Testing for Biological Macromolecules in Food Samples Lab Report PDF

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Lab report I completed for the Biological Macromolecules lab we did....

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Testing for Biological Macromolecules in Food Samples

Chloe Popov Mrs. Omand SBI4U1-2 February 20, 2019

2 Abstract The purpose of this lab was to identify and investigate the presence of common biological macromolecules in a variety of different food samples. There were four standard tests used to identify the presence of carbohydrates, lipids, proteins, and starch. Solutions containing these macromolecules were tested for carbohydrates using Benedict’s reagent, lipids on brown paper, proteins using Biuret reagent, and starch using Lugol’s solution. These indicators were also used in testing five food samples for the previously mentioned macromolecules. The five food samples used during this experiment were cheese, a cracker, yogurt, cream, and a raisin. The results gathered from this lab indicated that each of the food samples tested had differing combinations of macromolecules present within them. The cracker, cream, yogurt, and raisin contained carbohydrates and had an approximated 1.5 - 2.0% sugar concentration (Aryal, 2015). The cream, yogurt, and cheese produced a film on the brown paper, revealing that they contained lipids. The cream, yogurt, and cheese also tested positive for proteins. Only the cracker tested positive for starch. The results from this lab showed that the food samples tested differed greatly in nutritional value because of the different combinations of biological macromolecules that they possessed. In addition, to have a balanced, healthy diet, people must consume foods, alike the food samples used in this lab, that contain a variety of essential biological macromolecules. Discussion A positive test for proteins would be when the sample being tested, which contains protein macromolecules, turns a pink or purple hue, after the indicator Biuret reagent is added to the sample (Humagain, 2018). The gelatin solution and egg albumen experienced a purple colour change when the Biuret reagent was added to them. For the food samples, only the cream, yogurt, and cheese solutions turned purple. A positive test for starch, a carbohydrate, would be

3 when the sample being tested, which contains starch macromolecules, turns a dark blue or black hue, after the indicator Lugol’s solution, made up of iodine, is added to them (What is the Iodine…, n.d). Only the starch solution experienced a black colour change when the Lugol’s solution was added to it. For the food samples, only the cracker solution turned black. Q1 A positive test for sugars would be when the sample being tested, which contains sugar macromolecules, turns a yellow, orange, brick-red, or green hue, after the Benedict’s reagent is added to the sample (Karki, 2018). Only the glucose solution experienced an orange (1.5 - 2.0% sugar concentration) colour change when the Benedict’s reagent was added to it. For the food samples, the cracker, cream, yogurt, and the raisin experienced an orange colour change, indicating that they had approximate 1.5 - 2.0% sugar concentrations (Aryal, 2015). A positive test for lipids would be when the sample being tested, which contains lipid macromolecules, leaves a translucent, oily film on the brown paper in which it was tested on (Kumar, n.d). A noticeable pattern that was observed during this lab was that all milk-based food samples (cream, yogurt, cheese) tested positive for both proteins and lipids, but tested negative for starch. The results of this lab indicate that only the cracker contains starch macromolecules and that cream, yogurt, raisins, and cheese do not contain starch macromolecules. It is revealed that only the cheese did not contain sugar macromolecules, whereas the cracker, cream, yogurt, and raisins did contain sugar macromolecules. It was also shown that the cream, yogurt, and cheese all contained lipids, but the cracker and raisin did not contain lipids. These results display that only the cream, yogurt, and cheese contained proteins, however, the cracker and raisin did not contain proteins. Overall, these results indicate that different foods contain different varieties and combinations of macromolecules. The objective of this lab was to identify and investigate

4 the macromolecules found in different food samples. This objective was fulfilled by testing different food samples (cheese, yogurt, raisins, cream, crackers) for specific biological macromolecules (lipids, proteins, starch, sugars) and analyzing the data collected during the lab. Distilled water was used as a control while it was tested each time with each of the solutions. It was important that the distilled water was kept as a control during the lab because it could then be compared and contrasted with the results regarding the biological macromolecules in the other tested solutions. There are limitations to the usefulness of these tests, when being used on food samples. The Benedict’s reagent is only able to recognize the presence of monosaccharides and some disaccharides, so it would not be useful when testing food samples that contain polysaccharides or certain disaccharides that it is unable to recognize (Benedict’s reagent test…, 2017). The lipids on paper test has limitations relating the uncertainty in how well it can be evaluated. For example, if the food sample solutions were too diluted, they may not leave a very visible, oily film on the brown paper, indicating that they do not contain lipids and test negative for them, even if they do happen to contain lipids. The Biuret reagent used in the test for proteins has limitations relating to it’s inability produce a visible colour change when involving small amounts of proteins. The Biuret reagent relies on peptide bonds in proteins, in order to change colour, and has trouble creating a noticeable colour change when it is used in a solution that contains small quantities of peptide bonds in proteins. This could cause a test for proteins using the Biuret reagent to come out negative, when it should be positive, due to the fact that it is unable to create a noticeable colour change when only small amounts of peptide bonds in proteins are present. It was a surprise that both the raisins and crackers did not test positive for protein, when the Biuret reagent was added to them, because it is known that these two foods do contain

5 protein. However, it is possible that there were not enough protein peptide bonds, causing the solution to show no apparent colour change, since the Biuret reagent relies on peptide bonds in proteins to change colour. The more peptide bonds the proteins in the solution has, the more intense the colour change. (Humagain, 2018) It is also possible that the results of these two tests could have been altered, due to the experimental error of cross-contaminating substances. There could have been excess residue remaining in the test tubes used to conduct these tests, even after rinsing them with water, which would contaminate other tests done in those test tubes. It is incredibly valuable to know the chemical components of the foods one eats because it can help people maintain a balanced, healthy diet that consists of a variety of the essential biological macronutrients that humans need in order to function healthily.

6 References Aryal, S. (2015). Benedict’s Test – Principle, Composition, Preparation, Procedure and Result Interpretation. Retrieved from https://microbiologyinfo.com/benedicts-testprinciple-composition-preparation-procedure-and-result-interpretation/ Benedict’s reagent test for Monosaccharides. (2017). Retrieved from https://medium.com/@worldofch emical/benedicts-reagent-test-formonosaccharides-8259e446606a. Humagain, S. (2018). Biuret test: Principle, Requirements, Procedure and Result Interpretation. Retrieved from http://onlinesciencenotes.com/biuret-test-principle-requirementsprocedure-and-result-interpretation/ Karki, G. (2018). Benedict’s Test: Objective, Principle, Reagents, Procedure and Result. Retrieved from http://www.onlinebiologynotes.com/benedicts-test-objectiveprinciple-reagents-procedure-and-result/. Kumar, P. (n.d). Qualitative and Quantitative Tests for Lipids. Retrieved from http://www.biologydiscuss ion .com/lipids/tests/qualitative-and-quantitative-tests-forlipids/13050. What is the Iodine Test for Starch? (n.d). Retrieved from http://brilliantbiologystudent.weebly.com/iodine-test-for-starch.html...