Question

Why the food product gelatine, derived from collagen has little nutritional value as a protein?

• A. Collagen is extremely low in many essential amino acids.
• B. Collagen is extremely low in many non essential amino acids.
• C. Collagen is rich in rare amino acids
• D. Collagen cannot be digested

Hint:

Nutritional quality of proteins is assessed using the PDCAAS (Protein Digestibility-Corrected Amino Acid Score). Gelatin has a PDCAAS of 0 because tryptophan is absent.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The nutritional value of a food protein depends on its digestibility and its amino acid profile.
Specifically, it must supply the essential amino acids that the animal body cannot synthesize endogenously in sufficient quantities.
A "complete" protein contains all essential amino acids in balanced proportions, whereas an "incomplete" protein lacks one or more essential amino acids.

Step 2: Detailed Explanation:
Gelatin is produced by the thermal denaturation or partial chemical hydrolysis of collagen, the main structural protein in connective tissues.
While gelatin is readily digestible, its amino acid profile is highly unbalanced:
It is rich in glycine (approx. \( 30\% \)), proline, and hydroxyproline.
It lacks the essential amino acid tryptophan completely.
It contains very low levels of other essential amino acids, particularly sulfur-containing amino acids like methionine, as well as isoleucine and threonine.
Because it lacks or contains low amounts of these essential amino acids, gelatin cannot serve as a primary protein source to support growth, tissue repair, or nitrogen balance. This limits its overall nutritional value as a protein.

Step 3: Final Answer:
Gelatin has low nutritional value as a protein because collagen is extremely low in several essential amino acids, particularly lacking tryptophan.