JPH0683651B2 - Manufacturing method of reduced salt soy sauce - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing reduced salt soy sauce.

(Conventional technology) Soy sauce usually contains 18 to 20% of salt in order to slowly ferment it during fermentation to give it a unique umami taste, but since the salt content is so high, the umami taste is high. There is a problem that soy sauce's original umami is hard to feel because it is killed. On the other hand, if the soy sauce is diluted with water or the like to reduce the salt concentration, even the unique umami will be diluted.
Of course, conventional soy sauce having a high salt concentration is unsuitable when a salt-reduced diet is required, such as in patients with kidney disease.

Therefore, various methods for producing reduced salt soy sauce have been conventionally proposed. For example, a method is known in which the raw material composition is changed from the beginning so as to reduce the salt concentration in the product soy sauce, or a method in which the manufactured soy sauce is treated with an ion exchange membrane to remove the salt. However, according to these methods,
There is a problem that chlorine is generated in the manufacturing or treatment process, or even umami components other than salt are removed.

Therefore, using a reverse osmosis membrane, a method of producing salt-reduced soy sauce by selectively removing only salt without losing aromatic components and umami components has been proposed, but soy sauce Due to the concentration of salt, the osmotic pressure is generally very high, and it takes a high pressure to remove the salt by the membrane treatment, and according to the conventional semipermeable membrane, an aqueous solution having such a high salt concentration is used. In all cases, the membrane water permeation rate is remarkably low, which is difficult as a practical method for producing reduced salt soy sauce.

Further, since a cellulose acetate membrane which has been well known as a reverse osmosis membrane has low pH resistance, it is difficult to treat soy sauce having a pH of about 4 for a long period of time without deterioration of the membrane. Further, since the chlorine resistance and heat resistance are poor, the method of cleaning the film after the film treatment is limited. For example, an effective detergent, hypochlorite, cannot be used. Also,
The semipermeable membrane cannot be heat sterilized if necessary.

On the other hand, a membrane made of polysulfone is known as a semipermeable membrane having excellent pH resistance, chlorine resistance, heat resistance, etc. However, since all conventional polysulfone ultrafiltration membranes have a large molecular weight cutoff, It is difficult to apply to the production of reduced salt soy sauce that selectively removes salt.

(Object of the Invention) As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a semipermeable membrane having a sulfonic acid group, particularly a skin layer having a solute separation activity, has a sulfonic acid group. The composite semipermeable membrane, which is formed into an extremely thin thin film, can remove salt even with high salt concentration soy sauce at a relatively low processing pressure and while maintaining a practical water permeability rate. The present invention has been completed by finding that it is possible to obtain a reduced salt soy sauce having a salt concentration of 6 to 15% by selectively removing the aromatic component and the umami component while remaining in the membrane impermeable liquid. Is.

(Structure of Invention) The method for producing a reduced salt soy sauce according to the present invention is characterized by treating soy sauce with a semipermeable membrane having a sulfonic acid group.

The semipermeable membrane having a sulfonic acid group used in the method of the present invention is a semipermeable membrane composed of a polymer in which the sulfonic acid group is the majority of all ion exchange groups, preferably 70% or more, particularly preferably 90% or more. is there. The remaining ion-exchange groups may be ion-exchange groups other than sulfonic acid groups, for example, carboxylic acid groups, as long as the sulfonic acid groups are in the above range of all ion-exchange groups.

In the present invention, as the semipermeable membrane having a sulfonic acid group, which can be particularly preferably used, the repeating unit A A sulfonated polyaryl ether obtained by sulfonation of a polyaryl ether consisting of
And repeating unit B (However, R represents —CO— or —SO ₂ — and R ′ represents a carbon-carbon bond or a divalent group containing —CO— or —SO ₂ —.) An example is a composite semipermeable membrane in which a skin layer made of a sulfonated polyaryl ether obtained by sulfonation of a united product is integrally laminated on an ultrafiltration membrane as a supporting membrane.

Such a composite semipermeable membrane is preferably a sulfonated polyaryl ether comprising the repeating unit A or a cotton-like polyaryl ether copolymer comprising the repeating unit A and the repeating unit B, respectively. An aryl ether is prepared, and 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-volatile organic compound as an additive, or It can be obtained by coating a film-forming solution containing an inorganic salt as an additive on a dried support film, and then evaporating an organic solvent from the film-forming solution.

The above-mentioned sulfonated polyaryl ether can be obtained by treating the corresponding polyaryl ether with concentrated sulfuric acid, but in the present invention, the sulfonated polyaryl ether thus obtained has 0.5 g thereof. It is desirable that the solution of 100 ml of N-methyl-2-pyrrolidone has a logarithmic viscosity of 0.2 or more measured at a temperature of 30 ° C. and an ion exchange capacity of 2.3 meq / g or less. Ion exchange capacity is 2.3 meq / g
When it exceeds, the sulfonated polyaryl ether becomes water-soluble and is unsuitable as a material for a semipermeable membrane for treating an aqueous solution.When the logarithmic viscosity is less than 0.2, pinholes, etc. This is because it is difficult to form a uniform skin layer without defects.

When a skin layer is formed by using a sulfonated polyaryl ether obtained by sulfonation of the cotton-like polyaryl ether copolymer, the cotton-like polyaryl ether copolymer is repeatedly used at 10 mol% or more. It is preferably composed of the unit A and 90 mol% or less of the repeating unit B.

The sulfonic acid group contained in the sulfonated polyaryl ether is represented by the formula —SO ₃ M, where M represents hydrogen, an alkali metal or tetraalkylammonium.

For example, after sulfonation of a polyaryl ether, the sulfonated polyaryl ether is washed with water and dried to obtain a sulfonated polyaryl ether having a free sulfonic acid group. Further, the sulfonic acid group can be converted to an alkali metal salt by suspending the sulfonated polyaryl ether in an aqueous solution of an alkali metal hydroxide or an alkali metal alcoholate, a methanol solution, an ethanol solution, or the like. Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, and examples of the alkali metal alcoholate include sodium methylate, potassium methylate, potassium ethylate and the like. Further, if the sulfonated polyaryl ether is treated in the same manner with a solution of tetraalkylammonium, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, etc. The acid group can be the corresponding tetraalkylammonium salt.

The composite semipermeable membrane which can be preferably used in the method of the present invention comprises the above-mentioned sulfonated polyaryl ether, a water-soluble and low-volatile 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 which may be contained to form a film-forming solution, coating this on a dried support film, and then evaporating an organic solvent from the film-forming solution. .

As the organic solvent for preparing the film forming solution, an alkylene glycol alkyl ether having an alkylene group having 2 to 4 carbon atoms and an alkyl group having 1 to 4 carbon atoms is particularly preferably used. This solvent has excellent solubility in the sulfonated polyaryl ether and is highly volatile, while, as will be described later,
This is because it does not dissolve the polysulfone ultrafiltration membrane that can be suitably used as the support membrane in the composite semipermeable membrane used in the present invention.

Specific examples of such alkylene glycol alkyl ethers include, for example, 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 high volatility.

However, depending on the sulfonated polyaryl ether used, it may be difficult to dissolve it in the above alkylene glycol alkyl ether, or it may simply swell. It has been found that it dissolves well in a mixed solvent prepared by adding an aprotic polar organic solvent. As such an aprotic polar organic solvent,
For example, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and the like are preferably used. In such a mixed solvent, the proportion of the aprotic polar organic solvent is preferably 5 parts by weight or less, particularly 3 parts by weight or less with respect to 100 parts by weight of the alkylene glycol alkyl ether. In the mixed solvent, when the aprotic polar organic solvent is more than 5 parts by weight with respect to 100 parts by weight of the alkylene glycol alkyl ether, a dry polysulfone ultrafiltration membrane as described below is used as a supporting membrane to form a membrane-forming solution. This is because, when this is applied onto this support film, this support film dissolves or swells, so that a composite semipermeable membrane with good performance cannot be obtained.

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

The concentration of the sulfonated polyaryl ether in the membrane forming solution is also related to the thickness of the semipermeable membrane made of these polymers in the obtained composite semipermeable membrane, but usually in the range of 0.05 to 10% by weight, particularly preferably , 0.1 to 5% by weight is preferable.

When producing a composite semipermeable membrane that can be suitably used in the method of the present invention, the above membrane forming solution contains a specific additive. Among such 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 compounds as these additives are water-soluble and have low volatility, and are required to be dissolved in the film-forming solution. Therefore, a polyhydric alcohol having 2 to 5 carbon atoms and a low molecular weight are required. Polyalkylene glycol, carboxylic acid, its salt,
Hydroxycarboxylic acid or a salt thereof is preferably used. Specific examples include polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, and 1,4-
Butanediol or the like, polyethylene glycol as diethylene glycol, triethylene glycol, dipropylene glycol or the like, carboxylic acid as citric acid, oxalic acid or the like, hydroxycarboxylic acid as lactic acid,
Examples thereof include hydroxybutyric acid, and examples of salts of carboxylic acid and hydroxycarboxylic acid include sodium salt and potassium salt.

Further, an inorganic salt which is water-soluble and is soluble in the film-forming solution can also be used as an additive. Examples of such inorganic salts include lithium chloride, lithium nitrate, magnesium perchlorate, and the like.

The concentration of these additives in the film forming solution is usually 0.1 to 8
It is in the range of 0% by weight. Although the effect of these additives on the formation of a composite semipermeable membrane is not always clear, it is related to the micropore size of the semipermeable membrane formed from the sulfonated polyarylether, and the membrane forming solution is used as a support membrane. When applied on a certain ultrafiltration membrane, the solvent and additives of the membrane-forming solution appear to modify the surface of the ultrafiltration membrane, thus
By selecting the type and amount of the additive to be used, the performance of the obtained composite semipermeable membrane, in particular, the removal rate for the solute containing the coloring component and the membrane permeated water amount can be controlled in a wide range.

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

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

As described above, when a mixed solvent containing an alkylene glycol alkyl ether or a small amount of the aprotic polar organic solvent is used as the solvent for the film-forming solution, usually,
It is possible to evaporate virtually all the solvent at room temperature without the need for heating, however, in order to evaporate the solvent after applying the film-forming solution onto the supporting film, it is necessary to evaporate the solvent. You may heat. The heating temperature may be appropriately selected depending on the solvent used, but a temperature of 150 ° C. or lower is usually sufficient. In addition, in order to accelerate evaporation of the solvent after applying the film forming solution on the support film, the film forming solution may be heated in advance and applied on the support film.

The film thickness of the thin film semipermeable membrane based on the sulfonated polyaryl ether 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 supporting membrane. Depending on the method, it is preferable that the composite semipermeable membrane be thin in order to increase the water permeation rate, and thicker in order to increase the strength. Therefore, although not particularly limited, the semipermeable membrane having solute separation activity based on the sulfonated polyaryl ether preferably has a membrane thickness of usually 0.01 to 5 μm.

As described above, the skin layer having a thickness of 10 μm or less and having a sulfonic acid group and having separation performance is made of a sulfonated polyaryl ether, and the skin layer is integrally laminated on the support membrane. A sulfonated polyaryl ether composite semipermeable membrane can be obtained.

In the composite semipermeable membrane thus obtained, the additive may remain in the membrane depending on the kind of the additive used, but the obtained composite semipermeable membrane is treated in water. Soak in
These additives are removed from the membrane by passing water or immediately permeating soy sauce.

Thus, the composite semipermeable membrane comprising the sulfonated polyaryl ether and having a skin layer having a thickness of 10 μm or less is stable over a pH range of 1 to 14 even at 80 ° C. Since soy sauce with a high salt content has a high water permeation rate and a high selective removal rate with respect to salt content, it is possible to practically obtain a reduced salt soy sauce that retains an umami component and an aroma component.

In the method of the present invention, the composite semipermeable membrane described above has a higher water permeation rate even with high salt concentration of soy sauce as compared with a conventional reverse osmosis membrane made of cellulose acetate or the like, but is still larger. Soy sauce as a processing stock solution is diluted to about 30 times the volume so that the soy sauce can be processed at a water permeation rate, and the osmotic pressure of the soy sauce is reduced to 0.2 to 2 volumes by volume of the stock solution.
It is preferable to concentrate to double to obtain reduced salt soy sauce. Particularly preferably, soy sauce as a stock solution is diluted 1 to 20 times, and concentrated in a range of 0.5 to 2 times that of the stock solution to give a salt concentration of about 6 to 15%. Thus, diluting the undiluted soy sauce for membrane treatment is also effective for retaining the umami and aroma components in the undiluted soy sauce in the membrane permeate.

The condition of the permeation treatment is usually 5 to 50 kg / cm ² , though it depends on the dilution rate of the undiluted soy sauce and the required degree of salt reduction, and the treatment temperature is the heat resistance of the composite semipermeable membrane described above. Because it ’s excellent,
The treatment can be carried out in the range of 0 to 95 ° C, but usually room temperature is sufficient. Of course, the higher the treatment pressure and the treatment temperature, the higher the water permeation rate can be.

Further, the above-mentioned composite semipermeable membrane used in the method of the present invention is excellent not only in heat resistance but also in chlorine resistance. Therefore, when washing the composite semipermeable membrane, use an aqueous solution of sodium hypochlorite. You can In particular, an aqueous solution having a sodium hypochlorite concentration of 5000 ppm or less can be preferably used. In addition, the above-mentioned composite semipermeable membrane may be heated to 95 ° C if necessary.
If the temperature is up to, heat sterilization can be performed if necessary.

(Effect of the Invention) As described above, according to the method of the present invention, a semipermeable membrane having a sulfonic acid group, in particular, having a sulfonic acid group having an ultrathin film solute separation activity composed of a sulfonated polyaryl ether is used. Since the semipermeable membrane has a sulfonic acid group and is highly hydrophilic, it is possible to secure a high water permeation rate even with a relatively low processing pressure for soy sauce having a high salt concentration, and to remove salt content. Since it can be selectively separated and removed, the salt concentration is about 6 to 15%, and the reduced salt soy sauce that retains the umami and aroma components can be easily and highly produced as a membrane permeate. Obtainable.

Further, since the composite semipermeable membrane described above has excellent pH resistance, it is possible to perform membrane cleaning with hypochlorite and heat sterilization as necessary.

(Examples) Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In the examples, the solute removal rate and the water permeation rate were calculated by the following equations.

Example 1 (1) Production of sulfonated polysulfone Repeating unit A ₁ Polysulfone (10 g) was added to 97% concentrated sulfuric acid (80 ml), and the mixture was gently stirred and reacted at room temperature for 4 hours to obtain a blackish brown viscous reaction solution. This was put into an ice bath to solidify the sulfonated polysulfone. After washing with water, the mixture was left overnight in 800 ml of 0.5N aqueous sodium hydroxide solution. Then, the polymer was washed until the washing solution became neutral, and then at 30 ° C. for 7 hours.
Vacuum dried for an hour. The pale yellow granular sulfonated polysulfone thus obtained had an inherent viscosity of 3.00, sulfonic acid groups of 100% of all ion exchange groups, and an ion exchange capacity of 1.92 meq / g.

(2) Preparation of composite semipermeable membrane An anisotropic ultrafiltration membrane comprising the repeating unit of the above formula C and having a removal rate of 10% for polyethylene glycol having an average molecular weight of 20,000 is dried at a temperature of 60 ° C, A dry ultrafiltration membrane for the support membrane was obtained.

After dissolving 0.8 g of the sulfonated polysulfone obtained above in 79.2 g of ethylene glycol monomethyl ether, 10 g of lactic acid was added, and the polymer solution obtained by filtering with 10 μm filter paper was used as a film forming solution.

This membrane-forming solution was applied onto the above dry ultrafiltration membrane, most of the solvent was volatilized at room temperature, and then the mixture was treated at a temperature of 60 ° C. for 5 minutes to give a composite semi-layer having a skin layer of 0.5 μm in thickness. A permeable membrane was obtained.

The performance of this composite semipermeable membrane is that the removal rate is 50% when treated with 0.5% sodium chloride aqueous solution at 25 ° C and 50 kg / cm ^2.
%, The water transmission rate was 6 m ³ / m ² / day.

The molecular weight cut-off here refers to the GPC of polyethylene glycol when the removal rate is about 90% when a 0.05% aqueous solution of polyethylene glycol having a different molecular weight is treated under the conditions of 25 ° C. and 20 kg / cm ^2. Dextran equivalent molecular weight.

(3) Manufacture of reduced salt soy sauce A commercially available soy sauce having a sodium chloride concentration of 18%, a total nitrogen concentration of 1.6% and a pH of 4.6 is used as a stock solution, which is diluted 10 times by volume,
Using the composite semipermeable membrane obtained above, process temperature 25 ℃, process pressure
Membrane-permeabilized at 50 kg / cm ² , concentrated to the same amount as the stock solution, sodium chloride concentration of 12%, total nitrogen concentration of 1.5%, reduced soy sauce with the same flavor and aroma as the stock solution. Got The average water permeation rate was 0.5 m ³ / m ² / day.

Example 2 (1) Production of sulfonated polysulfone copolymer 57 mole% of the repeating unit of the formula A ₁ and repeating unit of the formula B ₁ 97% of cotton-like polysulfone copolymer consisting of 43 mol%
80% concentrated sulfuric acid was added and dissolved, and the mixture was stirred and reacted at room temperature for 4 hours to obtain a blackish brown viscous reaction liquid. This was put into an ice bath to solidify the sulfonated polysulfone copolymer. After washing with water, 800m of 0.5N sodium hydroxide solution
l left in overnight. Next, this polymer was washed until the washing liquid became neutral, and then vacuum dried at 60 ° C. for 5 hours.

The sulfonated polysulfone copolymer thus obtained had an inherent viscosity of 0.84, sulfonic acid groups were 100% of all ion exchange groups, and an ion exchange capacity of 1.2 meq / g.

(2) Preparation of composite semipermeable membrane 0.8 g of the cotton-like sulfonated polysulfone copolymer obtained above was dissolved in 79.2 g of ethylene glycol monomethyl ether, 2 g of glycerin was added, and the mixture was obtained by filtering with 10 μm filter paper. The polymer solution was used as a film forming solution.

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

The performance of this composite semipermeable membrane is that the removal rate is 80% when treated with a 0.5% sodium chloride aqueous solution at 25 ° C and 50 kg / cm ^2.
%, The water permeability rate was 1.7 m ³ / m ² / day.

(3) Production of reduced-salt soy sauce The same soy sauce used in Example 1 was diluted 10 times by volume in the same manner, and concentrated under the same conditions until the same amount as the stock solution was obtained. Soy sauce with a total nitrogen concentration of 1.6% and a flavor and aroma that were almost the same as the stock solution was obtained.
The average water permeation rate was 0.2 m ³ / m ² / day.

Example 3 Cotton-like sulfonated polysulfone copolymer obtained in Example 2
After dissolving 8 g of ethylene glycol monomethyl ether in 79.2 g, 34 g of glycerin was added thereto and filtered through 10 μm filter paper to obtain a film forming solution.

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

The performance of this composite semipermeable membrane is that the removal rate is 10% when treated with a 0.5% sodium chloride aqueous solution at 25 ° C and 50 kg / cm ^2.
%, The water transmission rate was 21 m ³ / m ² / day.

Using this composite semipermeable membrane, the same soy sauce as in Example 1 was treated under the same conditions as in Example 1 to obtain a sodium chloride concentration of 14% and a total nitrogen concentration of 1.2%. I got soy sauce with low salt. The average permeation rate is 5 m ³ / m ²
/ It was a day.

Example 4 (1) Production of sulfonated polyaryl ether ketone) Repeating unit A ₂ Polyaryletherketone consisting of (PEEK manufactured by ICI
45 g) was added to 80 ml of 97% concentrated sulfuric acid, reacted at room temperature for 8 hours, and allowed to stand at room temperature for 17 hours to obtain a concentrated sulfuric acid solution of the above polymer.

The above solution was thinly poured onto pure water cooled in an ice bath so as to pull a thread to solidify the polymer, which was collected by filtration and washed with pure water.
Washed twice. 1N sodium hydroxide solution 60 in this polymer
After adding 0 ml, the mixture was left standing for 3 hours, and then washed until the pH of the washing liquid reached 7. Then, the polymer was dried at 60 ° C. for 16 hours to obtain 11.6 g of a sulfonated polyaryl ether ketone. That this polymer is sulfonated. It was confirmed by its infrared absorption spectrum and nuclear magnetic resonance spectrum.

The ion exchange capacity of this polymer is 1.5 meq / g,
A solution of 0.5 g of N-methylpyrrolidone in 100 ml had an inherent viscosity of 1.30 measured at 30 ° C.

(2) Preparation of composite semipermeable membrane After dissolving 9 g of the sulfonated polyaryl ether ketone obtained above in 89.1 g of ethylene glycol monomethyl ether, 10 g of glycerin was added, and the solution was obtained by filtering with 10 μm filter paper. It was a membrane solution.

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

The performance of this composite semipermeable membrane is that the removal rate is 20% when treated with a 0.5% sodium chloride aqueous solution at 25 ° C and 50 kg / cm ^2.
%, The water permeability rate was 10 m ³ / m ² / day.

(3) Production of reduced-salt soy sauce The same soy sauce used in Example 1 was similarly diluted 10 times in volume, and concentrated under the same conditions until the same amount as the stock solution, sodium chloride concentration 13.1%, With a total nitrogen concentration of 1.4%,
A reduced salt soy sauce having almost the same flavor and aroma as the stock solution was obtained.
The average water permeation rate was 1 m ³ / m ² / day.

Example 5 The same soy sauce used in Example 1 was not diluted, and was permeabilized with the composite semipermeable membrane obtained in Example 3 under the conditions of a treatment temperature of 25 ° C. and a treatment pressure of 50 kg / cm ^2. , Concentrated to 0.85 times the stock solution. Then, water is added to this concentrate until the same amount as the stock solution, sodium chloride concentration 15%, total nitrogen concentration 1.
It was 5%, and soy sauce reduced in salt, which had almost the same flavor and aroma as the undiluted solution, was obtained. The average water permeation rate was 0.3 m ³ / m ² / day.

Claims (3)

[Claims] 1. A method for producing reduced salt soy sauce, which comprises treating soy sauce with a semipermeable membrane having a sulfonic acid group. 2. A composite semi-permeable membrane having a sulfonic acid group, which comprises a thin film skin layer having a sulfonic acid group and having solute separation activity, and a support membrane integrally supporting the skin layer. The method for producing a reduced salt soy sauce according to claim 1, which is a permeable membrane. 3. A composite semipermeable membrane having a sulfonic acid group has a repeating unit A. A sulfonated polyaryl ether obtained by sulfonation of a polyaryl ether consisting of
And repeating unit B (However, R represents —CO— or —SO ₂ — and R ′ represents a carbon-carbon bond or a divalent group.) A sulfonated polyaryl ether obtained by sulfonation of a linear polyaryl ether copolymer. The method for producing a reduced salt soy sauce according to claim 2, wherein a skin layer having a solute separation activity consisting of is integrally laminated on an ultrafiltration membrane as a supporting membrane.