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

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SUMMARY

The Biuret test for proteins resulted in a brown color instead of the expected blue due to potential interference from reducing sugars present in the egg white sample. The test involves the reduction of copper(II) to copper(I) in the presence of proteins, which typically yields a violet color at high pH. However, if reducing sugars are also present, they can react with copper(II) to produce a brick red precipitate, complicating the results. The discussion highlights the importance of controlling pH and copper concentration to avoid misleading outcomes in protein testing.

PREREQUISITES
  • Understanding of Biuret test principles
  • Knowledge of copper(II) and copper(I) chemistry
  • Familiarity with protein structure and nitrogen group interactions
  • Basic concepts of pH and its effects on chemical reactions
NEXT STEPS
  • Research the effects of pH on the Biuret test results
  • Study the interaction between reducing sugars and copper(II) in Benedict's test
  • Learn about the proper preparation and concentration of CuSO4 for protein testing
  • Investigate alternative protein tests and their specific indicators
USEFUL FOR

Students in biochemistry, laboratory technicians performing protein assays, and educators teaching biochemical testing methods.

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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?
 
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?
 
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.
 

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