Discussion

How similar are pluots, a hybrid from 75% plum and 25% apricots, to their plum parent that they taste so similar to? We set out to see if this new hybrid fruit really had any major differences from a plum, because when we tasted them side by side, we could not tell any difference in taste. Are they just overpriced plums with a fancy name and speckled skin? We decided to compare them in three different aspects. First, how are the structures of their carbohydrates similar or different? Also, their skins look very different, so are there different pigments in their skin cells? Finally, we knew that the pluot has a much lower pH, so would the enzyme polyphenoloxidase have higher activity at lower pH values in the pluot than the plum? We came into this experiment believing that they should be very similar is all of these aspects based on our taste test.

In our first experiment we ran 3 trials for both Barfoed's and Selivanoff's tests for each extract and got positive results for both fruits at both 10% and 15% concentrations suggesting that monosaccharide reducing sugars and ketose structures are present in each (Figures 1 and 2, Tables 1 and 2). We based our positive results on sugar samples that we already knew the structures of. We ran glucose as a known positive because it is an aldose monosaccharide reducing sugar. For a negative result we ran sucrose, a disaccharide containing a ketose monomer.

For Barfoed's test we took the first trial's samples and took the absorption of them after dilution to try to quantify the positive result. We only chose to do the absorbance of one of the trials because all three showed very similar results. We found that all of the samples had low absorption at 400nm (violet) and 550 nm (green) and very high absorption at 700 nm (red) (Figure 4, Table3). The low absorption at the low end of the spectrum makes sense, because the solutions were obviously blue and all wavelengths at or around blue would be mostly transmitted. Since blue light is at around 450-500 nm, this correlates with our data. Also, the fruit extract samples had the highest absorption values and they were closest to sucrose, suggesting some correlation between all the positive samples. At the higher wavelength of 700, which is red light, we had hoped to show a lower absorption for the pigments and sucrose which all contained a red precipitate, but this was not seen in our data. Although we vortexed each tube before reading the absorbance to keep the precipitate from settling, we still could not quantify it. We believe this is because the precipitate was at such a low concentration, once resuspended in the solution after vortexing, it could not be picked up by the spectrophotometer. Despite this, we still consider all of the extracts to show positive for presence of monosaccharide reducing sugars because we could see an obvious red precipitate in all three of our trials, and see our attempt to quantify the precipitate as a poor procedure for doing so. To correct our poor procedure in the future, it would be better to pull off as much of the supernatant of the samples as possible and take the absorbance readings of the precipitate in a higher concentration from the supernatant. Also, we saw little difference from the low concentration (10%) solutions and the high concentration (15%) (Table3). There was a slight trend that the low concentrations showed higher absorbance at the low wavelengths and lower absorbance at high wavelengths than the high concentrations, but the variance between them was not large enough to justify a difference between the two samples. We believe that this is because the concentrations are too similar, and an improvement that could be made in the future would be to vary the concentrations more, possibly having one be twice the other (for example, if we repeated this we would use 10% and 20% or 7.5% and 15%). We consider both extracts to show very similar results for Barfoed's test and consider our hypothesis that they would have the same composition valid in the aspect of monosaccharide reducing sugars.

In Selivanoff's test, we saw all trials of all extracts at both concentrations show positive results for presence of ketoses (Figure 2). This was based off of the time that they took to turn color. They did not turn as quickly as sucrose, which changed at 15 seconds, but still were well under one minute for both concentrations, which was the listed time as the dividing point between a positive and negative result. Between the two fruit extracts, the plum began to change color the fastest, averaging 20 seconds in the three trials at the high concentration (Figure 3, Table 2). Also, the higher concentration, on average changed faster than the low concentration in the plum, suggesting a relationship between the concentration of sugars containing ketoses and speed at which the color change occurs. The pluot, on average, changed color slower than the plum. It averaged 30 seconds at the 15% concentration and 37 seconds at the 10% concentration (Figure 3, Table 2). The pluot showed the same differences in time between concentration, strengthening the evidence that there is a relationship between the concentration of sugars containing ketoses and speed at which the color change occurs. Because of this, and the fact that the pluot changed color consistently slower on average than the plum leads us to suggest that the plum has a higher concentration of sugars containing ketose groups than the pluot. This test showed presence in both fruits of ketose sugars, but in different concentrations, which begins to refute our hypothesis that they would be similar in all aspects of the carbohydrate tests that we would run.

We chose not to take absorbance of our positive results for Selivanoff's test because the strength of color change was not the factor that determined the difference between positive and negative results. Instead it is the time that was the important factor. From our testing each extract at different concentrations and finding faster color changes at higher concentrations leads us to believe that time can be used as a quantitative value of what concentration of the sugars in a solution are ketose. This is what allows us to suggest that the plum contains a higher concentration of ketose sugars than the pluot. We cannot conclude what sugars are in each of the fruits, or say that all the sugars are ketose and monosaccharide reducing sugars. We can only say that some of the sugars in each of the fruits are monosaccharide reducing and some are ketose.

In the paper chromatography, in both trials for both fruits we found one pigment present on the paper chromatography strip (Figures 5 and 6). For all of the trials, the pigment had a similar yellow color and the Rf values for all of the trials were very close. For the plum, the average Rf value between the two trials was 0.97 with the two trials varying little (.007 from the average or 0.7%) (Table 4). For the pluot the values varied even less (.002 from the average or 0.2%) with the average being 0.968 (Table 4). The average Rf values of the two fruit pigment extracts for the yellow pigment were also very close, varying by only 0.002, or approximately 0.2% (Table 4). This leads us to believe that the pigment extracted from each fruit in each trial is the same pigment. We cannot conclude what pigment this is, but comparing it to the previous week's experiment where spinach chloroplasts were extracted and the same chromatography test was done, a pigment similar in color was seen, xanthophyll, but the Rf value that was calculated for it had an average of 0.84, which is too different from the Rf value of this pigment to conclude that they are the same (Table 4). This data supports our hypothesis that the pigments of each fruit are similar in the aspects we tested, despite their obvious color differences.

We also conducted an absorption spectrum of each of the fruit pigment extracts. Our intentions here were to see what colors of light were absorbed most in each extraction, or more simply what colors each extract was made of. Wavelengths that had low absorbance would have high transmittance in the extracts and those would be the colors you would see in the solution. Our results show similar absorbencies for each of the pigment extract with the highest absorption at the lower wavelengths and the lowest absorption at the higher wavelengths showing more or less a negative linear regression (Figure 7, Table 5). This data would suggest that the pigments are made up primarily of red pigments with an intermediate concentration of green pigments, and the lowest concentration of blue and violet pigments. This correlates with the colors of our original pigment extract solutions, because both appeared reddish, with the pluot looking orangey/peach, and the plum was rose colored. Both of the pigment extracts showed very similar trends through the absorbance spectrum, suggesting similar pigment composition and further supporting our hypothesis.

We found that the pH value for our pluots were much lower than our plums. The pH of our plums was 5.0 and our pluots were 3.0 (Figure 9). This led us to wonder if the enzyme activity for each fruit would be at greatest activity at the pH that the fruit is naturally found. We tested and found presence of the enzyme polyphenoloxidase (PPO) in each of the fruits, and decided to take extracts from each fruit containing this enzyme and subject them to varying pH level (Figure 8). Then we would activate the enzyme and allow it equal time to react in each extract. The absorbance of each extract was taken at each pH, with high absorbance representing high PPO activity. We found that the plum had highest absorbance (meaning enzyme activity) in a pH buffer of 8.0 (Figure 10, Table 6). The pluot had the highest activity at a pH between 7.0-7.5, slightly lower than the plum (Figure 10, Table 6). This shift downward of the peak enzyme activity could be because of the pluot having a lower ph than then plum, but does not fully support it. We conducted two trials of this test for each fruit and saw similar trends for each trial. We would have conducted this same test at much lower pH level that are equal to that of the fruits, but there was not any buffer solution available below a pH of 5.0. If peak enzyme activity was seen at the actual pH values of the fruit, then it would support more strongly that the enzyme activity of the pluot is highest at lower pH values than the plum. Still, our data shows differences in both the pH and the enzyme activity at specific pH values between the two fruits tested, going against our hypothesis tested and ultimately causing us to refute our hypothesis.

All of our tests suggested that the plum and pluot are very similar in structure in many ways, but also suggests that there are certain aspects in which the fruits differ. In the carbohydrate tests run, both fruits showed presence for both ketose and monosaccharide reducing sugar structures, but we could conclude that the plum had a greater concentration of ketose sugars than the pluot based on the reaction time of each. In the tests based off of the pigment of the fruits, we could separate out only one pigment for each fruit, and believe that it is the same pigment in each of the fruits. We also saw similar pigment composition in the absorbance spectrum of each of the extracts. We see both of these results as possibly erroneous, because we could see obvious differences in skin color between the two fruits, and would have thought that they contain different pigmentation. Finally, we found that the fruits had very different pH values with the pluot having the lower, and also that the enzyme polyphenoloxidase had the greatest activity at a lower pH value in the pluot. Because of these factors, we are forced to refute our hypothesis that both of the fruits would be the same in the aspects that we are testing for, and we now understand that they do have some fundamental differences in organic composition.

This information is important because it allows us to begin to understand that hybridized and genetically alter foods have differences from the foods they are derived from. We only found small differences between our fruits, but some modifications could cause much larger changes that could have negative effects. A hybridized fruit could become more susceptible to pathogens or parasites, making it uneconomical to grow. Even more serious is that the hybrid could carry diseases, mutations, or allergies that the person eating is unaware of. Anything is possible in the realm of genetics. By seeing our small changes that occurred in the few things we tested for makes us realize the dangers of modifying our foods and suggests we should be cautious in the changes we make from the natural world.