Question

Cereal starches usually contain ____ amylose and \rule{1cm}{0.15mm} amylopectin.

• A. 25% and 75%
• B. 45% and 55%
• C. 55% and 45%
• D. 65% and 35%

Hint:

Native starches are always "Amylopectin Heavy." Think of Amylopectin as the main body ($75$%) and Amylose as the functional minority ($25$%).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the typical ratio of the two glucose polymers, amylose and amylopectin, that constitute native starch granules in cereal grains like wheat, rice, and corn.

Step 2: Detailed Explanation:

• Composition of Starch: Native starch is a mixture of two polysaccharides:
- Amylose: A primarily linear polymer with $\alpha$-1,4 linkages. It is responsible for gelation.
- Amylopectin: A highly branched polymer with $\alpha$-1,4 and $\alpha$-1,6 linkages. It is responsible for thickening.

• Cereal Starch Ratio: In the vast majority of cereal grains (normal corn, rice, wheat), the ratio is consistently around $20$ to $30$% amylose and $70$ to $80$% amylopectin. Option (A) $25:75$ is the most accurate representation of this average.

• Special Varieties:
- Waxy varieties (like waxy corn) contain $99$ to $100$% amylopectin.
- High-amylose varieties (like amylomaize) can contain $50$ to $70$% amylose.

• Significance: This ratio determines how the starch behaves when cooked; higher amylopectin makes a paste viscous and stable, while higher amylose makes it form a firm gel upon cooling.

Step 3: Final Answer:
The standard ratio for cereal starches is 25% amylose and 75% amylopectin.