Question

The chemical linkage(s) between the $\beta$-D-glucopyranose residues in the structure of $\beta$-glucans isolated from different sources such as cereals, mushroom, bacteria and yeast could be:

(A). Both $\beta$-(1,3) and $\beta$-(1,6)
(B). Both $\beta$-(1,3) and $\beta$-(1,4)
(C). $\beta$-(1,3) only
(D). Both $\beta$-(1,4) and $\beta$-(1,6)

Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (C) only.
• D. (B) and (D) only.

Hint:

Remember that cereal \(\beta\)-glucans are highly water-soluble due to their mixed \(\beta\)-(1,3) and \(\beta\)-(1,4) linkages, which disrupt the crystalline structure of the polysaccharide chain.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
\(\beta\)-glucans are diverse, non-starch polysaccharides consisting of D-glucopyranose polymers linked by \(\beta\)-glycosidic bonds. Their physical properties depend on their source organism.

Step 2: Detailed Explanation:
The structures of \(\beta\)-glucans vary depending on the biological source:
- (A) Fungal and yeast \(\beta\)-glucans (e.g., from mushrooms and Saccharomyces cerevisiae) consist of a \(\beta\)-(1,3)-linked backbone with \(\beta\)-(1,6)-linked side branches. Thus, statement (A) is correct.
- (B) Cereal \(\beta\)-glucans (e.g., from barley and oats) are unbranched linear chains containing both \(\beta\)-(1,3) and \(\beta\)-(1,4) linkages. Thus, statement (B) is correct.
- (C) Some bacterial \(\beta\)-glucans (such as curdlan produced by Agrobacterium) are linear homopolymers containing only \(\beta\)-(1,3) glycosidic linkages. Thus, statement (C) is correct.
- (D) \(\beta\)-(1,4) and \(\beta\)-(1,6) combinations are not typically found in natural \(\beta\)-glucans.
Therefore, the possible chemical linkages in isolated \(\beta\)-glucans include (A), (B), and (C).

Step 3: Final Answer:
Hence, the correct option is (B), containing (A), (B), and (C) only.