In the Laboratory
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An Alternative Procedure for Carbohydrate Analysis of Bananas: Cheaper and Easier C. Michele Davis-McGibony,* Randall R. Bennett, Arthur D. Bossart II, and S. Todd Deal Department of Chemistry, Georgia Southern University, Statesboro, GA 30460-8064; *
[email protected] Recently in this Journal, we published a laboratory experiment called “Ripening Bananas: What Is Happening and Can We Control It?” that is used in our nutritional biochemistry course, taken by students who are majoring in nutrition, not in chemistry or biology (1). While our students enjoy this experiment and have had much success with it, we decided to create an experiment that is more “user friendly” for these inexperienced laboratory students. Over the counter glucose test strips have been incorporated into this experiment similar to Melton’s note published in this Journal (2). The brand employed by our laboratory is Bayer Diastix Re-
Table 1. Instructor and Student Data on Carbohydrate Composition of Bananas (with Commercial Test Strips) Instructor Stage of Ripenessa
Research Students
Glucoseb (%)
Starchb (%)
Starchb (%)
Glucoseb (%)
Green
15.0 ± 0.9 02.3 ± 1.1 13.5 ± 1.3 02.3 ± 0.9
Yellow
07.4 ± 1.0 05.5 ± 0.9 07.0 ± 1.1 05.7 ± 0.8
Yellow with black spots
04.2 ± 1.2 10.8 ± 0.9 04.1 ± 0.9 11.0 ± 0.9
a
Based on appearance.
b
Based on wet weight of original sample.
Table 2. Student Data on Carbohydrate Composition of Bananas (with Colorimetric Assay) Stage of Ripenessa
Starchb (%)
Glucoseb (%)
Green
12.9
04.0
Yellow
06.2
04.4
Yellow with black spots
02.0
11.6
Based on appearance.
a
Based on wet weight of original sample.
b
Table 3. Student Data on Carbohydrate Composition of Bananas (with Commercial Test Strips, Benchtop Centrifuges, and Mortars and Pestles) Stage of Ripenessa
Starch (%)
Glucose (%)
Green
10.1 ± 1.9
02.6 ± 1.5
Yellow
06.5 ± 1.4
05.3 ± 1.7
02.1 ± 1.5
11.0 ± 2.0
b
Yellow with black spots
b
Based on appearance. Based on wet weight of original sample; averages of eight student teams. a
b
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agent Strips for Urinalysis. These strips are intended for home use and are also utilized by home health care nurses. Before implementing the test strips in an actual laboratory section, both the instructor and two research students conducted this experiment and acquired data comparable to the data obtained when utilizing the colorimetric assay and spectroscopy (Table 1 and Table 2) (1). As class sizes increase (and budgets proportionally decrease), the use of specialized equipment such as glass homogenizers and refrigerated centrifuges becomes a significant problem—mainly due to the fragility of the homogenizers and the lack of multiple refrigerated centrifuges, which results in long waits and extended lab times. To overcome these difficulties and further increase the adaptability of this experiment, we have incorporated common laboratory mortars and pestles in place of the homogenizers and regular benchtop centrifuges in place of the refrigerated ones. As the data in Table 3 indicate, the inclusion of these modifications along with the glucose test strips results in data that are comparable to that which has been previously reported (1). While the incorporation of the test strips into this laboratory exercise does involve a slight cost (strips are ∼$0.50 each), this modification seems to have removed student apprehension (many found spectrophotometric assay daunting) and improved their understanding of the experiment. Additionally, substituting common laboratory equipment for the less common and more expensive glass homogenizers and refrigerated centrifuges renders the experiment useful to a much broader range of institution size and type. Hazards Acetone is flammable and harmful if swallowed or inhaled. Contact can cause irritation to skin, eyes, and respiratory tract. All steps with this material should be performed in an efficient fume hood. W
Supplemental Material
Instructions for the students and notes for the instructor are available in this issue of JCE Online. Literature Cited 1. Deal, S. T.; Farmer, C. E.; Cerpovicz, P. F. J. Chem. Educ. 2002, 79, 479–480. 2. Melton, T. J. J. Chem. Educ. 2001, 78, 1243.
Vol. 83 No. 10 October 2006
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Journal of Chemical Education
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