Question

Inulin like fructans are used as prebiotics as they are non digestible. Resistance to digestion in the upper GI tract results from:

• A. Absence of digestive enzyme in the upper GIT
• B. Beta configuration of anomeric C2
• C. Low pH of the stomach
• D. Presence of alpha-osidic linkages

Hint:

Human amylases break alpha bonds only; inulin is linked in the beta form.

Answer 1

The Correct Option is B

Step 1: Inulin is a fructan, a chain of fructose units joined mostly by beta(2 to 1) glycosidic bonds, usually with a terminal glucose. Prebiotics work because the upper gut cannot digest them, so they reach the colon to feed beneficial bacteria.
Step 2: Human digestive enzymes such as salivary and pancreatic amylase and the brush-border maltases act on alpha glycosidic bonds (as in starch). They cannot hydrolyse beta linkages.
Step 3: In inulin the fructose units are linked through the anomeric carbon of fructose, which is C2, in the beta configuration. Because the bond is in the beta form at the anomeric C2, no human enzyme can cleave it, so inulin passes undigested through the upper GI tract.
Step 4: Checking the distractors: option A is too vague and not the chemical reason; humans simply lack a beta-fructosidase, but the bond chemistry is the precise cause. Option C, low stomach pH, does not break these bonds and is not why it resists. Option D is wrong because the linkage is beta, not alpha; alpha linkages would in fact be digestible.
Step 5: The correct chemical reason is the beta configuration at the anomeric C2.
Answer: Option B (Beta configuration of anomeric C2).