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Does Cooking Fruits and Vegetables Deplete Their Vitamin C Content

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Purpose

To determine whether cooking certain fruits and vegetables that are high in vitamin C (and are often eaten in a cooked form) will result in the depletion of vitamin C.

Hypothesis

Vitamin C is an essential vitamin for healthy skin, blood vessels, and connective tissue in the body. Vitamin C deficiency can lead to a condition called scurvy. Vitamin C is a water-soluble vitamin, meaning that it is easily dissolved in water and therefore can be found in the juices and extracts of certain fruits and vegetables. Cooking fruits and vegetables that are high in vitamin C is likely to deplete their vitamin C content.

Materials Needed

  • 1 cup cherries
  • 1 cup chopped tomatoes
  • food blender
  • cheesecloth
  • 6 500-ml glass lab beakers
  • burner or stove
  • cornstarch
  • distilled water
  • 4 250-ml glass lab beakers
  • 4 sterile droppers
  • 2% iodine solution
  • camera

Experiment

Since vitamin C is known to react with iodine, a titration test will be performed by adding iodine to a solution of a raw fruit extract mixed with a starch and then a raw vegetable extract mixed with a starch and then repeated on cooked fruit and vegetable extracts. Iodine in the solutions in excess of the amount that can be held by the vitamin C will turn the starch in the solution blue/black in color. Therefore, the color that results after the iodine is added will indicate the relative levels of vitamin C present in the fruit and vegetable extracts prior to and after cooking.

Procedure

  1. Remove the pits and stems from about a cup of cherries and place the fruit in the carafe of a food processor or blender. Place the carafe into the food processor or blender to chop and pulverize the fruit. Then turn the machine off.
  2. Add 150 ml of water to the fruit in the food processor or blender carafe and blend on "high" until the mixture is thoroughly blended to a liquid state.
  3. Turn off the machine and strain the contents from the carafe through the cheesecloth into a 500-ml beaker. Reserve half the liquid, set aside, and label as "fruit-raw." Then take the remaining half and pour into a clean 500- ml glass lab beaker, place on a stove or burner, and heat to simmer for 15 minutes. Then set the liquid aside and label as "fruit-cooked."
  4. Add 1 tablespoon of the cornstarch to a clean 500-ml beaker and add small increments of the distilled water. Mix with a clean spoon until you achieve a pastelike consistency.
  5. Add 250 ml of distilled water to the cornstarch paste and bring to a boil on a burner or stove. Boil for 5 minutes.
  6. Pour 75 ml of distilled water into a clean 250-ml lab beaker. Take the dropper and siphon some of the starch solution and then squeeze 10 drops of it from the dropper into the 75 ml of distilled water.
  7. Take the 2% iodine solution and add incremental drops of it to the starch/water solution so that the solution turns a deep purple/indigo blue color.
  8. With a clean dropper siphon some of the "fruit-raw" extract and then squeeze 10 drops of it from the dropper into the starch/iodine solution. The presence of vitamin C will cause the deep purple/indigo blue color of the starch/iodine solution to lighten in color. The lighter the color, the more vitamin C is present. Photograph the color result in the beaker.
  9. Repeat steps 6–8 using the "fruit-cooked" extract. Compare the colors of the "fruit-raw" and "fruit-cooked" extracts to determine if any vitamin C was depleted during the cooking process.
  10. Take the tomatoes and repeat steps 1–3 to prepare the raw and cooked vegetable extracts.
  11. Repeat steps 6–9 using the vegetable extracts and photograph your results.

Results

  1. Did the raw fruit extract show a relatively high content of vitamin C? How did it compare to the cooked fruit extract? Did the cooked fruit extract show any depletion in the content of vitamin C?
  2. Did the raw vegetable extract show a relatively high content of vitamin C? How did it compare to the cooked vegetable extract? Did the cooked vegetable extract show any depletion in the content of vitamin C?
  3. Which extract experienced a greater depletion after being cooked? Does this suggest that this fruit or vegetable should be eaten raw or undercooked to gain the benefits of its vitamin C?
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