JPS61224964A - Production of soy having low salt content - Google Patents

Abstract

PURPOSE:To produce a soy having low salt content and excellent taste and flavor in high productivity, by treating a soy with a semi-permeable membrane having sulfonic acid group, thereby separating and removing salt selectively at a high rate of permeation under a relatively low pressure even in the case of a soy having high salt concentration. CONSTITUTION:A soy having low salt content can be produced by treating a soy with a semipermeable membrane having sulfonic acid group. The semipermeable membrane having sulfonic acid group is preferably a composite semipermeable membrane composed of (A) a skin layer having solute-separation activity and consisting of (i) a sulfonated polyaryl ether obtained by sulfonating a polyaryl ether composed of the unit of formula I (R is -CO- or -SO2-) or (ii) a sulfonated polyaryl ether obtained by sulfonating a linear polyaryl ether copolymer composed of the recurring unit of formula I and the recurring unit of formula II (R' is C-C bond or bivalent group) and (B) an ultrafiltration membrane integrated with the layer A and acting as the supporting membrane of the layer B.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing low-salt soy sauce.

(Prior Art) Soy sauce usually contains 18 to 20% salt in order to ferment slowly during production to give it a unique umami taste.
Because of this high salt concentration, there is a problem in that the umami is diminished by the salt, making it difficult to experience the umami inherent in soy sauce. On the other hand, if soy sauce is diluted with water or the like to lower its salt concentration, the unique umami flavor will also be diluted. Of course, conventional soy sauce with a high salt concentration is inappropriate for patients who require a low-salt diet, such as patients with kidney disease.

Therefore, various methods for producing low-salt soy sauce have been proposed. For example, methods are known in which the raw material composition is changed from the beginning to lower the salt concentration in the product soy sauce, and a method in which the produced soy sauce is treated with an ion exchange membrane to remove salt.

However, these methods have problems in that chlorine is generated during the production or treatment process, or even umami components other than salt are removed.

To this end, a method has been proposed that uses a reverse osmosis membrane to selectively remove only salt without losing aromatic or umami components to produce low-sodium soy sauce. Due to the concentration of salt, the osmotic pressure is generally very high, and high pressure is required to remove salt through membrane treatment. In either case, the membrane water permeation rate is extremely low, making it difficult to use as a practical method for producing low-salt soy sauce.

Furthermore, cellulose acetate membranes, which have traditionally been well known as reverse osmosis membranes, have low pH resistance, so it is difficult to process soy sauce with a p)l level of about 4 over a long period of time without deteriorating the membrane. . Furthermore, since the chlorine resistance and heat resistance are poor, methods for cleaning the membrane after membrane treatment are limited. For example, hypochlorite, which is an effective cleaning agent, cannot be used. Also, the semipermeable membrane cannot be heat sterilized if necessary.

On the other hand, membranes made of polysulfone are known as semipermeable membranes with excellent pH resistance, chlorine resistance, heat resistance, etc. However, all conventional polysulfone ultrafiltration membranes have a large molecular weight cutoff, so It is difficult to apply this method to the production of low-salt soy sauce, which selectively removes salt.

(Objective of the Invention) As a result of intensive research to solve the above-mentioned problems, the present inventors have discovered that a semipermeable membrane having a sulfonic acid group, particularly a skin layer having solute separation activity, has a sulfonic acid group and The composite semipermeable membrane, which is formed into an extremely thin film, can remove salt from soy sauce with a relatively low salt concentration while maintaining a practical water permeation rate. In addition to selectively removing aromatic and umami components, they are allowed to remain in the permeate under the membrane, resulting in a salinity concentration of 6 to 15%.
The present invention was achieved by discovering that it is possible to obtain a reduced-salt soy sauce.

(Structure of the Invention) The method for producing low-salt soy sauce according to the present invention is characterized in that soy sauce is treated with a semipermeable membrane having sulfonic acid groups.

The semipermeable membrane having sulfonic acid groups used in the method of the present invention is a semipermeable membrane made of a polymer in which sulfonic acid groups account for most of the total ion exchange groups, preferably 70% or more, particularly preferably 90% or more. be.

As long as the sulfonic acid group is within the above range among all ion exchange groups, the remaining ion exchange group may be an ion exchange group other than the sulfonic acid group, for example, a carboxylic acid group.

In the present invention, as a semipermeable membrane having a sulfonic acid group that can be particularly suitably used, simple repeating sulfonated polyaryl ether, or the above repeating unit A and repeating unit B (where R is 100- or -SO From sulfonated polyaryl ether obtained by sulfonating a linear polyaryl ether copolymer consisting of Examples include a composite semipermeable membrane in which a skin layer is integrally laminated on an ultrafiltration membrane as a support membrane.

Such a composite semipermeable membrane is preferably produced by sulfonating a polyarylether consisting of the above-mentioned repeating unit A or a linear polyarylether copolymer consisting of the above-mentioned repeating unit A and repeating unit B, respectively. The aryl ether is prepared and mixed with an alkylene glycol alkyl ether such as ethylene glycol monomethyl ether, which may contain a small amount of an aprotic polar organic solvent, and a water-soluble and low-volatility organic compound as an additive or It can be obtained by applying a film-forming solution containing an inorganic salt as an additive onto a dried support film, and then evaporating the organic solvent from this film-forming solution.

The above-mentioned sulfonated polyarylether can be obtained by treating the corresponding polyarylether with concentrated sulfuric acid. In the present invention, the sulfonated polyarylether obtained in this way is
The logarithmic viscosity measured at a temperature of 30 ° C. for a solution prepared by dissolving g in 100 ml of N-methyl-2-pyrrolidone is 0.2 or more, and the ion exchange capacity is 2.3 mE-It/g or less. It is desirable that there be. Ion exchange capacity is 2.3 millimeters! /g, the sulfonated polyarylether becomes water-soluble and is unsuitable as a material for semipermeable membranes for treating aqueous solutions, and when the logarithmic viscosity is less than 0.2. This is because it is difficult to form a uniform skin layer without defects such as pinholes.

In addition, when forming a skin layer using a sulfonated polyarylether obtained by sulfonating the linear polyarylether copolymer, the linear polyarylether copolymer has a repetition rate of 10 mol% or more. Unit A and 9
It is preferable that the repeating unit B is 0 mol % or less.

The sulfonic acid group possessed by the above-mentioned sulfonated polyarylether is represented by the formula -302M, where M is hydrogen,
Indicates an alkali metal or tetraalkylammonium.

For example, by sulfonating a polyaryl ether, washing the sulfonated polyaryl ether with water, and drying it, a sulfonated polyaryl ether having free sulfonic acid groups can be obtained. Furthermore, by suspending and treating this sulfonated polyarylether in an aqueous solution, methanol, ethanol solution, etc. of an alkali metal hydroxide or alkali metal alcoholade, the sulfonic acid group can be converted into an alkali metal salt. As the alkali metal hydroxide, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. are used, and as the alkali metal alcoholade, for example, sodium methylate, potassium methylate, potassium ethylate, etc. are used. Furthermore, if a sulfonated polyaryl ether is similarly treated with a solution of tetraalkylammonium, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, etc., the polymer The sulfonic acid group can be the corresponding tetraalkylammonium salt.

The composite semipermeable membrane that can be suitably used in the method of the present invention comprises the above-mentioned sulfonated polyarylether, a water-soluble and low-volatility compound as an additive, and a small amount of an aprotic polar organic solvent. It can be obtained by dissolving it in an alkylene glycol alkyl ether that may contain it to form a film-forming solution, applying this onto a dried support film, and then evaporating the organic solvent from this film-forming solution.

As the organic solvent for preparing the film-forming solution, alkylene glycol alkyl ethers in which the alkylene group has 2 to 4 carbon atoms and the alkyl group has 1 to 4 carbon atoms are particularly preferably used.

This solvent has excellent solubility for the sulfonated polyarylether and is highly volatile, and on the other hand, as described later, it is suitable for use as a support membrane in the composite semipermeable membrane used in the present invention. This is because it does not dissolve the polysulfone ultrafiltration membrane that can be used.

Specific examples of such alkylene glycol alkyl ethers include alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and ethylene glycol dimethyl ether. , ethylene glycol methyl ethyl ether,
Mention may be made of alkylene glycol dialkyl ethers such as ethylene glycol diethyl ether. In particular, ethylene glycol monomethyl ether is preferably used because it has excellent solubility in sulfonated polyaryl ether and is highly volatile.

However, depending on the sulfonated polyaryl ether used, it may be difficult to dissolve it in the alkylene glycol alkyl ether, or it may simply swell, but such polymers may also contain a small amount of aprotons in the alkylene glycol alkyl ether. It was found that it dissolves well in a mixed solvent prepared by adding a polar organic solvent.

As such an aprotic polar organic solvent, for example, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, etc. are preferably used.

In such a mixed solvent, the proportion of the aprotic polar organic solvent is as follows:
00 parts by weight is preferably 5 parts by weight or less, particularly 3 parts by weight or less. In the mixed solvent, if the amount of the aprotic polar organic solvent is more than 5 parts by weight per 100 parts by weight of the alkylene glycol alkyl ether, use a dry polysulfone ultrafiltration membrane as described below as the support membrane to prepare the membrane forming solution. This is because when applied on this support membrane, the support membrane dissolves or swells, making it impossible to obtain a composite semipermeable membrane with good performance.

In addition, as a solvent for the membrane-forming solution, using alkylene glycol alkyl ether or a mixed solvent of this and a small amount of the aprotic polar organic solvent can be used, as described later, after applying the membrane-forming solution to the support membrane. In the step of evaporating and removing the solvent from the film-forming solution, it is advantageous because substantially all the solvent can be removed by heating at room temperature to a small amount, and a uniform thin film without defects can be obtained.

The concentration of the sulfonated polyaryl ether in the membrane forming solution is related to the thickness of the semipermeable membrane made of these polymers in the resulting composite semipermeable membrane, but is usually 0.05 to 1.
A range of 0% by weight is preferred, and a range of 0.1 to 5% by weight is particularly preferred.

When manufacturing a composite semipermeable membrane that can be suitably used in the method of the present invention, the membrane forming solution contains specific additives. Among these additives, as the organic compound, at least one selected from the group consisting of polyhydric alcohols, polyalkylene glycols, carboxylic acids, salts thereof, hydroxycarboxylic acids and salts thereof is used. The organic compound used as the agent is water-soluble and has low volatility, and needs to be dissolved and dissolved in the film forming solution. Polyalkylene glycol, carboxylic acid, its salt,
Hydroxycarboxylic acids or salts thereof are preferably used. Specific examples include ethylene glycol, propylene glycol, glycerin, 1.4-
butanediol, etc., polyalkylene glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, etc., carboxylic acids such as citric acid, oxalic acid, hydroxycarboxylic acids such as lactic acid, hydroxybutyric acid, etc. Examples of carboxylic acid salts include sodium salts and potassium salts.

Furthermore, inorganic salts that are water-soluble and dissolve in the membrane forming solution can also be used as additives. Examples of such inorganic salts include lithium chloride, lithium nitrate, and magnesium perchlorate.

The concentration of these additives in the film forming solution is usually 0.1
~80% by weight. Although the effects of these additives on the formation of composite semipermeable membranes are not necessarily clear,
It is related to the micropore diameter of the semipermeable membrane formed from sulfonated polyaryl ether, and when the membrane forming solution is applied onto the ultrafiltration membrane that is the supporting membrane, the solvent and additives of the membrane forming solution are It seems to modify the surface of the ultrafiltration membrane, and thus, by selecting the type and amount of the additive used, the performance of the resulting composite semipermeable membrane, especially the removal rate for solutes containing colored components and the amount of water permeated through the membrane, can be changed. can be controlled over a wide range.

The membrane forming solution prepared as described above is then applied onto a dry ultrafiltration membrane as a support membrane. As is well known, a dry ultrafiltration membrane is produced by heating a wet ultrafiltration membrane prepared by a wet method to an appropriate temperature to evaporate the water contained in the pores of the membrane. It can be obtained by substantially drying.

In the above method, the ultrafiltration membrane as a support membrane for applying the membrane-forming solution is not particularly limited, but is preferably an ultrafiltration membrane made of polysulfone, for example, a repeating membrane of the following formula C. An ultrafiltration membrane consisting of units is preferably used.

As mentioned above, when using an alkylene glycol alkyl ether or a mixed solvent containing a small amount of the aprotic polar organic solvent as the solvent for the membrane forming solution, usually
Substantially all of the solvent can be evaporated at room temperature without the need for heating; however, after the coating solution is applied onto the support membrane, it is possible to evaporate the solvent if necessary. May be heated. The heating temperature may be appropriately selected depending on the solvent used, but a temperature of 150° C. or lower is usually sufficient. Incidentally, in order to promote evaporation of the solvent after the film-forming solution is applied onto the support film, the film-forming solution may be heated in advance and then applied onto the support film.

The thickness of the thin semipermeable membrane based on sulfonated polyarylether in the composite semipermeable membrane thus obtained depends on the concentration of these polymers in the membrane forming solution and the coating thickness of the membrane forming solution on the support membrane. Although it depends on the situation, it is better to make the composite semipermeable membrane thinner to increase the water permeation rate, and thicker to increase the strength.

Therefore, although not particularly limited, it is preferable that a semipermeable membrane having a solute separation activity based on sulfonated polyaryl ether generally has a membrane thickness in the range of 0.01 to 5 μm.

In this way, the thickness is usually less than 108 m,
A sulfonated polyaryl ether composite semipermeable membrane can be obtained in which a skin layer having sulfonic acid groups and separation performance is made of sulfonated polyaryl ether, and this skin layer is integrally laminated on a support membrane.

In addition, depending on the type of additive used, additives may remain in the composite semipermeable membrane obtained in this way, but if the composite semipermeable membrane obtained is immersed in water. death,
These additives are removed from the membrane by passing water through it or by immediately permeating the soy sauce.

As described above, the composite semipermeable membrane having a skin layer made of the above-mentioned sulfonated polyarylether and preferably having a thickness of 10 μm or less has a pH of 1 to 1 even at 80°C.
It is stable over a range of 14, has a high water permeation rate, and has a high selective removal rate for salt when it comes to high-salt soy sauce, making it practical to produce low-salt soy sauce that retains umami and aromatic components. Obtainable.

In the method of the present invention, the above-described composite semipermeable membrane has a higher water permeation rate than a conventional reverse osmosis membrane made of cellulose acetate, even for soy sauce with a high salt concentration; In order to process soy sauce at a water permeation rate, we dilute the soy sauce as a processing stock solution to about 30 times the volume, lower the osmotic pressure of the soy sauce, and dilute this by 0.2 times the volume of the stock solution.
It is preferable to concentrate up to 2 times to obtain a low-salt soy sauce.

Particularly preferably, soy sauce as a stock solution is diluted ~20 times, and this is concentrated to a range of 0.5 to 2 times the stock solution.
The salt concentration should be about 6-15%. Diluting the undiluted soy sauce and subjecting it to the membrane treatment in this way is also effective for retaining the umami and aroma components in the undiluted soy sauce in the membrane-permeated liquid.

The conditions for permeation treatment depend on the dilution rate of the undiluted soy sauce and the degree of salt reduction required, but are usually 5 to 50 kg/d.
Since the above-mentioned composite semipermeable membrane has excellent heat resistance, the treatment temperature can be in the range of 0 to 95°C, but usually room temperature is sufficient. Of course, the higher the treatment pressure and treatment temperature, the higher the water permeation rate.

Furthermore, the above-described composite semipermeable membrane used in the method of the present invention has excellent not only heat resistance but also chlorine resistance, so when cleaning the composite semipermeable membrane, an aqueous sodium hypochlorite solution may be used. I can do it.

In particular, an aqueous solution having a sodium hypochlorite concentration of 5000 ppm or less can be suitably used. Further, the composite semipermeable membrane described above can be heat sterilized at temperatures up to 95° C., if necessary.

(Effects of the Invention) As described above, according to the method of the present invention, a semipermeable membrane having a sulfonic acid group, particularly a semipermeable membrane having a sulfonic acid group having a solute separation activity in the form of an ultra-thin film made of sulfonated polyaryl ether The semi-permeable membrane has sulfonic acid groups and is highly hydrophilic, so it can ensure a high water permeation rate even at relatively low processing pressure for soy sauce with a high salt concentration, and it also reduces salt content. Since it can be selectively separated and removed, low-salt soy sauce with a salt concentration of about 6 to 15% and retaining umami and aromatic components can be easily and highly productively produced as a membrane permeate. Obtainable.

Furthermore, since the above-mentioned composite semipermeable membrane has excellent pH resistance, membrane cleaning with hypochlorite or
Heat sterilization can also be performed.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way. In the examples, the solute removal rate and water permeation rate were determined by the following formulas.

Example 1 (Production of 11 sulfonated polysulfone) 10 g of polysulfone consisting of repeating unit A1 was dissolved in 80 ni1 of 97% concentrated sulfuric acid.
In addition, the mixture was stirred slowly at room temperature for 4 hours to obtain a blackish brown viscous reaction liquid. This was placed in a water bath to solidify the sulfonated polysulfone. After washing with water, 0
．． The mixture was left overnight in 800 ml of 5N aqueous sodium hydroxide solution. Next, the polymer was washed until the washing solution became neutral, and then vacuum-dried at 30° C. for 7 hours. The pale yellow granular sulfonated polysulfone thus obtained has a logarithmic viscosity of 3.00. Sulfonic acid group is one of all ion exchange groups
00%, and the ion exchange capacity is 1.92 meq/g.
Met.

(2) Preparation of composite semipermeable membrane Consisting of repeating units of the above formula C, with an average molecular weight of 20,000
An anisotropic ultrafiltration membrane having a removal rate of 10% for polyethylene glycol was dried at a temperature of 60° C. to obtain a dry ultrafiltration membrane for a support membrane.

After dissolving 0.8 g of the sulfonated polysulfone obtained above in 79.2 g of ethylene glycol monomethyl ether, g of lactic acid was added thereto, and the resulting polymer solution was filtered through a 10 μm filter paper and used as a membrane forming solution.

This membrane-forming solution was applied onto the dry ultrafiltration membrane, and after volatilizing most of the solvent at room temperature, it was heat-treated at 60°C for 5 minutes to form a composite film with a skin layer of 0.5 μm in thickness. A semipermeable membrane was obtained.

The performance of this composite semipermeable membrane was that when treated with a 0.5% sodium chloride aqueous solution at 25° C. and 50 kg/cIa, the removal rate was 50% and the water permeation rate was 6 m''/m''/day.

In addition, the molecular weight cut-off here refers to 0.05% aqueous solutions of polyethylene glycols with different molecular weights at 25°C, 20 kg/
- refers to the dextran-equivalent molecular weight of the polyethylene glycol measured by GPC when the removal rate is approximately 90%.

(3) Production of low-salt soy sauce Sodium chloride concentration 18%, total nitrogen concentration 1.6%, pH
A commercially available soy sauce of No. 4,6 was used as a stock solution, diluted 10 times by volume, and treated at a treatment temperature of 2 using the composite semipermeable membrane obtained above.
Membrane permeation treatment was performed at 5°C and a treatment pressure of 50 kg/cmt,
Concentrate to the same volume as the stock solution, and reduce the sodium chloride concentration to 1.
A low-salt soy sauce with a total nitrogen concentration of 1.5% and a flavor, aroma, etc. almost the same as the original solution was obtained. The average water permeation rate was 0.5 m'/m'' for 7 days.

Example 2 (1) Production of sulfonated polysulfone copolymer 10 g of a linear polysulfone copolymer consisting of 57 mol% of repeating units of the above formula A and 43 mol% of repeating units of NiB1.
was added to 80ml of 97% concentrated sulfuric acid, dissolved, and dissolved at room temperature for 4 hours.
The reaction was stirred for a period of time to obtain a blackish brown viscous reaction liquid. This was placed in a water bath to solidify the sulfonated polysulfone copolymer. After washing with water, it was left in 800 ml of 0.5 N aqueous sodium hydroxide solution overnight. The polymer was then washed until the washing solution became neutral, and then heated at 60°C.
It was vacuum dried for 5 hours.

The sulfonated polysulfone copolymer thus obtained had a logarithmic viscosity of 0.84, sulfonic acid groups accounted for 100% of the total ion exchange groups, and an ion exchange capacity of 1.2 meq/g. .

(2) 0.8 g of linear sulfonated polysulfone copolymer obtained in the preparation of composite semipermeable membrane
79.2 g of ethylene glycol monomethyl ether
After dissolving in the solution, 2 g of glycerin was added, and the obtained polymer solution was filtered through a 10 μm filter paper, and the resulting polymer solution was used as a membrane forming solution.

This membrane forming solution was applied onto the same polysulfone dry ultrafiltration membrane as in Example 1, and after volatilizing most of the solvent at room temperature,
A heat treatment was performed at a temperature of 60° C. for 5 minutes to obtain a composite semipermeable membrane having a skin layer with a thickness of 0.5 μm.

The performance of this composite semipermeable membrane was as follows when treated with 0.5% sodium chloride aqueous solution at 25°C and 50 kg/aJ.
The removal rate was 80% and the water permeation rate was 1.7 m''/m'' in 7 days.

(3) Production of low-salt soy sauce The same soy sauce used in Example 1 was similarly diluted 10 times in volume, concentrated under the same conditions until it reached the same volume as the original solution, and
A low-salt soy sauce was obtained which had a sodium chloride concentration of 10% and a total nitrogen concentration of 1.6%, and whose flavor, aroma, etc. were almost the same as the original solution. The average water permeation rate was 0.2 m'/m'' for 7 days.

Example 3 Linear sulfonated polysulfone copolymer 0 obtained in Example 2
．． 8g of ethylene glycol monomethyl ether79.
After dissolving in 2 g, add 34 g of glycerin to it,
It was filtered through a 10 μm filter paper to obtain a membrane forming solution.

This membrane forming solution was applied to the same polysulfone dry ultrafiltration membrane as in Example 1, and after volatilizing most of the solvent at room temperature,
A composite semipermeable membrane having a skin layer with a thickness of 0.5 μm was obtained by heat treatment at a temperature of 0° C. for 5 minutes.

The performance of this composite semipermeable membrane is that when treated with an IJium aqueous solution (0.5% chloride) at 25°C and 50ksr/J, the removal rate was 10% and the water permeation rate was 21 m'/m'' in 7 days. there were.

Using this composite semipermeable membrane, the same soy sauce as in Example 1 was treated under the same conditions as in Example 1, and the sodium chloride concentration was 14%.
A low-salt soy sauce with a total nitrogen concentration of 1.2% and almost the same flavor, aroma, etc. as the original solution was obtained.

The average water permeation rate was 5 m'/m'' for 7 days.

Example 4 (1) Production of sulfonated polyaryletherketone) Polyaryletherketone consisting of repeating unit A2 (PE produced by ICI)
FiK 45G) 10g in 97% concentrated sulfuric acid 80ml
1 and reacted at room temperature for 8 hours, and then left at room temperature for an additional 17 hours to obtain a concentrated sulfuric acid solution of the above polymer.

The above solution was poured into a thin thread onto pure water cooled in a water bath to solidify the polymer, collected by filtration, and poured with pure water for 50 minutes.
Washed twice. 600 ml of IN sodium hydroxide aqueous solution was added to this polymer, and after being allowed to stand for 3 hours, the polymer was washed until the pH of the washing solution became 7.

After this, the polymer was dried at 60° C. for 16 hours to obtain 11.6 g of sulfonated polyaryletherketone. This polymer is sulfonated.

This was confirmed by its infrared absorption spectrum and nuclear magnetic resonance spectrum.

The ion exchange capacity of this polymer was 1.5 milliequivalents/g, and the logarithmic viscosity of a solution prepared by dissolving 0.5 g of the polymer in 100 n+1 N-methylpyrrolidone at 30° C. was 1.30.

(2) A solution obtained by dissolving 9 g of the sulfonated polyaryletherketone obtained in the preparation of the composite semipermeable membrane in 89.1 g of ethylene glycol monomethyl ether, adding 10 g of glycerin, and filtering through a 10 μm filter paper. was used as a film forming solution.

The above membrane forming solution was applied onto the same dry polysulfone ultrafiltration membrane as used in Example 1, and after volatilizing most of the solvent at room temperature, it was heat treated at a temperature of 60 ° C. for 5 minutes. A composite semipermeable membrane was obtained.

The performance of this composite semipermeable membrane was as follows when treated with 0.5% sodium chloride aqueous solution at 25°C and 50 kg/cd.
The removal rate was 20% and the water permeation rate was 10 m"/m" for 7 days.

(3) Production of low-salt soy sauce The same soy sauce used in Example 1 was similarly diluted 10 times by volume, and tlIfW was added under the same conditions until the volume was equal to that of the original solution.
So, the sodium chloride concentration was 13.1%, and the total nitrogen concentration was 1.
A low-salt soy sauce with a concentration of 4% and almost the same flavor, aroma, etc. as the undiluted solution was obtained. In addition, the average water permeation rate is l m'/
It was 7 days.

Example 5 The same soy sauce used in Example 1 was subjected to permeation treatment using the composite semipermeable membrane obtained in Example 3 under conditions of a treatment temperature of 25 ° C. and a treatment pressure of 50 kg/aJ without diluting it. It was concentrated to 0.85 times the original solution. Next, water was added to this concentrate until the volume was equal to that of the stock solution, and the sodium chloride concentration was 15%.
A low-salt soy sauce with a total nitrogen concentration of 1.5% and almost the same flavor, aroma, etc. as the original solution was obtained. The average water permeation rate was 0.3 m''/m2/day.

Claims (3)

[Claims] (1) A method for producing low-salt soy sauce, which comprises treating soy sauce with a semipermeable membrane having sulfonic acid groups. (2) a thin film-like skin layer in which the semipermeable membrane has a sulfonic acid group and has a solute separation activity;
2. The method for removing colored components according to claim 1, wherein the method is a composite semipermeable membrane comprising a support membrane that integrally supports the semipermeable membrane. (3) A composite semipermeable membrane having a sulfonic acid group is a sulfonated polyaryl ether made by sulfonating a polyaryl ether consisting of the repeating unit A ▲There are mathematical formulas, chemical formulas, tables, etc.▼A, or the above repeating unit A
and repeating unit B ▲There are mathematical formulas, chemical formulas, tables, etc.▼B (However, R represents -CO- or -SO_2-, and R' represents a carbon-carbon bond or a divalent group.) A linear polyaryl consisting of Claim No. 1, characterized in that a skin layer having a solute separation activity and made of a sulfonated polyarylether obtained by sulfonating an ether copolymer is integrally laminated on an ultrafiltration membrane as a support membrane. The method for removing colored components according to item 2.