Vitamin C posted by Alexander James Krzyston

Happiness by Alexander J Krzyston

Introduction:

The purpose of the this experiment was to determine the vitamin C concentration of vitamin c in various foods, a vitamin C tablet, orange juice, and fresh lime juice.  We did this by first making an ascorbic acid solution consisting of ascorbic acid (from the food), 5mL of HCl, 1.0g of KI, 2-3mL of a 0.5% starch solution, and 50mL of water.

Alexander Krzyston |Vitamin C Alexander J Krzyston |Vitamin C Alex James Krzyston
Alex Krzyston |Vitamin C Alex J Krzyston |Vitamin C Alexander James Krzyston
NORTHWESTERN UNIVERSITY |Vitamin C EVANSTON |Vitamin C BURR RIDGE

We titrated the ascorbic acid solution against 0.01M KIO3-.  Vitamin C is easily oxidized in acidic conditions, which is why we added the HCl.  The IO3- ions will react with the ascorbic acid, oxidizing it, to form dehydro-L-ascorbic acid and I3-.  When all of the ascorbic acid is used up, I2 will build up and react with I- to form I3-, which produced a purple color in the presence of starch.  When the solution turned purple, we had reached the end point.  My knowing the mass of the vitamin c table and the volume of orange juice and fresh lime juice in the ascorbic acid solution, we can determine the amount of vitamin C in each of the three.

Overview

In this experiment we found that the bottled orange juice had a higher concentration of vitamin c than the fresh lime juice.  This surprised me at first because I would think that the fresh fruit juice would have more vitamin c than bottled juice.  However, according to http://www.naturalhub.com/natural_food_guide_fruit_vitamin_c.htm
Lime juice has 29mg of vitamin C per 100mg of fruit, which it approximately 1mg per average slice, where as an orange has 53mg of vitamin C per 100mg of fruit, which is approximately 70mg per orange.  Thus, the differences in vitamin C concentration do not depend on whether the juice is bottled or not, but on the fruit.  To determine whether or not bottled versus fresh juice had an impact f vitamin C concentration, we should have tested the same fruit juice both bottled and fresh. By doing so we could determine if processing has any impact on vitamin C concentration. 

Procedure:

Procedure was same as in lab manual. 
*For the titration of fruit juices and powered drink mixes, we titrated orange juice (no pulp)
*For the titration of fresh fruits we titrated lime juice, we had to use more than one lime to get 50.0mL of juice so in the final calculations we could not calculate the amount of vitamin C per fruit so value so given in mg/mL.

Data:
Part 1: Vitamin C Tablet
Trial 1:                            Trial 2:
mass of 1/2 vitamin C tablet    0.1624g        mass of 1/2 vitamin C tablet    0.1208g
initial volume of KIO3    0.00mL        initial volume of KIO3    0.00mL
final volume of KIO3    24.00mL        final volume of KIO3    18.15mL


Part 2: Orange Juice
volume of orange juice    20.0mL
initial volume of KIO3    0.00mL
final volume of KIO3    1.26mL
   
Part 3: Fresh Lime Juice
   
volume of fresh lime juice    50.0mL
initial volume of KIO3    0.00mL
final volume of KIO3    2.71mL

Calculations:
    See attached sheet for calculations.
Discussion:
1.    3C6H8O6 + IO3- → 3C6H6O6 + I- + 3H2O
2.    Two electrons are involved in the redox reaction.  Ascorbic acid is oxidized (loses 2 electrons) and iodine is reduced.
3.    Vitamin C will react with dissolved oxygen under acidic condition because vitamin C is easily oxidized in acidic conditions: 3C6H8O6 - → 3C6H6O6 + 2H+ + 2e-
4.    Pasteurization would decrease the concentration of vitamin C in juices.  Pasteurization involves heating of the juices to kill bacteria, this in turn also destroys vitamin C.  The concentration of vitamin C decreases as pasteurization temperature and time increases this was proven in a study of the Effect of Pasteurization on Vitamin C in Guava Juice in January 2008 at King Mongkut’s University of Technology Thronburi in Thailand (http://pdfcast.org/pdf/effect-of-pasteurization-on-vitamin-c-content-of-guava-juice) and has alos been rproven in various experiments involving raw and pasteurized milk.  “Eighty percent of a food's vitamin C content is lost merely by boiling it for twenty minutes and at 120°C” (http://www.daviddarling.info/encyclopedia/P/pasteurization.html).

5.    Describing vitamin C as an antioxidant would be a correct description.  Vitamin C is an electron donor which makes means that it is a reducing agent. By donating electrons, it prevents other compounds from being oxidized, in humans this would be radicals such as oxygen related radicals (superoxide, hydroxyl radical, peroxyl radical), sulfur radicals, and nitrogen-oxygen radicals or compounds that are reactive, but not radicals like hypochlorous acid, nitrosamines, and other nitrosating compounds, nitrous acid related compounds and ozone.  “all known physiological and biochemical actions of vitamin C are due to its action as an electron donor” (http://www.jacn.org/cgi/reprint/22/1/18.pdf).

*Other source also used: http://www.vitaminstuff.com/antioxidants.html

In this experiment we found that the bottled orange juice had a higher concentration of vitamin c than the fresh lime juice.  This surprised me at first because I would think that the fresh fruit juice would have more vitamin c than bottled juice.  However, according to http://www.naturalhub.com/natural_food_guide_fruit_vitamin_c.htm
Lime juice has 29mg of vitamin C per 100mg of fruit, which it approximately 1mg per average slice, where as an orange has 53mg of vitamin C per 100mg of fruit, which is approximately 70mg per orange.  Thus, the differences in vitamin C concentration do not depend on whether the juice is bottled or not, but on the fruit.  To determine whether or not bottled versus fresh juice had an impact f vitamin C concentration, we should have tested the same fruit juice both bottled and fresh. By doing so we could determine if processing has any impact on vitamin C concentration.