How Should Apples be Prepared for a Fruit Salad?
Catecholase, also known as catechol oxidase or tyrosinase, is an enzyme found in many plants, animals, and fungi. The general function of catecholase is to accelerate the reaction between oxygen and phenolic compounds to produce quinones and water. Enzyme activity and susceptibility to browning have been shown to have varietal dependence2,6 in addition to differences among different types of fruit.
The reaction we will study to address the question in the title of the experiment is the catalyzed oxidation of catechol by molecular oxygen to form 1,2-benzoquinone and water. Quinone is the only species in the reaction mixture that absorbs light in the visible region.
We include timing options for running this experiment, such as four 3-hr lab periods, two 3-hr lab periods.
Learning Objectives
At the end of this experiment, students will be able to
- Describe the Michaelis-Menten mechanism for enzyme catalysis, including the meaning of the Michaelis-Menten parameters
- Analyze and manipulate equations and graphical representations to appropriately model experimental data/results.Fit a nonlinear function to data.
- Convert a nonlinear relationship to a linear form.
- Choose experimental conditions to obtain appropriate data for analysis.
Instrumentation and Materials
- Visible spectrophotometer such as Ocean Optics or Spectra Vis that monitors visible absorption as a function of time
- Catechol (Sigma-Aldrich)
- Different varieties of apples
- pH meter and/or indicating pH paper
- Strong acid (HCl) or base (NaOH)
- Vacuum filtration apparatus
Reference
Sally Hunnicutt, Virginia Commonwealth University
Renée Cole, University of Iowa
The Instructor’s Handbook with implementation details, sample data, and expected answers is available through the POGIL-PCL project.