Why did my Biuret's test on eggwhite result in a brown color?

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In summary, the conversation revolved around trying to figure out why a test came out as BROWN instead of the expected result of blue. The tests being discussed were the Biuret test for protein and Benedict's test for reducing sugars. During the conversation, it was mentioned that the presence of reducing sugars can affect the results of the protein test. There were also questions about the effects of a high pH or high copper concentration on the Biuret test. The person also mentioned making a mistake in their report by not considering the presence of reducing sugars in the sample.
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Fluff
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I can't seem to figure out why the test came out as BROWN. I've been researching for HOURS and I can't find out why. I'm not asking any of you to give me an answer, but PLEASE throw me a hint. PLEASE. I heated the egg to 37C by the way.
 
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Did you add too much CuSO4?
 
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Biuret is a test for protein. The copper(II) is reduced to copper(I) in the presence of protein and it complexes the nitrogen groups, turning violet at high pH.

Benedict's test is a test for reducing sugars. It contains copper(II) that reacts with the reducing sugar to produce a brick red ppt of copper(I) oxide.

What might happen if the pH were too high in the Biuret test or if the copper concentration were too high? What might happen if the protein test sample also contained reducing sugars?
 
  • #4
I didn't add too much CuSO4 -_- there was an amount we were supposed to put. =P

Yes. I knew that about the Biuret's but the result for negative was supposed to be blue =S And it was BROWN. So yeah. It buffled me. So if eggwhite had a reducing sugar, would it have a brickred precipitate too? And I did the report but I just moved on quickly so the teacher wouldn't have enough time to ask what caused the brown instead of blue -_-

I slipped away but I focused to the brown thing that I didn't read the other questions properly so I answered wrong. Bad days.

Haha, sorry if I just pop in here when I need something. -_- Thank you for the hint though haha.
 

1. What is Biuret's Test on Eggwhite?

Biuret's Test on Eggwhite is a chemical test used to detect the presence of protein in egg white. It involves adding a copper sulfate and sodium hydroxide solution to a sample of egg white, which causes a color change if protein is present.

2. How does Biuret's Test on Eggwhite work?

The copper ions in the Biuret reagent react with the peptide bonds in proteins, forming a violet complex. This color change indicates the presence of protein in the egg white sample.

3. What is the purpose of performing Biuret's Test on Eggwhite?

Biuret's Test on Eggwhite is commonly used in food science and nutrition to determine the protein content in egg white. It can also be used in research to identify the presence of protein in various biological samples.

4. What are the potential sources of error in Biuret's Test on Eggwhite?

Potential sources of error in Biuret's Test on Eggwhite include contamination of the sample, inaccurate measurement of reagents, and improper mixing of the reagents and sample. It is also important to use fresh samples, as spoiled or denatured proteins may produce inaccurate results.

5. Are there any limitations to Biuret's Test on Eggwhite?

Biuret's Test on Eggwhite is a qualitative test, meaning it only indicates the presence of protein and not the amount. It also cannot differentiate between types of proteins or distinguish between different amino acids. Additionally, other substances in the sample, such as reducing sugars, can interfere with the test and produce false positive results.

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