The microwave power is 1. This resulted in a temperature of about o F 43 o C which is in the recommended temperature range for activation. The cap was loosened to allow the carbon dioxide to escape. The mass of the reaction mixture was measured as a function of time. The reaction mixture was kept at ambient temperature, and no attempt at temperature control was used.
This method of studying chemical reactions has been reported by Lugemwa and Duffy et al. Although fermentation is an anaerobic process, it is not necessary to exclude oxygen to do these experiments. Lactose and galactose dissolve slowly. Mild heat using a microwave greatly speeds up the process. When using these sugars, allow the sugar solutions to cool to room temperature before adding the yeast and microwaving for an additional 15 seconds.
All samples had Initially the mass loss was recorded every 30 minutes. We continued taking readings until the mass leveled off which was about minutes. If one wanted to speed up the reaction, a larger amount of yeast could be used.
The results show that while sucrose readily undergoes mass loss and thus fermentation, lactose does not. Clearly the enzymes in the yeast are unable to cause the lactose to ferment. However, when lactase is present significant fermentation occurs. Lactase causes lactose to split into glucose and galactose. A comparison of the sucrose fermentation curve with the lactose containing lactase curve shows that initially they both ferment at the same rate.
Comparison of the mass of CO 2 released vs time for the fermentation of sucrose, lactose alone, and lactose with a lactase tablet.
Each However, when the reactions go to completion, the lactose, lactase and yeast mixture gives off only about half as much CO 2 as the sucrose and yeast mixture. This suggests that one of the two sugars that result when lactose undergoes hydrolysis does not undergo yeast fermentation.
In order to verify this, we compared the rates of fermentation of glucose and galactose using yeast and found that in the presence of yeast glucose readily undergoes fermentation while no fermentation occurs in galactose. Comparison of the mass of CO 2 released vs time for the fermentation of sucrose, glucose and fructose. Each 20 g sugar sample was dissolved in mL of water and then 7. Next we decided to compare the rate of fermentation of sucrose with that glucose and fructose, the two compounds that make up sucrose.
We hypothesized that the disaccharide would ferment more slowly because it would first have to undergo hydrolysis. In fact, though, Fig. Our hypothesis was wrong. Although there is some divergence of the three curves at longer times, the sucrose curve is always as high as or higher than the glucose and fructose curves. The observation that the total amount of CO 2 released at the end is not the same for the three sugars may be due to the purity of the fructose and glucose samples not being as high as that of the sucrose.
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 A fifth flask can be used as a control.
Place a balloon on each flask. If you can use a warm water bath, this will speed up the reactions, though some changes should be visible within 20 minutes. Leave overnight for more dramatic changes. Have students make observations and develop a CER chart that explains what happened and answers the experimental question. The balloons inflate as yeast consumes glucose and releases carbon dioxide glycolysis.
Inflation will occur with glucose and sucrose, but not with lactose. Yeast do not have the lactase enzyme and cannot break down lactose. If you add lactaid, lactose will be broken down into glucose and galactose, which can be used by the yeast.
For the control experiment, does glycolysis happen? The control only has the yeast in it, so there is no nutrient source glucose. Glycolysis does not happen, the balloon will not inflate. How much glucose, lactose, sucrose are you putting in each flask?
I used 5g of each nutrient. I put about a teaspoon of each in about ml. I do warm up the liquid which seems to make it work best. Lactose will not work at all unless you add lactase to it, yeast cannot break down lactose.
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