Question

Which enzyme is primarily responsible for the de-greening of citrus fruits during ripening?

• A. Pectinase
• B. Chlorophyllase
• C. Polygalacturonase
• D. Phenylalanine ammonia-lyase (PAL)

Hint:

De-greening literally means the removal of "chlorophyll." The enzyme that hydrolyzes and breaks down this pigment is logically named "chlorophyll-ase."

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the specific enzyme responsible for breaking down the green chlorophyll pigment in the peel of citrus fruits during ripening, a process known as de-greening.

Step 2: Detailed Explanation:

• The De-greening Process: Unripe fruits are green due to high concentrations of chlorophyll in their plastids. As fruits ripen, chlorophyll is degraded, unmasking underlying yellow/orange carotenoid pigments.

• Role of Chlorophyllase: Chlorophyllase (specifically chlorophyll chlorophyllido-hydrolase) is the key enzyme that initiates this degradation pathway. It catalyzes the hydrolysis of the ester bond in chlorophyll to remove the hydrophobic phytol tail, producing water-soluble chlorophyllide. This is the first step in the breakdown of green pigments.

• Why Other Enzymes are Incorrect:

• Pectinase and Polygalacturonase: These are cell-wall hydrolases that break down pectin, leading to cell wall degradation and fruit softening, not pigment changes.

• Phenylalanine ammonia-lyase (PAL): An enzyme involved in the phenylpropanoid pathway, which is responsible for synthesizing phenolic compounds, flavonoids, and anthocyanins (red/blue pigments), not for degrading green chlorophyll.

Step 3: Final Answer:
Chlorophyllase is the primary enzyme responsible for degrading chlorophyll during fruit de-greening, making option (B) the correct choice.