What is the Shelf Life of Natural or Processed Vitamin C?

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Updated on Feb 17, 2010

Difficulty of Project (Easy, Medium, Hard)

Hard

Grade Level (Elementary, Middle, High School)

High School Cost

Approximate Cost

$8-$25

Safety Issues

Iodine and potassium iodide are chemicals used in this experiment. A designated supervisor such as an adult, parent, or guardian should supervise the experiment. Gloves and protective goggles should be worn to reduce the chance of staining and/or chemical burns that may result from a spillage. Material Availability (Are the materials required readily available?) The equipment for the project can be found in a high school laboratory. Iodine and potassium iodide can be purchased from a chemical supply catalog. The juices and corn starch can be purchased from the local grocery store.

Approximate Time Required to Complete the Project (Hours, days, weeks)

4-8 weeks

Objective

To investigate the rate of vitamin c degradation in natural and processed orange juices.

The project goals include measuring the concentration of vitamin c in organic and processed orange juices and determination of the subsequent change in vitamin c concentration over time.

Materials and Equipment / Ingredients

Corn starch
Distilled water
Erlenmeyer flasks
Funnel
Iodine
Organic orange juices
Permanent marker
Potassium Iodide
Processed orange juices
Transfer pipettes
Triple beam balance
Organic Juice (A) /Processed Juice (B)
Volume of Starch-Iodine Solution
Concentration of Vitamin C
Control
8 mL
25 mg
A1
5 mL
X
A2
9 mL
X
B1
12mL
37.5mg
B2
13mL
X

Introduction

Vitamin C is naturally produced by citrus fruits and is an essential nutritional organic compound. Vitamin C like other organic compounds deteriorates over time. Oxidants react with the functional groups of the vitamins causing bonds to distort and the functional shape to lose its original structure. Shape in nature is related to function. As shape changes, the function of the substance changes. Indicators are chemicals that change color in response to chemical change. In this experiment a starch-iodine indicator is used to indirectly estimate the concentration of vitamin c in organic and processed orange juices. The starch-iodine indicator will change from colorless to blue/black in the presence of vitamin c. In this titration, the volume of indicator added in solution relates to the volume of vitamin c in the orange juice.

Research Questions

What techniques are used to measure concentration in solution?

What are the nutritional sources of vitamin C?
What is the difference between organic and processed orange juices?
How is vitamin c concentration measured?
What is an indicator?

What methods are used to process and produce commercial orange juice?

Terms, Concepts and Questions to Start Background Research

Deterioration
Indicator
Organic compound
Rate
Titration
Vitamin C

Experimental Procedure

  1. To prepare starch solution, bring a mixture of 1 gram corn starch dissolved in 100 milliliters of distilled water to its boiling point.
  2. Transfer 4 milliliters of the starch solution to 500 milliliters of distilled water.
  3. To prepare the iodine solution, dissolve 4.5 grams of iodine in 100 milliliters of ethanol and dissolve the solution in 110 milliliters of distilled water and add 5 grams of potassium iodide, KI.
  4. Transfer 1 milliliter of the iodine solution to the starch solution to produce the starch iodine solution or indicator for the experiment.
  5. To determine how much of the starch-iodine solution is required to neutralize a highly concentrated sample of vitamin c, crush a 250 milligram vitamin c tablet and dissolve in 100 milliliters of water. Transfer the solution to a 250 milliliter volumetric flask and add distilled water to make a 1 molar solution of vitamin c. Decant 20 milliliters of the solution into an Erlenmeyer flask.
  6. Transfer the starch-iodine solution to the solution of vitamin c milliliter by milliliter using a 1 milliliter pipette. Swirl the mixture in the Erlenmeyer flask following each transfer.
  7. Record the volume of starch iodine solution transferred at the point the solution changed color during the titration. If 8 milliliters of starch-iodine was added to 20 milliliters of a 20 milligram solution of vitamin c causing neutralization, this proportion can be used to compare and estimate the concentration of vitamin c in other solutions.
  8. Transfer 20 milliliters of organic and processed orange juices to separate Erlenmeyer flasks.
  9. Transfer the starch-iodine solution to the solution of vitamin c milliliter by milliliter using a 1 milliliter pipette. Swirl the mixture in the Erlenmeyer flask following each transfer.
  10. Record the volume of starch iodine solution transferred at the point the solution changed color during the titration.
  11. Estimate the concentration of vitamin c in other solutions using the following proportion: 25milligram/8milliliter = Concentration of vitamin c/Volume of starch-iodine solution.
  12. Repeat the experiment to estimate the average concentration of vitamin c in the various orange juices.
  13. Place the orange juices in the refrigerator and repeat steps 8-12 every 2 days for several weeks up to and past the expiration date of the juices to determine how the concentration of vitamin c changes over time and to compare the change in vitamin c concentration in organic and processed orange juices.

Bibliography

Aqueous Acid-base Equilibria and Titrations by Robert de Levie, February 15, 2001, Oxford Chemistry Primers

Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Ausiello D, eds. Cecil Medicine . 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 237.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press, Washington, DC, 2000.

Christine Ryder Combs, B.A. Honors Biochemistry, teaches high school Chemistry and Biology and serves as her school's science fair coordinator and science club sponsor. Since the development of an intensive science research program at her school, Christine has been nominated as an exemplary science teacher and has won awards for exemplary student participation at the regional science fair and recognized as teacher of the year.

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