Measuring protein concentration in egg

[Maya55]

Hello,

My 8th grader wants to assess if there is a difference in the protein concentration of an egg (white) depending on how it is cooked/eaten (raw vs. boiled vs. scrambled vs.poached) for an upcoming science fair project (due in October). After some preliminary research, he decided that he is going to measaure the protein concentration in the egg white using the Biuret assay. But apparently in order to measure the protein concentration he needs a spectrophotometer. I am wondering about the feasibility of this project and have some questions:

(i) Is this project doable/feasible to do at home?
(ii) Is the Biuret assay the right method to use in this setting - doing this project at home (not in his school lab) where he will be measuring the protein concentration in cooked eggs (egg white, specifically)?
(iii) I am willing to spend upto $100 to $150 to buy a spectrophotometer, but so far have been unable to find where I can purchase one in this price range?
(iv) Is the spectrophotometer easy to use at home, if we are able to find one?
(iv) Is there any other way/a better method to measure the concentration of protein in cooked egg whites other than using a spectrophotometer and/or Biuret assay?

Thanks for your help!

[deleted-76520]

Hello Maya55!

I think this is a great idea for a science fair project!

I'll answer your questions as best as I can, and provide a few suggestions along the way.

(i) This project should be feasible. Biuret reagent is a relatively-inexpensive option. A 110 mL bottle from Sigma-Aldrich is less than $40, and your child's science teacher may be able to help you get just the amount that you need. I trust that the eggs won't be too difficult to get.
(ii) The Biuret assay is usually a reliable choice. My main worry is more to do with the eggs. When cooked, the protein will denature; this causes it to no longer be soluble and fluid. My recommendation here would be to try to blend or otherwise puree the egg, so that most of the protein can be identified by the test.
(iii / iv) I wouldn't recommend using a spectrophotometer. If they aren't calibrated regularly, their results can be off, and they're also pricey. I was able to find one transmittance spectrophotometer for $145, but that one was used and didn't look too user-friendly. Your child's science teacher might be able to help you with this-- I'm not sure that it would be effective to use a spectrophotometer at home.
There are easier ways to do it, though! As the Biuret test causes color changes, you could try printing out a row of purple tints. By holding the test solution against a white piece of paper, you could measure each result on your own intensity scale, from 1 to 10 or so. To make concentrations measurable (the Biuret test effectively distinguishes between protein concentrations of 5-160 mg/mL) you would want to take a bit of each egg and find its mass first.
Once you have the mass, you can calculate how much you will need to dilute it. The mass in grams divided by the volume of the diluted solution in liters should be between 5 and 160.
Add the dilution liquid (preferably a buffer like PBS, though water might work), stir thoroughly, and then pour out solution into a test tube and perform the test. If all of your egg samples turn dark purple or don't change color, you may have to adjust this.
(v) As for a different method-- I think that the Biuret test is your best bet. There are other assays, but most of them are either very sensitive or otherwise less suitable for a home experiment. I can't think of any that would work better, though I'll rack my brains a bit and get back to you if I think of one.

You may also want to check out [[this project]], as it appears to have a similar method, and also suggests a kit. However, it relies on a spectrophotometer, which doesn't seem to be included in the kit.

I hope this makes some sense! I threw a lot of information in this post, so be sure to let me know if I was unclear or you have more questions.

Hope this helped,