Question

Which of the following can be used to prevent browning of cut fruits and vegetables?

• A. Water
• B. Sucrose
• C. Ascorbic acid
• D. Enzymes

Hint:

Lemon juice is effective at home because it contains both citric acid (lowers pH) and ascorbic acid (reduces quinones). In industry, sulfites were used, but ascorbic acid is the safer, label-friendly alternative.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question focuses on the methods used to inhibit enzymatic browning in fresh-cut produce. Enzymatic browning is a chemical reaction involving the enzyme Polyphenol Oxidase (PPO) that causes the formation of brown pigments (melanins) on the surface of cut fruits like apples or potatoes.
Key Formula or Approach:
To prevent browning, one must either eliminate the substrate (phenols), inactivate the enzyme (PPO), or remove oxygen from the system. Ascorbic acid (Vitamin C) works primarily as an antioxidant and a reducing agent.

Step 2: Detailed Explanation:

• Mechanism of Ascorbic Acid: When fruits are cut, phenols are oxidized to o-quinones by PPO in the presence of oxygen. Ascorbic acid acts by reducing these o-quinones back to their original phenol state before they can polymerize into brown melanin pigments.

• Secondary Effect: Ascorbic acid also lowers the pH of the surface environment. Since PPO has an optimum pH range (usually around 5.0 to 7.0), the acidic nature of ascorbic acid reduces the enzyme's catalytic activity.

• Other Options:
• Water: Can limit oxygen access slightly but is not a permanent chemical inhibitor.

• Sucrose: Used in candying or syrupping but is not the primary chemical agent for preventing browning in standard cut vegetables.

• Enzymes: Some enzymes (like proteases) might degrade PPO, but "enzymes" as a general category is incorrect as PPO itself is an enzyme that causes the problem.

Step 3: Final Answer:
Ascorbic acid is a widely used food additive and antioxidant specifically valued for its ability to stop the enzymatic browning reaction.