The rate of cane sugar fermentation with Saccharomyces cerevisiae was studied at temperatures between 30°C and 42°C in order to characterize the process using thermodynamic parameters such as enthalpy (ΔH*)...The rate of cane sugar fermentation with Saccharomyces cerevisiae was studied at temperatures between 30°C and 42°C in order to characterize the process using thermodynamic parameters such as enthalpy (ΔH*), activation energy (ΔE*), entropy (ΔS*), Gibbs free energy (ΔG*) and equilibrium constant (K). The parameters were evaluated on the basis of a consideration of Arrhenius, Eyring and Van’t Hoff’s equations. The results obtained are ΔH*, 91.85 KJ·mol-1;ΔE*, 91.85 KJ·mol-1, ΔS*, 2763 J·mol-1K-1;ΔG*, -762.09 KJ·mol-1, and equilibrium constant, K, 1.34 dm3·mol-1. These values were subsequently used to obtain by calculation the rate constant of the fermentation k, 1.43 × 1011 min-1, Arrhenius constant A (pre-exponential or frequency factor), 4.79 × 1026 min-1, orientation parameter, P, 4.48 × 1015 and the collision frequency Z, 1.07 × 1011 min-1. Finally the fermentation efficiency calculated on the basis of a complete combustion of glucose is 377.8%. The results showed that though the fermentation process is kinetically controlled, it is suggested that the positive impact of the feasible thermodynamics is limited by other process variables.展开更多
The fermentation of cane sugar as substrate by Saccharomyces cerevisiae (enzyme) was critically investigated to obtain certain useful kinetic parameters and to determine the effect of temperature, pH, substrate and ye...The fermentation of cane sugar as substrate by Saccharomyces cerevisiae (enzyme) was critically investigated to obtain certain useful kinetic parameters and to determine the effect of temperature, pH, substrate and yeast (enzyme) concentration on the rate of fermentation. The results indicate that the rate of fermentation (measured as rate of production of CO2) increased in proportion with temperature (optimum 32°C?-?36°C), pH (optimum 5.5) substrate (optimum 50?v/v%) and yeast concentration (optimum 3.5?-?4.5?w/v%) up to a limit and subsisted?either as a plateau and/or, decreases as the case may be. This suggests that the reaction takes place in two steps. The kinetic parameters examined are maximum rate of reaction Vmax (2.0?×?102 M·min-1), catalytic constant, k2 (1.81?×?10-1 min-1), overall rate constant, k (1.53?×?101 min-1),?order of initial reaction (approx. first order),?dissociation constant of enzyme-substrate complex, ks (2.74?×?103),?Michaelis constant, km (2.74?×?103 M),?and the specific activity of enzyme on substrate concentration (1?×?10-1 w/v%). The result of this study showed that the equilibrium step involving k-1/k1 is the limiting step deciding the direction of reaction as well as the specific activity of the enzyme.展开更多
文摘The rate of cane sugar fermentation with Saccharomyces cerevisiae was studied at temperatures between 30°C and 42°C in order to characterize the process using thermodynamic parameters such as enthalpy (ΔH*), activation energy (ΔE*), entropy (ΔS*), Gibbs free energy (ΔG*) and equilibrium constant (K). The parameters were evaluated on the basis of a consideration of Arrhenius, Eyring and Van’t Hoff’s equations. The results obtained are ΔH*, 91.85 KJ·mol-1;ΔE*, 91.85 KJ·mol-1, ΔS*, 2763 J·mol-1K-1;ΔG*, -762.09 KJ·mol-1, and equilibrium constant, K, 1.34 dm3·mol-1. These values were subsequently used to obtain by calculation the rate constant of the fermentation k, 1.43 × 1011 min-1, Arrhenius constant A (pre-exponential or frequency factor), 4.79 × 1026 min-1, orientation parameter, P, 4.48 × 1015 and the collision frequency Z, 1.07 × 1011 min-1. Finally the fermentation efficiency calculated on the basis of a complete combustion of glucose is 377.8%. The results showed that though the fermentation process is kinetically controlled, it is suggested that the positive impact of the feasible thermodynamics is limited by other process variables.
文摘The fermentation of cane sugar as substrate by Saccharomyces cerevisiae (enzyme) was critically investigated to obtain certain useful kinetic parameters and to determine the effect of temperature, pH, substrate and yeast (enzyme) concentration on the rate of fermentation. The results indicate that the rate of fermentation (measured as rate of production of CO2) increased in proportion with temperature (optimum 32°C?-?36°C), pH (optimum 5.5) substrate (optimum 50?v/v%) and yeast concentration (optimum 3.5?-?4.5?w/v%) up to a limit and subsisted?either as a plateau and/or, decreases as the case may be. This suggests that the reaction takes place in two steps. The kinetic parameters examined are maximum rate of reaction Vmax (2.0?×?102 M·min-1), catalytic constant, k2 (1.81?×?10-1 min-1), overall rate constant, k (1.53?×?101 min-1),?order of initial reaction (approx. first order),?dissociation constant of enzyme-substrate complex, ks (2.74?×?103),?Michaelis constant, km (2.74?×?103 M),?and the specific activity of enzyme on substrate concentration (1?×?10-1 w/v%). The result of this study showed that the equilibrium step involving k-1/k1 is the limiting step deciding the direction of reaction as well as the specific activity of the enzyme.
