Research Question:- How does the time of boiling effect the amount of vitamin C in food

Data Processing;-

1. Calculation of volume of glacial acetic acid, lemon juice + distilled water needed for trial.

Volume of glacial acetic acid = 10 cm3 ± 0.1 cm3

Volume of lemon juice + distilled water = 100 cm3 ± 0.1 cm3

2. Calculation of average of glacial acetic acid and lemon juice + distilled water (from number of trials)

Average of glacial acetic acid                        

 10 + 10 = 10 cm3 ± 0.1 cm3

       2

Table 2 shows the average volume of food to decolourise DCPIP

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3. Calculation of concentration of vitamin C in lemon juice

1. Mass of ascorbic acid equivalent to 1cm3 0f DCPIP solution given as 0.05mg
2. Let ‘V’ (cm3) be the average volume of mixture used.
3. Now V cm3 of the mixture is need to reduce 1 cm3 of DCPIP solution from dark blue to colourless

 V cm3 of the mixture contains 0.05mg of ascorbic acid.

     1 cm3 of the mixture contains mg of ascorbic acid

          1cm3 of the original lemon juice contains  mg of ascorbic acid

          However, unit must be in mg/100cm3

            mg must multiply by 100

Where

                V         - Average volume needed to decolourise DCPIP solution

For fresh juice,

=

        = (5.00/ 112.4) x 100

        = 4.45 mg/100cm3

For 10 min,

        =

                = (5.00/ 151.6) x 100

        = 3.30 mg/100cm3

For 1 hour,

        =

        = (5.00/ 180.0) X 100

        = 2.78 mg/100cm3

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Discussion:-

1. This experiment is conducted to calculate the concentration of ascorbic acid (C6H8O6) or vitamin C in different samples of lemon juice. To find the concentration, we titrated the sample juice against 1 cm3 of 2-6 dichlorophenol indophenol (DCPIP). The ascorbic acid contained inside the sample juice will bleach the dark blue colour of DCPIP to become a colourless solution because of its strong reducing agent properties. It is assumed that 0.05 mg of ascorbic acid will reduce 1 cm3 of DCPIP, a value which has been internationally standardised.
2. The highest concentration of ascorbic acid (vitamin C) is contained in the fresh lemon juice which is 4.45 mg/100cm3, while the boiled samples have a lower concentration of ascorbic acid, 3.30 mg/100cm3 for 10 minutes and 2.78 mg/100cm3 for 1 hour.
3. Ascorbic acid is very sensitive towards heat, which can destroy the acid molecules inside it by breaking the weak Van der Waals bonds between the molecules. We can also see that the difference between concentrations of ascorbic acid in the 10-minute boiled juice and the 1-hour boiled juice is not much. In fact, there is even a sample in which the concentration of ascorbic acid in the 1-hour boiled juice is more that the 10-minute boiled juice. This is because both samples are boiled, destroying a large amount of vitamin C. However, as the juice is further heated to one hour, another additional amount of vitamin C is destroyed in the heating or ‘cooking’ process.
4. The solution containing ascorbic acid (lemon juice) should not be shaken too vigorously, as this will allow reaction between oxygen and the acid. When the ascorbic acid molecules bond with oxygen atoms, they no longer carry out their normal functions as ascorbic acid, which is for growth, assisting in formation of blood cells and prevention of diseases like scurvy and colds.
5. The results could be accurate as it is known that the theoretically, the amount of ascorbic acid will decreased as it heated. The results obtained do shows that the concentration of Vitamin C decreases as the time of boiling the Lemon juice increased. So, the results can be considered as consistent. Therefore, we can deduce that the longer the time in boiling the juice, the lesser the amount of the ascorbic acid in the solution.

Limitations and Suggestion

Conclusion:-

From this experiment, it is known that fresh lemon juice has the highest concentration of ascorbic acid or vitamin C. This shows that the longer we cook a fruit, the less concentration of vitamin C will present as heat will destroy ascorbic acid in our foods. Hypothesis is accepted.

Reference:-

• Biology for the IB Diploma, CJ Clegg, Hodder Murray Publication 2007