JPH01152104A - Preparation of water-soluble chitosan salt powder - Google Patents

Abstract

PURPOSE:To prepare the subject powder which is colorless and is rapidly and homogeneously dissolved in water, by grinding a completely frozen sponge-like molded item obtd. by freeze-drying an aq. soln. of chitosan in a mineral acid or an org. acid. CONSTITUTION:A powdery chitosan is added and stirred in water and a mineral acid or an org. acid (e.g., hydrochloric acid, acetic acid, propionic acid, etc.) is added thereto to dissolve chitosan completely. A sponge-like molded item is obtd. from this soln. and is ground. As this method where the chitosan salt is dried under a frozen solid condition causes less deterioration of quality such as discoloration, decrease in viscosity etc. than the conventional method where dehydration and drying are carried out under soln. condition and a sponge-like porous molded item can be obtd., the powder obtd. therefrom exhibits good solubility in water and is suitably used in the fields of cosmetics, medicines and foods.

Description

[Detailed Description of the Invention] [Field of Application] The present invention provides a water-soluble chitosan salt powder that is free from coloration and dissolves quickly and uniformly in water from an aqueous solution of chitosan dissolved in a dilute mineral acid or organic acid. The present invention relates to a manufacturing method.

[Conventional technology]

In recent years, as the use of chitosan has been developed, water-soluble chitosan salt powder with the following properties is in demand in the fields of cosmetics, medicine, food, etc.

(1) Something that dissolves uniformly and quickly in water (2)
Chitosan that dissolves in high concentration and has low viscosity (3) No coloration Chitosan, which is obtained by deacetylating natural chitin with a concentrated alkali such as caustic soda, is insoluble in water, but has free amino groups, so It dissolves in dilute acid as a salt. The acids in this case include mineral acids such as hydrochloric acid and nitric acid, or formic acid, acetic acid,
Organic acids such as lactic acid, oxalic acid, and adipic acid are commonly used. However, since chitosan obtained from natural chitin is a polymer, although it dissolves in dilute acid as it is, a highly concentrated chitosan salt solution cannot be obtained.

Several methods have been known to reduce the molecular weight of chitosan by which solutions with high concentration and low viscosity can be prepared.

For example, there are the following lives.

JP-A-54-148890 (hydrogen peroxide treatment method) JP-A-60-186504 (chlorine gas treatment method) JP-A-61-40303 (perboric acid treatment method) All of these methods do not cause coloring. This paper is about a method of reducing the molecular weight of chitosan to a minimum amount as possible, and the low-molecular-weight chitosan obtained in this way can be dissolved in a dilute acid at a relatively high concentration.

Furthermore, JP-A-58-164601 describes a method for producing chitosan salt with less coloration by ultrafiltering a solution of chitosan dissolved in dilute acid to remove coloring substances in the solution. ing. Although such conventionally known methods can produce an aqueous solution of low-molecular-weight chitosan or its salt with little coloring, there are several problems in producing dry chitosan salt powder without coloring. It has been pointed out. In other words, polysaccharides such as chitosan, in which amino sugars are condensed through glycosidic bonds, are thermally unstable and prone to hydrolysis, detachment of functional groups, and opening of glucose rings, and this tendency has led to lower molecules. This is more remarkable when chitosan is made water-soluble. Therefore, if an aqueous solution of low-molecular-weight chitosan salt is heated to a high temperature or left for a long period of time, the above-mentioned undesirable reactions occur, leading to quality deterioration such as coloration, decrease in viscosity, and formation of precipitates. When producing chitosan salt powder, dehydration and drying methods are generally used to avoid such problems. This method includes, for example, concentrating under normal pressure or reduced pressure with as little temperature as possible and then drying it in a film form under reduced pressure, drying under reduced pressure and low temperature while stirring, or exposing it to high temperatures for a period of time. Methods such as spray drying, which minimizes the length of time, are used. However, in such a drying method, even though it is low-temperature vacuum drying, the temperature is limited to 30 to 50°C, and quality deterioration such as coloring cannot be completely avoided in long-term drying in an aqueous solution state. Also, like spray drying,
If it comes into contact with a high-temperature air stream of 100°C or higher, even for a very short time, quality deterioration will still occur.

Furthermore, the dried chitosan salt obtained by this method has a film-like shape, a shape in which thin fibers are entangled,
They form solid particles, and when the powder obtained by pulverizing them is dissolved in water, there are disadvantages such as it takes a long time or the powder becomes lumpy and cannot be dissolved uniformly.

[Problem to be solved]

In order to avoid the defects of the conventional method as described above, the present invention
An object of the present invention is to provide a method for producing chitosan salt powder that is free from coloration and has excellent solubility.

[Means to solve]

The present invention is based on the finding that quality deterioration such as discoloration does not progress when chitosan salt prepared by dissolving low-molecular-weight chitosan in an aqueous solution of mineral acid or organic acid is frozen, and furthermore, it is obtained by drying in this frozen state. Dry chitosan salt becomes a porous sponge-like molded product, which is not only easy to crush, but when this sponge-like porous molded product is pulverized, its surface area increases, the dissolution time in water is short, and it is uniformly powdered. It has been found that this has the excellent advantage of being soluble in

That is, according to the present invention, a method for producing a water-soluble chitosan salt powder is characterized in that an aqueous solution of chitosan dissolved in a mineral acid or an organic acid is freeze-dried to form a sponge-like molded body, and this is pulverized. is provided.

The aqueous chitosan salt solution used in the present invention can be any salt formed with a dilute acid in which chitosan can be dissolved, such as acetate, lactate, formate, butyrate, propionate, succinate, hydrochloride, or nitrate. Although the concentration of chitosan salt is not particularly limited, it is generally used at 1 to 20%. If the concentration is low, the sponge-like molded product obtained by freeze-drying will be very porous, and the powdered product will be very bulky and has good solubility in water, but will take a long time to dry. If the energy efficiency is poor or the concentration is high, the sponge-like molded material obtained by freeze-drying becomes a dense porous material, and the material obtained by powdering this material has a relatively large bulk specific gravity. Although the dissolution time is slightly longer, the drying time is shorter, and in terms of energy efficiency,
It has some advantageous characteristics. Therefore, the concentration of chitosan salt can be arbitrarily selected depending on the properties of the desired chitosan salt.6 The chitosan salt aqueous solution is placed in a container and frozen, and the shape of the container is the shape of the sponge-like molded product obtained by drying. , so you can arbitrarily select one that is convenient for handling. The freezing temperature may be lower than the temperature at which the aqueous solution freezes, and is completely frozen by cooling to -50C to 50C using general-purpose refrigeration equipment. The frozen chitosan salt aqueous solution is placed in a vacuum dryer with a cold trap and dried under vacuum. The degree of vacuum at this time depends on the cooling capacity of the cold trap, but is generally 5 torr or less.
Not particularly limited. However, it is important to maintain conditions in which the frozen chitosan salt aqueous solution does not melt during drying. If it melts during drying, not only will the temperature of the melted part increase, causing quality deterioration such as discoloration, but the resulting molded product will no longer be porous, and its solubility in water will be extremely poor. This is because it becomes The higher the degree of dryness, the more stable it will be thermally, but the moisture content should usually be 10% or less, preferably 5% or less. When the water content reaches this level, it is thermally stable, and quality deterioration such as discoloration and viscosity reduction hardly occurs even if it is stored at room temperature for several months.

The dried chitosan salt is obtained as a sponge-like porous molded body. This compact is usually powdered to make it easier to handle, but since it is porous, it is extremely easy to grind, and the means of grinding is not particularly limited. It is preferable to set it to about 1-5 .mu./m. If the particles are too finely divided, the dissolution time in water tends to be longer, and if the particles are too coarse, they become bulky and are inconvenient to handle. Therefore, the size of the particles may be appropriately determined depending on the handling method.

〔Effect of the invention〕

The present invention, in which chitosan salt is dried in a frozen solid state, has significantly less quality deterioration such as discoloration and viscosity reduction than the conventional chitosan salt production method in which dehydration and drying is performed in a solution state, and moreover, it can be formed into a sponge-like porous structure. Since it becomes a body, it can be powdered to produce a product with good solubility in water.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples.

The viscosity and chromaticity of the chitosan solution and the dried chitosan salt solution were measured as follows.

(1) Concentration of solution The concentration for measuring viscosity and chromaticity was 1% chitosan equivalent for both the chitosan solution and the chitosan salt solution.

(2) Take 400w + Q of the viscosity solution in a 500mQ tall beaker, keep it at 20℃, and use a B-type rotational viscometer (rotation speed 6O
r, p, ■, rotor Nα1).

(3) Chromaticity The solution was determined by a colorimetric method using an APHA standard solution.

Further, the dissolution time of the dried chitosan salt was measured as follows. That is, a flat blade (68 mm) was placed in a 500 mm beaker.
m/m x 25m/■) Set up a stirrer. Take 400 m Q of water and keep the water temperature at 25°C while stirring at 200 r, p, m. Add dry chitosan salt powder to this water at once in an amount equivalent to 1% chitosan, until the powder is completely The time required for the solution to dissolve was measured.

Example 1 20 g of powdered chitosan (degree of deacetylation 93%, average molecular weight: 160,000) was added to 400 m Q of water under stirring conditions.
20 Q of various acids shown in Table 1 were added to completely dissolve the chitosan. Next, 100 mΩ of this solution was poured into a glass Petri dish (capacity 220+*Q,
125 m in diameter and 18 m in height), -30
It was placed in a freezer kept at ℃ and left for 18 hours to completely freeze.

This frozen chitosan salt is dried in a Petri dish using a freeze dryer (Nippon Sanso Edwards Vacuum Co., Ltd., Modulio E!F-4 model).
The mixture was placed in a vacuum chamber of 2 to 3 torr and dried in a frozen state for about 72 hours. After drying, the chitosan salts were all in the form of a bulky sponge and had the same shape as a petri dish, and the volume did not change much. This spongy chitosan salt was crushed to 3 m/m or less using a laboratory rotary cutter type crusher, and then dissolved in water to examine its physical properties.
The results shown in the table were obtained.

The chitosan salt powder obtained as described above had an extremely small rate of change in physical properties compared to the comparative example described below.

Example 2 12 g of powdered chitosan (deacetylation degree 93%, average molecular weight 60,000) was dispersed in 400 mΩ water with stirring, and 12 mQ of 35% hydrochloric acid was added to completely dissolve the chitosan. 150 m Q of the solution was poured into a glass Petri dish (capacity 220 m Q, diameter 125 o+/m
, height 18n+/m), and the same method as in Example 1 was used for subsequent freezing and drying.

The dried chitosan salt was pulverized to 3 m/m or less using a laboratory rotary cutter pulverizer, and then dissolved in water to examine its physical properties, and the results shown in Table 2 were obtained.

The chitosan salt powder obtained as described above had an extremely small change in physical properties compared to the comparative example described below.

Table 2 Comparative Examples Experiments were conducted in accordance with a conventional vacuum drying method. That is, powdered chitosan (deacetylation degree 93%, average molecular weight 60.00
0) Disperse 20g of various acids shown in Table 3 20n n
was added to completely dissolve the chitosan.Next, 10g of this solution was put into an IQ eggplant-shaped flask, and heated in a rotary vacuum evaporator (Tokyo Rikakiki Co., Ltd. N-1).
When the mixture was dried under reduced pressure at 35 torr and 37° C. for 24 hours, a brownish film-like dried chitosan salt was obtained. The chitosan salt film obtained by repeating this same operation was crushed to 3n+/m or less using a laboratory rotary cutter type crusher, and then dissolved in water to examine its physical properties.The results are shown in Table 3. was gotten. According to this, the dried product was in the form of a film that was difficult to crush, and the rate of change in physical properties such as chromaticity and viscosity was large, and the dissolution time was extremely long.

Reference Example An aqueous solution of chitosan dissolved in a dilute acid was very likely to be colored depending on the temperature.As a result of examining the change in the degree of coloring over time, the results were as follows. The test method was as follows.

That is, powdered chitosan (
Degree of deacetylation 93%, average molecular Ji 160,000)
20g of chitosan was dispersed and 20mA of various acids shown in Table 4 was added to completely dissolve the chitosan.Next, 100μΩ of this solution was placed in a glass bottle with a lid (200mm volume), and the bottle was tightly stoppered. The samples were left in constant temperature water baths kept at 25°C and 50°C. Immediately after melting and for 3 hours at each temperature.
The chitosan salt solutions that had been used for O days were taken, the chitosan concentration was adjusted to 1%, and the chromaticity was measured, and the results shown in Table 4 were obtained.

From the results shown in Table 4, it can be seen that the rate of change in physical properties of the chitosan salt aqueous solution increases as the temperature increases and time passes.

Claims (1)

[Claims] (1) A method for producing a water-soluble chitosan salt powder, which comprises freeze-drying an aqueous solution of chitosan dissolved in a mineral acid or an organic acid to form a sponge-like molded body, and pulverizing the molded body.