- cheuklongLv 41 decade agoFavorite Answer
Actually, this is a question related to biology but you can understand it easily.
Oxidation is a process in which a species is oxidized while reduction occurs to reduce another species.
In apples, oxidation makes its color rusty but actually, it's not rusting but the enzymatic reaction, forming a brown chemicals. It is not related to the change of sugars or organic acids. They are what they are when harvested and stored. The same principle works with the banana.
If you want to prevent the oxidation process, you can put a layer of lemon juice on the cut fruits, and you can taste the differences of sweets for treated and untreated fruits.