Minute Differences in Carbohydrates, Pigments, and Enzymes of

Varieties of Capsicum annuum, Bell Peppers,

Through Testing of Organic Compounds

By Keowa Bonilla; Jarod Nenis
Crystal Passmore; Patrick Pavwoski

        In these laboratory tests we investigated differences in varieties of Capsicum annuum, commonly known as bell peppers.  Oftentimes, consumers of bell peppers claim that each color of pepper has a different taste.  We hoped to determine what, if any, differences existed between these peppers in regards to carbohydrates, pigments, and enzymes.  In our experiment we tested red, orange, and yellow peppers, and found few differences.  Using Benedict’s, Barfoed’s, Selivanoff’s, Bial’s, and the Iodine Tests, we identified which sugars and starch were present in each kind of pepper.  Using a spectrophotometer, we tested for the presence of chlorophyll and specific pigments.  We also tested for the presence of the enzyme polyphenoloxidase (PPO).

     Testing for carbohydrates disclosed that various sugars, such as glucose, fructose, galactose, and xylose were most likely present in all of the peppers.  There were no major differences in the various colors.

     When testing for chlorophyll, we discovered that there is no trace of the substance in any variety of peppers we tested.  On the other hand, we found that each pepper had different absorption spectrums.  The red peppers absorbed every color except red.  Orange peppers absorbed every color except red and yellow.  Yellow peppers absorbed every color except yellow.

     Finally, we have determined that all of the peppers contain the enzyme PPO.  This led us to conclude that the difference in taste in the red, yellow, and orange bell peppers is not due to any of the things we tested for, including the carbohydrates, pigments, and enzymes. 

Discussion:

This laboratory investigation was designed to identify any differences between the levels of organic compounds in a variety of bell peppers (Capsicum annuum).  We predicted that there would be a difference in the dominant sugar in each pepper, because each pepper has its own unique taste and the difference in carbohydrates could be the cause of this. We believed there would be no variance related to pigments because we predicted none of the peppers would have chlorophyll because they all lack green pigmentation.  We also predicted that each pepper would contain PPO, because they are closely related to potatoes which contain large amounts of PPO.

            After completing all of the experiments mentioned in the methods section, we were able to come to a number of conclusions.  Based on various carbohydrate tests and contrary to our predictions, we found that each pepper contained the same sugars and starch.  We were able to come to this conclusion due to the fact that in each of our tests, the various different solutions produced exactly the same results.

            In Benedict’s test, all of the solutions produced a precipitate meaning that, contained within each of the solutions is a reducing sugar.  A non-reducing sugar may also be present because our data (Table1) simply suggests that a reducing sugar is present.  However, there is no reason for us to believe that a non-reducing sugar was not also present with the reducing sugar which led to the production of the precipitate.  We have a sufficient level of confidence in our data because our control tests both turned out the way they should have (Fructose producing a precipitate and water producing no reaction).  We actually had to perform the test on the Fructose twice because the first run did not yield the desired result.  Therefore, we felt it would be best to run the test again to ensure that our reagent was functioning properly.  The second attempt was successful.  Glucose, Fructose and Galactose are the only sugars known to us that would produce these results.

            Again in Barfoed’s test, all of the solutions produced a precipitate.  In this test, the formation of a precipitate suggests that a monosaccharide is present in the solution.  Due to these results (Table1), we can safely say that there is a monosaccharide present in the solution but that does not mean that disaccharides and polysaccharides may not also be present.  Our controls for this test were again water and Fructose, both of which produced the expected results.  These particular results suggest that of our known sugars, Glucose, Fructose and Galactose (SpaysKraft, 2002) are the possible sources of the outcomes of the tests.

            Selivanoff’s test yielded exactly the same results (Table1) for each of our solutions again.  When performing this test, all of the solutions changed to a dark brown/red/maroon color in less than a minute.  This result implies that our dominant sugar in solution is monosaccharide ketoses.  As with all of the previous tests, other sugars may be present which not monosaccharide ketoses are but they are not dominant.  Our control tests on water and Fructose produced the expected results, giving us no reason to doubt our results.  Of our known sugars, the only sugar that is a monosaccharide ketose is Fructose (SpaysKraft, 2002).

            Bial’s test produced a color change to a light olive shade in every one of the solutions.  These data (Table1) suggest that there is an overall abundance of pentose-furanose sugars.  However, the presence of differently shaped sugars is still possible.  Again, our control tests on Fructose and water resulted as they should have.  Of our known sugars, only one sugar will lead to this result.  That sugar is xylose (SpaysKraft, 2002). 

In the Iodine test, as with all of our previous tests, all of the solutions provided the same results (Table1).  The result that we obtained was that they were all negative.  Negative results with this test suggest that there is no starch present in the solutions whatsoever.  This time our control tests were done on a starch solution and water, both turned out the way they should.  These results make it possible for the dominant sugar in the solution to be any of those which are known to us (SpaysKraft, 2002). 

            Based on the results of the tests (Table1), we would be very tempted to say that Fructose is the dominant sugar in all of the peppers because all of the tests gave results similar to what Fructose would yield.  All of the tests, except one.  In Bial’s test, the results clearly pointed towards that suggestion that Xylose was the dominant sugar in the solution.  Therefore, we cannot come to a conclusion as to what the dominant sugar is in the peppers.  It is quite possible that both of these sugars are present in the solutions due to the results of our tests.  It is also possible that neither of these sugars are present in the solutions and that our results were observed due to some sugar unknown to us.  What we can conclude is that, as far as we know, there is absolutely no difference between these peppers in carbohydrate content, thus overwhelmingly suggesting that our previous predictions were wrong. 

            As we predicted, our test results suggest that there is no chlorophyll present in any of the three colors of peppers tested.  This was shown by the absorption levels of varying wavelengths (Tables 2).  If these peppers did contain chlorophyll, they would have had maximum absorption levels continuing to rise past 445 nm (Luckie et al, 2002). 

            The results which we obtained for our PPO tests did not support our predictions.  We felt that all of the bell peppers would test positive for the enzyme, but numerous tests suggested that there was no PPO present.  This is shown by the lack of color change of the litmus paper in the experiment (Table 4).  The paper showed that the enzyme did not react with the 0.1% catechol solutions, because it would have turned from orange to light orange or yellow if a reaction had take place, but no color change occurred.  We also went on to perform an experiment using different concentrations of catechol on our samples. If PPO was present, this would have lead to a difference in the absorption readings of the spectrophotometer.  However, the absorption stayed the same for each sample regardless of the concentration of catechol.

            Overall, all of our tests suggested that the three varieties of Capsicum annuum were not different in any way.  However, our results may not be as accurate as possible.  One possible source of error is the fact that we performed the tests on a limited number (generally three) of each kind of pepper.  The fact that we used peppers that had been picked days before we were able to test them, could also have contributed to some inaccurate data, especially in the action spectrum test.  Along the same line, some of the peppers were not kept sufficiently chilled so decomposition could have started to occur before we got a chance to experiment on them. Other possible sources of error could be poor measurements, machine usage and timing inaccuracies all due to human error.

After performing these experiments and analyzing the results, we are left with a couple more questions. We know that PPO is an enzyme that helps some vegetables decompose, and since it is not present in peppers, and peppers have to decompose, we are curious as to what enzymes help facilitate their decomposition. Another question we came across was how green peppers would compare to the three variations of peppers we tested. Green peppers were not used in our experiments because they are an immature version of red, yellow, and orange peppers, and we would not have been able to distinguish between the different varieties. However, since our data implies that these three peppers really aren’t that different, it shouldn’t matter which variety of pepper the green peppers are destined to become. These are just a couple suggestions for complimentary research that could be performed.

As scientists and as heterotrophs, we have learned a great deal from these experiments.  The next time we choose to purchase bell peppers, we need not consider any basic chemical differences between these peppers.  We will simply pick whichever color is appealing to our senses without worrying about whether or not one selection has different carbohydrates, or has more photosynthetic pigments than the other.  Our results have shown us that the different colors on the outside of peppers do not symbolize any differences on the inside, though more experiments could be performed that would compliment our data and findings.

Figure 3: This is a picture of our test tubes of various colored pepper solutions after completing Benedict’s test.  From left to right, the test tubes contain glucose, fructose, yellow pepper 1-3, red pepper 1-3, and orange pepper 1-3 solutions. The red precipitate can be seen on the bottom of the pepper solution test tubes.