KR0159971B1 - A process for preparing a biomedical grade low nolecular weight chitosan - Google Patents

Abstract

The present invention is a high-molecular weight chitosan with a deacetylation degree of 90% or more and reacted with NaBO ₃ for 30 minutes to 30 hours at a temperature of 30 to 80 ℃, washed and filtered for 1 to 3 days in an organic solvent solution The present invention relates to a chitosan molecular weight lowering and control method for producing a low molecular weight chitosan having a molecular weight of 2,000 to 10,000, including dipping, filtration and drying. It can be produced in high yield and the low molecular weight chitosan obtained has excellent whiteness and is suitable for food and medicine.

Description

Method for preparing low molecular weight chitosan of biomedical grade

1 and 2 are graphs comparing the whiteness of low molecular weight chitosan prepared according to the present invention with TiO ₂ standards.

The present invention provides a method for preparing low molecular weight chitosan of biomedical grade, specifically, high molecular weight chitosan having a deacetylation degree of 90% or higher by treating with sodium perborate (NaBO ₃ ) to obtain high molecular weight and high deacetylation of low molecular weight. The present invention relates to a method for preparing biomedical grade chitosan with high degree of whiteness and high whiteness.

Chitin is a natural polymeric material that can be extracted from wastes of crustaceans, including shrimps and crabs, and chitosan is a water soluble polymeric material that can be readily obtained by deacetylating chitin. Chitin is generally water insoluble, and thus has difficulty in utilization, and water-soluble chitosan is more usefully used industrially.

In the 1970s, when the application range of chitin / chitosan became known, attempts to obtain high-purity chitin / chitosan from crustacean waste and to artificially synthesize its derivatives have been the mainstream of research and development. The production of chitin / chitosan from crustacean shells includes the removal of calcite by HCl aqueous solution and the removal of protein by NaOH aqueous solution, and the binding of glucosamine units constituting chitin / chitosan to hydrolysis during HCl treatment. Since the deterioration of the molecular weight is inevitably accompanied by the lowering of the molecular weight and the lowering of the molecular weight even during NaOH treatment, the attention has been mainly focused on preventing the rapid lowering of the molecular weight to obtain high purity and high molecular weight chitin / chitosan.

However, in the early and mid 1980's, when special and diverse applications of chitin / chitosan were revealed and the scope of application began to expand, more efforts were made to develop chitin / chitosan for each unique use rather than simple high molecular weight chitin / chitosan. The direction is reversed. Chitin / chitosan, which is suitable for a high-performance application, means chitin / chitosan characterized by its purity, degree of deacetylation, molecular weight, crystallinity, and the like.

Among the various applications of chitin / chitosan that have been revealed so far, the fields showing commercialization and industrialization potential include agriculture, wastewater treatment, health care, textile industry, pharmaceuticals, and food. Important factors that determine the application of chitin / chitosan are, in particular, purity, molecular weight and the type of shell from which they are derived.

First of all, in terms of purity, high purity products are not required in agriculture and wastewater treatment, but high purity biomedical grades are required in health care and pharmaceutical fields, and the intermediate grades of both fields are used in textile industry and food application. It can be used efficiently.

In addition, the average molecular weight of the chitin / chitosan not only affects its physical stability but also affects the crystallinity, the higher the molecular weight can be efficiently used in applications requiring the strength of the chitin / chitosan. In the field of textile industry and membranes, in most cases, the molecular weight is advantageous, while in the health care field, where human fitness is the most important, a relatively low molecular weight product is required because the molecular weight is too low. In the pharmaceutical field, it is essential that the low molecular weight chitin / chitosan is easily absorbed into the cell and thus exhibits its own pharmacological action.

In the pharmaceutical field, chitin / chitosan is known to express pharmacological action in the 2,000 to 20,000 molecular weight field, and it is reported that pharmacological action increases when most of the molecular weights are approximately 10,000 or less. In food-related applications, food preservatives, emulsifiers, cholesterol lowering agents and the like are the most important applications. In this field, low molecular weight chitosan with a molecular weight of approximately 10,000 or less is known to exhibit excellent efficacy.

In addition to purity and average molecular weight, the type of shellfish derived from chitin / chitosan has been discussed as a factor influencing the intrinsic properties of chitin / chitosan. Even chitin / chitosan having the same chemical composition and the same molecular weight can be subdivided into α, β, and γ types in crystal structure, and the degree of crystallinity will be different.The physical properties including crystallinity are different depending on the type of crust from which chitin / chitosan is derived. Totally different chitin / chitosan has been obtained. Chitin / chitosan obtained from crab shells has high crystallinity and hardness, and thus is low in human fitness, whereas those obtained from shrimp shells or shellfish have been found to have excellent human fitness because of relatively low crystallinity and softness.

By the mid-1980s, the market for health care, pharmaceuticals, and foods expanded, focusing attention on the production of low molecular weight chitin / chitosan rather than high molecular weight chitin / chitosan. When preparing a solution by dissolving high molecular weight chitin / chitosan, it is difficult to prepare a high concentration of chitin / chitosan solution because not only dissolution itself is difficult but also the viscosity of the chitin / chitosan solution becomes large, but in the case of low molecular weight chitosan, it is very dissolved. It is easy to use low molecular weight chitosan in that it is easy to prepare a high concentration of chitosan solution because it is easy and the viscosity of the solution in which chitosan is dissolved does not become large.

Prior methods for producing low molecular weight chitosan include the following methods. First, as the simplest method, when decalcification from crab shellfish or shrimp shellfish, treatment with HCl for a long time in a high concentration of HCl aqueous solution at high temperature causes the cleavage of molecular chains by HCl, followed by protein removal to obtain low molecular weight chitin and subsequently It is a method of deacetylating and obtaining low molecular weight chitosan. However, this method can be pointed out that the manufacturing process is not only complicated, but also high purity chitin / chitosan can not be obtained and the production yield is extremely low. In addition, in this method, the principle of low molecular weight of chitosan is to break down the binding of glucosamine units by HCl. Therefore, the low molecular weight reaction is easy to be carried out only by applying a high concentration of HCl aqueous solution of 4N concentration or higher for a long time, and under such extreme conditions, As a result of the cleavage of irregular molecular chains, not only low molecular weight chitosan having a very wide molecular weight distribution range is obtained, but also low reproducibility of the low molecular weight chitosan obtained, and the cleavage of the chitin molecular chain is a chitin oligomer state (polymerization degree 6-7 or less). As a result, the yield of low molecular weight chitosan is relatively low, and the manufacturing process is very complicated. In addition, in this method, it is impossible to obtain a product having excellent whiteness because the chitin molecular chain is irregularly destroyed by high concentration of HCl treatment during decalcification.

Another method to obtain low molecular weight chitosan is to cut the molecular chain of a previously prepared high molecular weight chitosan (hereinafter referred to as starting chitosan). The method of cutting the molecular chain is to use chemical reagents and strains. There are two ways. The method using dual chemical reagents is mainly used, which dissolves the starting chitosan with an organic solvent including acetic acid to form a homogeneous reaction system, and then applies a molecular chain cleavage reagent or dissolves the starting chitosan in a heterogeneous reaction system. Direct application of molecular chain cleavage reagents. At this time, typical molecular chain cleavage reagents used include sodium perborate (NaBO ₃ ), H ₂ O ₂ , nitrite ions, sodium hypochlorite, potassium permanganate, chlorine gas, peracetic acid and the like.

The method for obtaining low molecular weight chitosan by dissolving chitosan in an acid to generate a homogeneous reaction system and then applying a molecular chain cleavage reagent is disclosed in Japanese Patent Publication Nos. Hei 2-11601 and No. 62-184002. Since the chitosan main chain decomposition reaction proceeds in a state in which starting chitosan is uniformly dissolved in an aqueous acid solution, low molecular weight is easy and the molecular weight distribution of the obtained low molecular weight chitosan is also relatively narrow. However, in the acidic chitosan solution in which the starting chitosan is dissolved, the cleavage of the molecular chain is not preferable because the action of the molecular chain cleavage reagent is weak, and the chitosan solution is slowly added dropwise to the aqueous alkaline solution when recovering the low molecular weight chitosan. The low molecular weight chitosan, which is solidified, is recovered. However, solidification of the low molecular weight chitosan in an aqueous alkali solution is not easy, thereby obtaining a solid or low molecular weight chitosan having a very large volume. In addition, the filtration, washing and drying processes are time consuming and also produce salts as impurities.

Alternatively, a method of dispersing the starting chitosan in an aqueous neutral or alkaline solution without dissolving it in an acid solution and then cutting the molecular chain of chitosan is disclosed in Japanese Patent Publications Nos. 54-148890, 56-33401, and 41-08734. No. 61-40303. In this method, it is known that efficient low molecular weighting proceeds only when the pH of the starting chitosan dispersion aqueous solution is adjusted in the range of 6-12. Since this method is a heterogeneous polymer reaction which proceeds with low molecular weight reaction while maintaining solid state in neutral or alkaline aqueous solution without dissolving starting chitosan, the low molecular weight reaction is not uniformly compared with the above-mentioned method. Since the degree of low molecular weight reaction is different from each other on the surface and inside of the chitosan particles, the molecular weight distribution of the final low molecular weight chitosan obtained is wide. However, the method of dissolving in an acid solution to lower the molecular weight 돠 It can be considered that the low molecular weight chitosan, which has completed the low molecular weight reaction, is easy to clean, easy to wash, and can be obtained in a relatively high purity low molecular weight chitosan.

As another method for obtaining low molecular weight chitosan, a method of treating starting chitosan in an aqueous solution containing chlorine dioxide is disclosed in Japanese Patent Publication No. Hei 1-11101. Although this method proceeds with low molecular weight reaction by chlorine, it cannot rule out the risk of residual chlorine ion. In addition, in most cases, when the halogen element-containing compound and chitosan come into contact with each other, chitosan tends to yellow or brown, so this method also has difficulty in obtaining low molecular weight chitosan having high whiteness. Therefore, it is not preferable to obtain high purity low molecular weight chitosan excellent in whiteness.

There are many other methods, but most of them focus on the production of water-soluble chitosan rather than focusing on the production of high-purity low-molecular-weight chitosan, and the intrinsic properties of starting chitosan such as purity, molecular weight, whiteness, and deacetylation Since it has been used for the production of low molecular weight chitosan, it is unknown at what grade low molecular weight chitosan was obtained, and the molecular weight of the obtained chitosan ranges from approximately 20,000 to 100,000, which is not suitable for use in biomedical grades.

Thus, the present invention is in particular in the field of healthcare. An object of the present invention is to provide a method for preparing low molecular weight chitosan of biomedical grade having high purity, high deacetylation degree, and high whiteness, which can be effectively used in medicine, cosmetics, and food.

Specifically, the present invention provides a method for producing low molecular weight chitosan of biodegradability, high purity and high whiteness by using biomedical grade high molecular weight chitosan as a starting material.

That is, according to the present invention, the low molecular weight chitosan obtained by heating the biomedical grade high molecular weight chitosan using NaBO ₃ as the molecular chain cleavage reagent is washed with water and filtered, immersed in an aqueous organic solvent solution, and then filtered. And it relates to a method for producing a biomedical grade low molecular weight chitosan, including drying.

In general, in order to exhibit pharmacological activity in foods or pharmaceuticals, it has been found that in most cases, low molecular weight chitosan having a molecular weight of 10,000 or less should be used. Seikagaku Corporation, Product Report No. 78, page 2] and Japanese Patent Publication No. Hei 4-108734), even in the case of low molecular weight chitosan, having a molecular weight of 10,000 or more is not expected to exert excellent pharmacological activity and has no meaning as a low molecular weight chitosan having a special function. It seems to be. However, if the molecular weight is lowered to 2,000 or less by emphasizing only pharmacological activity, it is also not preferable because water-soluble chitosan oligomer is formed.

According to the present invention, it is possible to easily prepare a low-molecular chitosan having a molecular weight in the range of 2,000 to 10,000 while freely producing chitosan belonging to the other range, it is possible to obtain a product having a low molecular weight and excellent whiteness. Preferred for use as starting high molecular weight chitosan in the low molecular weight process of the present invention is a biomedical grade high molecular weight chitosan with a deacetylation degree of at least 90% and a viscosity value of approximately 100 to 900 as a 1% solution in 1% acetic acid solution. It is good to be centipoise. Moreover, it is preferable that the high molecular weight chitosan is derived from the red crab shell and has a viscosity value of 150 to 700 centipoise, but it is preferred that the high molecular weight chitosan is derived from the shrimp shell and has a viscosity value of 150 to 700 centipoise.

The biomedical grade high molecular weight chitosan used as the starting material can be obtained, for example, by the methods disclosed in Korean Patent Applications Nos. 93-1687 and 93-11599 to the applicants. As follows.

That is, the red crab shell is dried and decomposed, and the ground red crab shell is maintained in a hydrochloric acid solution for 10 to 25 hours at a temperature of -10 to 10 ° C, and then the temperature is rapidly increased to be maintained for 2 to 8 hours at 10 to 20 ° C. Or otherwise maintained in one step for 20 to 60 hours at a temperature of -10 to 8 ° C., or for 3 to 20 hours at a temperature of -40 to -10 ° C., followed by continuous washing with water, filtration and solvent treatment. And dried to obtain a decalcified Hong crab shell, and the obtained decalcitized Hong crab shell is immersed in an aqueous NaOH solution and heated, followed by washing with water, filtration, solvent treatment, and drying to prepare a biomedical grade chitin. NaOH aqueous solution was added to the obtained chitin, followed by heat treatment at a temperature of 80 to 100 ° C. for 2 to 12 hours, followed by washing with water and filtration. The obtained chitosan was immersed in an aqueous solution of organic solvent followed by deionized water. Then filtered and dried can be made of chitosan in the biomedical grade.

The amount of NaBO ₃ used as the molecular chain cleavage reagent in the low molecular weight process is preferably added in the range of 5 to 37 g per 1 L of water, and the reaction temperature and the reaction time are 35 to 75 ° C and 20 minutes to 25 hours, respectively. This is preferred. Most preferably, the reaction temperature was maintained at 35 to 45 ° C. and reacted for 7 to 20 hours while NaBO ₃ was added in a range of 23 to 36 g per 1 L of water.

The NaBO ₃ mildly progresses the cleavage reaction of the molecular chain, thereby narrowing the molecular weight distribution of the low-molecular weight chitosan obtained finally, and maintaining the yield at 90% or more while maintaining excellent whiteness. In addition, since the pH is maintained in the range of 9 to 12 when the low molecular weight is carried out in the NaBO ₃ aqueous solution of the above concentration, there is an advantage that the process of separately adjusting the pH of the reaction solution can be omitted.

The crude low molecular weight chitosan thus obtained is washed with water and filtered and then immersed in an aqueous solution of an organic solvent such as ethanol. The immersion period is preferably 1 to 3 days. The reason for the immersion in the organic solvent solution is to remove the crude low molecular weight chitosan because it is slightly brown or yellow due to impurities. The concentration of the organic solvent aqueous solution is preferably 10 to 60% by volume.

In this way, the low molecular weight chitosan from which impurities are removed can be filtered and then dried or lyophilized by conventional means, such as a vacuum oven, to finally obtain low molecular weight chitosan of high purity and excellent whiteness.

In the present invention, the low-molecular-weight chitosan having different molecular weight and complete dissolution time, respectively, was subjected to a low-molecularization reaction under the same conditions at the same time with the starting chitosan derived from the red crab shell and the shrimp crust having almost the same molecular weight. Got it.

This proves that if the type of crust from which the starting chitosan is derived differs, the conditions of the low molecular weight reaction must also be differentiated, and thus, as in the prior art, it is obtained from the low molecular weight reaction of the starting chitosan whose type of crust is not known. It can be seen that the conditions for producing low molecular weight chitosan cannot be applied collectively to all kinds of chitosan. According to the present invention, low-molecular-weight chitosan having excellent whiteness can be obtained in high yield by differentiating low-molecularization conditions according to the type of shells from which the starting chitosan used for low molecular weight is derived and performing under conditions suitable for the starting chitosan.

If the present invention is explained in more detail by the following examples, the present invention is not limited to these examples.

Example 1

Biomedical grade high molecular weight chitosan having a viscosity of 250 centipoise (in 1% solution in 1% acetic acid aqueous solution) prepared from red crab shell by the method of Korean Patent Application No. 93-1687 was used for low molecular weight.

500 mL of deionized water was added to a 1 L three-necked flask and warmed with a mechanical stirrer to reach 35 ° C., 50 ° C., 65 ° C. and 75 ° C., and then 4.7 g, 9.4 g and 15.98 g of NaBO ₃ .4H ₂ O , 24 g and 34 g were added to completely dissolve to adjust the concentration of NaBO ₃ in the reaction solution so that 4.98 g, 9.91 g, 16.75 g, 24.98 g, and 35.06 g were added to 1 L of water. After adding 30 g of chitosan, the low molecular weight reaction was continued while maintaining the temperature for 30 minutes to 21 hours while continuing stirring. When the low molecular weight reaction time specified for each data had elapsed, the contents in the flask were filtered to obtain a low molecular weight chitosan in which the low molecular weight reaction was completed.

The filtered low molecular weight chitosan was washed again with running water (deionized water) 5 to 10 times, filtered and immersed in an ethanol aqueous solution (ethanol / water = 8: 2, v / v) for 1 to 2 days and then filtered again. It was dried completely in a vacuum oven while maintaining the temperature below 40 ° C. The viscosity was measured using a viscometer (Haake, Rotovisco RV 20 type) as a 1% solution of dried low molecular weight chitosan in 1% aqueous acetic acid solution. When the viscosity of the low molecular weight chitosan is 4 centipoise, its average molecular weight corresponds to 10,000, so that the low molecular weight chitosan having a viscosity value of 4 centipoise or less is considered to have an average molecular weight of 10,000 or less.

The viscosity and yield of the low molecular weight chitosan according to the change of the low molecular weight reaction conditions are shown in Table 1 below.

Note 1) The viscosity value corresponding to 2.2 centipoise or less among the viscosity of low molecular weight chitosan is not described.

2) Values in parentheses () together with viscosity indicate yield of low molecular weight chitosan.

3) *: Whiteness value is shown in FIG.

4) The underlined data indicate embodiments which fall within a particularly preferred range in view of the object of the present invention.

Example 2

The same procedure as in Example 1 was conducted except that a biomedical grade high molecular weight chitosan having a viscosity of 230 centipoise prepared from shrimp shellfish was used for low molecular weight by the method of Korean Patent Application No. 93-1687. , The viscosity and yield of the low molecular weight chitosan according to the change of reaction conditions are shown in Table 2 below.

Note 1) The viscosity value of 2.2 centipoise or less among the viscosities of low molecular weight chitosan is inaccurate.

2) Values in parentheses () together with viscosity indicate the yield of chitosan.

3) *: Whiteness value is shown in FIG.

4) The underlined data indicate specific examples belonging to a range particularly suitable for the present invention that can obtain a low molecular weight chitosan having a relatively low molecular weight and excellent whiteness.

As can be seen from the above, according to the method of the present invention, while yielding a low molecular weight chitosan having a molecular weight of 10,000 (viscosity 4.0 centipoise) or less, the yield is maintained at 90% or more.

The whiteness of the low molecular weight chitosan obtained in accordance with the present invention was measured by using TiO as a pure white standard in the color measurement apparatus (Computor Color Matching Model TCM 4-8303) of ICS-Texicon. Whiteness profiles of the TiO and low molecular weight chitosan prepared according to the present invention are shown in FIGS. 1 and 2 as values ranging from 400 nm to 700 nm.

The lower the molecular weight, the lower the whiteness of the prepared low molecular weight chitosan. In the present invention, the whiteness of low molecular weight chitosan, which can be regarded as the lowest molecular weight, is presented without presenting the whiteness of all the low molecular weight chitosan prepared. Do. In the case of low molecular weight chitosan prepared from starting chitosan derived from red crab shells, 36.06 g of NaBO was added to 1 L of water with a low molecular weight reaction temperature of 35 ° C., and a viscosity of 3.1 centipoise was obtained after a low molecular weight reaction time of 21 hours. The whiteness of the sample was measured and shown in FIG. 1, and in the case of the low molecular weight chitosan prepared from the starting chitosan derived from the shrimp shell, 35.06 g of NaBO was added per 1 L of low molecular weight reaction temperature, The whiteness of the sample of 3.5 centimeters of viscosities prepared after 21 hours of low molecular weight reaction time was measured and shown in FIG.

From Figures 1 and 2, it can be seen that the low molecular weight chitosan prepared according to the present invention has a good whiteness value of about 75 to 85% compared to the whiteness of TiO.

Claims (7)

NaBO having a concentration of 17.1 to 36 g / l high molecular weight chitosan from Korean red crab or shrimp crust, having a deacetylation degree of 90% or more and a viscosity value of 100 to 900 centipoise as a 1% solution in 1% aqueous acetic acid solution ₃ , added to the aqueous solution, and reacted for 30 minutes to 30 hours at a temperature of 30 to 80 ℃, which is filtered, washed and filtered and then immersed in an aqueous organic solvent solution for 1 to 3 days, and then filtered and dried, 80 A method for producing chitosan having a degree of deacetylation of at least% and a viscosity value of 1 to 50 centipoise when measured as a 1% solution in an aqueous 1% acetic acid solution using a Haake RV 20 type viscometer. The method of claim 1 wherein said high molecular weight chitosan is derived from a red crab shell and has a viscosity value of 150 to 700 centipoise. The method of claim 1 wherein said high molecular weight chitosan is derived from a shrimp shell and has a viscosity value of 150 to 700 centipoise. The method of claim 1, wherein the NaBO ₃ is added in an amount of 23 to 36 g per 1 L of water, and the reaction temperature is 35 to 45 ° C., and the reaction time is 7 to 20 hours. The method of claim 1, wherein the aqueous organic solvent is an aqueous ethanol solution of 10 to 80% by volume. The method according to claim 1, wherein the obtained chitosan has a molecular weight in the range of 2,000 to 10,000. The method of claim 1, wherein the low molecular weight chitosan has a relative whiteness of 75 to 85% compared to TiO ₂ as a standard material.