Why does lemon juice affect an apple from turning brown?

Lemon juice prevents an apple from turning brown due to its acidic nature. Apples contain a compound called polyphenol oxidase (PPO), which is responsible for the browning reaction when exposed to oxygen. PPO is activated when the apple is cut or bruised, causing the release of enzymes that convert phenols into brown pigments called melanin.

Lemon juice contains citric acid, which is a natural acid. When the acidic lemon juice comes into contact with the apple, it lowers the pH of the apple's surface, creating an acidic environment. The acidic environment inhibits the activity of PPO, preventing the conversion of phenols into melanin. As a result, the apple retains its original color and does not turn brown.

Additionally, lemon juice also acts as an antioxidant, which helps to slow down the oxidation process and further prevents browning. The antioxidant properties of lemon juice contribute to its ability to maintain the freshness and color of the apple.

It's important to note that the effectiveness of lemon juice in preventing browning may vary depending on the type of apple and the amount of lemon juice used. Some apple varieties may be more prone to browning than others, and using a sufficient amount of lemon juice is essential to achieve the desired effect.