Kinetics of Substrate Utilization, Ethanol Production and Biomass Formation of Saccharomyces cerevisiae HBY3 Strain Under Aerobic Conditions

Author : Demegilo, Fleurdelis Jane Decolongon
Major Adviser : Calibo, Ronnie L.
Committee Members : Acda, Reynaldo I.; Arquiza, Apollo C.
Year : 1993
Month : August
Type : Thesis
Degree: BS
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The local distillery yeast strain, Saccharomyces cerevisiae HBY3, was cultivated in batch and continuous cultures to determine its substrate assimilation, biomass formation and ethanol production kinetics. Fermentation medium for the study was formulated using Restricted Random Balance Design. The basal medium for the study contained: 100 g/l sugar in molasses, 3 g/l urea, 1 g/l rice bran, 1 g/l MgSO₄-7H₂O and 1 g/l KH₂PO₄. Proportionate concentrations of the other components in the medium were used when sugar concentrations were varied during the study. Batch cultivation using this basal medium, at initial sugar concentration, So = 17, 87 and 168 g/l, resulted to a cell yield of 0.5 g-cell/g-sugar and an ethanol yield of 0.8 g-EtOH/g-sugar. These values were determined through a computerized trial-and-error method using BTCHSIM1 program, which contains the Runge-Kutta-Gill numerical method that solves the simultaneous differential equations of Nakatani (as cited by Takamatsu, 1985). Cell yield through ethanol consumption was also determined from the batch culture results using the second preparation technique, was 0.14/hr. The other constants used in the model adopted the following values : K1 = 0.0023 l/g-cell-hr, K2 = 0.0070 l/g-cell, n = 2 and m = 0.03. Initial inhibitor concentrations were varied at 0.0001, 0.001 and 0.003 g/l for So at 17, 87 and 168 g/l, respectively. Continuous cultivation using dilution rates of 0.50 g-cell/g-sugar and an increasing ethanol yield of 0.74, 0.76 and 0.77 g-EtOH/g-sugar. The values of the constants for the strain are close to those of Saccharomyces cerevisiae baker’s yeasts’ except ethanol yield, Ye/S, since its value determined for the strain is very high compared to baker’s yeast’s and the stoichiometric ration for ethanol production which is 0.51 g-EtOH/g-sugar. This verifies the claim that this local yeast strain is a high ethanol producer. Prediction of the effects of variables such as initial sugar, cell, and ethanol concentrations on the strain’s behavior was also done using the verified batch model constants.

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