By: Nathan Crawford, Ria Reyes and Megan VanderZwart
Abstract
Our group studied the differences in carbohydrates, photosynthetic pigments, and enzymes on cooked carrots versus raw carrots. It is often said that raw vegetables have more nutrients than cooked ones, but cooking also helps the body absorb some of the nutrients better (Neegaard, 2001). The carrots were cooked by steaming them in a "Rival Express Hot Pot." The carbohydrates were tested by using Benedict's test (presence of reducing sugars), Barfoed's test (presence of mono-,di-, and poly- saccharides), Selivanoff's test (presence of ketoses and aldoses), Bial's test (presence of five-membered rings), and the Iodine test (presence of starch). We tested for photosynthetic pigments by using paper chromatography to identify any pigments and compared the cooked and uncooked carrots absorption levels testing the absorption spectrum. We also tested for the enzyme, PPO. We predicted that there would be a difference in the chemical composition, specifically in the carbohydrates. Selivanoff’s and the Iodine test resulted in a difference which supported our predictions. More specifically, there was likely a difference in the chemical makeup with ketoses and aldoses and in the presence of starch. Our results indicated that the raw and cooked carrots had slightly different absorption levels at different wave lengths, and neither indicated any presence of PPO.
Figure
The results of the Selivanoff test on raw and cooked carrots.
The first three test tubes are the raw carrot solution, the next three test tubes are the cooked carrot solution, and the seventh test tube contains our control, Sucrose. All of the carrot solutions reacted in the Selivanoff test, but the cooked carrots reacted more quickly than the raw carrots. This means that there is a free ketose found in each of them and possibly an aldose in the raw carrots. There is a slight variation in color, but it seemed to have nothing to do with whether the solution was cooked or raw carrots.
Discussion
Our hypothesis was that cooking carrots alters their chemical structure. We specifically investigated this by looking at carbohydrates, photosynthetic pigments, and the enzyme PPO. We originally thought that cooked and raw carrots would be diverse in their carbohydrate structures, that there would be a higher presence of photosynthetic pigments in the raw carrots, and that raw carrots would contain PPO and cooked ones would not. We tested these ideas through a number of different tests.
The first test for carbohydrates performed was Benedict’s test, which tested for reducing sugars, meaning that it has a potentially free aldehydes or ketones. Of the sample did contain reducing sugars, the sugars would reduce the copper sulfate, producing cuprous oxide and a red precipitate. The red color indicates the presence of reducing sugars, such as glucose and fructose. We observed a dark red to brown color in the cooked carrots, indicating that there were reducing sugars. This could be from the previous exposure to heat when the carrots were cooked. Heat acts as a catalyst, and induces the break down of disaccharides into monosaccharides, which are what most reducing sugars are (Diabeto Valens, 2002). The raw carrots also showed a dark red to brown precipitate indicating that it, too, had reducing sugars (Figure 1).
The next test performed for carbohydrates was Barfoed’s Test. This test indicates the presence of mono-, di-, or polysaccharides. Neither the cooked nor raw carrots underwent a color change during this test, indicating that they both contain di- or polysaccharides and not mono saccharides (Figure 2).
The third test was the Selivanoff’s test. This test was used to determine whether a substance had aldoses or ketoses, and if it contains ketoses whether they are mono- or disaccharides. Because ketoses react more quickly than aldoses, the reaction time is a way to determine which is present. Monosaccharide ketoses usually react in less than one minute, while disaccharide ketoses react in about one minute, and aldoses usually react after more than one minute. The cooked carrot solution reacted within twenty to thirty seconds and the raw carrot solution reacted in fifty to sixty seconds (Figure 3). Since the cooked carrots reacted in less than a minute, that means they probably contain monosaccharide ketoses, and the raw carrots reacted at about a minute, they probably contain disaccharide ketoses. Our data definitely supports this, since it happened for all three trials. This was our first definitive evidence that cooked and raw carrots have different chemical structures. This change in structure could help increase the absorbance of nutrients in the human body (Parenting, 2001).
Bial’s test, our fourth test, was used to detect the presence of furanoses. The pentose furanose rings react and produce a green colored solution and the hexose furanose react to form an olive green solution. When tested, both the raw and the cooked carrots produced an olive green colored solution indicating that they both contain a hexose furanose ring (Figure 4).
Our final carbohydrate test was the Iodine test, it tests for the presence of starch. When we tested the cooked carrot solution, we observed a dark blue color change indicating the presence of starch. When we tested the raw carrots, we observed little color change at all. It seems that starch is present in the cooked carrot solution and not present, or a very small amount is present, in the raw carrot solution (Figure 5). This was our second piece of definitive evidence that cooked and raw carrots have different chemical structures. Maybe cooking the carrots caused usable nutrients to convert into harder-to-break-up starch, causing a lack of nutrients (Successful Meetings, 1994).
The first test for photosynthetic pigments we performed was paper chromatography, which is used for pigment identification. No pigment was found in the either the cooked or raw carrots, there was only a band of color on the solvent from. From this we could not calculate Rf values, therefore unable determine what pigments were in the carrots. But the bands of color were slightly darker on the raw carrot strips leading us to believe that there is a greater concentration of pigments in the raw carrots than the cooked carrots, but the bands were very faint to begin with (Figure 6).
The second test used for photosynthetic pigments was to analyze the absorption patterns of light for each sample. Our results showed that the raw carrots had their highest absorption rate at 490nm and lowest at 700nm. When we analyzed the absorption rate of the cooked carrots, we found that the highest point of absorption was at 460nm and lowest was at 700nm (Table 1 and Figure 7). The low points for samples are in the dark orange area, which means that this color is reflected. The raw carrots also had a lower absorption at 700nm than cooked carrots. This means that the raw carrots reflected more of the light at 700nm, meaning that we see that color better.
For the testing of the presence of enzymes, we first applied an experiment for finding the enzyme polyphenoloxidase (PPO), which is responsible for the browning of most fruits and vegetables. When we performed the analysis we found that neither cooked or raw carrots contained PPO, or none that was detectable. The pH paper had no significant color change between the raw and cooked carrots, and the addition of catechol had no affect during each of our three trials, meaning we did not detect the presence of PPO (Figure 8). Because we could not find any PPO, we decided not to perform any of the other tests for that enzyme.
Sources of error for the carbohydrate portion of our experiment could include the fact that we did not accurately make solutions of the same concentration, though we did estimate very closely; our concentration could have been off so that we could not see color changes for each of the tests; and we might not have seen the color changes due to the fact that our solution was orange in the beginning. Errors in the photosynthetic pigment experiments may have been because the solutions we made were not correct, we may not have let the solution dry correctly for the paper chromatography, and we may not have cleaned the cuvettes for the spectrometer well enough. A possible error in test for the presence of PPO could be that there was a color change, but it was so minute that we did not notice it.
Our results are not very conclusive. What did we determine? We figured out that carbohydrate structure of cooked and raw carrots are different through the Selivanoff’s and Iodine test, that cooked and raw carrots absorb different wavelengths of light, and that neither cooked nor raw carrots contain PPO, or at least none detectable by our methods. These results do match our hypothesis; the chemical structure of carrots is changed by cooking, but they do not match our original ideas on how the chemical structures would be different.
Our group studied the differences in carbohydrates, photosynthetic pigments, and enzymes on cooked carrots versus raw carrots. It is often said that raw vegetables have more nutrients than cooked ones, but cooking also helps the body absorb some of the nutrients better (Neegaard, 2001). The carrots were cooked by steaming them in a "Rival Express Hot Pot." The carbohydrates were tested by using Benedict's test (presence of reducing sugars), Barfoed's test (presence of mono-,di-, and poly- saccharides), Selivanoff's test (presence of ketoses and aldoses), Bial's test (presence of five-membered rings), and the Iodine test (presence of starch). We tested for photosynthetic pigments by using paper chromatography to identify any pigments and compared the cooked and uncooked carrots absorption levels testing the absorption spectrum. We also tested for the enzyme, PPO. We predicted that there would be a difference in the chemical composition, specifically in the carbohydrates. Selivanoff’s and the Iodine test resulted in a difference which supported our predictions. More specifically, there was likely a difference in the chemical makeup with ketoses and aldoses and in the presence of starch. Our results indicated that the raw and cooked carrots had slightly different absorption levels at different wave lengths, and neither indicated any presence of PPO.
Figure
The results of the Selivanoff test on raw and cooked carrots.
The first three test tubes are the raw carrot solution, the next three test tubes are the cooked carrot solution, and the seventh test tube contains our control, Sucrose. All of the carrot solutions reacted in the Selivanoff test, but the cooked carrots reacted more quickly than the raw carrots. This means that there is a free ketose found in each of them and possibly an aldose in the raw carrots. There is a slight variation in color, but it seemed to have nothing to do with whether the solution was cooked or raw carrots.
Discussion
Our hypothesis was that cooking carrots alters their chemical structure. We specifically investigated this by looking at carbohydrates, photosynthetic pigments, and the enzyme PPO. We originally thought that cooked and raw carrots would be diverse in their carbohydrate structures, that there would be a higher presence of photosynthetic pigments in the raw carrots, and that raw carrots would contain PPO and cooked ones would not. We tested these ideas through a number of different tests.
The first test for carbohydrates performed was Benedict’s test, which tested for reducing sugars, meaning that it has a potentially free aldehydes or ketones. Of the sample did contain reducing sugars, the sugars would reduce the copper sulfate, producing cuprous oxide and a red precipitate. The red color indicates the presence of reducing sugars, such as glucose and fructose. We observed a dark red to brown color in the cooked carrots, indicating that there were reducing sugars. This could be from the previous exposure to heat when the carrots were cooked. Heat acts as a catalyst, and induces the break down of disaccharides into monosaccharides, which are what most reducing sugars are (Diabeto Valens, 2002). The raw carrots also showed a dark red to brown precipitate indicating that it, too, had reducing sugars (Figure 1).
The next test performed for carbohydrates was Barfoed’s Test. This test indicates the presence of mono-, di-, or polysaccharides. Neither the cooked nor raw carrots underwent a color change during this test, indicating that they both contain di- or polysaccharides and not mono saccharides (Figure 2).
The third test was the Selivanoff’s test. This test was used to determine whether a substance had aldoses or ketoses, and if it contains ketoses whether they are mono- or disaccharides. Because ketoses react more quickly than aldoses, the reaction time is a way to determine which is present. Monosaccharide ketoses usually react in less than one minute, while disaccharide ketoses react in about one minute, and aldoses usually react after more than one minute. The cooked carrot solution reacted within twenty to thirty seconds and the raw carrot solution reacted in fifty to sixty seconds (Figure 3). Since the cooked carrots reacted in less than a minute, that means they probably contain monosaccharide ketoses, and the raw carrots reacted at about a minute, they probably contain disaccharide ketoses. Our data definitely supports this, since it happened for all three trials. This was our first definitive evidence that cooked and raw carrots have different chemical structures. This change in structure could help increase the absorbance of nutrients in the human body (Parenting, 2001).
Bial’s test, our fourth test, was used to detect the presence of furanoses. The pentose furanose rings react and produce a green colored solution and the hexose furanose react to form an olive green solution. When tested, both the raw and the cooked carrots produced an olive green colored solution indicating that they both contain a hexose furanose ring (Figure 4).
Our final carbohydrate test was the Iodine test, it tests for the presence of starch. When we tested the cooked carrot solution, we observed a dark blue color change indicating the presence of starch. When we tested the raw carrots, we observed little color change at all. It seems that starch is present in the cooked carrot solution and not present, or a very small amount is present, in the raw carrot solution (Figure 5). This was our second piece of definitive evidence that cooked and raw carrots have different chemical structures. Maybe cooking the carrots caused usable nutrients to convert into harder-to-break-up starch, causing a lack of nutrients (Successful Meetings, 1994).
The first test for photosynthetic pigments we performed was paper chromatography, which is used for pigment identification. No pigment was found in the either the cooked or raw carrots, there was only a band of color on the solvent from. From this we could not calculate Rf values, therefore unable determine what pigments were in the carrots. But the bands of color were slightly darker on the raw carrot strips leading us to believe that there is a greater concentration of pigments in the raw carrots than the cooked carrots, but the bands were very faint to begin with (Figure 6).
The second test used for photosynthetic pigments was to analyze the absorption patterns of light for each sample. Our results showed that the raw carrots had their highest absorption rate at 490nm and lowest at 700nm. When we analyzed the absorption rate of the cooked carrots, we found that the highest point of absorption was at 460nm and lowest was at 700nm (Table 1 and Figure 7). The low points for samples are in the dark orange area, which means that this color is reflected. The raw carrots also had a lower absorption at 700nm than cooked carrots. This means that the raw carrots reflected more of the light at 700nm, meaning that we see that color better.
For the testing of the presence of enzymes, we first applied an experiment for finding the enzyme polyphenoloxidase (PPO), which is responsible for the browning of most fruits and vegetables. When we performed the analysis we found that neither cooked or raw carrots contained PPO, or none that was detectable. The pH paper had no significant color change between the raw and cooked carrots, and the addition of catechol had no affect during each of our three trials, meaning we did not detect the presence of PPO (Figure 8). Because we could not find any PPO, we decided not to perform any of the other tests for that enzyme.
Sources of error for the carbohydrate portion of our experiment could include the fact that we did not accurately make solutions of the same concentration, though we did estimate very closely; our concentration could have been off so that we could not see color changes for each of the tests; and we might not have seen the color changes due to the fact that our solution was orange in the beginning. Errors in the photosynthetic pigment experiments may have been because the solutions we made were not correct, we may not have let the solution dry correctly for the paper chromatography, and we may not have cleaned the cuvettes for the spectrometer well enough. A possible error in test for the presence of PPO could be that there was a color change, but it was so minute that we did not notice it.
Our results are not very conclusive. What did we determine? We figured out that carbohydrate structure of cooked and raw carrots are different through the Selivanoff’s and Iodine test, that cooked and raw carrots absorb different wavelengths of light, and that neither cooked nor raw carrots contain PPO, or at least none detectable by our methods. These results do match our hypothesis; the chemical structure of carrots is changed by cooking, but they do not match our original ideas on how the chemical structures would be different.