Differences between Uncooked and Cooked Zucchini (Cucurbita pepo) and Summer Squash (Cucurbita spp.) based on Carbohydrate, Pigment, and Enzyme Tests

Mehdi Jafri, Katie Graham and Dane Coulberg

Team Darwin

LBS 145

Wednesday 7 ö 10 pm

 

Abstract:

The question of interest was whether cooked or uncooked vegetables have a higher nutrient value, based on carbohydrate, pigment, and enzymatic tests.Ê Zucchini (Cucurbita pepo) and yellow zucchini (summer squash) (Cucurbita spp.) were used.Ê It was hypothesized that the process of cooking would eliminate the presence of reducing sugars, eliminate the presence of photosynthetic pigments, and decrease the amount of enzymes present in the zucchini, making it a less healthy choice when compared to its raw form (as less sugars and protein is available for the body, this decreases the value of the food for the body).Ê When examining the carbohydrate aspect, Benedicts, Barefoeds, Selivanoffs, and Iodine tests were performed.Ê While dealing with the photosynthesis portion, the zucchini underwent the paper chromatography test.Ê Lastly, the enzyme test performed was the Bradford.Ê Six total treatments were used for research; three zucchinis and three summer squash.Ê Two slices from each zucchini were cut, and separated into cooked and uncooked categories respectfully.Ê Each slice was massed using a scale; all slices were between 10 - 15 grams each.Ê The ãcookedä slices were placed in a hot pot for a duration of 10 minutes.Ê The slices were blended and then diluted with water; this slurry solution was used for experimentation.Ê It was found that the cooking did decrease the intensity and concentration of reducing sugars, decreased the amount of pigments present, and decreased the concentration of protein, supporting the hypothesis that the cooking process decreases the nutritional nature of zucchini.

 

 

Discussion:

Carbohydrate Tests:

We began by testing for select carbohydrates: reducing sugars (Benedicts), mono, di- and polysaccharides (Barfoeds), ketoses and aldoses (Selivanoffs), and starch (Iodine).Ê All slurry solutions formed precipitates in the test for reducing sugars, and therefore all contain mono, di- and/or polysaccharides.Ê Cooking seemed to have affected the reducing sugar composition in the intensity of the precipitate formed for the trials.Ê

When distinguishing for monosaccharides, nearly all solutions formed a red precipitate.Ê While nearly all formed precipitates, there were a few cases in each treatment which showcased no resulting precipitate when the same solution produced results twice before.Ê For example, uncooked zucchini trial A showed some precipitate, while trails B and C displayed none.Ê We felt that an error could have been made in contamination of trail A, using a contaminated test tube or micopipette.Ê CookingÊ affected the monosaccharides present in each solution, as the precipitate formed had varying intensity.Ê The cooked zucchini and summer squash samples seemed to form lighter colored precipitates, perhaps indicating less monosaccharides present, however because these experiments only test for the presence of sugars this needs to be confirmed with other tests.Ê

Both uncooked and cooked zucchini slurries formed red precipitates in over one minute, while uncooked and cooked summer squash slurries formed red precipitates in less than one minute while differentiating between ketoses and aldoses.Ê The resulting red precipitates in more than one minute for uncooked and cooked zucchini suggests that they contain aldoses, and that the cooking process did not affect this.Ê The cooked and uncooked summer squash turned red in less than one minute, suggesting that they contained a monosaccharide ketose, and once again the cooking process showed that the cooked samples still had sugars, but lighter in color.

Both cooked zucchini and summer squash displayed the presence of starch in the starch test.Ê However, uncooked zucchini and summer squash slurries showed no presence of starch.Ê When hypothesizing as to where the starch came from, the solution we came up with was contamination.Ê The cooked treatments were exposed to a hotpot, which could have contained starch from previous usage, and thereby causing starch to be found in the testing.Ê

Photosynthesis Tests:

We tested for photosynthetic pigments in the cooked and uncooked zucchini and summer squash by running the chromatography test.Ê As in the previous carbohydrate portion of the study, slurry solutions of zucchini and summer squash were prepared and used for experimentation.Ê We made the slurry solution by cutting slices of a zucchini and then adding 150 mLâs of water to a blender and blending for 2 minutes.Ê 40 drops of each slurry solution were added to each chromatography strip.Ê Because of time restraints this was as far as we got in the lab time provided, and we completed the experiment during the following open lab.Ê During the open lab we added 3 mL of petroleum ether chloroform solution to the test tube and then placed each respective chromatograph strip in a separate test tube.Ê Here is where we encountered a very interesting problem, as not one of the strips showed pigments moving up the strip.Ê Working with our TAâs, we came to one of two possible conclusions.Ê Either the nature of zucchini is that the pigments are contained in the leaves where all the photosynthesis occurs, and not in the actual zucchini.Ê Another possibility was the fact that the strips sat for 5 days, and this could have allowed the chloroplasts to dry out and thereby making it impossible for us to obtain results from the experiment.Ê We were forced to repeat this part of the experiment, this time with a modified approach.Ê Previously, we used a 70% ethyl alcohol solution, and in this second trial we used 100%.Ê Because the center of the zucchini is mostly composed of water, we decided to further modify the experiment by using only the skins each zucchini during the test.Ê This allowed us to have a more concentrated solution of chloroplasts.ÊÊÊ We performed this experiment in one lab period instead of spread out over many days, so the dots werenât completely dried out.Ê

To our relief we found that these modifications were very successful in obtaining results.Ê When comparing the cooked to uncooked treatments, a noticeable distinction in pigment intensity was observed.Ê Cooked and uncooked zucchini solutions showcased four pigments; both had nearly identical Rf values.Ê The cooked summer squash displayed no visible pigments, while the uncooked summer squash showcased only pigments 1 and 2.Ê We concluded that zucchini was green, and therefore contained a wider array of pigments (pigments 1-4), while summer squash is yellow and only contained pigments 1 and 2.Ê When compared to the spinach leaves, the spinach leaves had much clearer defined pigments on the strip, as well as more evenly distributed Rf values.Ê Because of the large concentration of pigments in the zucchini, cooking it had minor affects on its pigments, while the summer squash had a much smaller concentration of pigments, which led to finding none in our cooked treatments.

Enzyme Tests:

Lastly, the enzyme test performed was Bradfords.Ê Using BSA, at different concentrations, a standard curve was made so that we could calculate the protein concentration present in the samples.Ê Bradfords test determines the total protein concentration in the slurry solution.Ê We found that in both zucchini and summer squash treatments, the uncooked solutions had a higher protein concentration when compared to the cooked solutions.Ê The reason behind this was because during the cooking process, some of the protein is lost, either it was denatured, or it was lost to the water it was cooked in.Ê

Based on our experiment, we found the cooking process does decrease the nutritional value of zucchini as it provides less sugars and less protein when compared to its raw form.Ê The cooking process also decreases the presence of pigments, which combined with the sugar and protein results, supports our hypothesis.

 

 

Table 5: Table of Average Rf Values for Spinach Leaves, Cooked and Uncooked Zucchini and Summer Squash, and Water.Ê Values for Rf Averages for uncooked and cooked zucchini and summer squash, as well as positive and negative controls (spinach leaves and water).Ê Controls were used to verify the validity of results.

 

Pigment 1

Pigment 2

Pigment 3

Pigment 4

 

Rf Values (Avg)

Rf Values (Avg)

Rf Values (Avg)

Rf Values (Avg)

Spinach Leaves

.186

.336

.57

.306

Water

0

0

0

0

Cooked Zucchini

.285

.285

.19

.285

Uncooked Zucchini

.285

.333

.19

.238

Cooked Summer Squash

0

0

0

0

Uncooked Summer Squash

.695

.347

0

0

 

 

 

 

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