Fresh bananas, Musa pacuminata, and fresh pineapple, Ananas
comosus were compared to their dried counterparts. The level of carbohydrates
in each type of fruit was studied to test if drying causes changes. Barfoed’s,
Selivanoff’s, Bial’s, and Iodine Tests were used to compare carbohydrates
found in each. These tests were preformed to determine the structural components
and sugars present. As predicted, there was no variation in the results between
the fresh and dried fruit.
Photosynthesis does not occur in
the pulp of the fruit, (Freeman, 2002) paper chromatography was used to determine
the pigments present. There was little difference found between fresh and
dried forms of the pineapple and banana.
In order to test the enzyme activity
of the four variations of fruit, the presence of PPO and levels of heat and
pH that it could withstand were tested, as well as the quantity of protein
in the fresh and dried fruit. When the fruit was exposed to different pH levels
and heats, the dried fruit was able to withstand changes in pH and heat more
than the fresh fruit. The PPO levels were tested and compared, supporting
the hypothesis that fresh fruit would have PPO present while dried would not.
We also performed pH and taste tests on the four fruits.
While some differences were found between fresh and dried fruit, we concluded
that the main hypothesis was supported; there is little difference in structural
components and pigments, but a larger difference in enzyme activity of fresh
and dried fruit.
In this experiment, we tested the structural composition and the enzyme activity to find the similarities and differences between bananas and pineapple and their dried counterparts. We predicted that the drying process of fruit would not alter the structural components, but would alter the enzyme activity. We predicted this because extracting the water from fruit should not change which sugars or chemicals are present in the fruit but it should change how the enzymes react, especially in regards to pH and temperature.
In testing the different aspects of the carbohydrate composition, we predicted that the fresh and dried fruit would remain the same. Our experiments were on two different fruits, pineapple, Ananas comosus, and bananas, Musa pacuminata in both the dried and fresh forms. Four tests were performed: Selivanoffâs Test to test for the presence of ketoses or aldoses, Bialâs Test to test for furanoses or five-membered rings, the Iodine test which tested for the presence of starch, and Barfoedâs Test to test for reducing sugars that are monosaccharides.
Our results of Selivanoffâs Test supported our hypothesis because both the fresh and dried pineapple and banana solutions turned red in approximately less than one minute. This shows that they all contain a disaccharide ketose. Our results were also consistent with previous LBS 145 research determined that fresh pineapples (Barton, et.al., 2002) and bananas are made up of ketoses (Boerman et. al., 2003).
Bialâs Test showed no change in the fresh pineapple solution, which means that the sugar is a pyranose while the dried pineapple solution turned an olive-brown color showing the presence of a pentose-furanose sugar. These results were not supportive of our hypothesis. This could be due to an effect of the drying process or an error our group had while performing the experiment such as not letting the solution heat in the hot water bath for a long enough period of time. In addition, since the original color of these solutions is not entirely transparent, but has a brownish tint, it was difficult to distinguish the actual color change. All the solutions for fresh and dried bananas came out brown in color showing the test was positive for a hexose (or higher) furanose sugar. This result was consistent with our hypothesis.
The Iodine staining in the Iodine Test will help to distinguish starch, which is a polysaccharide, from monosaccharides, disaccharides, and other polysaccharides (Krha et. al., 2004). Our results for the Iodine Test showed a yellow solution for both the fresh and dried pineapple. This was supportive of our hypothesis because we predicted that both fresh and dried pineapple would not contain starch. While the water-based solution of the fresh banana mixture did not change, the suspended pieces of banana changed to a dark brown color, showing that the fresh bananas do contain starch. The dried banana solutions however remained the color of the original solution showing no presence of starch. The absence of starch in the dried banana solution could be due to the drying process, since as a banana ripens the abundance of starch changes into free sugars. Before a banana becomes ripe, starch makes up 80-90 percent of the carbohydrate content, (Hermansen et. al., 1992). Therefore, the dried bananas were most likely over-ripe before they were dried to allow for the presence of no starch that was seen in our tests.
The results of Barfoedâs Test showed no change in the bright blue solutions for both the fresh and dried pineapple and banana. In the solutions of dried pineapple and banana, the pulp of the fruit was visible, however there was no change of color or formation of an orange-red precipitate. Therefore, the test was negative for monosaccharides for all of the fresh and dried fruits tested.
The second aspect of the testing on our fruits analyzed the photosynthetic
qualities of the different forms of the fruit. We predicted that both
the dried and the fresh fruit would have the same pigments present with the
same Rf values on the chromatogram strip. There were no
visible pigments in the paper chromatography test for the fresh and dried
pineapple and banana. The only measurable lines were that of the solvent
front and the first line on the strip. The first line on the strip was
not considered a visible pigment, but instead a expansion of the original dot.
The last aspect of the analyzing the different of the forms of fruit is the enzyme lab. The enzyme being tested for is polyphenol oxidase (PPO), the enzymes oxidation of phenolic substrates is believed to cause the browning in fresh fruits (Gooding et. al., 2001). We predicted that the fresh fruit would have the enzyme PPO while the dried fruit would have negligible amounts. Bananas have significant amounts of the enzyme PPO, the browning enzyme, present in its flesh (Gooding et. al., 2001). The pH was recorded as five for all twenty solutions with the litmus paper. We attribute the lack of variation to be the generalized coloring of the litmus paper, and the high water concentrations in each of the solutions. The addition of catechol gave a pinkish tint to the fresh banana solutions, supporting the presence of PPO. The fresh pineapple solutions showed no color change, which goes against our original predictions. The absence of a positive PPO test in the fresh pineapple may be on account of a very low level in the actual fruit, which was further diluted in the making of the solutions. The dried fruit was supportive of our predictions, testing negative for PPO in most solutions of both fruits. The only positive result of PPO in the dried fruit came from the 15 percent solution of banana. The addition of catechol caused a slight pink tint, which was greatly masked by the overall brown color of the solution. The fact that the pink overtone of the solution was so light, we attribute this positive result to what may have been an experimental error.
When testing for the effects of heat and inhibitors consistent
with our other results, we predicted that the heat and inhibitors would have a
more dramatic effect on the fresh fruit then on the dried. While the
overall results were skewed, the general trend supported our hypothesis.
Some of the control solutions of the fresh banana, and all of the fresh
pineapple solutions did not change after the addition of catechol, which may
have been due to a poor mixture of the sample solution, which contained mostly
water. Boiling the fresh banana solutions or adding an inhibitor did not
allow for the PPO to react with the catechol when added, therefore there was
no color change visible. The heating of the solutions hindered the PPO
reaction. The inhibitors, phenylthiourea
When comparing the effects of various pH levels on the absorbency of fresh and dried fruits, we expect a peak in all of the absorbencies in the middle of the pH scale for both fresh fruits. The lack of PPO in the dried fruits lead us to determine that there would be no readable absorbencies for this portion of research. This fact is the reason that the effect of pH was run only on the fresh fruit solutions, leaving little room to compare the fresh and the dried.
The Bradford Assay was used to determine the total protein concentrations in the fresh pineapples and bananas versus the dried versions. We predicted that the concentrations would be similar in the fresh and dried version of each fruit but the dried fruit concentration would be slightly less. We choose to use a 10μg sample and 25μg sample of our concentrations when performing this assay. The 25μg sample held consistent with .4μg of protein found in each solution, fresh and dried banana and pineapple. The 10μg samples produced very skewed results, leading the overall experiment to be inconclusive. The error in producing readable results for this portion of the experiment may be attributed to the time sensitive nature of this test. A simple miscalculation may have caused the entire experiment to falter.
The straight pH test was used to determine the effect of the drying process on the value of pH found in the fruits. We predicted that the results of the pH test for the fresh pineapple and banana solutions to be consistent with our predictions of 3.4-4.1 for the pineapple (anonymous-2, unknown), and 4.4-4.6 for the banana, (Badr, 2002). The pH for the dried pineapple and banana solutions will decrease slightly in value due to the effects of the drying process. The fresh pineapple and banana were supportive of our predictions, the pineapple having an average pH of 3.68, and the banana an average pH of 4.36. With an average pH of 4.04 for the dried banana and an average of 3.54 for the dried pineapple, our original predictions were further supported.
A taste test was conducted to determine whether the fresh or dried fruits were preferred according to sweetness, consistency/texture, and overall taste by randomly selected people. We predicted that the fresh fruits will be preferred overall according to the survey taken because the drying process can reduce the quality of the fruit. With comments from those surveyed such as, ãThe dried fruit tastes like cardboardä, and ãDried didnât seem to have much flavor,ä it is easy to see that our predictions were correct. Overall the texture of both types of fresh fruit was preferred much more then the texture of the dried pineapple and banana. While some people found the dried banana sweet, it was the fresh pineapple and banana that were ranked sweeter, and the fresh fruit that won out in overall taste.
If the results of the experiments are as predicted then the data will support our hypothesis. Any data recorded that does not support our hypothesis could be due to a number of human weaknesses or possible errors the may have occurred during the individual experiments.
Some of the weaknesses in this experiment are the lack of trials due to time constraints. The results may not be as accurate due to the limited amount of trials we needed to use because some experiments take large amounts of time. A second time issue was the long duration of time for the lab, because of the lab being over so many weeks the possibility of obtaining a second set of fresh fruits could alter the results. Another possible reason for strange results could be that different processes of drying can cause different changes in the fruit. For example, hot air drying can cause thermal degradation of important components in the fruit. Where freeze-drying may not cause these problems but is more expensive. Vacuum microwave drying is a third possible drying process, which can potentially improve the quality of the dried fruit (Mui et. al., 2002). If the technique of drying is not known, our results may vary due to the drying process.
Some possible errors that could have occurred in this experiment are measurement errors. There is a chance that a chemical was measured wrong, as we found when pipetting the dried solutions and those of higher concentration especially. Many times, a piece of the fruit would clog the pipette tip not allowing the exact amount of the solution to enter the pipette. A wrong chemical could have been added, or something added to the experiment out of order as well. Another possible error, especially in the Bialâs test, would be in judgment of color, since there is only a small difference in olive/brown versus olive/green (Krha et al., 2004). Specimens can be contaminated also by unclean test tubes, airborne particles, or other unknown possibilities.
Overall, we found that there are only slight differences between the structural components and pigments present of fresh and dried pineapples and bananas but there are differences between the enzyme activity of the dried fruits versus the fresh fruits. The difference in enzyme activity is an important factor in the storage of the fruits. Because of these differences, fresh fruit spoils while dried fruit lasts for long periods of time. The preference between dried and fresh fruits depend on the individual, however dried fruits offer a more convenient alternative to fresh fruits while still offering nutritional value, but the fresh fruits offer a more appealing taste.
Table 1: Results for
Carbohydrate Tests: Selivanoff's, Bial's, Iodine, and Barfoed's.
Selivanoff's tells us that since they all reacted in less than a minute they
all contain a disaccharide ketose. Bial's test displayed that the fresh
and dried banandas which turned brown in color all contained a hexose furanose.
The pineapple contained a pyranose due to the lack of color change, the dried
pineapple since it turned olive/green tells the presence of a pentose-furanose.
The iodine test for the presence of starch came back negative for all of the
fruits except the fresh bananas which contain starch. None of the fruits
contain monosaccharides due to the lack of formation of a precipitate in the
Barfoed's test.
|
|
%
solution |
Selivanoff's |
Bial's |
Iodine |
Barfoedâs |
|
|
Fresh Banana |
1 |
≤ 1 min |
Yellow |
Black
Specs in Yellow Solution |
Bright
Blue |
|
|
3 |
≤ 1 min |
Yellow |
Mostly black with Yellow Solution |
Bright Blue |
||
|
5 |
≤ 1 min |
Dark
Yellow |
Mostly Black with yellow solution |
Bright Blue |
||
|
10 |
≤ 1 min |
Light
Brown |
Grayish black |
Bright Blue |
||
|
15 |
≤ 1 min |
Light
Brown |
Black |
Bright Blue |
||
|
Dried
Banana |
1 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
|
|
3 |
≤ 1 min |
Brown
Yellow |
Yellow |
Bright Blue |
||
|
5 |
≤ 1 min |
Light
Brown |
Yellow |
Bright Blue |
||
|
10 |
≤ 1 min |
Brown |
Yellow |
Bright Blue |
||
|
15 |
≤ 1 min |
Dark
Brown |
Yellow |
Bright Blue |
||
|
Fresh Pineapple |
1 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
|
|
3 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
||
|
5 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
||
|
10 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
||
|
15 |
≤ 1 min |
Yellow |
Yellow |
Bright Blue |
||
|
Dried
Pineapple |
1 |
≤ 1 min |
Olive
Brown |
Yellow |
Bright Blue |
|
|
3 |
≤ 1 min |
Olive
Brown |
Yellow |
Bright Blue |
||
|
5 |
≤ 1 min |
Olive
Brown |
Yellow |
Bright Blue |
||
|
10 |
≤ 1 min |
Dark
Olive |
Yellow |
Bright Blue |
||
|
15 |
≤ 1 min |
Dark
Olive |
Yellow |
Bright Blue |
||