Does The Ammount Of Sugar Change The Fermentation Rate

Introduction

Enzyme catalysis¹ is an important topic which is often neglected in introductory chemical science courses. In this paper, we nowadays a simple experiment involving the yeast-catalyzed fermentation of sugars. The experiment is easy to comport out, does non require expensive equipment and is suitable for introductory chemistry courses.

The sugars used in this study are sucrose and lactose (disaccharides), and glucose, fructose and galactose (monosaccharides). Lactose, glucose and fructose were obtained from a health nutrient store and the galactose from Carolina Science Supply Visitor. The sucrose was obtained at the grocery store as white sugar. The question that we wanted to respond was "Do all sugars undergo yeast fermentation at the same rate?"

Sugar fermentation results in the production of ethanol and carbon dioxide. In the instance of sucrose, the fermentation reaction is:

\[C_{12}H_{22}O_{11}(aq)+H_2 O\overset{Yeast\:Enzymes}{\longrightarrow}4C_{two}H_{v}OH(aq) + 4CO_{2}(g)\]

Lactose is also C₁₂H₂₂O₁₁ but the atoms are bundled differently. Earlier the disaccharides sucrose and lactose can undergo fermentation, they have to be broken down into monosaccharides by the hydrolysis reaction shown below:

\[C_{12}H_{22}O_{xi} + H_{ii}O \longrightarrow 2C_{half-dozen}H_{12}O_{six}\]

The hydrolysis of sucrose results in the formation of glucose and fructose, while lactose produces glucose and galactose.

sucrose + water \(\longrightarrow\) glucose + fructose

lactose + h2o \(\longrightarrow\) glucose + galactose

The enzymes sucrase and lactase are capable of catalyzing the hydrolysis of sucrose and lactose, respectively.

The monosaccharides glucose, fructose and galactose all accept the molecular formula C_viH₁₂O_half-dozen and ferment as follows:

\[C_{6}H_{12}O_{6}(aq)\overset{Yeast Enzymes}{\longrightarrow}2C_{2}H_{five}OH(aq) + 2CO_{2}(thou)\]

Experiment

In our experiments 20.0 g of the sugar was dissolved in 100 mL of tap water. Side by side 7.0 g of Cherry Star^® Quick-Rise Yeast was added to the solution and the mixture was microwaved for fifteen seconds at total power in order to fully activate the yeast. (The microwave power is 1.65 kW.) This resulted in a temperature of most 110^oF (43^oC) 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 part of time. The reaction mixture was kept at ambience temperature, and no attempt at temperature control was used. Each package of Red Star Quick-Rise Yeast has a mass of 7.0 yard so this amount was selected for convenience. Other brands of baker'south yeast could take been used.

This method of studying chemical reactions has been reported past Lugemwa and Duffy et al.^2,iii We used a balance expert to 0.i g to do the measurements. Although fermentation is an anaerobic process, it is not necessary to exclude oxygen to practise these experiments. Lactose and galactose dissolve slowly. Mild oestrus using a microwave profoundly speeds upwards the process. When using these sugars, allow the sugar solutions to absurd to room temperature before adding the yeast and microwaving for an additional 15 seconds.

Fermentation rate of sucrose, lactose alone, and lactose with lactase

Fig. 1 shows plots of mass loss vs fourth dimension for sucrose, lactose alone and lactose with a dietary supplement lactase tablet added 1.v hours earlier starting the experiment. All samples had 20.0 k of the corresponding carbohydrate and 7.0 g of Ruby Star Quick-Rise Yeast. Initially the mass loss was recorded every thirty minutes. Nosotros continued taking readings until the mass leveled off which was nigh 600 minutes. If one wanted to speed upwards the reaction, a larger amount of yeast could exist 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 crusade the lactose to ferment. Even so, when lactase is nowadays significant fermentation occurs. Lactase causes lactose to split into glucose and galactose. A comparing of the sucrose fermentation bend with the lactose containing lactase bend shows that initially they both ferment at the aforementioned rate.

Fig. i. Comparison of the mass of CO₂ released vs time for the fermentation of sucrose, lactose alone, and lactose with a lactase tablet. Each 20.0 k sample was dissolved in 100 mL of tap h2o and then 7.0 g of Carmine Star Quick-Rise Yeast was added.

Still, when the reactions go to completion, the lactose, lactase and yeast mixture gives off only about half every bit much CO₂ as the sucrose and yeast mixture. This suggests that one of the two sugars that issue 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 establish that in the presence of yeast glucose readily undergoes fermentation while no fermentation occurs in galactose.

Fig. 2. Comparing of the mass of CO_two released vs time for the fermentation of sucrose, glucose and fructose. Each 20 1000 sugar sample was dissolved in 100 mL of water and so 7.0 g of yeast was added.

Fermentation rate of sucrose, glucose and fructose

Next we decided to compare the rate of fermentation of sucrose with that glucose and fructose, the 2 compounds that make upwardly sucrose. We hypothesized that the disaccharide would ferment more slowly because information technology would first have to undergo hydrolysis. In fact, though, Fig. two shows that the three sugars give off CO₂ at near the aforementioned charge per unit. Our hypothesis was wrong. Although there is some divergence of the three curves at longer times, the sucrose curve is ever as high every bit or higher than the glucose and fructose curves. The observation that the full amount of CO₂ released at the end is not the same for the 3 sugars may be due to the purity of the fructose and glucose samples not beingness as high as that of the sucrose.

Fermentation rate and sugar concentration

Next, nosotros decided to investigate how the rate of fermentation depends on the concentration of the sugar. Fig. three shows the yeast fermentation curves for 10.0 g and 20.0 g of glucose. It tin be seen that the initial rate of CO₂ mass loss is the same for the 10.0 and 20.0 1000 samples. Of grade the total amount of CO₂ given off by the 20.0 g sample is twice as much as that for the ten.0 g sample as is expected. Later, we repeated this experiment using sucrose in place of glucose and obtained the same outcome.

Fig. 3. Comparing of the mass of CO₂ released vs time for the fermentation of 20.0 g of glucose and x.0 g of glucose. Each sugar sample was dissolved in 100 mL of water and so 7.0 m of yeast was added.

Fermentation rate and yeast concentration

Later on seeing that the rate of yeast fermentation does not depend on the concentration of sugar under the conditions of our experiments, nosotros decided to see if it depends on the concentration of the yeast. We took two 20.0 thousand samples of glucose and added vii.0 grand of yeast to one and iii.5 m to the other. The results are shown in Fig. 4. Information technology can clearly be seen that the rate of CO_two release does depend on the concentration of the yeast. The slope of the sample with seven.0 g of yeast is nearly twice as large as that with 3.5 k of yeast. Nosotros repeated the experiment with sucrose and fructose in identify of glucose and obtained similar results.

Fig. 4. Comparing of the mass of CO_two released vs fourth dimension for the fermentation of two 20.0 g samples of glucose dissolved in 100 mL of water. One had 7.0 g of yeast and the other had 3.5 g of yeast.

Discussion

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 exist explained to students in very uncomplicated terms. A molecule such as glucose is rather small compared to a typical enzyme. Enzymes are proteins with large molar masses that are typically greater than 100,000 yard/mol.¹ Clearly, at that place are many more glucose molecules in the reaction mixture than enzyme molecules. The large molecular ratio of sugar to enzyme clearly ways that every enzyme site is occupied past a sugar molecule. Thus, doubling or halving the sugar concentration cannot make a meaning difference in the initial rate of the reaction. On the other manus, 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 like shooting fish in a barrel to perform and require simply a remainder good to 0.1 g and a timer. The results of these experiments can be discussed at diverse levels of sophistication and are consistent with enzyme kinetics as described past the Michaelis-Menten model.¹ The experiments can exist extended to look at the effect of temperature on the charge per unit of reaction. For enzyme reactions such as this, the reaction does not take place if the temperature is likewise high because the enzymes get denatured. The effect of pH and salt concentration can also be investigated.

References

1. Jeremy M. Berg, John L. Tymoczko and Lubert Stryer,Biochemistry, 6th edition, W.H. Freeman and Visitor, 2007, pages 205-237.
2. Fugentius Lugemwa, Decomposition of Hydrogen Peroxide,Chemical Educator, April 2013, pages 85-87.
3. Daniel Q. Duffy, Stephanie A. Shaw, William D. Bare, Kenneth A. Goldsby, More Chemistry in a Soda Bottle, A Conservation of Mass Activity,Journal of Chemical Teaching, August 1995, pages 734-736.
4. Jessica L Epstein, Matthew Vieira, Binod Aryal, Nicolas Vera and Melissa Solis, Developing Biofuel in the Teaching Laboratory: Ethanol from Diverse Sources,Periodical of Chemical Didactics, April 2010, pages 708–710.

Does The Ammount Of Sugar Change The Fermentation Rate,

Source: https://uwaterloo.ca/chem13-news-magazine/april-2015/activities/fermentation-sugars-using-yeast-discovery-experiment

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