It is commonly known that freshly cut fruits turn a brownish color when exposed to the air for a number of minutes. This is due to the action of the enzyme polyphenoloxidase. It is also well known that the formation of the brown color can be prevented or slowed by chilling the fruit, boiling it, or rubbing it with lemon juice (which contains ascorbic acid). Explain why each of these methods works to slow down the browning process.
Chilling the fruit works to slow down its browning by reducing the activity of the enzyme polyphenoloxidase. Lower temperatures inhibit the enzyme's ability to catalyze the oxidation reaction, which is responsible for the browning of the fruit.
Boiling the fruit works to slow down its browning by denaturing the enzyme polyphenoloxidase. The high temperature of boiling causes the enzyme to lose its structure and functionality, preventing it from catalyzing the browning reaction.
Rubbing the fruit with lemon juice works to slow down its browning by providing ascorbic acid. Ascorbic acid acts as an antioxidant and inhibits the oxidation reaction, which is responsible for the browning of the fruit. By applying lemon juice, which contains ascorbic acid, the browning process is slowed down.