What keeps apples and bananas from browning?

Lemon juice or soaking in acidic water prevents apples and bananas from browning due to the presence of ascorbic acid (vitamin C) and citric acid. When fruits are cut or bruised, an enzyme called polyphenol oxidase reacts with oxygen in the air, leading to an oxidation process that turns the fruit brown. The acids in lemon juice and acidic water inhibit the activity of this enzyme, effectively slowing down or stopping the browning reaction. This method is a common and effective way to preserve the color and freshness of fruits after they have been sliced or exposed to air.

Other methods such as covering with plastic wrap may reduce exposure to air but do not actively inhibit the enzymatic browning reaction. Freezing fruits can prevent browning but typically changes the texture and may not be practical for fresh consumption. Exposure to sunlight does not help; in fact, it may accelerate the browning process. Therefore, the use of acidic solutions is the most effective technique for maintaining the visual appeal and quality of cut apples and bananas.