Yeast ferments which sugars

In this paper, we present a simple experiment involving the yeast-catalyzed fermentation of sugars. The experiment is easy to carry 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 food store and the galactose from Carolina Science Supply Company.

The sucrose was obtained at the grocery store as white sugar. Sugar fermentation results in the production of ethanol and carbon dioxide. In the case of sucrose, the fermentation reaction is:. Lactose is also C 12 H 22 O 11 but the atoms are arranged differently. Before the disaccharides sucrose and lactose can undergo fermentation, they have to be broken down into monosaccharides by the hydrolysis reaction shown below:.

The hydrolysis of sucrose results in the formation of glucose and fructose, while lactose produces glucose and galactose. The enzymes sucrase and lactase are capable of catalyzing the hydrolysis of sucrose and lactose, respectively.

The monosaccharides glucose, fructose and galactose all have the molecular formula C 6 H 12 O 6 and ferment as follows:. In our experiments Next 7. The microwave power is 1. This resulted in a temperature of about o F 43 o C 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 ambient temperature, and no attempt at temperature control was used.

This method of studying chemical reactions has been reported by Lugemwa and Duffy et al. Although fermentation is an anaerobic process, it is not necessary to exclude oxygen to do these experiments.

Lactose and galactose dissolve slowly. Mild heat using a microwave greatly speeds up the process. When using these sugars, allow the sugar solutions to cool to room temperature before adding the yeast and microwaving for an additional 15 seconds. All samples had Initially the mass loss was recorded every 30 minutes. We continued taking readings until the mass leveled off which was about 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 cause the lactose to ferment. Use this practical to investigate how solutions of the halogens inhibit the growth of bacteria and which is most effective. Site powered by Webvision Cloud. Skip to main content Skip to navigation. Larger conical flasks can be used, but this dilutes the carbon dioxide concentration, and makes testing for carbon dioxide with limewater more difficult.

Health, safety and technical notes Read our standard health and safety guidance Wear eye protection. Procedure Lesson 1 Put 5 g of glucose in the conical flask and add 50 cm 3 of warm water. Swirl the flask to dissolve the glucose. Add 1 g of yeast to the solution and loosely plug the top of the flask with cotton wool. Wait while fermentation takes place. Remove the cotton wool and pour the invisible gas into the boiling tube containing limewater.

Take care not to pour in any liquid as well. Gently swirl the limewater in the boiling tube and note what happens. Replace the cotton wool in the top of the flask.

Additional information This is a resource from the Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry. Level years years. The carbon dioxide gas made during fermentation is what makes a slice of bread so soft and spongy.

The pockets of gas are produced by yeasts when the dough is allowed to rise before baking. Observations and results Did the balloon on the bottle with only yeast and water remain un-inflated? Did the balloon on the bottle with only sugar added inflate the most? When yeasts eat sugar and turn it into energy, they also produce carbon dioxide. In this activity, the balloons on the bottles should have captured carbon dioxide produced by the yeasts during fermentation.

In the bottle that contained yeasts but not sugar, the yeasts did not have food i. In the bottle that contained yeasts and sugar but not salt, baking soda or vinegar , the yeasts should have thrived and made a lot of carbon dioxide, clearly inflating the balloon.

When salt, baking soda or vinegar was added, the yeasts should have made less carbon dioxide, inflating the balloon less than when only sugar was used. This is because the addition of these substances changed the environment and made it less ideal for the yeasts.

Specifically, adding salt increased the salinity of the environment, and adding baking soda or vinegar changed the pH of the environment, making it more basic or acidic, respectively, compared to the neutral environment provided by the plain water.

Cleanup When you are done with this activity, dispose of the yeasts by composting them or with permission dumping them outside somewhere.

Do not pour the yeasts down the drain without diluting them with water, as they may damage pipes when they expand. This activity brought to you in partnership with Science Buddies. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science.

Materials Three plastic two-liter bottles Measuring tablespoon White table sugar Salt, baking soda or vinegar Permanent marker optional Measuring cups Warm tap water One medium-sized pot or bowl, at least two quarts in size Six packets of dry yeast or an equivalent amount from a jar Three standard-sized latex balloons Clock or timer Preparation Rinse each bottle thoroughly with water and remove any labels.

Add two tablespoons of sugar to two of the three bottles. How do you think the sugar will affect the activity of the yeast? To one of the bottles that you added sugar to, also add two tablespoons of salt, baking soda or vinegar.

How do you think adding salt, baking soda or vinegar will affect the activity of the yeast? Throughout the experiment, keep track of what you added to each bottle.