D-mannose, a 6-carbon monosaccharide, is an isomer of glucose. It mainly exists in plants, microorganisms and animals in the form of mannan, hemicellulose and cellulose.

A small amount of free D-mannose exists in citrus, apple, peach and other fruits. Under normal conditions, the concentration of D-mannose in mammals is about 50 ~ 100 μ Mol / L, the concentration of mannose in human plasma shall not exceed 50 μ mol/L。

D-mannose enters cells mainly by means of hexose transport receptors on cell membrane. D-mannose entering the cell is catalyzed by hexokinase (HK) to produce mannose-6-phosphate (M6P), and then is catalyzed by phosphomannose isomerase (PMI) to produce fructose 6 phosphate, which is decomposed by glycolysis pathway (about 95 ~ 98%), or by phosphomannose mutase, PMM2) catalyzes the production of mannose 1 phosphate and participates in the protein glycosylation pathway (about 2%).

D-mannose has important physiological functions, such as promoting the balance of intestinal flora and promoting insulin secretion; D-mannose can also be used as a component of vitamin synthesis, antitumor drugs and immune regulation drugs. In addition, D-mannose has the characteristics of non-toxic side effects, strong sweetness and low calories. It is often used in food production as a food additive. Because of its many advantages and applications, D-mannose has attracted more and more attention and research.