Method for preparing water soluble chitosan

Abstract

The process of preparing water soluble chitosan includes adding chitosan into 2-8 wt% concentration acetic acid aqua to compound acetic acid solution of chitosan of 2-10 wt% concentration, adding enzyme or oxidant to degrade chitosan to polymerization degree below 1000, cooling the solution to 0-10 deg.c, adding ethanol or methanol solution of acetic anhydride, stirring first at normal temperature for 2-24 hr and then at 20-40 deg.c for another 20-40 deg.c, adding alkali to regulate pH to over 8 under stirring, adding ethanol to deposit, centrifugation to obtain solid product, soaking in alcohol solution of KOH, centrifugation, alcohol washing, and drying to obtain water soluble chitosan of acetyl degree of 45-55%. The present invention has simple preparation process, and the product is used as material for tumor resisting and immunity raising medicine and health product and as additive for cosmetics and food.

Description

technical field [0001] The invention relates to a new method for preparing water-soluble chitosan (non-salt) with an acetylation degree of 45% to 55% and a polymerization degree of less than 1000. The method simplifies the preparation process of the water-soluble chitosan with a higher polymerization degree and reduces costs. Background technique [0002] Chitin is the second largest natural macromolecular polysaccharide after cellulose on the earth, but macromolecular chitin is insoluble in water and most common organic solvents, which limits its application, so chitin must be chemically modified. Chitosan is the deacetylation product of chitin. Generally speaking, when the degree of polymerization of chitosan is greater than 10, the water solubility is not good, but it can be dissolved in aqueous solutions such as acetic acid, formic acid, and hydrochloric acid. As a natural alkaline polysaccharide, chitosan has some unique functions, but its poor water solubility seriou...

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Problems solved by technology

[0003] It has been reported that the preparation methods of water-soluble chitosan with a higher degree of polymerization are as follows: the first method is to freeze chitin and deacetylate it with strong alkali [Sannan et al.Makromol.Chem., 1976,177:3589 -3600; Kurita et al.Makromol.Chem., 1978:3197-3202], but this method takes too long and requires the use of a large amount of acetone and ether; the second method is to mix chitosan in acetic acid-water- Methanol-pyridine uses acetic anhydride for acetylation reaction [Kurita et al.Chem.Lett., 1989:1597-1598], but the solvent is complex; the third method is to use NaBO 3 First degrade, then acetylate with acetic anhydride in a high-concentration (10%) acetic acid solution, but the amount of acetic anhydride is too large, about 8 to 9 times the molar number of amino groups in chitosan [Kubota et al.Carbohydrate Research, 2000,324:268-274.]; the fourth method is to use enzymes to degrade chitosan with an acetylation degree of 10-30%, and use the difference in the ability of the enzyme to recognize and cut different glycosidic bonds, and the acetylamino group in chitosan Inhomogeneous distribution of raw materials to prepare low molecular weight products, but the yield of water-soluble chitosan products with a degree of polymerization above 10 is generally less than 20% [Qin et al. International Journal of Biological Macromolecules, 2002, 31: 111-117.]