PROJECT 3 : CARBOHYDRATE

Title : 

Measure vitamin c using starch-iodine test

Objective :

To measure the amount of vitamin c in many different types of foods.

Introduction :

This method determines the vitamin C concentration in a solution by a redox titration using iodine. Vitamn C more properly callled ascorbic acid, is an essential antioxidant needed by the human body. As the iodine is added during the titration, the ascorbic acid is oxidised to dehydroascorbic acid, while the iodine is reduced to iodide ions.

ascorbic acid + I₂ → 2 I^- + dehydroascorbic acid

Due to this reaction, the iodine formed is immediately reduced to iodide as long as there is any ascorbic acid present. Once all the ascorbic acid has been oxidised, the excess iodine is free to react with the starch indicator, foring the blue-black starch iodine complex. This is the endpoint of the titration. The method is suitable for use with vitamin C tablets, fresh or packaged fruit juices and solid fruits and vegetables.   

 

Materials : Vitamin C standard (0.2 mg/ml), Rice, Papaya, Chrysanthemums, 100 plus drink, Starch solutions (1%), Iodine solutions, Hydrochloric Acid (HCL) 1M 5 ml, Blender, Filter / Cheesecloth, Burette, Conical flask, Retort stand. 

Procedure :

A ) Preparing the Vitamin C extracts

1 1. The food materials was chopped into small pieces and placed into blender. 
    2. 100 ml if distilled water was added to the blender. 
    3. The materials was blend using the highest speed until it is throughly ground.

    4.The ground strain was extract.

    5. 30 ml of the strained extract was measured into a 250 ml Erlenmeyer flask or a beaker

B ) Measuring Vitamin C in the standard and food sample :

    1. 30 ml of the Vitamin C standard was placed in a 250 ml flask or beaker.

     2. 2 drops of the 0.1 M HCL was added to the flask.

     3. 5 ml of starch solutions was added to the flask.

     4. A burette was filled with the iodine solutions.

     5. The reading of initial volume was recorded.

    6. The iodine solutions was added in 1 ml increment to the flask while swirling the flask.

    7. The iodine was added until the solutions stay blue-black for 15 seconds.

    8. The volume reading on the burette was recorded.

    9. Step 1 to 8 was repeated to measured the vitamin c in the food sample.

  10. The amount of vitamin c in the food sample was calculated using this formula :

 

C ) Comparing cooked foood and raw food’s vitamin c

1. The food material was chopped into small pieces and places into blender. Then it was placed into beaker.

2. The food materials was placed into freezer for a few minutes.

3. After few minutes, the food materials was take out from the freezer.

4. The data was obtained using the same method in previous section.

5. The volume reading of burette was recorded.

6. The relatives amount of ascorbic acid present in the sample was compared.

     Discussion:

            The amount of vitamin C in 100 plus drink, broccoli, orange, papaya, rice, and chrysanthemum has been tested using iodine-starch test. From the test, it is observed that chrysanthemum has the highest vitamin C, which is 3.06mg/ml. The result that obtained from the experiment is differs greatly from the expected value which is 1.4mg. Orange has the second highest vitamin C, which is 1.53mg/ml. The result that obtained from the experiment is differs greatly from the expected value which is 53.2mg. The amount of vitamin C in papaya is 1.40mg/ml which also differ greatly from the expected value which is 60.9mg. Next, the amount of vitamin C in broccoli is 1.06mg/ml which is also differs greatly from the expected value 89.2mg. The amount of vitamin C in rice and 100 plus drink is 0.33 and 0.05 mg/ml respectively. The result obtained also differs from the expected value as there is no vitamin C in rice and 100 plus drink.

            The results that obtained from the experiment differ greatly many due to some error in the experiment. One of the errors maybe due to the colour change of the food sample such as rice and chrysanthemum is not obvious so too much iodine solution is added. There also maybe have some contamination in the apparatus used. During the preparing process, maybe some of the vitamin C is oxidised. 
    

     Question:

   1.What juices or drinks had the most vitamin C?       Chrysanthemum  

    2. Did the drinks have the vitamin C that they advertised on the labels?
    The drinks we choose is 100 plus. There are no vitamin C that they advertised on that labels.  

    3. What food sources had the most vitamin C? 
      Fruits.            

    4.What families or groups had the most vitamin C? 
      Orange, Lime

   5. Did plants that you do not normally eat have vitamin C?
      No. for example, aloe vera does not have vitamin C. 

   6. Did heat affect the vitamin C content of food?
      Yes. Heat will affect vitamin C content of food. 

   7. Did heat increase or decrease the vitamin C levels?Heat decreases the vitamin C levels in food. 

    8. What way of food preparation would be the most nutritious?
      Steaming would retain most of the nutrient in food. 

    9. Do you have any ideas now to get more vitamins from your meals?
I need to eat more fruit and vegetables that rich in vitamin. Besides that I also need to avoid cooking method that will destroy vitamin such as deep fry. I also need to avoid cooking food for too long period as it will destroy more vitamins in food. 

     Magic Writing  

     Result:

Chris Roxa

Ting Mee Ping

Lendra N

   

     Discussion

            When the paper with written message is submerse in the iodine solution, the starch in the paper will react with iodine to form blue-black coloured complex. The lemon juice contains vitamin C which prevents the reaction between starch and iodine as vitamin C can react with iodine. Thus, the paper turns blue but the message still stays white.
  
     Conclusion:

    As a conclusion, the highest content of vitamin C are found in Chrysanthemum which is 3.06 mg/ml in every 100g food sample. The lowest content of vitamin C are found in 100 plus drink which is only 0.05 mg/ml in every 100g food sample. 

   

     Reference:

    Mary K. Campbell, Shawn O. Farrell (2015) Biochemistry.8th Ed. Cengage Learning

Garret, R.H., & Grisham, C.M. (2013). Biochemistry (3^rd ed.). USA: University of Virginia

Nelson, L.D and Cox, M.M. (2012) Principles in Biochemistry (6^th Ed). Lehninger. W.H. Freeman. 

     
    Reflection:
          

    

    

Titration

Blending The Food Sample