The rates of biomass growth R X , product formation Rp and R ' p and substrate consumption Rs and Rs during the reactor filling phase may be calculated by equations 16 to Table 1 shows the results obtained during the reactor filling phase of a fed-batch ethanol fermentation of sugar-cane molasses medium carried out under the following experimental conditions Koshimizu, ; Koshimizu et al.
In the case of ethanol fermentation, the concentration of intracellular ethanol would be equal to the concentration of ethanol in the medium aqueous phase Pamment and Dasari, Hence, if the purpose of the test is to study the process performance taking account of both the intracellular and the extracellular ethanol, the values of P , P f and P i could be used in Equations 11 , 14 and 18 instead of P ', P ' f and , respectively.
If, however, the purpose would be to study the process performance taking account of only the extracellular ethanol, since only the medium aqueous phase is distilled, Equations 11 , 14 and 18 must be used.
Calling , Q '' and the ethanol yield factor, the process productivity and the ethanol production rate, respectively, calculated taking account of both the extracellular and the intracellular ethanol, Equation 23 to 25 must be used. Table 2 shows the calculated values of V , D , S ' and P ' during the reactor feeding phase.
The above values showed that Y X was 1. It was then possible to conclude that, in this example, the volume of the biomass in the fermenting medium: a did not affect the calculated value of the biomass yield factor; b did not affect the calculated values of the ethanol yield factor and process productivity when the intracellular ethanol was also considered; c affected the values of the ethanol yield factor and process productivity when only the extracellular ethanol was considered.
Abrir menu Brasil. Brazilian Archives of Biology and Technology. Abrir menu. Walter Borzani About the author. Aqueous Phase Volume Considering that the biomass concentrations are measured in the whole medium, and that the substrate and product concentrations are measured in the medium aqueous phase, that is, in the filtered or centrifuged medium, it is necessary to evaluate the aqueous phase volume in order to calculate the actual masses of the substrate and product in the fermenting medium.
Borzani, W. Lett , 17 , The amount of carbon dioxide released by the yeast in three minutes can be compared for each of the carbohydrates. The more carbon dioxide that was released in three minutes, the faster the rate of respiration with that carbohydrate substrate.
To be able to compare results we need to ensure that control variables are kept the same during the experiment. Name two control variables for the experiment above. Two from:. In an experiment, Sarah found that 1 g of yeast produced 20 cm 3 of carbon dioxide in three minutes when using glucose as a substrate. What was the rate of respiration in cm 3 of CO 2 per minute when using glucose?
The rate needs to be calculated in cm 3 of CO 2 per minute. We know that 20 cm 3 of CO 2 was produced in three minutes. To calculate the rate of CO 2 produced per minute we need to divide the volume of CO 2 produced by the time it took to produce that volume of CO 2.
Next, we decided to investigate how the rate of fermentation depends on the concentration of the sugar. It can be seen that the initial rate of CO 2 mass loss is the same for the Of course the total amount of CO 2 given off by the Later, we repeated this experiment using sucrose in place of glucose and obtained the same result.
Comparison of the mass of CO 2 released vs time for the fermentation of Each sugar sample was dissolved in mL of water and then 7. After seeing that the rate of yeast fermentation does not depend on the concentration of sugar under the conditions of our experiments, we decided to see if it depends on the concentration of the yeast.
We took two The results are shown in Fig. It can clearly be seen that the rate of CO 2 release does depend on the concentration of the yeast. The slope of the sample with 7. We repeated the experiment with sucrose and fructose in place of glucose and obtained similar results.
Comparison of the mass of CO 2 released vs time for the fermentation of two One had 7. In hindsight, the observation that the rate of fermentation is dependent on the concentration of yeast but independent of the concentration of sugar is not surprising. Enzyme saturation can be explained to students in very simple terms. A molecule such as glucose is rather small compared to a typical enzyme. The large molecular ratio of sugar to enzyme clearly means that every enzyme site is occupied by a sugar molecule.
Thus, doubling or halving the sugar concentration cannot make a significant difference in the initial rate of the reaction. On the other hand, doubling the concentration of the enzyme should double the rate of reaction since you are doubling the number of enzyme sites. The experiments described here are easy to perform and require only a balance good to 0. The results of these experiments can be discussed at various levels of sophistication and are consistent with enzyme kinetics as described by the Michaelis-Menten model.
For enzyme reactions such as this, the reaction does not take place if the temperature is too high because the enzymes get denatured. The effect of pH and salt concentration can also be investigated. Skip to main Skip to footer. April Introduction Enzyme catalysis 1 is an important topic which is often neglected in introductory chemistry courses.
Fermentation rate of sucrose, lactose alone, and lactose with lactase Fig. Fermentation rate of sucrose, glucose and fructose Next we decided to compare the rate of fermentation of sucrose with that glucose and fructose, the two compounds that make up sucrose.
Fermentation rate and sugar concentration Next, we decided to investigate how the rate of fermentation depends on the concentration of the sugar.
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