Experiment 6.2

Experiment 6.2: Determining the vitamin C content in various food juices Purpose: To determine the vitamin C content in various food juices Problem statement: Do different types of fruit juices contain similar amounts of vitamin C? Hypothesis: Lime juice contains a higher concentration of vitamin C compared to orange juice. Variables: Manipulated Manipulated variable variable : Type of of fruit juices juices Responding variable : Volume of fruit juice needed to decolourise DCPIP solution Control variable

: Volume of DCPIP solution, standard concentration concentrat ion of ascorbic acid solution

Materials: 1.0% dichlorophenolindophenol (DCPIP) solution, 0.1% ascorbic acid solution, freshly prepared lime juice and orange juice.  Apparatus: Specimen tubes, syringe (1ml), syringe (5ml), beakers (50ml), gauze cloth Technique: Measure and determine the volume of standard vitamin C solution/ fruit juices needed to decolourise of 1ml of DCPIP. Calculate the vitamin C content of juice by comparing it with the standard vitamin C solution. Procedure: Diagram showing the set-up of apparatus

1. 2. 3. 4.

1 ml of DCPIP solution is filled in a specimen tube using a 1 ml syringe. The 5 ml syringe is filled with 0.1% ascorbic acid solution. The tip of the syringe is placed into the DCPIP solution. The ascorbic acid solution is added to the DCPIP drop by drop. The mixture is gently stirred with the tip of syringe. The ascorbic acid solution is continuously added until the DCPIP solution is decolourised. The volume of ascorbic acid solution used is recorded. 5. Steps 1 to 4 are repeated for another two times. 6. Steps 1 to 5 are repeated using freshly squeezed lime juice and orange juice. The volume of fruit juice required to decolourise the DCPIP solution in each case is recorded in the table. 7. The results are tabulated. The percentage and the concentration of vitamin C in each of the fruit juices is calculated using the formulae below: Percentage of vitamin C in fruit juice = Volume of 0.1% ascorbic acid solution

x

0.1

Volume of fruit juice

Results: Concentration of vitamin C in fruit juice = Volume of 0.1% ascorbic acid solution

-3

x 1.0 mg cm

Volume of fruit juice

Results: Solution/ fruit juice

0.1 % ascorbic acid Lime  juice Orange  juice

Volume of solution/ fruit juice decolourise 1 ml of DCPIP solution 1 2 3 1.0

1.0

1.0

needed

to

Average

Percentage of vitamin C in fruit  juice (%)

Vitamin C concentration in fruit juice (mg cm-3)

1.0

Discussion: 1. Oxidation of vitamin C in juices causes the DCPIP solution to decolourise. / Vitamin C reduces blue DCPIP to become colourless. 2. The specimen tubes containing the DCPIP solution should not be shaken when the ascorbic acid solution and the fruit juices are being added. This is because oxygen from the atmosphere oxides the reduced DCPIP solution and turns it blue again.

More fruit juice is needed to reduce the DCPIP solution. Hence, accuracy of the experiment is affected since the actual vitamin C content cannot be determined. 3. Lime juice contains the highest concentration of ascorbic acid/ vitamin C. In this experiment, less volume of fruit juice is needed to decolourise DCPIP if the vitamin C content is higher. 4. The vitamin C in the fruit juice is destroyed if the fruit juice is prepared a day earlier. 5. In order to maintain the vitamin C concentration in canned fruit juice, the can is sterilized under high pressure and high temperature. Conclusion: Hypothesis is accepted. Lime juice contains a higher concentration of vitamin C compared to orange juice.