JPS6013758A - Purification of tryptophan - Google Patents

Abstract

PURPOSE:To obtain the titled substance which is one of the essential amino acids and useful as a nutrient source, in high quality, by washing the crystal of tryptophan with acetic acid, etc., thereby dissolving the impurities such as coloring materials existing on the surface of the tryptophan crystal or in the gap between the crystals. CONSTITUTION:Tryptophan crystal is sprayed with acetica acid or an aqueous solution of acetic acid having a concentration of >=30% or stirred in acetic acid or an aqueous solution of acetic acid having a concentration of >=30% in a slurry state to remove the coloring substance from the tryptophan crystal and obtain a purified crystal. To avoid the strong smell of the acetic acid, the washing liquid is preferably an aqueous solution of acetic acid having a concentration of about 30-80%. The weight ratio of the acetic acid or the aqueous solution of acetic acid to the tryptophan crystal is about 0.1-10. The washing is carried out at normal temperature. The acetic acid remaining in the crystal separated after the acetic acid washing process can be removed by washing the crystal with water, and drying in vacuum at 60-80 deg.C for about 10-20hr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying tryptophan by washing tryptophan crystals with acetic acid or an aqueous acetic acid solution.

Tryptopha is one of the essential amino acids and is useful as a nutritional source for the human body or livestock. There is a demand for higher quality tryptophan used in these products.

Methods for producing tryptophan include chemical synthesis method, enzymatic method,
Fermentation methods are being used. The method for separating and purifying tryptophan in these manufacturing processes is the method of adding a metal salt to form a racemic double salt (Japanese Patent Publication No. 5O-1191).
4), a method using anion and cation exchange resins (
JP-A-53-111061) or a method combining an adsorption resin and an ultrafiltration membrane (JP-A-58-89'5).

However, since tryptophan has a strong tendency to be adsorbed and desorbed by the resin along with colored substances, complicated steps and operations are required to remove these impurities. Also, impurities such as colored substances are adsorbed to tryptophan crystals during crystallization.
Easy to mix. In order to prevent the contamination of these impurities, there is a method of crystallizing using an organic solvent such as alcohol, but this requires complicated steps such as recovery of the solvent.

Since the adsorption affinity of tryptophan is thus large, there is no means to easily remove impurities such as colored substances.

The present inventors investigated how to remove impurities such as colored substances from tryptophan crystals, and found that by washing the tryptophan crystals with acetic acid or an acetic acid aqueous solution of 30% or more, the quality of the tryptophan crystals was greatly improved. I found that it can be improved.

That is, for example, tryptophyl 1 obtained by crystallization separation
Clean the crystals by spraying acetic acid or an aqueous solution of 30% or more acetic acid on the separator, or
% or more of acetic acid aqueous solution in a slurry state, the coloring etc. of tryptophyl monocrystals are removed.

This is thought to have the effect of eluting impurities such as coloring present on the surface and interstices of tributophane crystals with acetic acid or an acetic acid aqueous solution.

The concentration of acetic acid or acetic acid aqueous solution used for cleaning is preferably 30% or more. At concentrations lower than this, the cleaning effect is significantly reduced. Furthermore, when acetic acid is used, it has a strong odor, so an aqueous solution having a concentration of about 30% to 80% is preferable.

The amount of acetic acid or acetic acid aqueous solution used may be approximately 0.1 to 10 times the weight of tryptophan crystals. In this case, it depends on the concentration of acetic acid used, and if the concentration is high, the amount used may be small. It also depends on the cleaning method, and the amount required when spraying on a separator is smaller than when cleaning in a slurry state.

The cleaning temperature may be room temperature. The odor of acetic acid becomes strong at high temperatures, so to avoid this, the process may be carried out at low temperatures.

The tryptophan crystals to be washed may be any one obtained by concentration crystallization, cooling crystallization, neutralization crystallization, crystallization using a solvent, or the like. Alternatively, it may be dried once after crystallization and separation.

Although the method of the present invention can be widely applied to tryptophan crystals, it is particularly effective in removing impurities derived from fermentation liquids and enzyme reaction liquids containing a large amount of colored substances.

Examples of such methods include crystallization from fermentation liquids, enzyme reaction liquids, their sterilized solutions, or liquids purified by using ion exchange resins, nonionic resins, ultrafiltration, reverse osmosis filtration, etc. Examples include isolated tryptophan crystals, crystals recrystallized from the crystals (crude crystals), and tryptophan/crystals crystallized from synthetic solutions, racemization solutions, process solutions after splitting the DL form, etc. can.

To remove acetic acid in the obtained crystals, for example, after washing with acetic acid, the separated crystals are further washed thoroughly with water and then heated at 60 to 80°C.
It may be dried under reduced pressure for about 10 to 20 hours.

This will be described in detail below using examples.

Comparative Example I L-) Liptov 7 fermentation liquid (JP-A-5F3-92796
) was passed through a strongly acidic cation exchange resin to adsorb L-tryptophan, and after washing the resin thoroughly with water, 2N
Eluted with NaOH solution. These 5 eluents were concentrated and an alkaline aqueous solution of tryptophan (tryptophan content: 3
0.3%, PH12.2) was obtained.

150 g of this concentrated solution was taken and added to 501 acetic acid to undergo neutralization and crystallization at 45°C for 2 hours (end pH 3).
, 4), the crystals were cooled to 25° C. and then centrifuged, and water 501 was sprayed onto the crystals to wash them. This was dried under reduced pressure at 70°C to give L-)lyptophan crystals of 43. Efg (purity 9&8%, yield 947%) was obtained.

The transmittance of this crystal was 77.5% (C-1, water,
430n■).

Example 1 Crystallization was carried out in the same manner as in Comparative Example 1, acetic acid 101 was sprayed onto the centrifuged crystals, and the crystals were further washed with water. This is 70
Dry under reduced pressure at °C to obtain 43.1 g of L-
A purity of 99.3% and a yield of 942% were obtained.

The transmittance of this crystal was 90.0% (measured in the same manner as Comparative Example 1).

Comparative Example 2 L-)Lyptophan fermentation liquid (Japanese Patent Application Laid-Open No. 56-92796)
was passed through a strongly acidic ion exchange resin to adsorb L-tryptophan, and after washing the resin thoroughly with water, 2N
The crystals were eluted with aqueous ammonia, concentrated and crystallized, and the crystals were centrifuged at 25°C and then thoroughly washed with water.

After taking a portion of this tryptophan crystal and drying it under reduced pressure at 70°C, the transmittance measured was 47.3% (C=
1, water, measured at 430 nm s O-3u Millipore degeneracy).

Example 2 30 g of the crystals thoroughly washed with water after centrifugation in Comparative Example 2 (Liptophan content: 66.8%)
The sample was made into a slurry in 80% acetic acid aqueous solution 501 at 25°C, stirred and washed for 1 hour, centrifuged, and thoroughly washed with water.

The transmittance measured by drying this tributofion/crystal under reduced pressure at 70° C. was 65.4%. Obtained crystal 19.3 g
The S purity was 97.7%, the yield was 941%, and the measurement of transmittance was the same as in Comparative Example 2.

Patent applicant: Ajinosaku Co., Ltd.

Claims (1)

[Claims] A method for purifying tryptophan, which comprises washing tryptophan crystals with acetic acid or a 30% or more acetic acid aqueous solution.