Which food gives purple colour when two drops of copper sulphate solution and 10 drops of caustic soda is added to it?

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Video showing Test for Presence of Protein in Food

What does the color change of food into violet color indicate when copper sulphate solution and caustic soda is added to it? SEND

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When two drops of copper sulphate and ten drops of caustic soda or NaOH is added to egg, it turns violet. This indicates the presence of proteins.This is Biuret's test and the principle is simple as follows:

In the presence of alkaline medium (caustic soda or NaOH), the $C u^{2 +}$ ions get reduced to $C u^{+}$ and binds to the egg proteins, thereby giving a violet color.