JPH072902A - Production of chitosan - Google Patents

Abstract

PURPOSE:To produce a high-purity chitosan little contaminated with heavy metals while using a usually used metal-made reactor by deacetylating chitin by immersing it in an aq. alkali soln. at a specified temp. CONSTITUTION:Chitin is deacetylated by immersing it in an aq. alkali soln. at 85 deg.C or lower in a usually used metal-made reactor having the surface comprising a metal (e.g. a stainless-steel reactor). Usually the deacetylation is conducted at 30 deg.C or higher for 12-60hr. The concn. of the alkali soln. during the reaction is usually 30-60wt.%. The reaction is, if necessary, carried out under stirring or by purging the reaction system with nitrogen. After the reaction is completed. the resulting product is subjected to known post-treatments such as cooling, washing with water, neutralization, and drying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing chitosan, and more particularly, to an industrially advantageous method for producing high-purity chitosan.

[0002]

2. Description of the Related Art Chitosan is expected as a dietary fiber due to its indigestibility characteristic, and many amino groups existing in the molecule adsorb bile acids in the digestive tract to reduce serum cholesterol. Therefore, it is expected to be applied as a functional food utilizing the cholesterol-lowering effect.

Chitosan is produced by deacetylation of chitin with alkali. Gi
lson (Berichte 28 821 (189
5); Bull (3) 11 1099 (1894)), that is, heating chitin and a high concentration of potassium hydroxide to 180 ° C., and Rigby (US Pat. No. 2,040,
879, May 1, 1936), i.e., heating chitin and 30-60 wt% sodium hydroxide to 80-160 ° C.

[0004]

By the way, since chitosan has the ability to chelate with a metal, when deacetylation is carried out under conventional reaction conditions using a metal reaction vessel, the metal in the chitosan molecule is Since it is taken in, high-purity chitosan cannot be obtained.

Recently, US Pat. No. 4,195,175
According to the specification, 30-50, which is 2 to 7 times that of chitin.
A method is proposed in which a weight% alkaline aqueous solution is added, mixed with a kneader or the like, and then reacted at 40 to 80 ° C.,
According to Japanese Patent Laid-Open No. 62-179503, chitin is added to 35
After dipping in a concentrated aqueous solution of 60% by weight of alkali, chitin has an alkali content of 0.5 to 0.5 per 1 part by weight of chitin.
A method has been proposed in which excess alkaline aqueous solution is removed so as to impregnate 2.5 parts by weight, and the resulting alkali-impregnated chitin is heated to 45 to 110 ° C. for deacetylation.

However, the above two methods are aimed at preventing the breakage of the polymer main chain of chitosan to obtain high molecular weight chitosan, and are intended to prevent the incorporation of metal into the chitosan molecule. Not the way Of course, prevention of metal uptake can be achieved, for example, by using a polyethylene-lined steel reaction vessel as described in the examples of US Pat. No. 4,195,175. The method of using a reaction container made of is disadvantageous in terms of cost. Further, the method described in JP-A-62-179503 is
The operation is complicated because a pretreatment for removing excess alkali aqueous solution to obtain alkali-impregnated chitin is required. An object of the present invention is to provide an industrially advantageous method for producing high-purity chitosan that uses an ordinary metal reaction vessel represented by a stainless steel reaction vessel and does not require a special pretreatment operation. To do.

[0007]

Means for Solving the Problems As a result of various studies to achieve the above object, the present inventors have achieved the above object easily by performing deacetylation under specific temperature conditions. The present invention has been completed with the knowledge that it can be obtained. That is, the gist of the present invention resides in a method for producing chitosan, which comprises immersing chitin in an alkaline aqueous solution and deacetylating the mixture at a temperature of 85 ° C. or lower in a reaction vessel having a metal surface. .

The present invention will be described in detail below. In the present invention, the raw material chitin, for example, crab, deproteinize the shell of crustaceans such as shrimp with a dilute alkali or an enzyme, further remove ash with a dilute acid, and then wash several times,
Alternatively, it can be obtained by neutralization. Then, it is crushed to an appropriate size and used.

The raw material chitin is immersed in an aqueous alkaline solution and converted into chitosan by a deacetylation reaction. In the present invention, the reaction vessel is a conventional metallic reaction having a metal surface. A container can be used. Examples of the metal reaction container include a nickel reaction container, a stainless reaction container, and the like, and a stainless reaction container such as SUS304 is usually used.

The alkaline aqueous solution is not particularly limited, and examples thereof include aqueous solutions of sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, and usually sodium hydroxide aqueous solution is preferably used. The concentration of the alkaline aqueous solution at the time of reaction is usually 30 to 60% by weight, preferably about 45 to 50% by weight.

In the present invention, the raw material chitin is deacetylated by immersing it in an alkaline aqueous solution in a genus reaction vessel. The most important feature of the present invention is that deacetylation is performed at a temperature of 85 ° C. or lower. There is a point to do. By adopting such a specific temperature condition, for example, an inexpensive stainless steel reaction container can be used and high-purity chitosan can be produced. That is, according to the present invention, a heavy metal,
In particular, it is possible to industrially produce highly pure chitosan with a small intake of iron, cum, nickel, etc.

In the present invention, the deacetylation temperature is
As described above, it is extremely important that the temperature should be 85 ° C. or lower, but if the temperature for deacetylation is too low, the reaction rate becomes too low. Therefore, the deacetylation temperature is usually selected from the range of 30 ° C. or higher, preferably 55 to 85 ° C., and more preferably 65 to 75 ° C. The reaction time varies depending on the particle size of the starting material chitin, the alkali concentration, the reaction temperature, the desired degree of deacetylation, etc., but is usually 12 hours or longer, preferably about 16 to 60 hours.

If necessary, the reaction is carried out under stirring conditions.
It is carried out by employing nitrogen substitution treatment in the reaction system, and after the completion of the reaction, known post-treatment operations such as cooling, washing with water, neutralization and drying are carried out. The chitosan obtained by the production method of the present invention has a particularly low heavy metal uptake amount, as shown in Examples below, and thus is particularly suitable for food applications.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the following examples, as a raw material, chitin (F
e: 19.6 ppm, Cr: ND (not detected), N
i: N.D.) and the alkaline aqueous solution is 48
A weight% sodium hydroxide aqueous solution was used, and a stainless (SUS304) reaction container was used as the reaction container. The degree of deacetylation was measured by a colloid titration method, and the heavy metal in the obtained chitosan was measured by an atomic absorption photometric method (detection limit 1.0 ppm).

EXAMPLE 1 Chitin 10 as a raw material was placed in a 5-liter stainless steel reaction vessel.
0 g and 2 liters of a 48 wt% sodium hydroxide aqueous solution were charged, deacetylation was carried out at the reaction temperature and time shown in Table 1, and after the reaction, it was sufficiently washed with tap water to obtain chitosan. The deacetylation degree and the heavy metal content of chitosan were measured, and the results are shown in Table 1 (Note that test N in Table 1
o. 2 is an example using a reaction vessel made of SUS316).

[0016]

[Table 1] ──────────────────────────────────── Test deacetylation conditions Deacetylation degree Heavy metal (Ppm) No. Temperature (° C) Time (Hr) (%) Fe Cr Ni 1 65 48 92.4 6.4 1.8 ND 2 65 20 88.2 10 NDND 3 55 55 24 76.4 4.1 NDND 4 55 48 85.6 5.3 NDND 5 65 24 249.7 7.4 NDND 6 65 65 48 93.0 7.6 1.4 ND 7 75 24 92.4 8.0 1.2 ND 8 75 48 48 96.9 11 1.4 ND 9 85 24 94.8 18 5.4 1.2 10 85 48 97.4 26 7.6 1.5 ───────────────────── ────────────────

Comparative Example Chitosan was produced in the same manner as in Example 1 except that the deacetylation conditions were changed as shown in Table 2. The deacetylation degree and heavy metal content of the obtained chitosan were measured, and the results are shown in Table 2.

[0018]

[Table 2] ──────────────────────────────────── Test deacetylation condition Deacetylation degree Heavy metal (Ppm) No. Temperature (℃) Time (Hr) (%) Fe Cr Ni 11 95 24 96.8 57 14 2.6 12 95 48 98.9 105 21 4.8 ─────────────────────── ──────────────

Example 2 200 kg of chitin as a raw material was placed in an 8-t stainless steel reaction vessel.
And 5000 kg of a 48% by weight aqueous sodium hydroxide solution were charged, deacetylation was carried out at the reaction temperature and time shown in Table 3, and after the reaction, chitosan was obtained by thoroughly washing with industrial water. The deacetylation degree and heavy metal content of chitosan were measured, and the results are shown in Table 3.

[0020]

[Table 3] ──────────────────────────────────── Test deacetylation conditions Deacetylation degree Heavy metal (Ppm) No. Temperature (℃) Time (Hr) (%) Fe Cr Ni 13 65 16 86.2 6.7 NDND 14 65 18 88.4 7.1 1.0 ND 15 65 20 90.2 8.0 1.2 ND ───────────────── ────────────────────

[0021]

Industrial Applicability According to the present invention described above, an industrially advantageous method for producing high-purity chitosan is provided which uses an ordinary metal reaction vessel and does not require a special pretreatment operation. To be done. Chitosan obtained by the production method of the present invention has a small amount of heavy metal taken up, and is therefore particularly suitable for food applications.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriko Mita 714-41 Shimokuroiwa, Tomioka City, Gunma Prefecture (72) Inventor Emiko Kurihara 2-194 Totehonmachi, Sachi-ku, Kawasaki City, Kanagawa Prefecture (72) Inventor Tomitaro Ibaraki Osaka Prefecture 2-5, Shinsenrihigashi-cho, Toyonaka City

Claims (1)

[Claims] 1. A method for producing chitosan, which comprises immersing chitin in an alkaline aqueous solution to deacetylate the solution at a temperature of 85 ° C. or lower in a reaction vessel having a metal surface.