Every phenomenon has a scientific explanation behind it. Even the brown colour formation over a sliced apple has a interesting reason behind it.
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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