Why do starch and iodine fade after heating and return to their original colors after cooling?

Starch is the polymerization of glucose molecules and the most common storage form of carbohydrates in cells. Starch, also known as starch in catering industry, is hydrolyzed into maltose in disaccharide stage, and monosaccharide (glucose) is obtained after complete hydrolysis.

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 a blue-black complex formed by the central hole of starch helix just enough to accommodate iodine molecules.

Iodine is extremely important to the life of animals and plants. Iodide and iodate in seawater enter the metabolism of most marine organisms. In advanced mammals, iodine is concentrated in the thyroid gland in the form of iodinated amino acids, and iodine deficiency can lead to goiter.

About two thirds of iodine and its compounds are used to prepare preservatives, disinfectants and drugs, such as tincture of iodine and iodoform chloroform. Sodium iodate as a food additive is not enough to supplement iodine intake. Radioisotope iodine-13 1 is used in radiotherapy and radioactive tracer technology. Iodine can also be used to make dyes and photographic films.

Extended data:

Starch is first decomposed into maltose by salivary amylase in human body, and then maltose is decomposed into glucose. Glucose is glycolytic to produce pyruvate, pyruvate; Or starch is directly decomposed into glycolytic intermediate glucose-1-P (this part has not been fully mixed with saliva). Then pyruvate is produced.

Pyruvate combines with enzyme to produce acetyl coenzyme A, and then enters citric acid cycle. Citric acid, sir. For every glucose consumed in the citric acid cycle, six NADH and two FADH2 (electron carriers) are produced. Then in the mitochondrial membrane structure, these electrons produce a lot of ATP and energy through ATPase.