Peeled apples are exposed to air, so they undergo an “oxidation” reaction. The specific reaction is that some phenolic substances are reacted with oxygen by the catalytic action of PPO to produce quinones. The so-called PPO is a phenolic enzyme, and this quinone reacts together to produce melanin.
Can I eat apples that have oxidized?
The enzymatic browning of cut apples turns the surface brown, affecting the appearance of the food and reducing the nutritional content of the surface layer, but it has no effect on the body. However, if the apple is left in the air for a longer period of time, the oxidation and decomposition of the surface will intensify, further decomposing the pectin and nutrients, easily deteriorating the pulp and producing substances harmful to the body, so apples that have been oxidized for a longer period of time cannot be eaten. Therefore, apples that have been oxidised for a short period of time can be eaten, and those that have been oxidized for a longer period of time should not be eaten.
Ways to prevent oxidation and discoloration of apples are
1. Use lemon juice. Apples turn brown because of a chemical reaction between the enzymes in the apple and the oxygen in the air. This process is called “oxidation” and lemon juice can prevent this because it contains citric acid, a potent antioxidant. Spoon the lemon juice directly over the apple slices in the bowl and stir well.
2. Use salt. Salt is a natural preservative that prevents apples from oxidising. To use this method, dissolve half a teaspoon of salt in cold water. Dip the cut apples into the salted water for 3 to 5 minutes. Then take the apples out.
3. There is no need to worry about the apples becoming salty. As long as you don’t use too much salt, avoid soaking them for too long and wash them thoroughly afterwards, the apples will be just as tasty.
4. Cover with cling film. A very simple way to prevent the apples from oxidising is to wrap them in cling film.
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