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Chapter: Biology laboratory Practicals: Biology Activities

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Food Test for Proteins

Proteins are organic food substances consisting of carbon, hydrogen, oxygen, and nitrogen. Proteins create growth and repairs damaged tissue. The main source of protein are beans and nuts, meat, sh, milk, cheese, and eggs.

Food Test for Proteins

Proteins are organic food substances consisting of carbon, hydrogen, oxygen, and nitrogen. Proteins create growth and repairs damaged tissue. The main source of protein are beans and nuts, meat, sh, milk, cheese, and eggs.

Learning Objectives

To carry out test for proteins in a given food sample.

Materials

Copper sulphate solution*, sodium hydroxide solution*, water, food sample containing protein such as egg, beaker*, empty plastic bottles, plastic spoon, test tube*, and citric acid*

Hazards and Safety

Copper sulphate solution is poisonous and should not be swallowed.

Use a plastic spoon for measuring caustic soda - the hydroxide will corrode a metal one.

Sodium hydroxide is corrosive - concentrated solutions can burn skin and wood. Even dilute solutions can blind if they get into eyes.

If sodium hydroxide solution spills, neutralize spills with citric acid solution or vinegar.

Close the container of sodium hydroxide solution after use to prevent reaction with atmospheric carbon dioxide.

Preparation Procedure

1.           Make a small hole at the tip of an egg.

2.           Pour some of the egg white into a beaker.

3.           Dilute the egg white with 150 mL water.

4.           Stir until the solution is clear.

Activity Procedure

1.           Put 2 mL of sample solution into a test tube.

2.           Add 1 mL of sodium hydroxide solution to the test tube, then 1 mL of copper sulphate solution to the test tube.

3.           Record results.

Results and Conclusions

The colour of the food sample will change from a clear colour to a violet or purple colour. This indicates the presence of protein in the food sample.

Clean Up Procedure

1.           Unused reagents should be stored in plastic bottles for further use. Do not store sodium hydroxide in glass bottles.

2.           Dispose chemical waste in a pit latrine.

Notes

Some textbooks may recommend using Millon's reagent to test for protein. This reagent contains mercury, which is extremely poisonous and should never be handled by students.

The purple colour from a positive test is the result of a complex between four nitrogen atoms and the copper (II) ion. Specifically, these nitrogen atoms are all part of peptide bonds. These peptide bonds are adjacent on a protein, either two from one protein and two from another, or two from one part of a protein and two from another part of the same protein.

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