6.2: Introduction
- Page ID
- 470187
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Many fruits and vegetables contain phenolic compounds, which play an important role in the flavor and color of the fruit. The oxidation of phenols into quinones, which polymerize into brown products, results in the browning of fruits and vegetables.1,2 However, most foods, such as bananas, potatoes, and apples, only produce significant amounts of quinones when they are exposed to the O2 in air after they have been cut or bruised. When the fruit is cut and cellular compartmentalization is disrupted, these compounds can be involved in both enzymatic and non-enzymatic browning reactions.1,3 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.3-5 Enzyme activity and susceptibility to browning have been shown to have varietal dependence2,6 in addition to differences among different types of fruit.
The production of quinones from the phenolic compounds is significant because quinones are part of a class of toxicological intermediates that can create a variety of hazardous effects.7,8 Quinones can be converted to semiquinone radicals, which can either directly interact with DNA or may interact with molecular oxygen to produce genotoxic reactive oxygen species that can cause oxidative stress and DNA damage.7-9 Many bacterial strains are very sensitive to the genotoxicity of oxidative stress9,10, so the production of quinones provides some anti-bacterial protection to the fruit. Unfortunately, it also results in unpleasant tastes and textures, which is a concern when preparing fruits for human consumption.
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.
References
- Rocha, A., & Morais, A. M. “Polyphenoloxidase activity and total phenolic content as related to browning of minimally processed ‘Jonagored’apple.” J of the Science of Food and Agriculture, 2002, 82, 120-126.
- Amiot, M. J., Tacchini, M., Aubert, S., & Nicolas, J. “Phenolic composition and browning susceptibility of various apple cultivars at maturity.” Journal of Food Science, 1992, 57, 958-962.
- Walker, J. R. L. “Enzymatic browning in fruits: Its biochemistry and control,” Enzymatic browning and its prevention: ACS Symposium Series, C. Y. Lee & J. R. Whitaker (eds.), American Chemical Society: 1995, pp. 8-22
- Joslyn, M. A., & Ponting, J. D. “Enzyme-catalyzed oxidative browning of fruit products.” Adv. Food Res, 1951, 3.
- Lerch, K. “Tyrosinase: Molecular and active-site structure.” Enzymatic browning and its prevention: ACS Symposium Series, C. Y. Lee & J. R. Whitaker (eds.), American Chemical Society: 1995, pp. 64-80
- Rocha, A. M. C. N., & Morais, A. M. M. B., “Characterization of polyphenoloxidase (PPO) extracted from ‘Jonagored’apple,” Food Control, 2001, 12, 85-90.
- Bolton, J. L., Trush, M. A., Penning, T. M., Dryhurst, G., & Monks, T. J. “Role of quinones in toxicology,” Chemical research in toxicology, 2000, 13, 135-160.
- Bast, A., & Haenen, G. R. “The toxicity of antioxidants and their metabolites.” Environmental toxicology and pharmacology, 2002, 11, 251-258
- Patrineli, A., Clifford, M. N., & Ioannides, C. “Contribution of phenols, quinones and reactive oxygen species to the mutagenicity of white grape juice in the Ames test,” Food and chemical toxicology, 1996, 34, 869-872.
- Hakura, A., Mochida, H., Tsutsui, Y., & Yamatsu, K., “Mutagenicity of benzoquinones for Ames Salmonella tester strains,” Mutation Research Letters, 1995, 347, 37-43.
Adapted from Cole, Renée S., Marc Muniz, Erica Harvey, Robert Sweeney, and Sally Hunnicutt. “How Should Apples Be Prepared for a Fruit Salad? A Guided Inquiry Physical Chemistry Experiment.” Journal of Chemical Education 97, no. 12 (December 8, 2020): 4475–81. https://doi.org/10.1021/acs.jchemed.0c00517.