Question

______ is essentially free from methyl ester groups.

• A. Pectin
• B. Pectic acid
• C. Pectinic acid
• D. Protopectin

Hint:

As fruits over-ripen, pectin is degraded into pectic acid by pectin methylesterase. This loss of methyl ester groups destroys the gelling property with sugar and acid, explaining why over-ripe fruits do not set well into jams.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Pectic substances are complex structural polysaccharides found in the primary cell walls and middle lamellae of plant tissues, composed primarily of \(\alpha\)-(1,4)-linked D-galacturonic acid residues.
These substances vary widely in their solubility and degree of methylation (esterification with methanol at the C-6 carboxyl groups).

Step 2: Detailed Explation:
The nomenclature of pectic substances is based on their structural characteristics:
- Protopectin: The water-insoluble, highly methylated parent pectic substance found in unripe fruit that gives rigid structure.
- Pectinic acid: A soluble colloidal polygalacturonic acid chain containing more than 7% methyl ester groups, capable of gelation.
- Pectin: A general term for soluble pectinic acids of varying methyl ester content that can form gels under proper conditions.
- Pectic acid: A de-esterified polygalacturonic acid substance containing virtually no methyl ester groups (essentially free of methyl ester groups).
During fruit ripening, enzymes like pectin methylesterase (PME) hydrolyze the methyl ester linkages of pectin, releasing methanol and converting the molecules into pectic acid.
Pectic acid contains free carboxyl groups (\(-COOH\)), making it incapable of forming sugars-acid gels, though it can form gels in the presence of divalent cations like calcium.

Step 3: Fil Answer:
Pectic acid is the fully de-esterified form of pectin and is essentially free from methyl ester groups.
Hence, the correct option is (B).