Touring the Tomato: A Suite of Chemistry Laboratory Experiments

Touring the Tomato: A Suite of Chemistry Laboratory Experiments

Sayantani Sarkar , Subhasish Chatterjee , Nancy Medina , and Ruth E. Stark *

Department of Chemistry, City College of New York, Graduate Center and Institute for Macromolecular Assemblies, City University of New York, New York, New York 10031, United States

J. Chem. Educ., 2013, 90 (3), pp 368–371

DOI: 10.1021/ed3004148

Publication Date (Web): December 14, 2012

Copyright © 2012 The American Chemical Society and Division of Chemical Education, Inc.

Supporting Documents (22 pages): Contains the complete student experimental handout for each of the 7 experiments; notes to instructor; sample experimental data; and detailed notes about reagents, hazards, equipment, and procedures.

ABSTRACT: http://pubs.acs.org/doi/abs/10.1021/ed3004148

This article is 3 years old but nevertheless it presents an interesting series of experiments that utilize various analytical and spectroscopic methods and instrumentation to study the chemical composition of the tomato fruit.  While the experiments described constitute a full laboratory course, its modular nature allows adaptability and modification for implementing single labs or as part of a workshop series. In particular, the authors and developers believe that Modules 1-5 can be implemented at all levels including high school chemistry (see supporting information).  The experiment modules were piloted as a summer course for college-bound high school students who have taken 1 year of biology and chemistry.  The only instrument that LPC does not have is the AFM; we also may not have the capability to do solid state NMR but FT-IR can be substituted for this.

The tomato is an important agricultural product and a mainstay of many meals, both American or otherwise. It contains quite a diversity of families of compounds that are amenable to well-established and documented analytical methods: water, lipid waxes, lycopene pigments, and distinctive polysaccharide and polyester biopolymers.

This paper describes a modular laboratory course designed to teach students and provide hands-on applications of different experimental techniques including “UV−vis spectroscopy, high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) spectroscopy, and atomic force microscopy (AFM) to examine various chemical constituents of the tomato fruit.” The techniques employed span the fields of general, analytical, biophysical, biochemical, and organic allowing macroscopic, microscale, and molecular analysis of the tomato.  See Table 1 in the article for a list of the 8 experiments.  The first five of these experiments focus on the study of the tomato’s macroscopic properties, followed by submicroscopic analysis of molecular properties through AFM and NMR analyses.  The lab design is also amenable to analysis of other fruits or vegetables or engineered polymers.

EQUIPMENT

·         The following list of equipment is required to carry out the experiments as described in this paper and in the supporting information: analytical balance, drying oven, incubator−shaker, UV−vis spectrophotometer, HPLC, NMR spectrometer, and atomic force.

EXPERIMENTS

Figure 1 in the article provides a graphical illustration of the 8 modules of analysis.

Experiment 1: determination of the mass percent of water in the tomato by oven drying

Experiments 2 - 5: analysis of the wax content of tomato skin.  Peeled skins are subjected to enzymatic reaction with cellulase and pectinase to remove cellulose and pectin from the cell wall components.   Thickness measurement of cuticle is done using calipers.  UV-vis absorption spectroscopy or HPLC can then be used to characterize the lycopene pigment extracted.  Solvent extraction collects the wax for analysis using solution state NMR and re-measurement of and change in cuticle thickness.

Experiments 6 – 7: AFM and NMR are used to study the microscale surface technology and molecular composition of cuticles, respectively.

Details of the experimental procedures are provided in the supporting documents.

HAZARDS

See article.

REPRESENTATIVE RESULTS (See supporting information for more detailed results)

MODULE 1: The water content measured average about 90% by mass. Rate of water loss was higher for the cut tomato at 75% after 3 hours compared to 55% for whole tomato.

MODULES 2 and 3:  Cuticle thickness caliper measurements showed that the wax adds some thickness to the cuticle.

MODULE 4: Lycopene absorption was detected at 471 nm using UV-Vis. This and HPLC results were compared to results for commercial lycopene for confirmation.

MODULE 5: The macroscopic appearance of extracted cutins from cuticle was similar.

MODULE 6:  NMR analysis revealed fingerprint spectra for alkane, alkanol, alkene, alkanoic acid, sterol, and triterpenoid molecular groupings.

MODULE 7: AFM study showed topographical and surface roughness properties.

DISCUSSION: the significance of the lab, its adaptability to various student levels, and the benefits to students are discussed briefly.  See article.