what type of molecules does yeast need to conduct fermentation

Introduction

Enzyme catalysis¹ is an important topic which is oftentimes neglected in introductory chemistry courses. In this paper, we present a simple experiment involving the yeast-catalyzed fermentation of sugars. The experiment is easy to conduct out, does not 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 Company. The sucrose was obtained at the grocery store equally white sugar. The question that we wanted to respond was "Do all sugars undergo yeast fermentation at the same rate?"

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

\[C_{12}H_{22}O_{eleven}(aq)+H_2 O\overset{Yeast\:Enzymes}{\longrightarrow}4C_{2}H_{5}OH(aq) + 4CO_{2}(g)\]

Lactose is besides C₁₂H₂₂O₁₁ just the atoms are arranged differently. Before the disaccharides sucrose and lactose can undergo fermentation, they accept to be broken down into monosaccharides by the hydrolysis reaction shown beneath:

\[C_{12}H_{22}O_{11} + H_{2}O \longrightarrow 2C_{half-dozen}H_{12}O_{6}\]

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

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

lactose + water \(\longrightarrow\) 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 C₆H₁₂O_vi and ferment as follows:

\[C_{half-dozen}H_{12}O_{vi}(aq)\overset{Yeast Enzymes}{\longrightarrow}2C_{two}H_{5}OH(aq) + 2CO_{2}(g)\]

Experiment

In our experiments 20.0 m of the sugar was dissolved in 100 mL of tap water. Adjacent 7.0 one thousand of Ruby-red Star^® Quick-Rise Yeast was added to the solution and the mixture was microwaved for 15 seconds at total power in gild to fully actuate the yeast. (The microwave power is ane.65 kW.) This resulted in a temperature of virtually 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 function of time. The reaction mixture was kept at ambience temperature, and no effort at temperature control was used. Each bundle of Blood-red Star Quick-Rise Yeast has a mass of vii.0 m and then this amount was selected for convenience. Other brands of bakery's yeast could have been used.

This method of studying chemical reactions has been reported by Lugemwa and Duffy et al.^ii,three Nosotros used a balance good to 0.1 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 deliquesce slowly. Balmy estrus using a microwave greatly speeds upward the process. When using these sugars, allow the sugar solutions to cool to room temperature earlier adding the yeast and microwaving for an additional fifteen 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 one.5 hours before starting the experiment. All samples had 20.0 g of the respective sugar and 7.0 m of Red Star Quick-Rise Yeast. Initially the mass loss was recorded every thirty minutes. Nosotros continued taking readings until the mass leveled off which was well-nigh 600 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 crusade the lactose to ferment. However, when lactase is nowadays 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.

Fig. 1. Comparison of the mass of CO_two released vs time for the fermentation of sucrose, lactose alone, and lactose with a lactase tablet. Each xx.0 g sample was dissolved in 100 mL of tap water and and so 7.0 g of Red Star Quick-Ascension Yeast was added.

Still, when the reactions go to completion, the lactose, lactase and yeast mixture gives off only nigh half as much CO₂ equally the sucrose and yeast mixture. This suggests that i of the two sugars that upshot 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 institute that in the presence of yeast glucose readily undergoes fermentation while no fermentation occurs in galactose.

Fig. 2. Comparison of the mass of CO₂ released vs time for the fermentation of sucrose, glucose and fructose. Each xx g sugar sample was dissolved in 100 mL of water then 7.0 g of yeast was added.

Fermentation charge per unit 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. We hypothesized that the disaccharide would ferment more slowly because information technology would first have to undergo hydrolysis. In fact, though, Fig. 2 shows that the 3 sugars give off CO₂ at about the same charge per unit. Our hypothesis was wrong. Although in that location is some divergence of the three curves at longer times, the sucrose curve is always as loftier equally or higher than the glucose and fructose curves. The observation that the total amount of CO₂ released at the cease is non the aforementioned for the 3 sugars may exist due to the purity of the fructose and glucose samples non being every bit high as that of the sucrose.

Fermentation rate and carbohydrate concentration

Next, nosotros decided to investigate how the rate of fermentation depends on the concentration of the sugar. Fig. iii shows the yeast fermentation curves for 10.0 g and 20.0 chiliad of glucose. It can be seen that the initial rate of CO_two mass loss is the same for the x.0 and 20.0 g samples. Of grade the total corporeality of CO₂ given off past the twenty.0 grand sample is twice as much equally that for the 10.0 one thousand sample as is expected. Later on, nosotros repeated this experiment using sucrose in place of glucose and obtained the same event.

Fig. 3. Comparison of the mass of CO₂ released vs time for the fermentation of 20.0 g of glucose and ten.0 k of glucose. Each sugar sample was dissolved in 100 mL of water and then 7.0 thousand of yeast was added.

Fermentation rate and yeast concentration

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 ii 20.0 g samples of glucose and added vii.0 yard of yeast to i and 3.5 m to the other. The results are shown in Fig. 4. It can clearly exist seen that the rate of CO₂ release does depend on the concentration of the yeast. The slope of the sample with 7.0 g of yeast is almost twice as large as that with three.5 g of yeast. We repeated the experiment with sucrose and fructose in place of glucose and obtained similar results.

Fig. 4. Comparing of the mass of CO₂ released vs fourth dimension for the fermentation of two xx.0 yard 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.

Give-and-take

In retrospect, the observation that the rate of fermentation is dependent on the concentration of yeast just 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. Enzymes are proteins with large tooth masses that are typically greater than 100,000 g/mol.¹ Clearly, at that place are many more than glucose molecules in the reaction mixture than enzyme molecules. The large molecular ratio of carbohydrate to enzyme conspicuously means that every enzyme site is occupied past a sugar molecule. Thus, doubling or halving the carbohydrate concentration cannot brand a significant difference in the initial charge per unit 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 hither are easy to perform and require only a balance good to 0.1 g and a timer. The results of these experiments can be discussed at various levels of sophistication and are consequent with enzyme kinetics as described by the Michaelis-Menten model.^ane The experiments can be extended to look at the effect of temperature on the rate of reaction. For enzyme reactions such as this, the reaction does non take place if the temperature is also high considering the enzymes get denatured. The event of pH and salt concentration can besides be investigated.

References

1. Jeremy M. Berg, John L. Tymoczko and Lubert Stryer,Biochemistry, 6th edition, W.H. Freeman and Company, 2007, pages 205-237.
2. Fugentius Lugemwa, Decomposition of Hydrogen Peroxide,Chemic Educator, Apr 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 Education, August 1995, pages 734-736.
4. Jessica Fifty Epstein, Matthew Vieira, Binod Aryal, Nicolas Vera and Melissa Solis, Developing Biofuel in the Teaching Laboratory: Ethanol from Various Sources,Journal of Chemical Education, April 2010, pages 708–710.

ivywhistenoter.blogspot.com

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

Share this post