Investigating the effects of cooking on the Vitamin C content of food.

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Table of Contents


Review of Literature


Preparation of food samples

Vitamin C indicator

Standardised Vitamin C Solution

Test for amount of Vitamin C




Reference list

Plagiarism Report


The aim of my research is to determine the effects of cooking on the Vitamin C content of food. I believe that the pickled cabbage would retain the greatest amount of Vitamin C, since it combines all the best possible circumstances for the retention of Vitamin C which is discussed in the review of literature. These factors include minimal exposure to air, an acidic medium and a lack of heat.

Vitamin C is a well-documented and essential factor in boosting a person’s immune system. Vitamin C plays an essential role in warding off inflammation, infections, and viruses (, n.d.). Thus my research will yield a result that will aid in maintaining the health of people.

With my research I intend to analyse the results in order to ascertain the best cooking method for retaining the largest amount of Vitamin C. I would like to apply this knowledge in order to keep me, my family and other people healthier during the winter period. Most people, myself included, are not aware of the fact that different cooking methods produce varied amounts of Vitamin C present in the food we eat.

In conducting my research I hope to educate the people that are unaware of the fact that cooking methods affect the amount of vitamin c in the foods we eat. This way I hope to establish the best possible cooking method for retaining the most amount of Vitamin C. This information could, in turn, be utilized to ensure that people stay healthier this winter by increasing the amount of Vitamin C that they ingest and as a result decrease the frequency in occurrence of illnesses.

Review of Literature

Vitamin C is the most studied of all the vitamins. It is also known as ascorbic acid and is found in a large variety of food substances, mainly citrus fruits, and leafy green vegetables. It is relatively unstable and undergoes oxidation easily, and means that a variety of factors can significantly reduce its quantity within food substances. The main factors owing to the loss of Vitamin C are heat, leeching, storage and change in pH (Lee and Kader, 2000).

Vitamin C deteriorates very rapidly, however, heat drastically speeds up the oxidation process with air. The heat, in turn, results in a faster rate of deterioration of Vitamin C. On the other hand, cooling the food substance containing Vitamin C will slow down the deterioration but not halt it completely. This means that in order for a food substance to retain the highest possible quantity of Vitamin C, the food substance needs to be exposed to as little heat as possible. The chemical decomposition due to heat is in fact caused by enzymes that accelerate oxidation at higher temperatures right up until they denature and cease to function (Margaret A. Allen and S. G. Burgess, April 1949). Another factor to note is that the amount of Vitamin C lost also depends on the duration for which the food substance is exposed to heat. In practice this means that a food substance that is exposed to a high heat for a short amount of time will lose a similar amount of Vitamin C compared to a food substance that is exposed to a low heat for a longer period of time.

Storage includes a combination of factors. These factors include heat and duration. It has been found that as time passes the amount of Vitamin C in a stored food will decrease (Lee and Kader, 2000). Again this is due to the unstable nature of Vitamin C and that its deterioration is controlled by enzymes. As discussed above, the best combination of factors for the highest retention of Vitamin C would be storage at low temperatures of about 0-10°C for the shortest duration possible.

Vitamin C is also highly soluble in water, which means that it will dissolve in water when the food substance that contains it is bathed in water. As a result, during the boiling of vegetables or other foods containing Vitamin C, a substantial amount of Vitamin C is lost to the surrounding water. The Vitamin C leeches into the water, which many people tend to discard. Many people remain unaware of the fact that the greatest source of Vitamin C after boiling is not the food, but rather the water. As a result the Vitamin C generally goes to waste.

Another factor that causes the deterioration of Vitamin C is pH level. Alkalinity tends to destroy vitamins in general and Vitamin C is no exception (Jean-Louis Tu, Looking at the Science on Raw vs. Cooked Foods, 1999). The surrounding pH level of a food substance affects the enzymes contained within the food and since enzymes control the deterioration of Vitamin C, the pH indirectly affects the amount of Vitamin C liberated. It has been determined that the pH level that is most suitable at preserving as much Vitamin C as possible is one that is slightly acidic. This is because it is a pH that enzymes find the most unconducive to operate in and at the same time safe for people to ingest.

The optimum method of cooking would therefore involve the least amount of heat for as little amount of time as possible, a slightly acidic medium, and little to no contact with water so as prevent the chemical decomposition of Vitamin C. These factors would, theoretically, result in the highest possible retention of Vitamin C within a food substance and would thus be the best possible cooking method in order to maintain one’s health.


Preparation of food samples:

  1. Label 5 plastic containers A, B, C, D, and E.
  2. Shred an entire raw head of cabbage and divide it into five equal masses of shredded cabbage using a mass scale.
  3. Liquidize one fifth of fifth of the raw cabbage using a food processor and place it into container A.
  4. Fry one fifth of the cabbage in a pan with 5ml of sunflower oil (1 teaspoon) for 3 minutes, with the use of a stopwatch for timing.
  5. Filter the fried cabbage for 5 minutes using filter paper before liquidizing the residue and placing the residue into container B.
  6. Steam cook one fifth of the cabbage for 3 minutes in a steam cooker.
  7. Filter the steam-cooked cabbage for 5 minutes and liquidize the residue before placing it into container C.
  8. Boil one fifth of the cabbage in 500ml of water, using a measuring jug to measure, for 3 minutes.
  9. Filter the boiled cabbage for 5 minutes and liquidize the residue before placing it into container D.
  10. Pickle the last one fifth of the cabbage in 1 cup of vinegar (250ml) for 14 days.
  11. Filter the pickled cabbage for 5 minutes and liquidize the residue before placing it into container E.

Vitamin C indicator:

  1. Boil 1.5 teaspoons (7ml) of cornstarch in 1 cup (250ml) of water for 2 minutes.
  2. Take 6ml of cornstarch mixture and add to 1 litre of distilled water.
  3. Mix thoroughly.
  4. Add 12ml of iodine solution to the mixture.
  5. Mix until a consistent deep blue colour arises.

Standardised Vitamin C Solution:

  1. crashed tablet of vitamin C Grind one 500mg Vitamin C tablet (e.g. Scorbex), using a pestle and mortar in 20ml of distilled water until it dissolves.
  2. Pour the solution through a filter paper in a filter funnel into a measuring cylinder.
  3. Make up the volume of the liquid to 500ml with distilled water and mix thoroughly.

Test for amount of Vitamin C:

  1. Label 6 test tubes A, B, C, D, E and F.
  2. Add 10ml of the Vitamin C Indicator liquid into each test tube.
  3. Fill a 2.5ml syringe with 2ml of the standardised Vitamin C solution.
  4. Add the standardised Vitamin C solution to test tube F, by lightly pushing the plunger.
  5. Mix the contents of the test tube well after each drop has been added.
  6. Continue to add drops until the indicator liquid has lost its blue colour.

  1. Measure the volume of Vitamin C solution added to the indicator liquid in order for it to lose its blue colour and record the value on a piece of paper.
  2. Repeat the previous steps with cabbage samples A to E in each corresponding test tube.
  3. Measure the volumes of cabbage samples added to the indicator liquid in order for it to lose its colour and tabulate these values.
  4. Calculate the concentration of Vitamin C in the food samples with the following formula:

I have identified the independent variable to be the food sample, the dependent variable to be the concentration of Vitamin C present in the food sample while a controlled variable would be the fact that the food samples consisted of a single cabbage divided into five equal masses.


A table showing the effects of cooking on the Vitamin C content of food

Food sample

Volume of liquid from the food sample to discolour the indicator solution

Concentration of Vitamin C present in the food sample (%)

Raw cabbage



Fried cabbage



Steamed cabbage



Boiled cabbage



Pickled cabbage




The pickled cabbage retained the least concentration of Vitamin C, thus proving my hypothesis to be incorrect. The boiled cabbage contained the second lowest concentration, therefore, it appears as though leeching seems to be a major factor in the loss of Vitamin C, more so than other factors such as heat. The steamed cabbage, which retained the highest concentration of Vitamin C, confirms this since steaming in no way involves submerging the cabbage in any liquid, unlike the other cooking methods. My research would, however, benefit if the experiment was to be repeated twice more in order to produce an average and generate a more accurate result.

Another important factor to note is the duration of time that is required for each sample to “cook”. The pickled cabbage was pickled for fourteen days, however, the steamed, boiled and fried cabbage were all cooked for three minutes. The effect is evident in the bar graph as the steamed, boiled and fried cabbage samples fall within a range of concentrations that are relatively close to one another. The pickled cabbage on the other hand, has a concentration that is significantly lower than the other methods. Since the major difference between the pickled cabbage and the other samples is time, it is evident that the time elapsed also plays a major role in the retention of Vitamin C. For this reason it would be best to conduct an experiment that involved cooking methods that could be done within the same time frame, such as by removing the pickling method and rather including grilling and sous vide’ing.

Despite being submerged in an acidic medium, the pickled cabbage produced the lowest concentration of Vitamin C. No fair conclusion can be reached, however, since no fair comparisons can be made the other methods of cooking, which involve different factors. Therefore, in the future it would be advisable to devise a separate experiment to test the acidity of a medium that would result in the greatest retention of Vitamin C in a food sample.

Ultimately my research means that steaming is the best method for cooking food in order to retain as much Vitamin C as possible. This, in turn, means that those learning from my research are able to apply the information by rather steaming their food as opposed to any other method. This will result in people absorbing more Vitamin C and will therefore remain healthy during the winter season. The greater amount of Vitamin C consumption aids one’s body in fighting inflammation, infections and viruses.


The best method for cooking food is steaming. It retains the highest concentration of Vitamin C and is not too far off when compared to the control, the uncooked cabbage. Pickling, however, resulted in the lowest concentration, thus in order to stay healthy, people should steam their food and avoid pickling their food.

Reference list

Plagiarism Report