Experiment 4 : Experiment on Vitamin C

Practical no. : 4

Experiment title : Determination of the Amount of Vitamin C in Food

1. Measuring Vitamin C using starch-iodine test

Abstract :

In this experiment, the main objective is to measure the amount of vitamin C in many different types of foods such as fruits (apples, honeydew, orange and papaya), vegetables (white cabbage, brocolli and spinach), and chrysanthemum flowers. Honeydew has been chosen and the extraction of vitamin C was conducted in few different ways either freshly made, boil at high temperature or bake in oven. This various techniques gave different readings for the amount of vitamin C. The solution of vitamin C was tested with iodine solution in the presence of starch and hydrochloric acid (HCl) by using a titration method. Vitamin C is able to bind with iodine, thus as the vitamin C can no longer bind with the iodine (all has been used up), the solution will turn into blue black solution. 

Introduction:

                                                            Vitamin C - Ascorbic acid

Vitamin C (ascorbic acid) is an antioxidant that is essential for human nutrition. Vitamin C deficiency can lead to a disease called scurvy, which is characterized by abnormalities in the bones and teeth. Many fruits and vegetables contain vitamin C, but cooking destroys the vitamin, so raw citrus fruits and their juices are the main source of ascorbic acid for most people.

One way to determine the amount of vitamin C in food is to use a redox titration. The redox reaction is better than an acid-base titration since there are additional acids in a juice, but few of them interfere with the oxidation of ascorbic acid by iodine. Iodine is relatively insoluble, but this can be improved by complexional the iodine with iodide to form triiodide:

As long as vitamin C is present in the solution, the triiodide is converted to the iodide ion very quickly. However  when the all the vitamin C is oxidized, iodine and triiodide will be present, which react with starch to form a blue-black complex. The blue-black color is the endpoint of the titration.

This titration procedure is appropriate for testing the amount of vitamin C in vitamin C tablets, juices, and fresh, frozen, or packaged fruits and vegetables. The titration can be performed using just iodine solution and not iodate, but the iodate solution is more stable and gives a more accurate result.

Materials:

Food sources of vitamin C (Honeydew)

Starch solution (1%)

Iodine solution

Hydrochloric acid (HCl) 1M, (5ml)

Blender

Filter

Procedure:

1. Vitamin C extract.

2. Vitamin C content in ascorbic acid is measured (standard solution)

3. Steps 1 and 2 are repeated by replacing ascorbic acid with microwave-heated honeydew extract (microwave) and boiled honeydew extract.

4. Vitamin C content in cooked food and raw food's sample is determined.


Result

Amount of vitamin C in 30 ml sample:

 Amount of vitamin C in 100 ml sample:

Discussion

Cooking can destroy the amount of vitamin C in the food. Raw citrus fruits and their juices are the main source of ascorbic acid for most people. When Iodine reacts with vitamin C both the iodine and vitamin C turn into different chemicals.  In this experiment, small amount of iodine was added to honeydew sample by using titration until iodine that we add no longer disappears as soon as it is added. This is because, when the amount of iodine added to the sample is greater than the amount of vitamin C that was there, all the vitamin C will be destroyed and there will be some iodine left over. Role of starch in this experiment is to pair up with iodine to make a dark blue material.

There are three samples for different types of honeydew preparation. The first sample is fresh honeydew. The second sample is baked honeydew and the third sample in boiled honeydew. Each sample shows different amount of vitamin C present.  The amount of vitamin C for fresh honeydew is 0.109 mg/ml whereas the amount of vitamin C in baked honeydew is 0.098 mg/ml and 0.088 mg/ml in boiled honeydew. Fresh honeydew show the higher amount of vitamin C compared to baked and boiled. This is because vitamin C in fresh honeydew is not being oxidized in a short time. However, the amount of vitamin C in baked honeydew is higher than the amount of vitamin C in boiled honeydew. This is because vitamin C in boiled honeydew is easily oxidized compared to baked honeydew.

Questions:

1)      Did heat affect the vitamin C content of food?

Yes, heat will affect the vitamin content of food. It is because vitamin C is a water-soluble vitamins and water-soluble vitamins are most vulnerable to heat, water and air.

2)      Did heat increase or decrease the vitamin C levels?

Heat will cause the decreasing of vitamin C levels due to the vaporization of the vitamin C into the surrounding air.

3)      What way of food preparation would be the most nutritious?

From the experiment, we found that eating fresh fruit will provide the most nutritious especially vitamin C to our body.

4)      Do you have any ideas now to get more vitamins from your meals?

Yes. Eating fresh fruit will give more nutrient rather that cook it. But if we still want to make it cooked, steaming it the best way because steaming can retained the most vitamin C inside the fruit. 

Conclusion: 

 The amount of vitamin C can be measured by testing it with iodine solution through a titration technique. Vitamin C is able to react and bind with iodine molecules. Hence, the higher the volume of iodine used, the higher the amount of vitamin C in the food sample. 

References:

Chet T. (2006). Vitamin C and Citrus Juices. Retrieved on May 9, 2013 from http://www.ultimatecitrus.com/vitaminc.html

Jan S and Demand M. Does Cooking Food Reduce the Vitamin Content? Retrieved on May 9, 2013 from http://healthyeating.sfgate.com/cooking-food-reduce-vitamin-content-5164.html

2. Application: Magic Writing

Materials

Beaker

Iodine

Lemon/Lime juice

Notebook paper

Cup 

Art Brush

Procedure

Results/ observations:

Discussion:

In this magic writing experiment, we had to prepare the vitamin C solution by using lemon. After that, by using art brush, write a message with the lemon juice on the paper. Then, the paper was put aside to let it dry. After the massage on the paper dry, dip the paper into iodine solution. As we had done in the previous experiment, their concept was the same. Vitamin C can be found in fruit and vegetables, particularly citrus fruit such as oranges and lemons. Vitamin C can react with iodine solution. When there were vitamin C, the iodine will turn from light brown solution into colorless solution.

The result for this experiment, we found that the massage that we had wrote before can be seen because the paper were made up by using plant materials. As we know, there are contain of starch. When iodine react with the starch, light brown solution will turn into dark blue-black solution. That why we can saw the massage that have been wrote before because the massage will appear white will the part that do not contain vitamin C will turn bluish. This massage only appear for about 5 minutes because when there are no more vitamin C that react with iodine, the iodine will start to react with the starch.

conclusion:

Vitamin C is able to react and bind with iodine molecules. The words inside the iodine solution look shine since it was written with vitamin C but then it seems to be blue black as the vitamin C has completely react with the iodine.  

References:

Margo B. (2010). How to Test for Vitamin C in Fruit and Vegetables. Retrieved on May 9, 2013 from http://www.livestrong.com/article/272622-how-to-test-for-vitamin-c-in-fruit-and-vegetables/#ixzz2TGO0OSoi