How to Determine the Vitamin C Concentration in Citrus Fruit

Vitamin C is often associated with citrus fruit, but some fruit contain more vitamin C than others. You can do a simple science experiment to compare the levels of vitamin C in various fruits. This is a good idea for a science fair project or just to teach students about vitamin concentrations in foods. This requires that you make a simple iodine indicator. Iodine can be found in most drug stores.

Things You'll Need

• Citrus fruit
• Juicer
• 1 tbsp. cornstarch
• Water
• Heat source
• 2 beakers
• 2 percent iodine solution
• 15 ml test tubes (1 per fruit tested)
• Several eyedroppers
• White paper

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Instructions

• 1

  Combine the cornstarch and 1 to 2 tbsp. of water in a beaker to make a paste. Add 250 ml of water to this in the beaker.

• 2

  Place the beaker on a heat source and bring to a boil. Boil for five full minutes. Remove from heat. This starch solution will be used to thicken the iodine indicator.

• 3

  Place 75 ml (about 5 tbsp.) of water into another beaker. Add about 10 drops of the cornstarch solution to the clean water. Stir well.

• 4

  Drop in enough of the iodine until the 75 ml of water is a dark purple or dark blue color. This is your iodine indicator.

• 5

  Drop about 1 tsp. (5 ml) of your iodine indicator into the bottom of each of the test tubes.

• 6

  Use a clean eyedropper every time you transfer a sample of 10 drops of citrus juice to a different test tube.

• 7

  Compare the test tube colors by placing them against a piece of white paper. The darker the purple in the tested sample, the less vitamin C it has.