Fermentation Lab Report

The Effect of Sugar Type on Rate of Energy Production During Yeast Fermentation Sarah Sulon Biology Lab 111L Dr. Murray October 25 2010

Abstract The experiment was conducted to determine the impact different sugar types have on yeast fermentation. It was hypothesized that glucose, sucrose and fructose would all produce energy through yeast fermentation, but that sucrose would have the greatest rate of energy production. The carbon dioxide production was tracked in the fermentation of yeast with solution of no sugar, glucose, fructose, and sucrose over a period of twenty minutes. All of the sugars produced energy, but glucose was the most efficient of the three, even producing energy at three times the rate of fructose. This difference in efficiency is a result of the various pathways the sugars must take to enter glycolysis. Glucose could enter directly while sucrose had to be broken down and fructose required modification to enter as an intermediate.

Introduction

Respiration makes up a cell’s metabolic process where carbohydrates are converted into energy to be used by the cell. Cellular respiration can take one of two pathways; aerobic or anaerobic respiration. Anaerobic respiration occurs in the absence of oxygen. This pathway produces much less oxygen than aerobic respiration because only glycolysis occurs. The Krebs cycle and the electron transport chain are blocked since oxygen is not present to accept the electrons at the end. In anaerobic respiration, glycolysis is followed by a side reaction to regenerate the NAD+ used to accept electrons from the carbohydrate. In animals, this reaction is lactic acid fermentation while in plants and fungi, ethanol fermentation occurs. These methods are far less efficient than aerobic respiration (Cellular, 54). Ethanol fermentation begins after glucose has been converted into two pyruvates during glycolysis. This pyruvate then is broken into acetylealdehyde and a carbon is released in the form of carbon dioxide. Ethanol is formed through the reduction of acetylealdehyde by NADH (Freeman, 2011). Saccharomyces cerevisiae or baker ’s yeast is a type of fungus that undergoes ethanol fermentation when there is a lack of oxygen. In the wild, it is found on the skins of fruit and uses their sugars for food. Through its anaerobic respiration, it is used to produce ethanol for alcoholic drinks and allows bread to rise with its carbon dioxide production (Cummings, 2008). Since carbon dioxide is an immediate by-product of the anaerobic respiration of yeast, its production can be tracked to determine the efficiency of the energy production. There are many environmental factors that can impact the efficiency of the energy yield of baker’s yeast. These include pH, temperature and available nutrients. The amount of carbon present is the most important nutritional requirement since yeast produces energy through the processing of carbohydrates (Cellular, 54).

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Yeast is not limited to glucose for its sugar requirement in glycolysis. Different types of yeasts can process different forms of carbon compounds but most yeast can metabolize glucose and sucrose. Stelling-Dekker’s detailed studies on yeast also concluded that if a certain species of yeast can process glucose, it can also metabolize fructose and mannose. The majority of yeasts ferment glucose most efficiently, though there are some exceptions (Berg, 2002). Both glucose and fructose have the same molecular formula, C6H12O6, and form a hexacarbon ring. The only difference lies in the hydrogen-oxygen arrangements (Freeman, 72-73).

Though

glucose is the reactant in glycolysis, fructose is an intermediate before the formation of pyruvate and the raw form can enter the chain at the appropriate step (Berg, 2002).

Sucrose is a

polysaccharide that consists of glucose and fructose. Many types of yeast contain the necessary enzymes to break sucrose into the monomer subunits necessary for glycolysis (Freeman, 189). It was hypothesized that during yeast fermentation glucose, sucrose and fructose would all produce energy but would vary in efficiency. Previous research and results supported that this hypothesis was plausible.

Yeast can process many forms of sugars through different

methods of integration into glycolysis but glucose is the most efficient since it is the original reactant in the chain (Berg, 2002).

Materials and Methods Preparing the Solution 3

Four 100 ml beakers were obtained and labeled 1-4. 5ml of deionized water were added to each of the beakers. 5% glucose, sucrose and fructose solutions was acquired and 15ml of glucose solution was added to beaker 2, 15ml of fructose solution was added to beaker 3 and 15ml of sucrose solution was added to beaker 4. Beaker 1 was designated as the control and contained no sugar solution. In a 200ml beaker, 14mg of yeast was added to 100ml of deionized water. The solution was mixed completely and set aside. A 30 degree Celsius water bath was prepared. Four fermentation tubes were obtained and labeled 1-4. 15ml of the yeast solution was added to each of the beakers at the same time so that fermentation time was consistent across the four solutions. Recording Fermentation Rates Solutions were transferred to their respectively labeled fermentation tubes. The initial height of the gas bubble was recorded at the top of the tube for all four solutions. Each of the fermentation tubes was placed in the 30 degree Celsius water bath. Every two minutes the actual height of the air bubble was recorded for each tube.

The carbon dioxide produced by

fermentation was determined by subtracting the initial height from the actual height. This process was continued for twenty minutes. After this was completed, the fermentation tubes were removed from the water bath.

Data Analysis A scatter plot graph of carbon dioxide production in mm versus time in minutes was created to analyze how different sugars impacted the rate of fermentation of yeast. 4

Each

fermentation tube had a designated point on the graph with each 2 minute increment marked at the appropriate carbon dioxide height. A line of best fit for each of the tubes was created. The slope of each line indicated the average rate of fermentation for each tube.

Results Production of CO2 by Yeast with Various Sugar Compounds time (min) tube 1 tube 2 tube 3 tube 4 actual 6 6 6 6 6 6 6 6 6 6

2 4 6 8 10 12 14 16 18 20

test

CO2 0 0 0 0 0 0 0 0 0 0

actual 28 45 55 68 85 97 105 115 122 132

CO2 14 31 41 54 71 83 91 101 108 118

actual 0 0 3 6 10 17 20 34 42 56

average rate of production (CO2

tube 1

sugar none glucos

mm/min) 0

2

e fructos

12.64

3

e sucros

3.99

4

e

9.27

5

CO2 0 0 3 6 10 17 20 34 42 56

actual 9 18 25 37 50 59 69 81 91 102

CO2 4 13 20 32 45 54 64 76 86 97

The different types of sugars used in fermentation had a significant impact on the amount of carbon dioxide produced. Glucose produced the most with a gas bubble of 132mm while sucrose yielded 102mm of carbon dioxide. The gas byproduct in fructose measured only 56mm. The control with no sugar resulted in 0mm of carbon dioxide and was the least productive of the tubes. The slope of the line of best fit was analyzed to determine the average rate of carbon dioxide production over the 20 minute time frame. Glucose was the most efficient, producing 12.64 mm of carbon dioxide per minute. Sucrose yielded 9.27 mm of carbon dioxide per minute during fermentation while fructose functioned at a rate of 3.99 mm of carbon dioxide per minute. The control that contained no sugar had no rate of carbon dioxide production. The rate of production of carbon dioxide for both glucose and sucrose remained fairly constant throughout the experiment. The rate for fructose began slowly but increased rapidly as time went on. The rate of production of carbon dioxide remained at a constant 0 throughout.

Discussion The hypothesis was supported in that all forms of sugar produced energy and that glucose was the most efficient. The carbon dioxide produced can be directly related to the energy produced through fermentation because carbon dioxide is a by-product of ethanol fermentation (Cellular, 54). The control that contained no sugar produced no energy because a source of sugar is required for glycolysis and fermentation to occur. Glucose had the greatest rate of energy production because its rate of carbon dioxide production was the largest. Sucrose had the second highest rate of production while fructose had the lowest rate out of the three sugars. Glucose’s rate of energy production was more than three times that of fructose. Glucose was directly used 6

in the glycolysis cycle and did not require any extra energy to convert it into a usable form (Freeman, 154). This supported why glucose was the most efficient. Sucrose required an enzyme and energy input to break it down into glucose and fructose in order for it to be processed in glycolysis (Freeman, 189). Fructose also could not be used immediately in the glycolysis chain but had to be altered to enter the chain as one of the intermediates (Berg, 2002). These processes required to convert the non-glucose sugars into a usable form reduced their efficiency when compared to glucose. The largest source of error for the experiment was the start time of fermentation. The yeast was added to the fructose solution well after the glucose and fructose yeast solutions began fermenting. Fermentation takes time to reach its maximum rate of energy production so the time gap left glucose and sucrose further ahead than fructose in the fermentation process (Berg, 2002). The data on rate of carbon dioxide production was therefore skewed because the start of fermentation was not controlled. Glucose and sucrose appear far more efficient than fructose because of this error. If this experiment were to be repeated, extra care would be taken to ensure that fermentation began at the same time. The measurements of sugars would be measured in equal molarity and not by percent in a solution so that the sugar molecules are equal across all of the tests.

Other follow-up experiments may

include testing other types of yeasts to see how fermentation rates are impacted. The results of these experiments could impact what sugars are the most efficient in alcohol fermentation. This could determine what types of sugar brewers should use for the most efficient production of alcohol.

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Works Cited Berg, Jeremy M., John L. Tymoczko, and Lubert Stryer. "16.1: Glycolysis Is an EnergyConversion Pathway in Many Organisms." Biochemistry. New York: W.H. Freeman, 2002. National Center for Biotechnology Information. Web. 24 Oct. 2010. . "Cellular Respiration and Fermentation." Symbiosis: The Pearson Custom Library for the Biological Sciences. Ed. Kelly Harris. New York: Pearson Custom, 2009. 53-54. Print. Cummings, Richard D., Jeffrey D. Esko, Hudson H. Freeze, Gerald W. Hart, and Marilynn E. Etzler. "Saccharomyces Cerevisiae, the Model Yeast." Essentials of Glycobiology. By Ajit Varki. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 2008. National Center for Biotechnology Information. Web. 24 Oct. 2010. . Freeman, Scott. "An Introduction to Carbohydrates, Cellular Respiration and Fermentation." Biological Science. San Fransicso, CA: Benjamin Cummings, 2011. 72+. Print.

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