Exercise 1: Saccharomyces cerevisiae fermentation of corn and sugarcane
Materials
Fleischman’s Rapid–Rise yeast (Saccharomyces cerevisiae)
Raw sugarcane (Saccharum officinarum)
Corn flour (Zea mays)
Glucose
DI H2O
Fermentation flasks
100 mL beakers
250 mL bottles
Graduated cylinders
10 mL graduated pipettes & pipette pumps
Laboratory digital scale, weigh boats & spatulas
37°C water–bath
Parafilm
Timers
Standard Yeast Solution
Weigh 4.0 g of yeast and add it to the 250 mL of warm DI water (keep the bottle in the water bath while
you weigh the yeast.)
Hypothesis
Prediction
Experimental Design
Methods
Each solution sample you test will consist of a standard yeast solution and added raw materials of interest: sugarcane, corn or glucose. It is not suggested to prepare a more concentrated solution than a 10% glucose (corn or sugarcane) solution. The volume of the solution in the fermentation tube should not exceed 15 ml. Do not forget to include controls and multiple trials.
Suggested Fermentation Experiment Protocol:
1. To prepare active yeast culture, weigh and pour 4.0 g of yeast into 250 mL of warm
deionized water and mix well. Put the bottle with yeast suspension back in the 37°C water–bath.
2. For each of your trials you should prepare 4 beakers:
1 – sugarcane
2 – corn
3 – positive control;
4 – negative control;
Weight _________ of each reactant and transfer it in the appropriately labeled beaker.
3. Add ___________ mL of yeast solution into each beaker, gently swirl the contents (or mix
them with a glass rod) and then transfer everything into a fermentation flask.
4. Cover the opening of the flask with a small piece of parafilm and then invert the flask a few times until the calibrated end is filled with the solution. Once that end is full, you can transfer the fermentation flasks in the water–bath and start the time. Make sure the water level in the water–bath is in line with the level of the liquid in the fermentation flasks.
5. Record the volume in mL of CO2 in 3–min intervals for 21 minutes. You can mark the volume with a sharpie every 3 minutes and record the actual volume readings after the experiment is done in order to minimize temperature fluctuations in the fermentation environment and decreasing the CO2 production rate.
Results
Record your group’s CO2 readings for all four conditions and all trials in a table format.
Calculate the rate of CO2 production (mL of CO2/min) for each solution tested for each time point.
Each group will enter their data in a table prepared by their lab instructor because the class data will go in their lab report. The analyzed class data (averages and standard deviations) will be presented in the Results section. One graph will show CO2 production over time – the average volume of released CO2 after each 3–min interval, and the other the mean rate of CO2 production for each condition (material
tested) at the end of fermentation (after 21 min).
Lab Report Format
You should follow the format used in your first lab report.
Remember to write down the standard recipe for the yeast solution, the type of yeast used, the specific solutions and their concentrations, and number of replicates that your group tested, as well as any other procedures used by your group. You will need this information for the Methods section of your lab report.
In preparing your Discussion section for this report you must consider not only your lab section’s results in relation to your research hypothesis; you must also consider your results in the broader context of the future of ethanol as biofuel. The following questions might help you compose your Discussion section:
1. Which raw material, corn or sugarcane, was biologically more efficient for fermentation? Cite your group’s key findings to support your answer. Explain why this raw material was more efficient than the other; cite any references you consult.
2. What did the controls for your experiment demonstrate? Describe what you learned from the results of each control solution that your group tested.
3. What do you perceive to be the major disadvantages to the use of corn for ethanol fuel production? What are the benefits? Do you think the U.S. government should continue to promote the use of corn from ethanol production? Explain.
4. What are the pros and cons for the use of sugarcane for ethanol fuel production in Brazil? What about in the United States? For regions of the U.S.A. that produce sugarcane, is its use to produce ethanol fuel a desirable renewable energy option? Why or why not?
5. In terms of global food security, what kinds of biofuels are most desirable (or least harmful)?Be sure to cite all references you use in your Discussion (and Introduction) section. Use (author, year) format in the text of the paper; write full references in References section at the end of the paper
