Sugar is a general term for polyhydroxyketones or polyhydroxyaldehydes and their derivatives. Sugar molecules contain three elements: carbon, hydrogen and oxygen, and most of the time we call them carbohydrates. According to the molecular weight of sugar, sugar can be divided into monosaccharide, oligosaccharide and polysaccharide.

Monosaccharide is the smallest unit of sugar and the basic unit of sugar and its derivatives, mainly including glucose, fructose, galactose, deoxyribose and ribose. Monosaccharide cannot be hydrolyzed further.

Oligosaccharides are sugars composed of 2~9 monosaccharides connected by chemical bonds. According to the number of monosaccharides, oligosaccharides can be divided into disaccharide, trisaccharide, tetrasaccharide and so on. Naturally occurring oligosaccharides consist of 2~4 monosaccharides.

Disaccharides mainly include sucrose, maltose and lactose. Trisaccharides are mostly composed of sucrose as the basic structural unit and then connected with other monosaccharides, such as raffinose; Tetrasaccharide continues to extend on the structure of trisaccharide, such as stachyose.

Plant polysaccharides include cellulose, starch, bacterial polysaccharides, mucus, etc. Among them, cellulose contributes to gastrointestinal peristalsis, and starch is a substance for storing nutrients in plants.

Plant polysaccharides include cellulose, starch, bacterial polysaccharides, mucus, etc. Among them, cellulose contributes to gastrointestinal peristalsis, and starch is a substance for storing nutrients in plants.