If Zack is guilty, and the mystery food sample contains protein, which test tube will the mystery food sample resemble?

This question is incomplete, but based on research, the mystery food sample will resemble the test tube used for testing for protein.

In order to identify proteins in food, Biuret reagent is usually used in the laboratory. When the Biuret reagent is added to a food that has protein, the color of the food will change to violet color or pink and this color change is usually used as an indication that protein is present in the food.