Key Enzyme in Enzymatic Browning of Fruits and Vegetables

Enzymatic browning is a common reaction that occurs in many fruits and vegetables when they are cut or bruised. This process leads to the brown discoloration often seen on surfaces of apples, bananas, potatoes, and avocados, among others.

This browning reaction is caused by enzymes present in the plant tissue. When the tissue is damaged, these enzymes come into contact with substrates (phenolic compounds) and oxygen, initiating a series of chemical reactions.

The primary enzyme responsible for initiating this enzymatic browning process is Polyphenol oxidase (PPO). PPO catalyzes the oxidation of monophenols and o-diphenols into o-quinones. These o-quinones are highly reactive compounds that then polymerize non-enzymatically to form brown pigments, which are the visible sign of browning.

Let's look at the options provided:

• Peroxidase: Peroxidase is another enzyme found in plants, but its main role is typically not the primary cause of enzymatic browning. It uses hydrogen peroxide to catalyze oxidation reactions, but PPO is the key player in the browning initiated by cutting.
• Polyphenol oxidase: As explained above, this is the enzyme that directly oxidizes phenolic compounds, leading to the formation of brown pigments. It is widely recognized as the main enzyme responsible for enzymatic browning in most fruits and vegetables.
• Catalase: Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. It is involved in protecting cells from oxidative damage but is not the enzyme that causes browning.
• Cholesterol oxidase: This enzyme oxidizes cholesterol and is primarily found in microorganisms or animal tissues. It is not involved in the browning of fruits and vegetables.

Therefore, Polyphenol oxidase is the key enzyme involved in the enzymatic browning of fruits and vegetables.