Use of Biuret Reagent to Test for Proteins In Food

Topics: Amino acid, Protein, Acid Pages: 3 (523 words) Published: December 13, 2014


“Use of Biuret Reagent to Test for Proteins In Food”
Cindy Zhou

Introduction
Protein is a series of amino acids that are connected together by peptide bond. The bond is located between the end of previous amino acid, which is the carboxyl group, and the head of next amino acid, which is a amino group. The Biuret reagent is a solution of copper sulfate and potassium hydroxide. When peptide bond are presented, the copper (II) will interact with them (MadSci Network: General Biology). It is a dark blue solution that can react with the peptide bond and change the color of the solution to purple. The positive test result is that the solution turns to purple. The negative test result is that the solution remains dark blue. The goal of the lab is to test if there are proteins presented in water, glucose, starch, egg albumin, bread, milk, and peanuts (Biomolecule Lab).

Materials and Methods
In this experiment, some water, glucose, starch, egg albumin, bread, milk, peanuts, and Biuret reagent are used. One dropperful of each solution are added to the test tubes. The peanuts and the bread are placed on a piece of paper. The peanuts are crushed into small particles. One dropperful of Biuret reagent is added to each test tube. A few drops of Biuret reagent is added on top of the bread and the crushed peanuts. Lastly, the results of colors changes of the test tubes, bread, and crushed peanuts are recorded.

Results
Table 1: The Effect of Biuret Reagent on Water, Glucose, Starch, Egg Albumin, Bread, Milk, Crushed Peanuts Test
Contents
The color after mixing
Positive/Negative?
Were proteins present?
1
Water
Light blue
Negative
No
2
Glucose
Light blue
Negative
No
3
Starch
Light blue
Negative
No
4
Egg albumin
Dark purple
Positive
Yes
5
Bread
Dark purple
Positive
Yes
6
Milk
Dark purple
Positive
Yes
7
Crushed peanuts
A little darker than before
Positive
Yes
The tests for egg...


Cited: http://www.madsci.org/posts/archives/2004-12/1102321490.Gb.r.html
http://www.livestrong.com/article/452820-what-proteins-are-found-in-eggs/
http://ansci.illinois.edu/static/ansc438/Milkcompsynth/milkcomp_protein.html
http://www.peanut-institute.org/health-and-nutrition/protective-nutrients/protein-fats-and-fiber.asp
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