General food tests

• What is the first step in preparing food samples for testing?

  Solid food is ground using a pestle and water, then distilled water is added to create a solution.
• What is the second step in preparing food samples for testing?

  The iodine test involves adding iodine solution to the sample, and if it turns black or dark purple, starch is present.
• What is the third step in preparing food samples for testing?

  To test for glucose and simple sugars, Benedict's solution is added to the sample and heated using a water bath, resulting in a colour change from blue to green, yellow, or orange, depending on the amount of sugar present.
• What is the fourth step in preparing food samples for testing?

  Biuret reagent is added to detect protein, turning the solution from blue to purple if protein is present.
• What is the fifth step in preparing food samples for testing?

  To test for lipids, cold ethanol is added to the sample, then added to a test tube of water. If the solution becomes cloudy, lipids are present.
• What are the safety precautions when performing food tests?

  Tie hair back, wear safety goggles, and handle chemicals carefully (Biuret and ethanol are hazardous).

  Keep ethanol away from flames and handle Biuret solution with care.
• What are sources of error in food tests?

  Colour changes in the Benedict's test and Biuret test may be subtle and difficult to judge if the concentration of the tested molecule is low.
• Mnemonic: “I Big Baked Eggs Softly”


  Iodine - Benedict's - Biuret's - Emulsion - Sadan III