Describe the procedures and positive results for testing starch and protein in food.

Here are the details for the food tests described:

• Starch Test (using Iodine solution)

  • Procedure: To test for starch, prepare a food sample (solid, cut surface, or crushed with water). Add a few drops of iodine solution to the sample.
  • Positive Result: The presence of starch is indicated if the straw-coloured iodine solution turns blue-black.

• Protein Test (using Biuret test)

  • Procedure:
    1. Place $2 \text{ cm}^3$ of the food sample (crush with water if solid) in a test tube.
    2. Add $2 \text{ cm}^3$ of dilute sodium hydroxide solution.
    3. Add $1\%$ copper sulphate solution drop by drop.
    4. Shake the mixture.
  • Positive Result: A purple (violet) colour indicates the presence of protein.

• Protein Test (using Millon's test)

  • Procedure:
    1. To a solution of the food sample (e.g., beans, egg white, or ground meat) in a test tube, add a few drops of Millon's reagent.
    2. Boil the mixture for one minute.
  • Positive Result: A deep red colour indicates the presence of protein.