Buiret solution is a blue liquid that changes to purple when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the color change.
Consequently, what do you use to test for starch?
Iodine test. The iodine test is used to test for the presence of starch. Starch turns an intense "blue-black" colour upon addition of aqueous solutions of the triiodide anion, due to the formation of an intermolecular charge-transfer complex. In the absence of starch, the brown colour of the aqueous solution remains.
What is a positive test result for the Benedict's test?
In lab, we used Benedict's reagent to test for one particular reducing sugar: glucose. Benedict's reagent starts out aqua-blue. As it is heated in the presence of reducing sugars, it turns yellow to orange. The "hotter" the final color of the reagent, the higher the concentration of reducing sugar.
What color indicates a positive reaction for starch?
Lugol's iodine yields a blue-black color in the presence of starch. Glycogen reacts with Lugol's reagent to give a brown-blue color. Other polysaccharides and monosaccharides yield no color change; the test solution remains the characteristic brown-yellow of the iodine reagent.