Effect of Sugars on Yeast Fermentation

THE EFFECT OF VARIOUS SUGAR TO YEAST FERMENTATION

Abstract

All living thing on earth can uptake energy from the environment to do biological work by cellular respiration and fermentation. Yeast breaks down glucose to conduct fermentation, release energy, and produce alcohol or other organic acid and carbon dioxide. This experiment is conducted to study the effective various forms of sugar that substitute to produce energy and influence the metabolic activities of yeast. Using five Ziploc bags with yeast and each with different solutions from varying sugar content, and one bag as the control analyzes the speed increase of fermentation of yeast and compare to each other. Throughout the experiment, the amount of CO₂ bubbles measures the bag thickness by a ruler, and measure the acidic of yeast production by pH indicator. From the experiment, the data gathered show that the higher sugar in a solution, the faster in the rate of fermentation. This means the amount of gas production and the acidic of the solution will be raised up.

Introduction

 Cellular respiration is the process of releasing energy in the form of adenosine triphosphate (ATP) from the glucose (C₆H₁₂O­₆) in the food. Cells need these energies for cellular work, all the activities of life. Cellular respiration occurs partially in the cytoplasm, and most of the steps occurs in the mitochondria. Cellular respiration involves four stages process: glycolysis, intermediate stage, Krebs cycle, and electron transport chain. Glycolysis occurs in the presence or absence of oxygen called anaerobic pathway. But the other stage requires the presence of oxygen called aerobic pathway. Substrate level phosphorylation includes glycolysis and Krebs cycle stage. Oxidative phosphorylation is the electron transport chain stage that produces ATP with oxygen as a terminal electron acceptor. The overall chemical reaction is

C₆H₁₂O­₆ + 6O₂  6CO₂ + 6H₂O + ~ 38 ATP

Fermentation is an anaerobic pathway for breaking down a glucose. Glycolysis is the only pathway to obtain energy in fermentation. Because of lacking the presence of oxygen, the pyruvate cannot continue to go the Krebs cycle and the electron transport chain. In fermentation, the electron transport chain isn’t functional, the NADH made in glycolysis cannot drop its electrons off, then it turns back into NAD⁺ and regenerates.

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 There are few different types of fermentation. One of them is lactic acid fermentation (figure 1). After glycolysis, NADH transfers its electrons to pyruvate to generate lactate as a product. Lactate is the deprotonated form of lactic acid. Muscle cell also carries out lactic acid fermentation. Then, lactic acid is transported through the bloodstream to the liver that converted back to pyruvate and processed in the remaining reactions of cellular respiration.

Another fermentation type is alcohol fermentation (figure 2). In this process, NADH donates its electron to pyruvate and produce ethanol. It involves two steps process to produce ethanol. At first, a carboxyl group is removed from pyruvate and released carbon dioxide and produce acetaldehyde. Second, NADH passes its electrons to acetaldehyde, regenerate NAD⁺ and forming ethanol. Alcohol fermentation by yeast produces the ethanol found in alcoholic drinks like beer and wine.

In this experiment, we will work with baker’s yeast or Saccharomyces cerevisiae that can metabolize sugar for both alcohol fermentation and cellular respiration, also known as facultative anaerobes, when in need. It is a living organism but safe to perform. We will measure the effect of varying sugar content in different solution to the rate of fermentation by gas production and pH indicator. If the solution with more sugar per serving size, then the more carbon dioxide will be produced and the more acidic it is, that indicates the increase in the rate of the fermentation. If the more carbon dioxide is produced, the diameter of airspace in the bag, which is the thickness of a bag, will be increased and bigger that indicates the amount of carbon dioxide was produced. If fermentation is taking place, it is more acidic that measured by pH indicator.

Materials and Methods

 In this experiment, the students need to have 6 Ziploc bags, baker’s yeast, water, orange juice (22g sugar per 240mL), berry drink (16g sugar per 240mL), mini calpico yogurt flavor (10g sugar per 80mL, which means 30g sugar per 240mL), rice punch (21g sugar per 240mL), Coke (39g sugar per 355mL, which means 26g sugar per 240mL), pH indicator, ruler, ¼ cup measuring, and stopwatch or timer from the phone.

To start, label 6 Ziploc bags with each solution water, orange juice, berry drink, mini calpico yogurt flavor, rice punch, and Coke to distinct and keep track it. With each bag add 1-teaspoon of the Saccharomyces cerevisiae yeast. Then add ¼ cup of each solution to each bag that identified by labeling. After adding the solution to each one of the bag, immediately measure the initiation pH indicator when yeast and the sugars do not react yet and record the measurement. The students must make sure the bag is zipped tightly to prevent the hole that leads to the escape of gas production. Start to time for twenty minutes. Then completely lay down the bag in the table, using the ruler to measure the thickness of the bag and record as initiation. Keep the bag lay down in the table. After twenty minutes have passed, note the change in the bubbles and the thickness of each bag that indicate the amount of carbon dioxide has been produced, record the observation. Again start to time for twenty minutes, measure and record the thickness of the bag as well as the bubble change. Repeat the process after twenty minutes each time for two hours. After two hours, observe and record the last process, open the Ziploc bag of each solution and measure the pH as a final product and record it. Now, it is time to clean up. The experiment is not hazardous. All material can be disposed of in the garbage can or down the drain.

Results 

 Table 1 represents the results of each solution with different sugar contents in the bag. The results indicate the amount of carbon dioxide produced in different solution in every twenty minutes for two hours long. The more sugar from the solution has, the more carbon dioxide is produced.

Table 1: Carbon Dioxide produced every twenty minutes in the different solution that contain different amount of sugar.

 Graph 1 shows the data from table 1 in a better form to compare and analyze the result. Coke has the highest sugar content than other solutions. The two peaks of orange juice and rice punch are almost produce the same amount of carbon dioxide.

Graph 1: Carbon Dioxide produced every twenty minutes by comparing the trends of data between the different solution.

 Table 2 shows the difference before and after of fermentation. Water set as the control, it does not change in its environment. Other solutions increase ten times more the acidic level, except rice punch is hundred times more acidic.

Table 2: Change in acidic of the different solution measured by pH indicator

Conclusion

 After looking at the experiment’s result, from table 1 and graph 1, we are able to determine that the relationship between the amount of sugar and the amount of carbon dioxide produced is directly proportional. Sugar increases the rate of fermentation, and it releases the higher gas produced. As we expect, Coke has 39g of sugar, in which the highest per serving size compared to other solution, produce the highest number of carbon dioxide. While berry drink contains the lowest amount of sugar, its rate of fermentation is lowest. From table 2, the fermentation does not occur in the water without sugar which is the control. Meanwhile, the fermentation had been occurred in other liquid food sources that make it more acidic by ten times, but only rice punch drink is hundred times more acidic from the initiation liquid. Therefore, our hypotheses were accepted and supported by the data.

 If I have a chance to perform this experiment again, I will be more careful about the bag that contains orange juice. What I expect is the orange juice and rice punch will have almost the same amount of carbon dioxide produced and constantly. But in the experiment, the data show that they are different, almost the same, then the gap is different again. Or if I do it in the second time, I will choose only orange juice or rice punch with another solution that will have much different sugar content, so we can have the result more specific.

References:

• Harwood, Jessica, and Douglas Wilkin. “Cellular Respiration Process.” CK-12 Foundation, CK-12 Foundation, 1 Sept. 2018, www.ck12.org/biology/cellular-respiration-process/lesson/Process-of-Cellular-Respiration-MS-LS/.
• “Cellular Respiration:” Chapter 3 – Proteins, 16 Feb. 2004, www.biology.iupui.edu/biocourses/N100/2k4ch7respirationnotes.html.
• “Saccharomyces Cerevisiae.” NeuroImage, Academic Press, www.sciencedirect.com/topics/neuroscience/saccharomyces-cerevisiae.
• “Fermentation and Anaerobic Respiration.” Khan Academy, Khan Academy, www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/variations-on-cellular-respiration/a/fermentation-and-anaerobic-respiration.