Three Apple Varieties Show Differences in Organic Composition
when Reducing Sugars, Pigments and Enzymes are Tested.
By: Leslie Madden, Michael Rak Elizabeth Brown
ABSTRACT:
Three apple varieties were investigated in order to determine the differences
in their organic make-up. In order to parameterize this make-up, we chose to
characterize the reducing sugar content, the pigment content, and the enzyme
activity. In quantifying the reducing sugar content, Benedict’s test for
reducing sugars was run and the resulting solutions were placed in a spectrophotometer
to quantify the sugar content. To characterize the pigments in the skins of
our apple varieties, paper chromatography was used. The absorption spectrum
was then taken to clearly represent the differences in the pigments. The next
test was done to display the activity of polyphenol oxidase (PPO) when it was
placed into different environments and the difference between the three apple
types regarding the activity of the PPO in each variety. Our experiments provided
evidence that there were different quantities of Free Ketoses and Aldoses in
the three apple varieties. There is Evidence that the Red Delicious and Granny
Smiths had few similar pigments, while Fuji apples had some pigments that were
the same as Red Delicious and some that were similar to the Granny Smith apples.
We found that PPO works best when in a basic environment and that the Granny
Smith apples tend to contain the most PPO, whose content is much greater than
both the Red Delicious and the Fuji varieties. The evidence contained herein
supports the hypothesis, that, although these three fruits tested are all apples,
on the molecular level they are not identical.
DISCUSSION:
The three different apples, from the everyday human perspective, appear quite
similar, but as we have found out are actually quite different. In the first
experiment, tests were run to qualitatively determine the presence of different
types of carbohydrates or sugars. These tests yielded similar results for all
the apples because all three formed a precipitate when the Benedict’s
test was run. This verifies that all three apples have free Aldhyde and Ketone
groups present. An inherent flaw of the Benedict’s experiment was that
there were no quantitative results. This afforded us no ability to determine
which apples had high or low sugar levels. We suspected that there was a difference,
due to the fact that the apples have different degrees of sweetness and bitterness
on the palate. Dr. Luckie recommended that we run our final solution after the
Benedict’s test through a spectrophotometer to solve this problem. In
order for the absorbance spectrum to read our results we had to dilute the solutions
after the Benedict’s test. It was hard to make sure that all of the precipitate
was evenly distributed throughout the solution. This was also a problem when
placing the cuvettes in the spectrophotometer because the precipitate tended
to settle quickly. Since this occurred for all of the trials we feel that this
has very little effect on our results. A second inherent flaw of this first
experiment is that the apples used could be at different points of ripeness,
which would cause different concentrations of different sugars as well. A way
to minimize this is to pick the apples by hand on the day that the experiment
is occurring. Unfortunately this was too difficult for us to do with the resources
at hand.
When running the spectrophotometer we tested for the % Transmittance. The higher
the % transmittance the more light is allowed to travel through. This means
that there is less precipitate in solution. We originally predicted that the
Granny Smith, Fuji, and then Red Delicious would have the highest to lowest
% transmittance. We found that Red Delicious had the highest % transmittance,
the Fuji apples had the next and the Granny Smiths had the lowest.
Experiment 2 was a pigment comparison of the three types of apples. This experiment
did not follow our predicted results; we felt that the Fuji would have pigments
that were closer to the Red Delicious since they are closer in lineage than
they are to Granny Smith apples. We ran two trials for each apple variety and
did not see variation between the trials for each variety. With the Granny Smith
Apples we found that there were at least three different pigments. For the Fuji
apples we found that there was only one pigment present which seemed to match
with the last line of pigment for the Granny Smith. Unfortunately for the Red
Delicious apple we only got very faint to no results. We feel that the reason
this occurred is because we were not able to get a solution of pure pigment
for the Red Delicious to place on the filter paper. (Figure 15) If what we thought
was pigment but instead was the fruit of the apple then there would be little
to no pigment since the fruit of the apple is white. If we were to redo this
portion of our experiment it would be helpful to find a way to minimize the
amount of fruit left on the apple peel. We can conclude from the experiment
that even though the Fuji and Granny Smith apples are not genealogically related,
they seem to share at least one pigment. This pigment may be a pigment found
in all apples or more broadly in plants, but more research needs to be done
to confirm this.
In experiment 3, we attempted to characterize the nature and amount of PPO in
each of the three varieties of apples. In this experiment, we observed that
the Red Delicious browned the fastest, followed by the Granny Smith, and the
Fuji’s. This led us to believe that the Red Delicious had the most PPO.
When testing to see if the apple pieces were affected by different pH levels
we obtained some interesting results. The lemon juice and the Fruit-Fresh kept
the apple from turning brown for about the same length of time, although, the
Fresh-fruit worked a little bit better. We feel that the reason for this difference
is because of the dextrose that is present in Fruit Fresh. The basic solution
that consisted of baking soda caused the apple to brown the fastest. We feel
this was because the acid irreversibly denatured the enzyme where as the base
catalyzes the PPO enzyme reaction. From this experiment we were able to conclude
that the best way to prevent fruit from browning would be to coat it ideally
with the product Fresh-Fruit or for a cheaper alternative to use lemon juice.
It would be interesting to test other edible household products to see if they
have any effect on the PPO reactions.
With all of the evidence at hand, we conclude that although all three selections
are all apples, there are a few things that are chemically different. This provides
quite an interesting outcome and platform for potential future research within
the realm of the apple.
Figure 16: These are the results of the first part of the PPO testing after 30 minutes. They were cut and treated with catechol. The resulting brown color is from the PPO in the apples reducing the catechol. From the left upper corner it is Granny Smith, Red Delicious and Fuji apple.
REFERENCES:
Dennis, Frank. Apple Varieties, yesterday, today and tomorrow: East Lansing,
MI, Michigan State University, 1996.
Marshall, Brian. “Question of the Day: Why do apples and potatoes turn
brown?”
How Stuff Works (1999-2002): accessed 8-29-02
< http://www.howstuffworks.com/question168.htm >
“Varieties” Washington Apples (2002): accessed 8-29-02
< http://www.bestapples.com/apple-info/varieties/ >
“Granny Smith Apples” Fruit from Washington (7-22-02): accessed
8-29-02
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