How Should Apples be Prepared for a Fruit Salad?
What is this experiment about?
Students are familiar with the browning of fruit, but they have typically not explored the chemistry behind the process. This experiment has students explore the kinetics of the oxidation of catechol catalyzed by the enzyme catecholase present to different degrees in different varieties of apples. Students engage in experimental design allowing for parameter variation (type of apple, pH) working with this natural system with many possible outcomes. Instructors can optionally have students explore enzyme inhibition
What do students do?
Pre-experiment work has students consider experiment design, from making solutions to extracting juice from apples to making predictions about absorbance changes for the catechol solution. In the first cycle, students explore the browning reaction with and without enzyme, and in buffered and unbuffered solutions, comparing their predictions with experimental results. They then design an experiment (with the class) that allows application of Michaelis-Menten kinetics and development of a quantitative answer to the title question. These cycles can be performed in two lab periods of three or four hour length. Instructors can use additional time to have students complete an optional third cycle in which they develop an enzyme inhibition experiment.
What equipment and supplies will you need?
- Visible spectrophotometer; pH meter (or pH paper)
- Equipment for pureeing and extracting juice from apples (blender, paring knife, vacuum filtration)
- Apples! catechol; Na2HPO4 and NaH2PO4 for making phosphate buffer solutions; inhibitors
What makes this experiment a physical chemistry experiment?
The study of enzyme kinetics links physical chemistry and biochemistry. Physical chemistry is represented in both the experimental design, particularly the investigation of multiple factors that can affect the kinetic behavior, and in the complexity and precision of the data analysis with an emphasis on comparing equation linearization to non-linear fitting. The investigation of enzyme inhibition provides a physical chemistry foundation to a significant biochemical concept.
And what makes it a POGIL-PCL experiment?
Students begin their work with both experiment design in considering how to obtain the data and making predictions about how the catechol oxidation reaction will be reflected in the absorbance data. Students share data to see the range of apple browning behavior and interact with other teams to do further work in experimental design. Students process information in multiple ways in this experiment: working with initial rates to see the range of kinetic behavior, then developing more substantial mathematical models and graphical representations to observe the underlying regularity and draw conclusions. The work on inhibition is helpful for students to demonstrate their understanding of the enzyme kinetics concepts.
Reference
Cole, R. S.; Muniz, M.; Harvey, E.; Sweeney, R.; Hunnicutt, S. How Should Apples Be Prepared for a Fruit Salad? A Guided Inquiry Physical Chemistry Experiment. J. Chem. Educ. 2020, 97 (12), 4475–4481. https://doi.org/10.1021/acs.jchemed.0c0051
The Instructor’s Handbook with implementation details, sample data, and expected answers is available through the POGIL-PCL project.
Highlight author: R. Whitnell