Enzyme catalysis1 is critical topic i m sorry is frequently neglected in introductory chemistry courses. In this paper, we existing a simple experiment including the yeast-catalyzed fermentation of sugars. The experiment is basic to carry out, does not require expensive equipment and is suitable for introductory chemistry courses.

You are watching: Do yeast equally utilize all sugars

The sugars offered in this study space sucrose and also lactose (disaccharides), and also glucose, fructose and galactose (monosaccharides). Lactose, glucose and fructose were derived from a health and wellness food store and the galactose from Carolina scientific research Supply Company. The sucrose was derived at the grocery keep as white sugar. The concern that we want to answer to be “Do every sugars experience yeast fermentation in ~ the very same rate?”

Sugar fermentation outcomes in the production of ethanol and also carbon dioxide. In the situation of sucrose, the fermentation reaction is:

Lactose is also C12H22O11 but the atoms room arranged differently. Before the disaccharides sucrose and lactose deserve to undergo fermentation, they need to be damaged down into monosaccharides by the hydrolysis reaction displayed below:

The hydrolysis that sucrose outcomes in the development of glucose and also fructose, while lactose to produce glucose and galactose.

sucrose + water (longrightarrow) glucose + fructose

lactose + water (longrightarrow) glucose + galactose

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

The monosaccharides glucose, furustos and galactose all have actually the molecule formula C6H12O6 and ferment as follows:


This an approach of studying chemical reactions has actually been reported by Lugemwa and Duffy et al.2,3 We provided a balance great to 0.1 g to perform the measurements. Back fermentation is an anaerobic process, that is not crucial to exclude oxygen to carry out these experiments. Lactose and galactose dissolve slowly. Mild warmth using a microwave greatly accelerates the process. As soon as using this sugars, permit the sugar services to cool come room temperature before adding the yeast and microwaving for secondary 15 seconds.

Fermentation price of sucrose, lactose alone, and lactose through lactase

Fig. 1 shows plots of massive loss vs time because that sucrose, lactose alone and also lactose with a dietary supplement lactase tablet added 1.5 hrs before beginning the experiment. Every samples had 20.0 g the the particular sugar and also 7.0 g the Red Star Quick-Rise Yeast. Originally the mass loss was recorded every 30 minutes. We ongoing taking readings till the mass leveled off which was around 600 minutes. If one wanted to speed up the reaction, a bigger amount the yeast could be used. The results show that while sucrose readily undergoes fixed loss and also thus fermentation, lactose walk not. Clearly the enzymes in the yeast room unable to cause the lactose come ferment. However, when lactase is present far-reaching fermentation occurs. Lactase causes lactose to break-up into glucose and galactose. A to compare of the sucrose fermentation curve with the lactose containing lactase curve shows that initially they both ferment in ~ the same rate.


Fig. 1. Compare of the massive of CO2 exit vs time for the fermentation that sucrose, lactose alone, and lactose with a lactase tablet. Each 20.0 g sample was liquified in 100 mL of tap water and also then 7.0 g of Red Star Quick-Rise Yeast was added.

However, once the reactions go to completion, the lactose, lactase and yeast mixture gives off just about half as lot CO2 as the sucrose and yeast mixture. This says that one of the 2 sugars that result when lactose experience hydrolysis does no undergo yeast fermentation. In order to verify this, we contrasted the rates of fermentation that glucose and galactose using yeast and found that in the visibility of yeast glucose conveniently undergoes fermentation if no fermentation wake up in galactose.


Fig. 2. To compare of the massive of CO2 released vs time because that the fermentation the sucrose, glucose and also fructose. Every 20 g sugar sample was liquified in 100 mL of water and also then 7.0 g of yeast to be added.

Fermentation price of sucrose, glucose and fructose

Next we made decision to to compare the rate of fermentation that sucrose with that glucose and fructose, the 2 compounds that comprise sucrose. Us hypothesized that the disaccharide would ferment much more slowly because it would very first have to experience hydrolysis. In fact, though, Fig. 2 mirrors that the 3 sugars provide off CO2 at about the same rate. Our hypothesis was wrong. Although there is some aberration of the 3 curves at much longer times, the sucrose curve is always as high together or greater than the glucose and also fructose curves. The monitoring that the complete amount that CO2 released at the end is no the exact same for the 3 sugars might be as result of the purity the the fructose and glucose samples not being as high as that of the sucrose.

Fermentation rate and sugar concentration

Next, we determined to investigate exactly how the price of fermentation depends on the concentration of the sugar. Fig. 3 shows the yeast fermentation curves because that 10.0 g and also 20.0 g of glucose. It deserve to be viewed that the initial price of CO2 mass lose is the very same for the 10.0 and 20.0 g samples. Of course the complete amount the CO2 given off by the 20.0 g sample is twice as lot as the for the 10.0 g sample together is expected. Later, we repetitive this experiment making use of sucrose in place of glucose and obtained the very same result.


Fig. 3. Comparison of the fixed of CO2 released vs time for the fermentation that 20.0 g the glucose and also 10.0 g of glucose. Each sugar sample was liquified in 100 mL the water and also then 7.0 g of yeast to be added.

Fermentation rate and also yeast concentration

After seeing that the rate of yeast fermentation does not rely on the concentration of street under the conditions of our experiments, we made decision to watch if it depends on the concentration of the yeast. Us took two 20.0 g samples the glucose and included 7.0 g that yeast to one and also 3.5 g come the other. The results are shown in Fig. 4. That can clearly be watched that the price of CO2 release does count on the concentration of the yeast. The slope of the sample through 7.0 g that yeast is around twice as large as that v 3.5 g the yeast. We recurring the experiment v sucrose and also fructose in ar of glucose and also obtained comparable results.


Fig. 4. To compare of the fixed of CO2 exit vs time because that the fermentation of two 20.0 g samples the glucose dissolved in 100 mL the water. One had actually 7.0 g the yeast and the other had actually 3.5 g that yeast.


In hindsight, the observation that the price of fermentation is dependence on the concentration of yeast but independent the the concentration of street is not surprising. Enzyme saturation can be explained to students in very basic terms. A molecule such together glucose is rather little compared to a common enzyme. Enzymes space proteins with big molar masses that are frequently greater than 100,000 g/mol.1 Clearly, there are many much more glucose molecules in the reaction mixture 보다 enzyme molecules. The large molecular ratio of sugar to enzyme clearly means the every enzyme site is occupied by a sugar molecule. Thus, copy or halving the street concentration cannot make a far-reaching difference in the initial price of the reaction. On the other hand, doubling the concentration that the enzyme should twin the rate of reaction because you space doubling the variety of enzyme sites.

The experiments described here are simple to perform and require just a balance great to 0.1 g and also a timer. The outcomes of these experiments deserve to be disputed at miscellaneous levels of sophistication and also are constant with enzyme kinetics as defined by the Michaelis-Menten model.1 The experiments can be expanded to look at the impact of temperature ~ above the rate of reaction. For enzyme reactions such together this, the reaction does no take ar if the temperature is too high due to the fact that the enzymes gain denatured. The effect of pH and also salt concentration can additionally be investigated.

See more: When A Guy Touches Your Breast What Happens When A Guy Touches Your Breast S


Jeremy M. Berg, john L. Tymoczko and Lubert Stryer, Biochemistry, 6th edition, W.H. Freeman and also Company, 2007, pages 205-237.Fugentius Lugemwa, Decomposition of Hydrogen Peroxide, Chemical Educator, April 2013, pages 85-87.Daniel Q. Duffy, Stephanie A. Shaw, wilhelm D. Bare, Kenneth A. Goldsby, much more Chemistry in a Soda Bottle, A conservation of mass Activity, Journal of chemical Education, august 1995, pages 734-736.Jessica L Epstein, Matthew Vieira, Binod Aryal, Nicolas Vera and Melissa Solis, Developing Biofuel in the to teach Laboratory: Ethanol from various Sources, Journal of chemistry Education, April 2010, pages 708–710.