Bonobos

Discussion
By: Emily Bond and Amy Colcomb
Revised by: Mindy Anderson, and again by Lindsay Ferguson

The distinct properties of organic Malus domestica, over inorganic red delicious apples create claims that they are better. Besides physical differences (organic apples are bigger than inorganic apples), chemical properties are dissimilar. The carbohydrate composition, photosynthetic properties, and enzyme functionality all help to form these distinctions.

According to Dr.Engei Gakkai of the Japanese Society for Horticulture Science, "the fructose content of fruits influences their sweetness, which is a major determinant of fruit quality" (Gakkai 2002). Taste tests show that organic apples are sweeter and less tart than inorganic apples after being stored for six months (Kirby 2001). Additionally, studies show that "the average organic crop has approximately 10-20 percent higher nutrient levels than a comparable conventional crop" (Worthington 1999). These studies, as well as others like them, support our claim that organic apples are worth the extra money to buy because of their physical and chemical superiority to inorganic apples.

To test the differences in carbohydrate composition between organic and inorganic apples, we used Benedict's, Barfoed's, and Bial's test (Table 1). These test help to determine the types of carbohydrates present as well as the structure of these sugars. Benedicts's test tests for the presence of reducing sugars. If the test is positive, and such sugars are present, a precipitate forms. The amount of reducing sugars in the solution will be represented by the amount of precipitate that forms. Also, the precipitate, if it forms, will be a red color, but could have some orange tint to it. The color of the precipitate is important in determining the reducing sugars present. In the organic solution, a red precipitate formed in all three trials. Red was also the color for all the 100%, 50%, and 25% solutions. In the inorganic solutions, however, the 50% solution produced more of an orange colored precipitate. This means that not as many of the cuprious ions in Cu2O were reduced, and thus the solution contains less reducing sugars than does the organic 50% solution.

Barfoed's test, which distinguishes between mono-, di-, and polysaccharides, produces similar results. Monosaccharides only will produce a precipitate and color change in a solution. Fructose is one such monosaccharide, and is essential in the sweetness of apples. We predicted that since organic apples are less tart, thus sweeter, that they should contain more monosaccharides than inorganic apples. The test proved positive for all three trials. All of the different concentrations of organic apples showed a red colored precipitate, also. The same holds true for the inorganic solution, except that the 50% solution, as in Benedict's test, displayed a rusty red coloring instead. This means that some di- or polysaccharides exist in the solution, and take up the space that monosaccharides fill in organic solutions.

Finally, Bial's test studies the structure of the carbohydrates, whether they are a 5 or 6-membered furanose ring, or a 6-membered pyranose ring. The more members present, the sweeter the sugar. This being the case, the organic solutions should contain more pyranose rings, and no color change, while the inorganic solutions should contain furanose rings, and thus produce a green/olive, or muddy brown color. In the study, however, each solution, both organic and inorganic produced an olive/brown coloring suggesting that both contain the same furanose rings.

Putting these entire tests together, organic red delicious contain more monosaccharides, and reducing sugars than inorganic apples. Though the difference is not very much, it is still an important answer to whether or not organic apples are worth the extra cost.

We made our conclusions on the types of carbohydrates present, and the colors that were produced based on pictures and finding of the pure sugars tested the previous week. We understand that the results may not be accurate due to the fact that they were based on our personal color decisions. One person's red may be another's rusty color. But we tried to be as consistent as possible with our determinations, and hopefully we were right on. The differences in colors can be seen in the pictures at the end of the report.

Next, we tested the photosynthetic properties of both types of apples. Photosynthesis is the system in which autotrophs convert glucose into energy. The cycle is dependent on light absorbency, for this is the fuel for the entire process. According to our studies, organically grown apples should absorb more light than inorganically grown apples. Organic red delicious are bigger and heavier than inorganic Malus domestica, which suggests that the photosynthesis cycle is being completed more times to produce more food for the plant, allowing it to grow larger. To test the absorbencies of the different apples, we used a solution of their peels (Plant pigments are located in the peel, and it is these pigments that absorb the light necessary for photosynthesis). We then took these solutions and recorded their absorbencies at different wavelengths. Contrary to our predictions, the inorganic solutions had a higher absorbency at every tested wavelength (Figure 1-2, Table 2-3). They both peaked at 400nm, but inorganic apples had an absorbency of 2.94, which organic apples were at 2.73. This indicates that the energy in inorganic apples is being used for something other than converting carbon into glucose. This makes sense since inorganic apples contain other chemicals (that reduce the breakout of blemishes) and substances such as protein and nitrogen that compete with carbohydrates for photosynthates (Weston and Barth 1997).

Also, the fact that the solutions peaked at a wavelength of 400nm means that it absorbs light best at that wavelength. This is the area of violet rays. Later we will see that apples are composed mostly of xanthophylls, which give off a yellow coloring. If they reflect yellow coloring, it means that they absorb mostly violet rays (they're at the opposite end of the spectrum).

We also tested for the pigments present in the apples. Chlorophyll is the most important pigment in the absorption of light energy (Maleszewski et. al 2002), but carotene and xanthophylls are other types. We were hoping that organic apples would contain more chlorophyll than inorganic apples, allowing it to absorb more light, like we had predicted, and be more efficient in converting the light energy into food. In actuality, however, the only pigment that showed up was xanthophylls, which is a pale yellow color. Though the pigment had the same flow rate in both organic and inorganic apples, the time it took for the flow rate to occur was much faster in organic apples than inorganic apples. This suggests that organic apples are more efficient in converting light energy into food. This perhaps could be the reason that organic apples tend to be larger than inorganic ones.

We did have to do the pigment test twice. The first time we did it, we dipped the chromatogram strips in a phosphate solution, which produced no results. The second time, we used petroleum ether: chloroform solution, and was able to observe the pigment xanthophylls. Perhaps if we had used a different solution a third time, more pigments would appear.

Lastly, we tested the enzymes working within the apple, and how their functions are altered. Enzymes are substances that catalyze reactions without being used up; they simply allow reactions to occur (Maleszewski 2002). Enzymes generally function best at a neutral pH and natural temperatures. With this known, we predicted that the enzymes in organic apples would work more efficiently due to the fact that organic apples are supposed to be more basic than inorganic apples. Catechol is a reagent that is supposed to speed up the reaction of enzymes as well. We tested the pH of the apples using litmus paper, and found them both to be the same at 4.0 (which gave an orange color to the litmus paper). After catechol was added to the slices of apple, however, the pH actually increased to 6.0 (which is a lighter orange color). The catechol also left a brown outline of the pH paper on the apple slices. This suggests that the catechol did indeed affect the enzymes in the apple, causing them to turn the apple brown.

Another test we did was used to determine the affects of heat on enzymes. We found that in both organic and inorganic apple solutions, catechol helps to speed up the reaction. After catechol was added to an organic apple solution, its color darkened to a reddish/brown color, which indicates that the enzymes were working. When the inhibitor phenylthiourea was added to the apple solution, the enzymes stopped working, but started again after CuSO4 was added. This compound put copper back into the solution that phenylthiourea takes out. This reaction put color back into the solution, from a cloudy white to a light red, which is how it is known that this event occurred. The boiling of the enzyme produced a white coloring, which indicated that the enzyme did not react. In the inorganic reactions, the coloring was never as dark or as apparent signaling that the enzymes are not working as efficiently as in the organic solutions.

The greater efficiency of enzymes in organic apples over inorganic apples can also be seen by comparing the absorbencies to the pH levels of the solutions. Since enzymes work best at neutral pH levels, they should peak at a higher pH level in organic solutions, as well as have higher absorbance levels. The organic solutions did peak at a more neutral pH of 7.0 over 6.5 in inorganic solutions. However, the absorbance for the organic was 0.558, while it was 1.652 for trial 1, and 0.631 vs. 1.228 for trial 2 at a wavelength of 445nm. The contradicting results could be due to the fact that the apple solution was not kept cold at all times, allowing the enzymes to react. Since the enzymes should react differently in organic and inorganic solutions, this would produce inaccurate results.

So, are organic apples worth the extra money? They are indeed. Though you pay for one organic apple, and for one inorganic apple, the pure size difference is enough to make up for the extra cents. Also, organic apples contain more monosaccharides, including fructose, which increase the sweetness in the taste. In addition to taste, you get purer apples. Inorganic apples contain nitrogen and other unnatural chemicals that affect the production and make-up of the apples. "Higher levels of nitrogen lead to a higher protein-carbohydrate ratio, and therefore a decline in the carbohydrate content" (Weston and Barth 1997). Organic red delicious apple are free from pesticides and other harmful substances. They're also better for the environment, and the health of individuals. In actuality, you are spending more for organic apples, but you are getting more in the process, too.