Statement I: After cutting an apple or a banana, the colour of the cut surface becomes brown. Statement II: Polyphenolic compounds present in fruits get oxidized in air and show colour.

Statement I is true as fruits like apples and bananas undergo rapid discoloration when cut or bruised [4]. Statement II is also true and provides the correct explanation for this phenomenon. This process, known as enzymatic browning, occurs when the fruit's tissue is damaged, allowing the enzyme polyphenol oxidase (PPO) to come into contact with phenolic compounds. In the presence of oxygen from the air, PPO catalyzes the oxidation of these polyphenolic compounds into quinones. These quinones subsequently polymerize to form melanin, a dark brown pigment that causes the visible browning on the cut surface [4]. This reaction is a physiological response to injury and is a major factor in the quality degradation of fresh-cut produce [2].

Sources

1. [1] https://www.sciencedirect.com/topics/food-science/enzymatic-browning
2. [4] https://en.wikipedia.org/wiki/Food_browning
3. [2] https://pubmed.ncbi.nlm.nih.gov/35416745/