Testing for Macromolecule: Lab Report

Introduction

The experiment for the Macromolecules lab is intended to verify the presence of lipids, proteins, starches, and sugar. The experiment consists of isolating the food samples and adding specific solutions to them. The solutions used in the process are Benedict’s, Iodine, and Biuret solutions. Each reactant should change color, and a specific color change indicates the presence of either a protein, starch, or sugar. A separate experiment for detecting the presence of lipids in the samples involves finding traces of oil through a piece of paper.

Positive or negative reactions based on color changes should be observed during each experiment. We hypothesize that the color will change to either blue or black in the protein sample but not in the sugar sample.

Materials and Methods

The materials used in this experiment include potato chips, Oreo cookies, corn starch, glucose, potato juice, onion juice, and albumin. The equipment used to prepare the samples includes filter paper, test tubes, beakers, droppers, and a hot plate.

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Lastly, the solutions used to react with the samples are Benedict’s reagent, Biuret Reagent, and Iodine.

Experiment 1: Iodine Test for Starch

For the Iodine test, predictions were recorded, and the results were categorized as either positive or negative.

Positive and negative controls were indicated. Test tubes were labeled, and 8 test tubes were filled with samples by adding 10 drops to each appropriate test tube. Subsequently, 10 drops of Iodine were added to each test tube, and the solutions were gently mixed. The reactions were observed for any color changes, which were then compared to the negative and positive controls to determine if the result was positive or negative. A positive result for the presence of starch is indicated by a color change to either blue or black.

Experiment 2: Benedict’s Test for Simple Sugars

Data was recorded, and positive or negative results were indicated, along with references to negative and positive controls. Test tubes were labeled, and 8 test tubes were filled with samples by adding 10 drops to each appropriate test tube. A beaker filled with water was placed on a hot plate to heat up. Subsequently, 10 drops of Benedict’s reagent were added to each test tube, which were then gently mixed and placed in the boiling beaker. Color changes in the test tubes were recorded and compared to the negative and positive controls. Samples were identified as sugar if the color changed to red or orange.

Experiment 3: Biuret Test for Proteins

Data was recorded, and results were categorized as either positive or negative. Positive and negative controls were indicated. Test tubes were labeled, and 8 test tubes were filled with samples. 10 drops of Biuret reagent were added to each of the 8 test tubes and gently mixed thoroughly. The reactants were allowed to settle for 2 minutes, and any color changes in the test tubes were carefully observed and recorded. The color turning to purple indicates the presence of protein.

Experiment 4: Beta Carotene Test for Lipids

A piece of paper was used for the Beta Carotene test. Eight squares were drawn on the paper, and each square was labeled with the name of the corresponding sample. Using a dropper, a drop of each sample was distributed to its designated section on the paper. The paper was allowed to sit for 2 minutes to observe for the presence of lipids. Any excess liquid that did not soak into the paper was wiped off. The paper was then held up to a light source, and any residues left behind in each section were recorded. The presence of lipids was determined by the presence of residues.

Discussion

Our hypothesis stated that the color would change to either blue or black in the presence of protein but not in the presence of sugar. However, our hypothesis was incorrect. In fact, the sugar sample turned from light blue to a yellowish color, while the protein sample turned purple. This indicates that a positive result for sugar is characterized by a color change to red or orange, and a positive result for protein is indicated by the color purple.

If a positive result were obtained for a negative control, several possibilities could explain this discrepancy. It could mean that the test was completely incorrect, the sample may have been contaminated, or too much liquid/solution was added, which could have overwhelmed the sample and caused confusion.

In this macromolecules lab, we utilized Benedict’s reagent, Lugol’s reagent, Biuret reagent, and filter paper to determine the presence of macromolecules (sugar, starch, protein, and lipids) in various food samples. The results generally agreed with our predictions, with the exception of the oil, potato juice, onion juice, and potato chips, as it was assumed that there would be some form of lipid-based product present in these samples.