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Skip to 0 minutes and 7 secondsAntioxidants protect cells against the damaging effects of free radicals, which are suspected culprits in heart disease, cancer and even the ageing process. Free radicals are so reactive because they possess one or more unpaired electrons, such as the hydroxyl radical (HO). Within the body, the hydroxyl radical can oxidise and damage lipids, proteins and nucleic acids, including DNA. To protect itself from the radical attack, and oxidation, our body has two basic forms of protection. One method uses enzymes, while the other uses organic compounds, such as vitamins, including vitamins C and E. Antioxidants are essential in the diet and are found in a range of foods and drinks, including tea.

Skip to 0 minutes and 50 secondsIt has been suggested that the health benefits are due to the antioxidants they contain, which counteract the damaging effects of oxidation caused by free radicals. This activity compares the antioxidant activities of various multivitamins on the browning of apples. Leaving slices of apples exposed to the air leads to the apple turning a familiar brown colour. This process, called enzymatic browning, is due to the reaction of certain enzymes with phenolic compounds, both present within the apple, that occurs when they are exposed to oxygen in the air. These oxidation reactions produce a number of compounds including a brown pigment called melanin. The longer the apple is exposed to the air, the more brown pigments are formed, and the darker the apple becomes.

Skip to 1 minute and 37 secondsSo, we will use the rate of browning of apple to compare the relative effectiveness of antioxidants - we are looking to see which antioxidants best protect the apple from browning. First, place freshly sliced apple pieces into different glasses of water together with an antioxidant tablet ??? then monitor the rate of browning over time, by inspecting the slices. Make sure you do a control reaction, as simply soaking an apple in water alone will temporarily reduce the level of browning by restricting the amount of oxygen in contact with the slices. Tabulate your results, noting the relative levels of browning against time, with the multivitamins you have chosen. Take photos and don't forget to post your 'radical' results.

Skip to 2 minutes and 19 secondsFinally, although enzymatic browning impairs the quality and stability of freshly cut vegetables and fruit, it is beneficial to the colour and flavour of tea and coffee - so the appearance of browning is not always bad news.

Antioxidants and apples: an experiment

The following ingredients will be required:

  • An apple
  • Vitamin C tablet (we used 99p vitamin C tablets from a local pharmacy)
  • Another type of nutrient tablet (we used an inexpensive variety of A-Z multivitamin tablets)
  • Water

The following items will be required:

  • Chopping board
  • Knife
  • One cup for each type of tablet you are testing plus one extra for a control

Ingredients and items

Ensure that you read through all of the instructions before beginning the experiment to ensure that you understand exactly what will happen at each step.

Step one

Fill each cup three quarters full with cold water. Then cut the apple into three, equally sized segments and drop one into each cup.

Apple segments in water

Step two

Carefully crush up each of the tablets that you have chosen, and place one into each glass, ensuring that you leave one glass with just water, as a control.

Make sure to stir each glass so that the tablet powder has dissolved into the water.

Step three

Once a day, monitor the apples to see how the oxidation process is progressing, our results, on a pink lady apple, are shown below.

Apples after 24 hours Figure 1. The three apples after twenty-four hours, from left to right; the apple in water, the apple in vitamin C the apple in A-Z minerals

Apples after 48 hours Figure 2. The apples after forty-eight hours, from left to right; the apple in water, the apple in vitamin C, the apple in A-Z minerals

Apples after 72 hours Figure 3. The apples after seventy-two hours, from left to right; the apple in water, the apple in vitamin C, the apple in A-Z minerals

Apples after 96 hours Figure 4. The apples after ninety-six hours, from left to right; the apple in water, the apple in vitamin C, the apple in A-Z minerals

Examining the results

When the apple is cut and exposed to oxygen, free radicals are released and the apple undergoes the oxidation process and turns brown. This is seen in the first apple, the one in water. Because the apples are in water, the rate of oxidation is reduced slightly. This is why the control glass (the apple in plain water) was necessary, otherwise it would not have been a fair comparison.

The apple in the vitamin C tablet (which contains antioxidants) has a very reduced rate of oxidation. This is because vitamin C is an antioxidant that reacts with the very reactive oxygen-centred radicals, turning them into less reactive species. Hence, this reduces the amount of oxidative damage to the apple flesh. This is why the apple in the vitamin C solution does not turn brown and remains fresh looking.

The apple in the A-Z minerals goes black and looks mouldy. While there is still some protection from oxidation due to the presence of antioxidant, the over the counter A-Z minerals contain traces of 'crude oils' and 'heavy metals', which turn the apple black. The A-Z minerals contain many ingredients that are used as fillers and colourants; such as titanium oxide, magnesium stearate and corn oil. While the vitamin C tablets also contain fillers and sweeteners, from the results, it appears that they probably do not contain any 'heavy metal' or 'crude oil' traces.

Overall, we have determined that the vitamin C tablets are the most effective at reducing the oxidative damage and produce the healthiest looking apple, but, we would like the see the results that you have found. Upload pictures of your apple experiment onto our open Padlet or the Twitter hashtag #FLchemistry.

Another biologically important antioxidant is vitamin E, so you could compare the effects of vitamin C and vitamin E and see which apple browns first! Also, consider trying other commonly available vitamins and/or different types of apples. There are around 7,000 varieties of apples, but around 20 common ones, to pick from.


Experiment adapted from: R. Torres, The Apple Oxidation Test (USANA Mega AntiOxidant vs other brands), www.youtube.com/watch?v=coPI2-s48cA, Accessed: September 2016.


For those of you keen to do some further practical work - we have added an extension activity below. This uses denture tablets, with a dye in them, to test for the antioxidant activity of vitamin C tablets.

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This video is from the free online course:

Exploring Everyday Chemistry

University of York

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