Biology-Food tests

• What is the purpose of the Benedict's test?


  To test for sugars
• What color change indicates the presence of reducing sugars in the Benedict's test?


  Blue to green, yellow, or brick red depending on concentration
• What is the first step in conducting the Benedict's test?


  Add 10 drops of Benedict's solution to a 5 cm³ food sample
• At what temperature should the water bath be prepared for the Benedict's test?


  75°C
• How long should the test tube be placed in the water bath during the Benedict's test?


  5 minutes
• What does a color change in the Benedict's test indicate?


  That sugar is present in the food sample
• What is the purpose of the iodine test?


  To test for starch
• What color change indicates the presence of starch in the iodine test?


  Brown/orange to blue/black
• What is the procedure for the iodine test?


  Add a few drops of iodine solution to 5 cm³ of food sample
• What does a color change in the iodine test indicate?


  That starch is present in the food sample
• What is the purpose of the Biuret test?


  To test for proteins
• What color change indicates the presence of proteins in the Biuret test?


  Blue to pink/purple
• What is the procedure for the Biuret test?


  Add 2 cm³ of food sample and 2 cm³ of Biuret solution in a test tube
• What does a color change in the Biuret test indicate?


  That proteins are present in the food sample
• What is the purpose of the Sudan III test?


  To test for lipids
• What indicates the presence of lipids in the Sudan III test?


  The mixture separates into two layers, with the top layer being bright red
• What is the procedure for the Sudan III test?


  Add 5 cm³ of food sample and 3 drops of Sudan III stain solution, then gently shake/mix
• What does the top layer being bright red in the Sudan III test indicate?


  That lipids are present in the food sample
• What are the four main food tests and their corresponding indicators?

  1. Benedict's test: Reducing sugars (blue → green/yellow/brick red)
  2. Iodine test: Starch (brown/orange → blue/black)
  3. Biuret test: Proteins (blue → pink/purple)
  4. Sudan III test: Lipids (top layer bright red)
• What is the first step in preparing a food sample for testing?

  Break it up using a pestle and mortar
• Why do you add distilled water to the ground food sample?


  To dissolve some of the food
• What is the purpose of filtering the solution after mixing the food sample?


  To get rid of the solid bits of food
• What are the steps to perform the Benedict's test for reducing sugars?


  1. Prepare a food sample and transfer 5 cm³ to a test tube.
  2. Set up a water bath at 75 °C.
  3. Add about 10 drops of Benedict's solution to the test tube.
  4. Place the test tube in the water bath for 5 minutes.
  5. Observe the color change: blue to green, yellow, or brick-red indicates reducing sugars.
• What types of foods commonly contain reducing sugars?


  Biscuits, cereal, and bread
• How do you test for starch using iodine solution?


  1. Prepare a food sample and transfer 5 cm³ to a test tube.
  2. Add a few drops of iodine solution and gently shake.
  3. A color change from browny-orange to black or blue-black indicates the presence of starch.
• Which foods are known to contain a lot of starch?

  Pasta, rice, and potatoes
• What is the procedure for the Biuret test for proteins?


  1. Prepare a food sample and transfer 2 cm³ to a test tube.
  2. Add 2 cm³ of biuret solution and mix gently.
  3. A color change from blue to purple indicates the presence of protein.
• What types of foods are rich in protein?


  Cheese and beans
• How do you test for lipids using Sudan III stain solution?


  1. Prepare a food sample and transfer about 5 cm³ to a test tube (no filtering needed).
  2. Add 2 drops of Sudan III stain solution and gently shake.
  3. A bright red top layer indicates the presence of lipids.
• Which foods commonly contain lipids?


  Olive oil, margarine, and milk
• What does it indicate if no separate red layer forms after the Sudan III test?


  No lipids are present in the sample
• What should you do before conducting food tests?

  Perform a risk assessment
• What is the purpose of the Benedict's test?


  To test for reducing sugars
• What color change indicates the presence of reducing sugars in the Benedict's test?


  Blue to green, yellow, or brick red depending on concentration
• What are the steps to perform the Benedict's test for sugars?


  1. Add 10 drops of Benedict's solution to a 5 cm³ food sample.
  2. Prepare a water bath at 75°C.
  3. Place the test tube in the water bath for 5 minutes.
  4. Observe for a color change.
• What is the purpose of the iodine test?


  To test for starch
• What color change indicates the presence of starch in the iodine test?


  Brown/orange to blue/purple
• What are the steps to perform the iodine test for starch?


  1. Add a few drops of iodine solution to a 5 cm³ food sample.
  2. Observe for a color change.
• What is the purpose of the Biuret test?


  To test for proteins
• What color change indicates the presence of proteins in the Biuret test?


  Blue to pink/purple