Chitosan is a biological material that is biocompatible with the human body. Compared with cellulose, it contains amino groups, in addition to the physiological functions of general dietary fiber, but also due to different structures, that is, the degree of deacetylation and molecular weight, it produces various physiological activities in the body, making chitosan and Its derivatives in food and medical chitosan are a kind of biological materials, which are biocompatible with the human body. Compared with cellulose, it contains amino groups, in addition to the physiological functions of general dietary fiber, but also due to different structures, that is, the degree of deacetylation and molecular weight, it produces various physiological activities in the body, making chitosan and Its derivatives have important application value in the fields of food and medicine.

There have been a lot of reports that chitosan can reduce cholesterol and fat levels in serum and liver tissues. The mechanism of this reduction is not very clear. It is speculated that chitosan may embed the micelles containing cholesterol. When chitosan reaches the small intestine, it will precipitate out, thus preventing the absorption of cholesterol in the small intestine. Chitosan blocks the conversion of cholesterol in the colon to steroids, which leads to an increase in cholesterol levels in the stool, which lowers the levels in serum and liver. Surprisingly, chitosan does not cause an increase in the concentration of bile acids in feces, and like other anticholesterol drugs such as cholestyramine, hypolipidemic drug No. 1, diethylamine ethyl dextran, are Alkaline cation exchanger, combined with bile acids, thereby increasing the excretion of bile acids in feces. But when chitosan precipitates in the intestine, it releases bile acids, but not cholesterol. At the same time, the blood lipid-lowering effect of chitosan is often enhanced by ascorbic acid, which has a synergistic effect with each other. When the mixture of chitosan and ascorbic acid reaches the stomach, chitosan will mix and emulsify dietary fat in the stomach. This emulsification process is effectively catalyzed by ascorbic acid. When this emulsified product enters the intestinal tract, the fatty oil droplets are encapsulated in the gelatinized chitosan matrix and are excreted in the feces without sufficient absorption. This characteristic of chitosan makes it play an important health role in weight loss, preventing high blood pressure, protecting the liver and so on. Because of this, the health products developed on the market based on this physiological activity appeared earlier and more.

Chitosan, especially chitosan with a degree of deacetylation (DD) of 70%, can promote nonspecific host resistance to E. coli and virus infection in mice. They believe that 70% DD chitosan is an immunomodulator that can activate peritoneal macrophages and neutral killer cells in guinea pigs, increase antibody production, increase delayed-type hypersensitivity, increase cytotoxicity in mice, and induce Cell division of interleukins, proliferation factors and interferons. This immunomodulatory effect increases with increasing water solubility, and it is confirmed that chitosan oligosaccharides can inhibit tumor growth by increasing immune function.

Chitosan can inhibit the growth of fungi and microorganisms, especially plant pathogenic bacteria. Chitosan can induce plants to produce defensive enzyme system-chitosanase, and exert antibacterial activity. Since chitosan is positively charged, its antibacterial activity is higher than that of chitin. Chitosan oligosaccharides with higher degree of polymerization have a greater inhibitory effect on fungi and bacteria than chitosan itself and chitosan oligosaccharides with low degree of polymerization. It has been reported that chitosan oligosaccharides have stronger bacteriostatic effects than chitosan and increase with the degree of deacetylation. The antibacterial properties of chitosan and its oligosaccharides are very beneficial to the development of food preservatives and antiseptic preservatives for food processing. Therefore, chitosan and its oligosaccharides are a kind of promising functional food additives.

Chitosan chelates metal ions. It is generally believed that when calcium or iron ions reach the intestine, absorption is reduced due to the formation of argon oxide precipitation. Chitosan can bind iron and calcium ions at low pH, so that when metal ions reach the intestine, they are absorbed through the intestinal wall in a soluble state. In order to make chitosan soluble under alkaline conditions and have strong chelating ability, this experiment modified chitosan to introduce a certain degree of carboxymethyl group. This derivative can chelate iron and iron under alkaline conditions. Calcium ions are in a soluble state, thereby increasing the absorption of these ions on the intestinal wall. This effect is similar to the casein phosphopeptide (CPP), a hydrolysate of cow cheese protein. Chitosan oligosaccharides are water soluble and increase the absorption of calcium and other minerals in the body.