How does lemon slow down browning of apple?

Lemon slows down the browning of Apples due to its high acidity and vitamin C content. The citric acid in lemon juice lowers the pH on the Apple's surface, inhibiting the activity of polyphenol oxidase, the enzyme responsible for browning. Additionally, vitamin C acts as an antioxidant, further reducing the oxidation process that leads to discoloration. This combination effectively preserves the Apple's appearance and freshness.