Science behind the brown colour formation over a sliced apple - Science, Technology, Nature and General Facts and News.


Saturday, 23 May 2020

Science behind the brown colour formation over a sliced apple

Brown colour formation over sliced apple

Apple, a fruit loved by everyone in the word, is cultivated mostly in the western countries, where the climate is suitable for its growth. Most of us have ate at least one apple in our lifetime. Some of us have noticed and some of us have ignored the brown colour forming over a sliced apple. Many who noticed probably didn’t bother about the reason for that appearance. But there is a scientific explanation behind this phenomenon. In this post, we can explore the science behind that brown colour formation.

Normally, the flesh of an apple contains an enzyme called polyphenol oxidase (PPO). When the apple is sliced this polyphenol oxidase enzyme gets exposed to the oxygen in the surrounding atmosphere. As a result, the phenolic compounds found in the apple rapidly oxidise to O-quinones. This reaction changes the colourless precursors found in the apple into brown-coloured secondary products. Further, O-quinones form polymers by self-assembling or forming complexes with amino acids and proteins found in the apple. This produces the well-documented brown colour over the sliced apple.

We can prevent the formation of this brown colour in two simple methods. In the first method, we can cut off the oxygen supply, since oxygen is needed for the activation of the polyphenol oxidase enzyme. This can be done by coating the apple with a sugary syrup or lemon juice. The second method is destroying the polyphenol oxidase enzyme by applying heat to the apple, either by cooking or blanching it in hot water. When heat is applied, the enzyme, a globular protein, will denature and lose its function. Moreover, coating with the lemon juice also affects the function of this enzyme by altering the pH of the medium.

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