- Introduction:
Biuret's test is a chemical test used for detecting the presence of peptide bonds. Polypeptides as proteins, are chains of amino acids link together by peptide bonds.
The biuret reaction can be used to assess the concentration of proteins because peptide bonds occurs with the same frequency per amino acid peptide.
- Materials:
-7 × 250mL beaker.
-6 test tubes.
-Test tube rack.
-6 × 10mL Pipet.
-Mortar.
-Glass marking pen.
-Gloves.
-Goggles.
-Milk.
-Rice Milk.
-Egg.
-Yogurt.
-Potato.
-Distilled water.
-NaOH 20%.
-10 drops of CuSO4.
- Procedure:
We are going to determine protein protein concentration in some foods: milk, rice milk, yogurt, potato and egg. Be careful, aa we are going to test separately the egg white and the yolk. Put gloves and use goggles, remember that NaOH is caustic!!
First of all we are going to dilute the protein.
1. Add 100mL of distilled water to each 250mL beaker. Label them with M(milk), R(rice milk) and EW(egg white), EY(yolk) and P(potato).
2. Separate the egg white and the yolk in another beaker.
3. Smash the potato in a mortar and add some amount of the of the smashed potato to the P beaker.
Prepare the samples:
4. Add 10mL of a dispersions of each food (M, S, EY, EW and Y) to the indicate beaker. Calculate the final concentration. All the groups will use the same dispersion from the beakers.
5. Prepare 6 test tubes (clean and dry) and label M, S, EW, EY, Y and P. Add 2mL of the every food dilution of each beaker.
6. Add 2mL of 20%NaOH dissolution.
7. Shake gently and add 5 drops of CuSO4 in each tube. Allow the mixture to stand for 5 minuts.
8. Note any colour change. Remember that proteins will turn solution pink or purple.
9. Compare the test tubes.
4. Add 10mL of a dispersions of each food (M, S, EY, EW and Y) to the indicate beaker. Calculate the final concentration. All the groups will use the same dispersion from the beakers.
5. Prepare 6 test tubes (clean and dry) and label M, S, EW, EY, Y and P. Add 2mL of the every food dilution of each beaker.
6. Add 2mL of 20%NaOH dissolution.
7. Shake gently and add 5 drops of CuSO4 in each tube. Allow the mixture to stand for 5 minuts.
8. Note any colour change. Remember that proteins will turn solution pink or purple.
9. Compare the test tubes.
- Questions:
1. Wich food has proteins? Egg white, milk, yogurt, potato.
2. Wich food has more proteins? Why? Egg white, because they are animal food and is rich in proteins.
3. Do you find any difference between soy rice and cow milk? Yes, rices milk doesn't have proteins, however cow milk does.
4. Is there any difference among milk and yogurt? Why? Yes, because yogurt has more proteins than milk.
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