Starch: A polysaccharide, which is a nutrient stored in plants. It mainly exists in seeds and tubers. It is a colorless and odorless white powder with a density of1.499 ~1.513. It is hygroscopic. It consists of amylose (starch granules) and amylopectin (starch cortex). Their proportion in starch varies with plant species.

Amylose is a chain compound formed by combining glucose with α- 1, 4- glycoside bond, which can be hydrolyzed into maltose by amylase. The content of starch is about 10~30%. Soluble in hot water, no paste. Blue in iodine.

Glucose molecules in amylopectin are linked by α- 1, 4- glycosidic bond, and some are linked by α- 1, 6- glycosidic bond. So there are branches, about 20 glucose units have one branch, and only the peripheral branches can be hydrolyzed into maltose by amylase. Insoluble in cold water, it swells into paste in hot water. It will turn purple or reddish purple when it meets iodine.

Starch can be gradually decomposed by amylase or acid, and the process is as follows: starch → red dextrin → colorless dextrin → maltose → glucose (red in iodine) (not colored in iodine).

So starch can be regarded as a high polymer of glucose. Starch can not only be eaten, but also be used to make dextrin, maltose, glucose and alcohol lamp, and can also be used to prepare printing paste, textile sizing, paper sizing and pharmaceutical tabletting. It can be extracted from starch-containing substances such as corn, sweet potato, wild acorn and pueraria lobata.

Starch indicator: refers to the soluble starch solution used to indicate the end point in iodine titration. In the presence of iodine ions, soluble starch can react with a very small amount of iodine to form blue adsorption compounds. Very sensitive reaction.

Soluble starch: starch derivatives obtained by treating starch with oxidants, acids, glycerol, enzymes or other methods. White or light yellow powder. Tasteless and odorless. Density 1.5. Insoluble in cold water, ethanol and ether. Dissolve or disperse in boiling water. 1% colloidal solution is a transparent emulsion liquid. The adhesion is very small. Used for paper sizing, textile sizing, chemical indicator and protective colloid.

Water starch is wet starch, that is, starch added with water, which is generally used for cooking or extruding starch for the first time. Water starch is a liquid made by adding water to starch or raw flour.