JPH0568459B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for concentrating an aqueous amino acid solution using a membrane. Amino acids are substances widely used in seasonings, foods, medicines, chemical products, feed, etc.
It is manufactured by fermentation, enzymatic methods, synthetic methods, etc. The manufacturing process is mainly performed in an aqueous solution state, and in particular, extraction methods and fermentation methods often involve concentrating an aqueous solution with a low amino acid concentration. Generally, concentration of aqueous solutions was carried out by evaporation, but since this method requires a large amount of energy, recently, from the viewpoint of energy saving, membranes such as reverse osmosis membranes, ultrafiltration membranes, and ion exchange membranes have been used. It is being converted into a concentration method. however,
There are various disadvantages when using these membranes to concentrate an aqueous amino acid solution that is concentrated in the manufacturing process. That is, in the case of a reverse osmosis membrane, other impurities are concentrated together with amino acids, and as a result, not only is there little purification effect, but the concentration limit is also low because the osmotic pressure increases. In the case of an ultrafiltration membrane, amino acid molecules pass through the membrane and cannot be concentrated. In addition, in the case of electrodialysis using an ion exchange membrane, it is possible to prevent amino acids from passing through the membrane near the isoelectric point of the amino acid and concentrate it. This has the inconvenience of restricting its use because it has to be The present invention was made in view of these points, and by using a specific ultrafiltration membrane,
The purpose of the present invention is to provide a method that can concentrate an amino acid aqueous solution in a wide pH range while saving energy, and can also concentrate it while separating contaminating low-molecular substances. The present invention is characterized in that an aqueous solution containing at least one amino acid and having a pH higher than the isoelectric point of any of the amino acids contained therein is passed through an ultrafiltration membrane having a sulfonic acid group. This invention relates to a method for concentrating amino acids. The types of amino acids contained in the aqueous solution do not matter; examples include acidic amino acids such as glutamic acid and aspartic acid, neutral amino acids such as glycine, alanine, isoleucine, phenylalanine, glutamine, threonine, and methionine, and basic amino acids such as lysine and arginine. Amino acids, etc. It is sufficient that the aqueous solution contains at least one kind of these amino acids, and it goes without saying that it may contain many kinds of amino acids. The pH of the aqueous solution must be higher than the isoelectric point of any amino acid it contains. The target amino acids are those to be concentrated; for example, when concentrating two types of amino acids, it is necessary to make the pH higher than the isoelectric point of the amino acid with a higher isoelectric point. In the method of the present invention, the passage of negatively ionized amino acids through the membrane is attempted to be prevented by repulsion with the anions contained in the membrane. Therefore, if the pH of the aqueous solution is higher than the isoelectric point of the amino acid, However, it is preferable to set the pH at which the amino acid is anionized to nearly 100%. Anionized to isoelectric point and close to 100%
Since PH is known for many amino acids, that value can be used, and for other amino acids, it can be easily measured or calculated by known methods. If the PH of the aqueous solution is within this PH range, the aqueous solution can be concentrated as is by the filtration method described below; if not, hydrochloric acid,
The pH can be adjusted to a specified level using caustic soda or the like. Something other than amino acids may be present in the aqueous solution. Depending on the amino acid production method, inorganic salts, sugars, and other low-molecular substances are often included, but many of these must be separated and removed from the amino acid to be concentrated by passing through a membrane during the filtration process described below. I can do it. Examples of inorganic salts include sodium ion,
Examples include various types obtained by combining cations such as potassium ions, ammonium ions, and calcium ions with anions such as chloride ions, sulfate ions, nitrate ions, and phosphate ions. Examples of saccharides include various monosaccharides such as glucose and sucrose, oligosaccharides, and the like. On the other hand, aqueous solutions may contain macromolecular substances such as proteins or microparticles such as bacterial cells that are larger than the pore size of the ultrafiltration membrane, but these may be treated by known denaturation treatment, aggregation treatment, etc. as necessary. Just remove it. The type of amino acid aqueous solution that can be concentrated by the method of the present invention is not limited, and includes various intermediate process solutions for producing amino acids by extraction methods, fermentation methods, enzymatic methods, synthetic methods, etc. Moreover, it can be applied not only to the production of a single amino acid, but also to the production process of amino acid mixtures and even soy sauce. The membrane is an ultrafiltration membrane that is negatively charged at the pH of the aqueous solution it passes through, and specifically contains sulfonic acid groups. Such a membrane can be prepared by introducing sulfonic acid groups into a material normally used for ultrafiltration membranes. An example of a membrane is a sulfonated polysulfone membrane (A.Noshay et al., J.App.Poly.Sei.,
Vol.20, PP1885-1903 (1976), Mihara, Kimura, 47th Annual Meeting of Chemical Industry F104 (1982)). A normal ultrafiltration device may be used as the device for attaching the membrane, and the ultrafiltration conditions may be the same as normal ultrafiltration conditions. The pressure and temperature depend on the pressure resistance, heat resistance, and stability of the amino acid of the membrane, but the pressure is, for example, 1 to 10
Kg/cm ² and temperature may be appropriately selected within the range of, for example, 20 to 90°C. Although the method of the present invention is a method for concentrating amino acids,
If the aqueous solution to be concentrated contains inorganic salts or other low-molecular substances that pass through the membrane, this can be separated, and if it contains two or more types of amino acids, the pH of the aqueous solution can be adjusted to By setting the isoelectric point between the isoelectric points of the amino acids, it is possible to separate them into amino acids with a higher isoelectric point and amino acids with a lower isoelectric point than the PH. That is, if the purpose is only to concentrate amino acids, the pH of the aqueous solution should be set to 4 or higher if the amino acid is an acidic amino acid, 9 or higher if the amino acid is a neutral amino acid, and 9 or higher if the amino acid is a basic amino acid. For example, it may be set to 12 or more. When concentrating and separating multiple amino acids from each other, the pH of the aqueous solution may be adjusted as shown in the table below.

[Table] In the above table, acidic amino acids are A, their isoelectric points are pI _A , neutral amino acids are N, their isoelectric points are
pI _N , and the basic amino acid is B, its isoelectric point is
They are respectively indicated as pI _B. Furthermore, when the purpose is to concentrate amino acids and separate inorganic salts, the same method as the above-mentioned case where only the purpose is to concentrate amino acids may be used. Needless to say, after the concentration according to the present invention is carried out, it is sufficient to carry out processing according to a conventional process. The case where a negatively charged ultrafiltration membrane is used has been described above, but it goes without saying that amino acids can be concentrated using the same principle even if a positively charged ultrafiltration membrane is used. Concentration of amino acids by the ultrafiltration method of the present invention can be carried out over a fairly wide pH range, and not only can amino acids be concentrated by simply applying pressure, but also mutual separation and desalting of amino acids is possible. be. This will be further explained in Examples below. Example 1 Known method (Journal of Applied Polymer
Science, 20 . 1887 (1976), polysulfone (UCC,
P-1700) was sulfonated. Using this polymer, a film was formed under the conditions shown in the table below.

[Table] For ultraviolet rays, use a normal steady-state flow experiment equipment.
Glutamic acid at a concentration of 1.3 meq/or glycine at a concentration of 3.4 meq/was used as the solute. The pressure is 5Kg/cm ² , the flow rate is 4/min, and the liquid temperature is
It was kept constant at 25°C. The pH was adjusted with HCl or NaOH and was carried out in the range of PH2 to 11. From the data obtained as a result, the σ value indicating solute exclusion ability was calculated using a known method. each on the drawing
The σ values of glutamic acid (white circles) and glycine (black circles) at PH are shown. If the concentration is held constant and the pH is changed, the exclusion rate will change. In this case, the exclusion property is approximately proportional to the abundance ratio of the charged solute. Example 2 Ornithine hydrochloride 0.3g and isoleucine 0.3g
Aqueous solution 1 containing the following was subjected to ultrafiltration treatment using the same membrane and conditions as in Example 1. The liquid pH was 7.4. At this time, the inhibition rate of ornithine was 70% and that of isoleucine was 15%, and as a result,
Ornithine and isoleucine were separated. Example 3 Aqueous solution 1 containing 0.3 g of glutamic acid and 0.3 g of isoleucine was subjected to ultrafiltration treatment using the same membrane and conditions as in Example 1. The pH of the solution was adjusted to 7 with NaOH. At this time, the rejection rate of the glutamine membrane was 95% and the rejection rate of isoleucine was 20%, and as a result, glutamic acid and isoleucine were separated. Example 4 Aqueous solution 1 containing 2 g of sodium glutamate and 1 g of sodium chloride was subjected to ultrafiltration treatment using the same membrane and conditions as in Example 1. The liquid pH was 7. At this time, the inhibition rate of glutamic acid was 70%, while the inhibition rate of salt was 10%, and as a result, glutamic acid and salt were separated.

[Brief explanation of drawings]

The figure shows the results of measuring the ability of the sulfonated polysulfone membrane to exclude glutamic acid and dalicin at each pH.

Claims (1)

[Claims] 1 Amino acid concentration characterized by filtering an aqueous solution containing at least one type of amino acid and having a pH higher than the isoelectric point of any of the amino acids contained therein using an ultrafiltration membrane having a sulfonic acid group. Method.