat culture, a medium was optimized for Pseudomonas AM-1 a methanol utilizing bacterium, for the concentrations of various inorganic salts. This was done in a series of chemostat cultures at a dilution rate of 0.1 h−1. Optimum amounts of NH4+, PO43- and Mg2+ were estimated from the minimum concentration of the salt at which methanol became growth limiting. The optimum concentrations of Ca2+, Fe2+, Mn2+, and Zn2+ as a group were determined in the same way. Cu2+, Mo6+, Co2+ and B3+ are required at concentrations of μg/l and they were not studied as these very low level can be introduced as contaminants from other salts. The optimum medium composition (in g/l) was as follows: (NH4)2SO4, 1.0; H3PO4, 75×10−3; MgSO4 · 7H2O, 30×10−3; CaCl2 · 2H2O, 3.3×10−3; FeSO4 · 7H2O, 1.3×10−3, MnSO4 · 4H2O, 0.13×10−3; ZnSO4 · 7H2O, 0.13×10−3; CuSO4 · 5H2O, 40×10−6; Na2MoO4, 40×10−6; CoCl2 · 6H2O, 40×10−6; H3BO3, 30×10−6 and methanol 4.