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PRODUCTION OF YEAST
A general kinetic and mass transfer model to simulate the growth of baker’s yeast in bio-reactors [1-3]
The proposed model can also simulate the Pasteur effect.The experiment by Oura was performed in a continuous reactor fed with a synthetic medium containing glucose. An air or gas mixture with variable oxygen content was used as the aerating gas. When the oxygen content of the gas aerating the culture was changed, samples were taken daily from the out-flowing suspension to ensure that a steady state had been attained. This usually occurred after three or four days. The experiment provides all the experimental data regarding glucose consumption, ethanol formation, oxygen consumption and carbon dioxide evolution for all different aerating gas conditions. Oura also reported the values of oxygen mass transfer for the different aerating conditions. These values have been determined using the sulphite oxidation method. The data reported in the figures show that the anaerobic, fermentative metabolism weakens as the aerobic oxidative metabolism increases until the oxygen content of gas reaches 20-25%, at which point the fermentative metabolism is completely suppressed. The oxidative metabolism of ethanol is inoperative in the condition of the performed run, because the glucose concentration there is always greater than 0. The curves in the figures represent the values calculated by simulation using the parameters reported in the table obtained by mathematical regression on experimental data. Because the fit is satisfactory, we can conclude that the proposed model can also simulate the Pasteur effect.
[1]Industrial & Engineering Chemistry Research (2003), 42(21), 5109-5116.
[2] Catalysis Today (2001), 66(2-4), 437-445
[3] Chemical Engineering Journal (2001), 82(1-3), 347-354.