Sugar Tests Show Fructose in GM, Organic Oranges, and Tang,

but Photosynthesis and Enzyme Tests Reveal Differences


by Wendy Andersen, Josh Campbell, and Shaun O’Toole



February 27, 2003





by Shaun O’Toole, revised by Wendy Andersen, second revision by Josh Campbell


The differences between organically grown, genetically modified (GM) oranges, and Tang orange drink were investigated with respect to carbohydrates, pigments, their absorption spectra, and enzymes.  A series of carbohydrate tests, including Benedict’s, Barfoed’s, Selivanoff’s, Bial’s, and iodine tests, were performed.  Paper chromatography helped identify the pigments present, and the spectrophotometer measured the absorption spectra for all orange products.  The digestive action of the enzyme salivary amylase on the juice of both types of oranges and on the Tang solution was tested by measuring the initial and final absorbencies of the orange products.  Both types of oranges and Tang contained the carbohydrate fructose, but they were also tested for the presence of glucose, galactose, xylose, lactose, maltose, sucrose, and starch, which were absent.  Both types of oranges contained the pigments xanthophyll and lacked the pigments chlorophyll a and chlorophyll b, and the GM oranges also contained the pigment carotene.  However, no pigments were separated during paper chromatography for Tang.  Tests revealed that both types of oranges reached peak levels of absorbency at 400 nm, with the GM oranges absorbing more light than the organic oranges, while Tang reached a peak level of absorbency at 430 nm.  At 460 nm, the amylase appeared to digest the Tang solution quicker than it digested the organic orange juice and the GM orange juice.  In terms of carbohydrates and pigments, both types of oranges were similar whereas Tang had the same sugar but no pigments were separated.



Figure 1: Results of Benedict’s Test.  The positive control, galactose, is on the right and the negative control, starch, is on the left.  In between the controls are the three replications of the test done on GM oranges, organic oranges, and Tang orange drink, respectively.  The red precipitate present in the positive control and in all the tested solutions indicates the presence of a free or potentially free aldehyde or ketone group, which is also known as a reducing sugar (Maleszewski et al., 2003).  The aldehyde is oxidized and the copper is reduced, which forms the red precipitate.  The lack of a red precipitate in the negative control indicates the absence of a reducing sugar.



by Wendy Andersen, revised by Josh Campbell, second revision by Shaun O’Toole


            To the naked eye, genetically modified, or GM, oranges and organically grown oranges may appear quite similar in size, shape, and color.  However, the insides of these oranges tell a different story through the results of various carbohydrate, photosynthetic, and enzymatic tests.  Tang, on the other hand, is a completely different story when compared to both kinds of oranges and was analyzed to add another angle to our research.

It was hypothesized that the GM oranges would have more sugars present, different rate of flow values for pigment paper chromatography, a slower digestion of its orange juice due to salivary amylase, and higher absorbency levels affecting photosynthesis when compared to organically grown oranges.  It was also hypothesized that, compared to both kinds of oranges, Tang would have more sugars present, different rates of flow, lower absorbency levels, and the slowest digestion rate of the three orange products due to salivary amylase. 

Careful and considerable experimentation verified some of the hypothesis.  The beliefs that GM oranges would have greater absorbency levels, slower digestion rates due to salivary amylase, and different rates of flow than those of organically grown oranges were correct.  However, to our surprise, organically grown oranges had the same sugars present as the GM oranges and Tang did, and Tang, when compared to both the GM oranges and the organic oranges, had the fastest digestion rate due to the amylase and paper chromatography separated no pigments.

            The first analysis that was performed on the three orange products was a series of carbohydrate tests.  Comparison of the results of a previous lab that tested carbohydrates with our carbohydrate test results indicated the presence of fructose and the absence of glucose, sucrose, starch, lactose, maltose, galactose, and xylose (Table 1).  However, according to research, both types of oranges should have tested positive for glucose and sucrose as well (Spiegel-Roy and Goldschmidt, 1996).

            The next portion of the hypothesis stated that GM oranges, organically grown oranges, and Tang would have different pigment paper chromatography and rates of flow.  Under previously stated assumptions, we believed that the GM oranges would have extra additives to darken their color, which would cause the general composition of the pigments to differ from those of organically grown oranges.  The rates of flow for Tang were believed to be different because Tang does not contain any chlorophyll because Tang obviously does not carry out photosynthesis.  Paper chromatography was performed on acetone solutions of both the organic and GM versions of the oranges and on a solution of acetone and Tang.  The average Rf-value for the pigment in the organically grown oranges was 1.00 and this pigment was yellow orange in color (Table 2).  The average Rf-values for the GM oranges were 0.91 and 1.00, and these pigments were pale yellow and yellow orange in color, respectively.  The average Rf-values for the Tang solution were zero.  These data values verify the hypothesis.

            A paper chromatogram of the pigments that are present in oranges showed that the pigment with the highest Rf-value was yellow orange in color and called xanthophyll and another pigment with a lower Rf-value was pale yellow in color and known as carotene (Sinclair, 1961).  Comparison of these results with our own revealed that organically grown oranges contained the pigments xanthophyll, whereas GM oranges contained the pigments carotene and xanthophyll.  Both kinds of oranges lacked the pigments chlorophyll a and chlorophyll b, which could be because “as the fruit approaches maturation, chlorophyll is gradually lost and chloroplasts are transformed into carotenoid-rich chromoplasts” (Spiegel-Roy and Goldschmidt, 1996).

            It was hypothesized that GM oranges would have higher absorbency levels than organically grown oranges and still higher than Tang because it was thought that the scientists who modified the oranges would inject the fruit with certain additives to darken their color and make the oranges healthier looking.  Thus, darker peel colors would cause higher absorbency levels in photosynthesis.  Although the absorbency of Tang was measured, the data is actually irrelevant compared to the data of GM and organic oranges because Tang does not perform photosynthesis.  The oranges and the Tang were tested at 15-nm intervals from 400 nm to 700 nm, but the highest average absorbency values were obtained at 400 nm for organic and GM oranges and 430 nm for Tang.  The organically grown oranges had an average maximum absorbency level of 1.184, the GM oranges had an average maximum absorbency of 1.211, and the Tang had an average maxium absorbency level of 0.964 (Figure 6 and Table 3).  This data supports the previously stated hypothesis.

            It was hypothesized that when salivary amylase had begun to digest all three orange products, the Tang would digested the slowest, followed by the GM oranges, and finally the organic oranges.  One reason to help explain this hypothesis was “the organic acids [in orange juice] are destroyed by the process of digestion,” meaning that salivary amylase might help make the digestion of orange juice quicker than the digestion of Tang (Sinclair, 1961).  In addition, Tang might have a more complex chemical structure than the oranges, making it the most resistant of the three orange products to the digestive effects of salivary amylase, which would cause Tang to be digested the slowest.  The results, however, showed that this was not the case.  Instead Tang was digested the fastest followed by organic oranges and then GM oranges.

            To improve this experiment, it would be more beneficial if the sugars could be measured quantitatively instead of qualitatively.  If we had the chance to do this experiment again, a wider variety of fruits and vegetables would be studied to get a better understanding of the experimentation.  Orange juice would be used instead of Tang for a more direct comparison to the oranges.  Instead of using the orange rinds for the photosynthesis lab, leaves from the actual orange tree would be used because they are most likely where the most photosynthesis occurs and they probably contain the pigment chlorophyll.  To better understand the pigment color bands, paper chromatography of pure carotene or pure xanthophyll would be performed to see how their color(s) would separate.  Some error in this experiment may have been due to incorrect procedure tactics or the fact that when we tested the salivary amylase the decomposition of the fruits had already begun to set in.  For further research on this topic, some other questions one could explore would be what is the shelf live of organically grown oranges compared to GM oranges, do GM oranges lack some basic amino acids that our body’s need, or is organically grown food becoming less and less common and how is that affecting us.