Question

Which of the two components of starch is water soluble?

Answer 1

Hint: The solubility of the components is mainly influenced by the branching of the polymer chain. The more branched component of glucose will be water insoluble. And, the linear chain polymer of glucose will be water soluble.

Complete step by step solution:
- Starch can be defined as an $\alpha$- polymer of glucose.
- Starch is also known by the name - amylum.
- Starch is a polymeric carbohydrate that consists of numerous glucose units joined by glycosidic bonds.
- Starch is seen as a white powder which is tasteless and odourless in nature.
- Amylose and amylopectin are the two components of starch.
- Amylopectin is basically a branched chain polymer of $\alpha$-D glucose. Starch generally consists of 75 – 80 % of amylopectin. Amylopectin is actually the water insoluble component of starch.
- Amylose is basically the linear chain polymer of glucose.Starch generally consists of 20 – 25 % of amylose. Amylose is actually the water soluble component of starch.
- Hence, out of the two components of starch, amylose is the water soluble component.

Additional Information:
- Most green plants store the extra glucose present as starch. Starch is stored in the form of starch granules called amyloplasts.
- Starch is actually the most common carbohydrate in our diet. It is contained in many staple foods.
- Starch is also used as an additive for food processing,
- Starch has many industrial applications like paper making, glue making etc.

Note: Amylose is the water soluble component because of its linear nature. It is important to note that it was recently discovered that amylose is not completely unbranched. Some of its molecules do contain some branch points.