Testing for sugars

In this experiment you will test one or more foodstuffs for the presence of carbohydrates.

METHOD

• Food to be tested

• A pestle and mortar

• A stirring rod

• Filter funnel and filter paper

• 2 beakers, 250 ml

• A conical flask

• 2 test tubes

• Benedict’s solution

• Iodine solution

• A Bunsen burner

• Tripod

• Gauze

• A heatproof mat

• A thermometer

• Safety goggles

INSTRUCTIONS

1) Prepare a food sample and transfer 5 cm³ to a test tube.

2) Prepare a water bath so that it's set to 75 °C.

3) Add some Benedict's solution to the test tube (about 10 drops) using a pipette.

4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure the tube is pointing away from you.

5) If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue color to green, yellow or brick-red it depends on how much sugar is in the food.

Testing for starch

In this experiment you will test one or more foodstuffs for the presence of starch.

1) Make a food sample and transfer 5 cm³ of your sample to a test tube.

2) Then add a few drops of iodine solution and gently shake the tube to mix the contents. If the sample contains starch, the color of the solution will change from browny-orange to black or blue-black.

Testing for proteins

In this experiment you will test one or more foodstuffs for the presence of proteins.

METHOD

• Food to be tested

• A pestle and mortar

• A test tube

• Biuret solution

INSTRUCTIONS

1) Prepare a sample of your food and transfer 2 cm³ of your sample to a test tube.

2) Add 2 cm³ of biuret solution to the sample and mix the contents of the tube by gently shaking it.

3) If the food sample contains protein, the solution will change from blue to purple. If no protein is present, the solution will stay blue.

Testing for lipids

In this experiment you will test one or more foodstuffs for the presence of lipids (fats).

METHOD

• Food to be tested

• A pestle and mortar

• A stirring rod

• A filter funnel and filter paper

• 2 beakers, 250 ml

• A test tube

• Sudan III stain solution

INSTRUCTIONS

1) Use a pestle and mortar to grind up a small sample of food.

2) Transfer the ground up food into a small beaker and add distilled water.

3) Stir in order to allow some of the food content to dissolve in the water.

4) Use a filter funnel and filter paper to obtain as clear a solution as possible.

5) Half fill a test tube with some of this solution.

6) Add 3 drops of Sudan III stain to the solution in the test tube. Shake gently to mix.

7) A red-stained oil layer will separate out and float on the water surface if fat is present.

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