JPH0133482B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for purifying chitosan. In general, chitosan is a basic polysaccharide obtained by deacetylating chitin, which is the main component of crab shells. Chitin, the raw material for chitosan, is derived from invertebrates, especially marine crustaceans such as shrimp and crabs, as well as the outer shell components of terrestrial insects.
It is widely present in the outer skin components of molluscs and in the cell walls of fungi, and although its annual biosynthesis is estimated to be several billion tons, it is one of the resources that is hardly used. Shrimp, the most commonly used
The crab's outer shell component is a composite material consisting of chitin, protein, and calcium carbonate, and to make chitin, the protein must be removed with dilute alkali and the lime content must be removed with dilute acid. The chitin thus obtained is a polymer substance with a molecular weight of several hundreds of thousands of N-acetylglycosamines connected in series with β-1,4 bonds. When this chitin is deacetylated by heating in the presence of 40-50% concentrated alkali, chitosan is obtained. However, it still retains the remains of its shell, has a very strong crab shell odor, and also retains the pale red pigment derived from its shell. Conventionally, chitosan has been widely used as a flocculant for various dispersions due to its strong cohesive force. In addition, in recent years, chitosan is expected to have pharmacological effects, and its use as a medicine has been studied. Therefore, the presence of impurities and the degree of purification become a problem, and in some cases, their usefulness may be affected. However, chitosan itself has a very strong aggregation effect, making purification difficult and making it impossible to obtain a pure product in large quantities. The present inventors conducted extensive research in search of a method for industrially purifying chitosan in large quantities, and found that if salt is present in the chitosan solution, chitosan will precipitate even in the presence of various impurities. I learned that. In addition, in the present invention, chitosan precipitates due to the presence of salt are separated and dissolved well in acid, so if the chitosan solution is made into a chitosan solution again and salt is present to precipitate chitosan, the purification can be significantly improved. It is possible to obtain chitosan produced by The present invention is a method for purifying chitosan, which is characterized by adding a salt to a chitosan-containing liquid, adjusting the pH to a level that causes precipitation if necessary, and producing a precipitate. In addition, the present invention includes adding a salt to the chitosan-containing liquid, adjusting the pH to a level that causes precipitation if necessary, washing the obtained precipitate as necessary, and dissolving the precipitate in an acid. This is a unique chitosan purification method. In addition, the present invention adds a salt to the chitosan-containing liquid, adjusts the pH to a level that causes precipitation as necessary, washes the obtained precipitate with water as necessary, dissolves the precipitate in acid, and precipitates. The precipitate obtained is washed as necessary, the precipitate is dissolved in acid again, and the above precipitation-washing-dissolution operation is repeated if necessary. This is a method for purifying chitosan. The chitosan-containing liquid that can be applied to the purification method of the present invention can be a deacetylated treatment liquid that contains many impurities. The salt added to the chitosan-containing solution is one or more salts including the following salts. Namely, hydrochlorides such as potassium chloride, sodium chloride, calcium chloride, ammonium chloride, nitrates such as potassium nitrate, sodium nitrate, acetates such as sodium acetate, sulfates such as dipotassium sulfate, ammonium sulfate, calcium sulfate, copper sulfate, Examples include phosphates such as dipotassium phosphate, monopotassium phosphate, disodic phosphate, and monosodium phosphate. Any amount of salt can be added as long as it is in a dissolved state, but it is preferable to add salt to the chitosan-containing liquid.
It is about 0.5 to 50%, more preferably about 2 to 40%. Depending on the type of salt added, the pH will be 7 or more, so in this case, chitosan will precipitate without adjusting the pH, so the precipitate can be separated. If precipitation does not occur even after adding salt, it is preferable to adjust the pH to 7 to 9, more preferably around 8.5, using an alkali such as caustic soda. Addition of salt to chitosan-containing liquid and optionally pH7
By carrying out the adjustment in steps 9 to 9, chitosan, which did not easily precipitate due to the interference of impurities, will precipitate and separate from the impurities. This precipitate can be easily separated by centrifugation or filtration with a filter cloth. Considering that chitosan has traditionally been purified with extremely low yields by methods such as gel filtration, it is extremely surprising that chitosan can be completely precipitated just by adding salt. . Since the separated precipitate contains a large amount of salt,
This is washed with water or a solvent to desalt it, and then dissolved in an acid. The acid may be any acid such as an organic acid such as acetic acid or an inorganic acid such as hydrochloric acid or sulfuric acid, and the concentration is preferably about 0.01 to 3 mol. After dissolving the precipitate in acid, it is easy to precipitate by simply treating it at a pH of around 7 to 9.
Add alkali such as caustic soda, pH 7 to 9,
Preferably, the pH is adjusted to 8.5 to obtain a precipitate. For further purification, the precipitate can be obtained by washing the precipitate with water or the like, dissolving it again in acid, and adjusting the pH to 7 to 9. This purification process can be repeated any number of times, making it possible to obtain almost pure chitosan. Next, test examples and examples of the present invention will be shown. Test example: Dissolve 25 g of commercially available chitosan in 0.5 mol of acetic acid 5, prepare 20 bottles of 100 ml each, add the salt in Table 1, adjust the pH in Table 1, and measure the amount of precipitate. did. The results obtained are shown in Table 1. Recovery rate in Table 1 = Dry weight of precipitate/Dry weight of dissolved chitosan (10
(in 0ml)

【table】

[Table] Example 1 50 g of commercially available chitosan was dissolved in 0.5 mol of acetic acid 10, and insoluble materials were removed by centrifugation (20000G).
The resulting clear liquid was divided into 5 portions each of A and B. 1.5 kg of sodium acetate was added to A and dissolved. The resulting precipitate was collected on a Saran cloth, thoroughly washed with water to remove soluble materials, and then dried to obtain 20 g of white powdered chitosan. Similarly, 1.5 kg of sodium acetate was added to B and dissolved therein. Next, the pH was adjusted to 7.5 with 40% caustic soda. The resulting precipitate was collected on a saran cloth, thoroughly washed with water to remove soluble materials, and dried to obtain 23 g of white powder chitosan. Example 2 100 g of commercially available chitosan was dissolved in 0.5 mol of acetic acid 10, undissolved matter was removed by centrifugation (20,000 G), and 3 kg of common salt was added and dissolved in the resulting clear liquid. The pH was then adjusted to 8.5 using 40% caustic soda. The resulting precipitate was collected by centrifugation, further dialyzed, and then dried to collect 94 g of white powdered chitosan. Example 3 3 kg of well-washed and dried snow crab shells were prepared using a known method (Makromol.Chem.vol.177 3589 (1976))
Approx.
Obtained 800g. 50 g of this crude chitosan was dissolved in 0.5 mol of acetic acid 10, and undissolved matter was removed by centrifugation. 500 g of ammonium sulfate was added to and dissolved in the resulting clear liquid. then 40
% caustic soda was used to adjust the pH to 8.5. The resulting precipitate was collected by centrifugation. This precipitate was then dispersed in water to remove ammonium sulfate. Furthermore, the desalted precipitate was dissolved in 0.5 mol of acetic acid, and the pH was adjusted to 8.5 with 40% caustic soda. The resulting precipitate was collected on a saran cloth and washed with a large amount of water to remove soluble materials. After washing, the precipitate was dried to obtain 44.4 g of odorless chitosan in the form of a white powder. Table 2 shows the properties and analytical values of the crude and purified products. The colors in the table were measured with a colorimeter manufactured by Nippon Denshoku Kogyo Co., Ltd. and expressed as L, a, and b. The degree of residual crab shell odor was determined by a sensory test. The glucosamine content was calculated by hydrolyzing each chitosan with 4N hydrochloric acid and then measuring by the Elson-Morgan method, and expressed as a percentage of dry matter.

[Table] As is clear from the table, the lightness (L) increases, red (a) decreases, yellow (b) also decreases, and the overall color becomes white. The fragrance has also become odorless. The glucosamine content also increased, and almost pure chitosan containing almost no impurities was obtained.

Claims (1)

[Scope of Claims] 1. A method for purifying chitosan, which comprises adding a salt to a chitosan-containing liquid and adjusting the pH to a level that causes precipitation, if necessary, to generate a precipitate. 2. Chitosan-containing solution characterized by adding a salt to a chitosan-containing liquid, adjusting the pH to a level that causes precipitation if necessary, washing the obtained precipitate as necessary, and dissolving the precipitate in an acid. Purification method. 3 Add salt to the chitosan-containing liquid, adjust the pH to a level that causes precipitation if necessary, wash the obtained precipitate with water as necessary, dissolve the precipitate in acid, and adjust the pH to a level that causes precipitation. A method for purifying chitosan, which comprises washing the obtained precipitate as necessary, dissolving the precipitate again in acid, and repeating the above precipitation-washing-dissolution operation if necessary.