Identifying Macromolecules in Common Foods Free Essay Example

Abstract:

We tested five common food items to determine which macromolecules were present. We tested for the macromolecules of simple and complex carbohydrates (sugars and starch), lipids, and proteins. The foods tested were coconut milk, karo syrup, potato chips, peanut butter, and banana baby food. We hypothesized that coconut milk would contain all four types of macromolecules, karo syrup would only contain simple sugars which are monosaccharides and/or disaccharides, potato chips would contain starches and fats, peanut butter would contain sugars, fats, and proteins, and banana baby food would consist of sugars and starch.

Each macromolecule test consisted of five test tubes of the food item individually diluted into solutions for reacting each with Benedict’s reagent to show the presence of sugar, IK2I for starch presence, and Buiret’s reagent for protein presence. A simple paper test was used evaluting lipid existence for each food. Our results confirmed our estimations of the foods’ compounds. The testing results verified that coconut milk contained all four types of macromolecules, karo syrup contain only simple sugars, potato chips were starches and fats, peanut butter contained sugars, fats, and proteins, and banana baby food consisted of sugars and starches.

Introduction:

Identifying macromolecules in the foods we eat is essential in comprising a healthy well-rounded diet ensuring our nutritional needs for cellular processes in the human body. The largest biological molecules are known as carbohydrates, lipids, and proteins. Carbohydrates are compounds of monosaccharides, disaccharides, and polysaccharides known as sugars and starches. Lipids, known as fats, are storage molecules in animals and plants.

Proteins bind to other molecules performing key roles in DNA and RNA functions.

Five different food items were tested for the presence of specific macromolecules identified as sugars, starch, lipids, and proteins. The food items were coconut milk, karo syrup, potato chips, peanut butter, and banana baby food. We used chemical indicators and brown paper to detect the presence of different macromolecules in various solutions made from each food sample. If sugars were present in a food, then the Benedict’s reagent and heat would turn the solution orange and precipitate will form. If starch was present, then the iodine potassium iodide would turn the solution dark purple or brown and form a precipitate. If lipids were present in a food, then the brown paper it was rubbed onto would form a transparent area.

If a food contains protein, then the Buiret’s reagent would turn the solution violet or purple in color. Our observations of the changes to the solutions in color and consistency indicated the presence of each different macromolecule according to the food item (see Table 1, Chart 1). We predicted that coconut milk would contain sugars, starch, lipids and proteins; karo syrup would only be a simple sugar; potato chips were made of starch and lipids; peanut butter would contain sugars, lipids, and proteins; and banana baby food would only contain sugars and starch.

Materials and Methods:

We tested five food items for sugars, starch, lipids, and protein. The items tested were cocunut milk, karo syrup, potato chips, peanut butter, and banana baby food. All of these food items were thick in consistence. Also, several of the foods had heavy coloring which would make some of the tests difficult to visually measure. Solutions were made of each food item. Our lab professor dilute the foods with water to form solutions for us to test. According to our lab manual, The Pearson Custom Library for the Biological Sciences, chapter Macromolecules, the testing methods are as follows (reference II).

Before any testing chemicals or testing procedures were performed, the intial states and colors of the food solutions were as follows: the negative control water was clear and colorless; coconut milk was opaque and white; karo syrup solution was completely transparent and colorless; potato chip solution was cloud and slightly yellow; peanut butter solution was cloudy and slightly beige; banana baby food solution was cloudy and slightly yellowish beige.

Simple Carbohydrates (Sugar) Testing:

Using Benedict’s testing on our food items, we tested for simple sugars. Six clean test tubes were labeled individually with each testing food item plus one negative control test tube. Solutions of each food item in the quantity of one full dropperful was added to each labeled test tube and one full dropperful of water was added to the control tube.

Then, each test tube received one full dropperful of Benedict’s reagent and was gently shaken to mix the solution. Each test tube was then placed in a hot water bath in a beaker of water on a hot plate for approximately 2 minutes.

After approximately 2 minutes, the test tubes were removed from the water and placed into the test tube rack for us to observe any changes to the solutions. The resulting states and colors of the test tubes were as follows: The negative control water was clear and blue in color; coconut milk was opaque with a dark orange precipitate in the bottom and orange through the rest of its solution; karo syrup was opaque with a dark orange precipitate in the bottom and orange throughout its solution; potato chips solution remained cloudy with no precipitate and was blue in solution; peanut butter solution was opaque with a brown precipitate in the bottom and brown through its solution; and the banana baby food solution was opaque, dark brown in color and formed a dark brown precipitate in the bottom of the test tube.

Complex Carbohydrates (Starch) Testing:

Iodine potassium iodide (IK2I) was used to test for polysaccarides. Six clean test tubes were labeled and placed in a test tube rack. Five of the test tubes were individually labeled with each of our five food items and one test tube was labeled “control”. The control test tube one full dropperful of water, the other five test tubes received their identified food item in the quantity of one full dropperful.

Then, one droplet of the IK2I reagent was added to each of the six test tubes and were mixed well. The resulting states and colors of the test tubes were as follows: The negative control water was clear and yellow amber in color; coconut milk formed a dark brown precipitate and an opaque solution color of violet-beige; karo syrup remained translucent and deep amber in color; potato chips solution formed a dark purple precipitate with an opaque solution color of purple; peanut butter solution remained cloudy and yellow in color; and the banana baby food solution formed a purple brown precipitate and an opaque solution of pinkish beige.

Lipid Testing:

We performed a non-coated paper test on our chosen food items to identify the presence of lipids. Six squares of non-coated brown paper were obtained and labeled with the five food items to be tested and one control paper labeled “water”. The control paper received a droplet of water rubbed into the paper. Each of the five separate foods were added and rubbed onto the center of each of their identified brown paper. The papers were set aside for 30 minutes to absorb the contents and dry.

After the 30 minutes, each paper was held towards the overhead light. The coconut milk, potato chips, and peanut butter papers all showed translucent areas where the food was applied. The Karo syrup and the banana baby food dried completely and showed no translucent areas, being completely opaque in their paper centers.

Protein Testing:

The Biuret’s test was performed on each of our five food items to identify the presence of protein in the foods. Six clean test tubes were labeled and placed in a test tube rack. Five of the test tubes were individually labeled with each of our five food items and one test tube was labeled “control”. The control test tube had one full dropperful of water, the other five test tubes received their identified food item in the quantity of one full dropperful.

Then we added one full dropperful of of buiret’s reagent to each of the test tubes, agitated the tubes to mix thoroughly, and observed any changes. The
resulting states and colors of the test tubes were as follows: The negative control water was clear and light blue in color; coconut milk was opaque and violet-brown; karo syrup remained translucent with slightly blue solution color; potato chips solution remained cloudy and turned more slightly grayish in color; peanut butter solution was opaque and became pinkish in color; and the banana baby food solution was opaque and turned brownish slightly green color.

Results:

Coconut milk tested positive for sugar indicated by a dark orange precipitate forming and an orange solution. Coconut milk tested positive for starch as it formed a brown precipitate with a beige colored solution. Coconut milk tested positive for lipids as the paper developed transparency. Coconut milk tested positive for proteins by resulting in an opaque, violet-brown solution.

Karo syrup tested positive for sugar by exhibiting a dark orange precipitate and an orange solution. Karo syrup tested negative for starch, lipids, and proteins as there was no resulting changes.

Potato chips tested positive for starch by producing a dark purple precipitate and a purple solution. Potato chips tested positive for lipids forming transparency on the testing paper. Potato chips tested negative for sugars and proteins indicated by no trend changes to their solutions.

Peanut butter tested positive for sugar forming a brown precipitate and a brown solution. Peanut butter tested positive for lipids by developing transparency on the testing paper. Peanut butter tested positive for protein by resulting in a pinkish beige solution. Peanut butter tested negative for starch as the solutuion remained yellow in color.

The banana baby food tested positive for sugar resulting in a dark brown precipitate and dark brown solution. Banana baby food tested positive for starch by resulting a brown precipitate and a pink-beige solution. Banana baby food tested negative for lipids and proteins observing no trending changes.

Discussion:

Our results supported our hypotheses and predictions developed from our previous exposure to these foods with knowledge of taste, texture and common dietary information. Coconut milk contained sugars, starch, lipids and proteins; karo syrup contained simple sugars; potato chips contain starch and lipids; peanut butter contained sugars, lipids, and proteins; and banana baby food contained sugars and starch (see Table 1 and Chart 1).

According to Functional Properties of Food Macromolecules, Second Edition (reference IV), Benedict’s reagent is a clear, blue liquid used to test for simple sugars such as monosaccharides and disaccharides. When Benedict’s reagent and simple carbohydrates are heated together, the solution will turn color to orange red. This color change is caused by the copper (II) ions in the reagent are reduced to copper (I) ions. Sometimes a reddish precipitate forms in the base of the test tube.

Information provided by Science and Health Education Partnership, SEP Lessons by University of California San Francisco (reference III) details that Buiret’s reagent is a clear, blue liquid that when in the presence of proteins will change to a purple or even pink color when the copper atoms of the reagent react with proteins or polypeptide chains. Iodine solution or Lugol’s reagent changes from an amber color to dark purple of even black.

Due to the original coloring of the foods, the resulting color changes and formed precipitates were adjusted according to the mixture of the reacting coloring. For examples, the peanut butter and banana baby food both were an original brown color so as they reacted with Benedict’s reagent and were heated they resulted in a darker brown color as the common orange reacting color mixed with their original brown coloring. These brown colorings were taken into consideration as we reviewed the ending reactions to justify a positive or negative identification.

References Cited:

I. Molecular Biology Initiative. Georgia Southern University, GA.
http://cosm.georgiasouthern.edu/biology/mbi/activities/Macromolecules%20in%20food/Macromolecules%20in%20food%20activity.pdf. Accessed February 11, 2013.

II. Pearson Learning Solutions. “Macromolecules,” in The Pearson Custom Library for the Biological Sciences. Boston, MA: Pearson Learning Solutions, 2012, pp. 69-87.

III. Science and Health Education Partnership, SEP Lessons. University of California San Francisco. http://seplessons.ucsf.edu/node/362. Accessed February 11, 2013.

IV. S.E. Hill, D.A. Ledward, and J.R. Mitchell. Functional Properties of Food Macromolecules, Second Edition. Gaithersburg, MD: Aspen Publishing, 1998.