Starch is a kind of high molecular carbohydrate, which is polymerized by glucose molecules. Its basic unit is α-D- glucopyranose, and its molecular formula is (C6H10O5) n N. 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.

Carbohydrate consists of three elements: carbon, hydrogen and oxygen. It is the most abundant organic compound with broad-spectrum chemical structure and biological function in nature. It can be represented by the general formula CX (H2O) y. Because it contains two to one hydrogen and oxygen like water, it is called carbohydrate. It can provide heat energy for human body. Carbohydrates in food are divided into two categories: effective carbohydrates that people can absorb and utilize and ineffective carbohydrates that people can't digest. Carbohydrate is the main source of energy needed by all living things to maintain life activities. It is not only a nutrient, but also some of them have special physiological activities.

chemical composition

Carbohydrates are composed of three elements: C, H and O. The ratio of H and O in molecules is usually 2: 1, which is the same as that in water molecules, so they are called carbohydrates. It can be represented by the general formula Cm(H2O )n n n. Therefore, such compounds were once called carbohydrates. However, it was later found that some compounds should belong to saccharides according to their structures and properties, but their compositions did not conform to the general formula of Cm(H2O )n, such as rhamnose (C6H 12O5) and deoxyribose (C5H 10O4). However, some compounds, such as formaldehyde, acetic acid (C2H4O2) and lactic acid (C3H6O3) conform to the general formula Cm(H2O )n, but their structures and properties are completely different from those of carbohydrates. So the name carbohydrate is not exact, but it existed a long time ago and is still in use today. [6] (In addition, carbonic acid (H2CO3), carbonate (XXCO3), simple carbon (C), carbon oxides (CO2, CO) and water (H2O) are not organic substances, that is, they are not carbohydrates.

Carbohydrates in food can be divided into two categories: effective carbohydrates that people can absorb and utilize, such as monosaccharides, disaccharides, polysaccharides and ineffective carbohydrates that people can't digest, such as cellulose.