LBS 145
Thursday 3-6 pm
James Hardie & Rebecca DeGraaf
November 16, 2004

Abstract:
To determine and understand the difference in the chemical make-up and changes that take place during the ripening stages of a banana (Musa acuminata), several components of the pulp of a banana and the pigments of its rind were analyzed. Three replicates each of under-ripe (green peel), ripe (yellow peel), and overripe (brown peel) banana pulp were used in Barfoed’s test to determine whether the sugars in the pulp are monosaccharides or disaccharides and polysaccharides, the Iodine test to determine the levels of starch, and Selivanoff’s tests to determine the presence of ketoses or aldehydes. Photosynthetic pigments in rinds were measured by paper chromatography and an absorbance spectrum. A Bradford assay was also performed to determine the protein concentration in the pulp. It was predicted that as a banana ripens starch decreases, monosaccharides increase, proteins decrease and photosynthetic pigments change. From the assays it was found that starch levels decreased relatively as the banana ripened and all of the samples gave positive results for ketoses and monosaccharides. Relatively, there were more monosaccharides in the overripe banana pulp. The chromatography strip showed no results. The absorption spectrum showed the highest level of absorbance at all wavelengths for the ripe banana rind and the lowest absorbance at all wavelengths for the overripe banana rind. There were no absorbance peaks for any of the solutions. The Bradford Assay showed increasing protein concentration as the ripeness increased. Overall, it was found that as bananas ripen, protein concentration increases and starch levels decrease.

Table 1- Results from the Carbohydrate lab: The Iodine test shows that the raw specimens have some starch content while the overripe specimens have no starch. The Barfoed’s test shows that the raw specimens have very few monosaccharides while the overripe specimens have relatively more than the other two specimens. The Selivanoff’s test shows that all three specimens contain ketoses.

Discussion:

From the original hypothesis, it was predicted that the sugar content of the bananas would increase in monosaccharides as the banana ripened. It was expected that these sugars would be converted from a starch base, of which the original green bananas showed a higher concentration of starches. The results of the Barfoed’s and Iodine tests indicate that early pulp of the bananas contain relative high starch concentrations with low levels of monosaccharides. The unripe banana pulps and rinds actively process reactions of which starch is converted into simple sugars as the fruit matures. The long chains of glucose (starches) are converted by reduction/oxidation reactions within the pulp and rind. This describes the presence of more simple sugars later in the fruit’s development. Our results are consistent with the observation that over-ripened bananas taste much sweeter than starchy, green, under ripe bananas. The Selivanoff’s test simply shows that the sugars found within all the pulps were reducible (containing ketoses). Although these tests are only qualitative, they did indicate relative differences between ripe and un-ripened bananas.
The hypothesis that photosynthetic pigments of the bananas would decrease as the rind ripened due to oxidation and the darkness of color was inconclusive. The results from the pigment strips were inconclusive. One possible reason it was not possible to read the pigments was that the concentration levels could have been too low to visualize the pigments found within the rind. It is also possible that the rind had no pigments. In addition, by separating the pulp from the rind, some of the pulp was still found on the rind, which would have diluted the pigmentation. The separation errors could have been from passing the mixtures through too many layers of cheesecloth, restricting the pigments from the solutions.
The absorption spectrum run on the rind solutions showed that the rind of a ripened banana absorbed the highest amounts of light. The over-ripened banana absorbed the lowest at all wavelengths. The results showed that there were no peaks in absorbance at different wavelengths between the different ripeness. This could also be from a lack of pigments in the rinds. The level of absorbance seemed to come more from the overall darkness of the rind, than any pigments that may be in them. The yellow rind had the most absorbance and appears the lightest, where the overripe rind absorbed the least. This was not expected; the black rind (over-ripened banana) was thought that it would have absorbed the most. This could be because there were small particles in the samples that settled during the readings, affecting the overall absorbance at higher wavelengths. The hypothesis, that as the banana ripens its ability to absorb wavelengths and perform photosynthesis should decrease, was incorrect. There was no evidence found of a decreasing ability to perform photosynthesis since there were no particular photosynthetic pigments found.
From the results of the Bradford Assay, the overall protein of the banana increases as the pulp ripeness. Thus, the original hypothesis that the denaturing of the protein would occur was false. As the cells in the banana progress, they produce more enzymes. This concurs with our data that shows the increase of protein level increases with ripeness. This reasoning, combined with the fact that more monosaccharides are formed from the original fruiting structure, suggest that the actual cells within the fruit do not denature, they simply continue with basic cellular functioning, producing simple sugars and more enzymes to sustain cellular life for the seeding structure of the banana tree.
Our study indicates that the sugar and protein content of bananas increase as they ripen. Although blacked rinds may not look appetizing, they contain the most abundant source of protein and sugar content. It is no wonder why many athletic figures look to the fruits for an extra boost.