Starch is the polymerization of glucose molecules and the most common storage form of carbohydrates in cells. Starch, also known as starch powder in catering industry, has the general formula of (C6H 10O5)n, and the stage of hydrolysis to disaccharide is maltose, with the chemical formula of C 12H22O 1 1. Monosaccharide (glucose) was obtained after complete hydrolysis, and the chemical formula was C6H 12O6.

Starch includes amylose and amylopectin. The former is a spiral structure without branches; The latter consists of 24~30 glucose residues connected end to end by α- 1, 4- glycosidic bond, and the branch is α- 1, 6- glycosidic bond. Amylose is blue when exposed to iodine, while amylopectin is purple when exposed to iodine.

This is not a chemical reaction between starch and iodine, but the central hole of the starch spiral can just accommodate iodine molecules, and they form a blue-black compound through van der Waals force.

Extended data

Types of starch:

1, dough powder

Starch used for thickening, also known as dough powder, is a polysaccharide polymer concentrated by multiple glucose molecules. Cooking starch mainly includes mung bean starch, potato starch, wheat starch, water chestnut starch, lotus root starch, corn starch and so on. Starch is insoluble in water, and when heated to 60℃ with water, it is gelatinized into colloidal solution. Thickening is to use this characteristic of starch.

2. Mung bean starch

Mung bean starch is the best starch and seldom used. It is made by soaking mung beans in water, grinding and precipitating. Features: enough viscosity, small water absorption, white and shiny color.

3. Potato starch

At present, potato starch is widely used in families. It is made by grinding, washing and precipitating potatoes. The characteristics are: enough viscosity, fine texture, white color, luster better than mung bean starch, but poor water absorption.

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