JP7182960B2 - SOY SAUCE MANUFACTURING METHOD USING POROUS MEMBRANE - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing soy sauce, including a step of filtering pasteurized soy sauce using a porous membrane. More specifically, the present invention relates to a soy sauce manufacturing method comprising a filtration step using a porous membrane for removing agglomerates from pasteurized soy sauce containing agglomerates of starch components, wherein The present invention relates to a method in which the change in components is low, the sediment component removal rate is high, and the recovery of the water permeation amount after the washing process of the porous membrane and the resistance to the washing solution (chemical solution) are high.

Purified water treatment for obtaining drinking water and industrial water from natural water sources such as seawater, river water, lake water, groundwater, etc., which is suspended water A solid-liquid separation operation (turbidity removal operation) for separating and removing suspended solids is required for sewage treatment to make soy sauce, a method for producing soy sauce including a step for removing lees from pasteurized soy sauce, and the like. In such a turbidity removal operation, suspended matter (clay, colloid, bacteria, etc.) derived from natural water source water, which is suspended water, is removed for clean water treatment, and suspended matter in sewage, activated sludge, etc. is removed for sewage treatment. Suspended matter (sludge, etc.) in the treated water that has undergone biological treatment (secondary treatment) is removed, and in the method for producing soy sauce, starch component aggregates aggregated by heating are removed.

Conventionally, these turbidity removal operations have mainly been carried out by pressure flotation, sedimentation, sand filtration, coagulation sedimentation sand filtration, diatomaceous earth filtration, etc. In recent years, membranes have been used instead of these methods. Filtration is becoming popular. Advantages of the membrane filtration method include: (1) high level of turbidity in the obtained water quality and stability (obtained water is highly safe); and (3) ease of automatic operation. For example, in the pretreatment of seawater desalination reverse osmosis filtration, as an alternative to the pressure flotation method or after the pressure flotation method, the membrane filtration method is used to further improve the quality of the treated water that has undergone pressure flotation treatment. is used. For the clarification operation by membrane filtration, a flat membrane or hollow fiber porous ultrafiltration membrane or microfiltration membrane having an average pore size ranging from several nanometers to several hundred nanometers is used.
Thus, the clarification operation by the membrane filtration method has many advantages that the conventional pressurized flotation method, sand filtration method, etc. do not have. etc., and an organic film composed of a resin as described in Patent Document 1 below is often used as a porous film.

In addition, diatomaceous earth filtration has been mainly used to remove sediment from pasteurized soy sauce, but membrane filtration has been used as an alternative means in recent years due to the high disposal cost of used diatomaceous earth. However, it is important that the total nitrogen content of the pasteurized soy sauce does not change before and after membrane filtration to remove sediment components. The use of high-concentration sodium hydroxide poses the problem of high chemical costs and wastewater treatment costs.

JP 2011-168741 A

As described above, organic membranes composed of resins are often used as porous membranes. A difference appears. In addition, in the filtration for removing sediment components from pasteurized soy sauce, it is required to keep the sediment removal rate high while suppressing the decrease in the total nitrogen content as much as possible. Furthermore, since the membrane usually clogs if the filtration operation is continued, the operation of the filtration method using the porous filtration membrane is accompanied by a washing step. On the other hand, the use of chemicals in the cleaning process induces deterioration of membrane strength. At this time, if there is a difference in the microstructure of the materials that make up the porous filtration membrane, the degree of damage to the porous filtration membrane caused by the cleaning solution (chemical solution) used in the repeated cleaning process will differ. There is also the issue of impact.
In view of such problems, the problem to be solved by the present invention is to provide a method for producing soy sauce that includes a filtration step using a porous membrane for removing aggregates of starch components from pasteurized soy sauce containing aggregates, To provide a method in which the change in the total nitrogen content of pasteurized soy sauce before and after is low, the sediment removal rate is high, and the recovery of the water permeability after the washing process of the porous membrane and the resistance to the washing solution (chemical solution) are high.

As a result of intensive studies and repeated experiments in order to solve the above-described problems, the inventors of the present application have found that the communication of pores from the inside of the membrane, which is the liquid to be treated side of the porous filtration membrane, to the outside of the membrane, which is the filtrate side. In a method for producing soy sauce including a filtration step using a porous membrane for removing agglomerates from pasteurized soy sauce containing agglomerates of lees by using a membrane with good properties, the soy sauce production method includes a method for producing soy sauce before and after filtration. change in total nitrogen content is low, the sediment removal rate is high, and further, as the cleaning solution (chemical solution) used in the cleaning process, hot water at 50 ° C. to 90 ° C. and / or 0.05% by weight or more 0.5 It is expected that membrane degradation can be minimized even when aqueous solutions containing 0.4% to 4% by weight of sodium hypochlorite or 0.4% to 4% by weight of sodium hydroxide are used. I found it outside and came to complete the present invention.

That is, the present invention is as follows.
[1] the following steps:
A heating step of heating soy sauce containing a lees component to form an aggregate of the lees component; to separate the filtrate from the aggregates of the sediment component;
A method for producing soy sauce comprising
In the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane, a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view including the outer surface of the membrane, and photographed at equal intervals between these fields 2 The total area of the resin portion having an area of 1 μm ² or less is 70% or more of the total area of the resin portion in each region of a total of 4 fields of view, and
X1/X0×100<5, where X0 is the sediment component ratio of the heated soy sauce before the filtering step, N0 is the total nitrogen component, X1 is the sediment component ratio of the heated soy sauce after the filtering step, and N1 is the total nitrogen component. %, and satisfies the relationship N1/N0×100≧97%,
The method for producing soy sauce, characterized by:
[2] the following steps:
A heating step of heating soy sauce containing a lees component to form an aggregate of the lees component; to separate the filtrate from the aggregates of the sediment component;
A method for producing soy sauce comprising
In the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane, a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view including the outer surface of the membrane, and photographed at equal intervals between these fields 2 In each region of a total of four visual fields, the total area of the resin parts having an area of 10 μm ² or more is 15% or less of the total area of the resin parts, and
X1/X0×100<5, where X0 is the sediment component ratio of the heated soy sauce before the filtering step, N0 is the total nitrogen component, X1 is the sediment component ratio of the heated soy sauce after the filtering step, and N1 is the total nitrogen component. %, and satisfies the relationship N1/N0×100≧97%,
The method for producing soy sauce, characterized by:
[3] the following steps:
A heating step of heating soy sauce containing a lees component to form an aggregate of the lees component; to separate the filtrate from the aggregates of the sediment component;
A method for producing soy sauce comprising
In the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane, a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view including the outer surface of the membrane, and photographed at equal intervals between these fields 2 In each region of a total of four visual fields, the total area of the resin portion having an area of 1 μm ² or less is 70% or more of the total area of the resin portion, and the resin has an area of 10 μm ² or more. The total area of the part is 15% or less of the total area of the resin part, and
X1/X0×100<5, where X0 is the sediment component ratio of the heated soy sauce before the filtering step, N0 is the total nitrogen component, X1 is the sediment component ratio of the heated soy sauce after the filtering step, and N1 is the total nitrogen component. %, and satisfies the relationship N1/N0×100≧97%,
The method for producing soy sauce, characterized by:
[4] The porous membrane has a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view of these in an SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane. The total area of the resin portion having an area of more than 1 μm ² and less than 10 μm ² in each region of a total of 4 fields of view taken at equal intervals between 2 fields is 15% or less of the total area of the resin part The method according to any one of [1] to [3] above.
[5] The method according to any one of [1] to [4], wherein the porous membrane has a surface open area ratio of 25 to 60%.
[6] The method according to any one of [1] to [5], wherein the porous membrane is a hollow fiber membrane.
[7] The method according to any one of [1] to [6] above, wherein the resin constituting the porous membrane is a thermoplastic resin.
[8] The method according to [7], wherein the thermoplastic resin is a fluororesin.
[9] The fluororesin includes vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-monochlorotrifluoroethylene copolymer (ECTFE ), hexafluoropropylene resin, and mixtures of these resins.
[10] The method according to [7], wherein the thermoplastic resin is polyethylene (PE).
[11] After the filtration step, further comprising a washing step of passing or immersing a washing liquid through the porous membrane to wash the inside of the porous membrane, wherein the washing liquid is hot water of 50°C to 90°C. The method according to any one of [1] to [10].
[12] After the filtration step, further comprising a washing step of passing or immersing a washing liquid through the porous membrane to wash the inside of the porous membrane, wherein the washing liquid is 0.05% by weight or more and 0.5% by weight. % or less of sodium hypochlorite or 0.4 wt% or more and 4 wt% or less of sodium hydroxide. The method according to any one of the above [1] to [10].
[13] The relationship between the tensile elongation at break E0 of the porous membrane before the washing step and the tensile elongation at break E1 of the porous membrane after the washing step is E1/E0×100≧80%. , the method according to the above [11] or [12].
[14] Tensile elongation at break E0 of the porous membrane before the washing step and of the porous membrane after repeating the washing step X times (where X is an integer of 2 to 100) The method according to the above [11] or [12], wherein the relationship with the tensile elongation at break EX is EX/E0×100≧70%.
[15] The above [11] or, wherein the relationship between the flux L0 of the porous membrane before the filtering step and the flux L1 of the porous membrane after the washing step is L1/L0×100≧95%. The method according to [12].
[16] The flux L0 of the porous membrane before the filtering step, and the flux LX of the porous membrane after repeating the washing step X times (where X is an integer of 2 to 100). is X/L0×100≧90%, the method according to [11] or [12].
[17] The above-mentioned [11] to [16], wherein the cleaning step includes a cleaning liquid step of performing cleaning with the cleaning liquid, and then a rinsing step of performing rinsing with rinse water to remove remaining cleaning liquid components. Any method described.
[18] The method according to [17] above, wherein the amount of rinsing water used in the rinsing step is 100 L/m ² or less per unit area of the porous membrane.
[19] The above [17] or [17] or [ 18].

In the filtration step in the method for producing soy sauce according to the present invention, a membrane with good communication of pores from the inside of the membrane on the side of the liquid to be treated of the porous filtration membrane to the outside of the membrane on the side of the filtrate is used. Therefore, the change in the total nitrogen content of the pasteurized soy sauce before and after filtration is low, and the sediment removal rate is high. Even when using an aqueous solution containing 0.5% to 0.5% by weight of sodium hypochlorite or 0.4% to 4% by weight of sodium hydroxide, the deterioration of the membrane is minimized. can be reduced to Therefore, the method for producing soy sauce according to the present invention is excellent in filtering performance, recoverability, and chemical resistance, and has a long life. Specifically, since the porous membrane used in the filtration step in the method for producing soy sauce according to the present invention has high pore continuity, the adsorption of the total nitrogen component of the pasteurized soy sauce to the membrane is small, and the total nitrogen content before and after filtration is reduced. The component change is less than 3% and the sediment removal rate is over 95%. Furthermore, in the washing step, even when a sodium hydroxide aqueous solution with a relatively low concentration of 1% by weight is used as the washing liquid, the water permeation rate of the porous membrane can be sufficiently restored.

It is an example of an SEM image of a cross section of a porous membrane used in the filtration step in the method for producing soy sauce according to the present embodiment (black portions indicate resin and white portions indicate pores (apertures)). In the SEM image of the film cross section in the film thickness direction perpendicular to the inner surface of the porous film used in Example 1, a field of view including the inner surface, a field of view including the outer surface of the film, and between these fields of view, etc. 2 is a histogram showing the ratio (%) of the total area of a resin portion having a predetermined area to the total area of a resin portion in each region (circles 1 to 4) of a total of 4 fields of view of 2 fields photographed at intervals. In the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane used in Example 2, a field of view including the inner surface, a field of view including the outer surface of the membrane, and between these fields of view, etc. 2 is a histogram showing the ratio (%) of the total area of a resin portion having a predetermined area to the total area of a resin portion in each region (circles 1 to 4) of a total of 4 fields of view of 2 fields photographed at intervals. In the SEM image of the film cross section in the film thickness direction perpendicular to the inner surface of the porous film used in Example 3, a field of view including the inner surface, a field of view including the outer surface of the film, and between these fields of view, etc. 2 is a histogram showing the ratio (%) of the total area of a resin portion having a predetermined area to the total area of a resin portion in each region (circles 1 to 4) of a total of 4 fields of view of 2 fields photographed at intervals. In the SEM image of the film cross section in the film thickness direction perpendicular to the inner surface of the porous film used in Comparative Example 2, a field of view including the inner surface, a field of view including the outer surface of the film, and between these fields of view, etc. 2 is a histogram showing the ratio (%) of the total area of a resin portion having a predetermined area to the total area of a resin portion in each region (circles 1 to 4) of a total of 4 fields of view of 2 fields photographed at intervals.

Hereinafter, embodiments of the present invention (hereinafter also referred to as present embodiments) will be described in detail. It should be noted that the present invention is not limited to this embodiment.

<Soy sauce manufacturing method>
The method for producing soy sauce according to the present embodiment includes the following steps:
A heating step of heating soy sauce containing a lees component to form an aggregate of the lees component; to separate the filtrate from the aggregates of the sediment component;
wherein X0 is the sediment component ratio of the heated soy sauce before the filtration step, N0 is the total nitrogen component, X1 is the sediment component ratio of the heated soy sauce after the filtration step, and N1 is the total nitrogen component. when satisfying the relationships X1/X0×100<5% and N1/N0×100≧97%,
It is characterized by
X1/X0×100<0.5% is preferred, and X1/X0×100<0.3% is more preferred.
Also, N1/N0×100≧98% is preferable, and N1/N0×100≧99.5% is more preferable.
The shape of the porous membrane is not particularly limited, and may be a flat membrane, a tubular membrane, or a hollow fiber membrane. Hollow fiber membranes are preferred because they can be

As the filtration step in the soy sauce production method of the present embodiment, for example, pasteurized soy sauce (liquid to be treated) containing aggregates of sediment components aggregated by heating is supplied to the hollow portion (inner surface) of the porous hollow fiber membrane. Then, it may be a so-called internal pressure filtration step in which the liquid that seeps out from the outer surface of the porous hollow fiber membrane is taken out as filtrate by passing through the film thickness (thickness) part of the porous hollow fiber membrane. , a so-called external pressure filtration step in which the liquid to be treated is supplied from the outer surface of the porous hollow fiber membrane, and the filtrate oozing out from the inner surface of the porous hollow fiber membrane is taken out through the hollow part. .
As used herein, the term "inside the porous membrane" refers to a membrane (thickness) portion in which a large number of pores are formed.

Preferably, the method for producing soy sauce of the present embodiment further includes, after the filtration step, a washing step of washing the inside of the porous membrane by passing or immersing a washing liquid through the porous membrane, wherein the washing liquid is It can be hot water of 50° C. to 90° C. (hereinafter also referred to as hot water).
More preferably, the method for producing soy sauce of the present embodiment further includes, after the filtering step, a washing step of passing or immersing a washing liquid through the porous membrane to wash the inside of the porous membrane, is an aqueous solution (hereinafter also referred to as a chemical solution) containing 0.05% by weight or more and 0.5% by weight or less of sodium hypochlorite or 0.4% by weight or more and 4% by weight or less of sodium hydroxide. can. In the cleaning step, it is preferable to carry out chemical cleaning after hot water cleaning.
The cleaning step can include a cleaning liquid step of cleaning with the cleaning liquid, and then a rinse step of rinsing with rinse water to remove remaining cleaning liquid components. When the cleaning liquid is hot water, the temperature of the hot water can be preferably 55°C or higher and 85°C or lower, more preferably 60°C or higher and 80°C or lower. When the cleaning liquid is the chemical solution, the temperature of the chemical solution is preferably 15° C. or higher and 35° C. or lower, more preferably 20° C. or higher and 35° C. or lower. Further, the concentration of sodium hydroxide in the chemical solution is more preferably 0.7% by weight or more and 4% by weight or less, and further preferably 1% by weight or more and 4% by weight or less. The concentration of sodium hypochlorite in the chemical solution is more preferably 0.1% by weight or more and 0.5% by weight or less, and further preferably 0.2% by weight or more and 0.5% by weight or less. In the washing process, for example, the washing liquid is passed in the direction opposite to the flow direction of the pasteurized soy sauce in the filtration process, that is, from the filtrate side to the pasteurized soy sauce side, so that the filtered surface of the porous membrane (the pasteurized soy sauce side surface) Examples include back pressure water washing for separating and removing deposits (undissolved components), and air scrubbing for shaking the porous membrane with air to shake off undissolved components adhering to the porous membrane. The amount of rinsing water used in the rinsing step is preferably 100 L/m ² or less, more preferably 50 L/m ² or less per unit area of the porous membrane. Further, it is preferable that the chlorine concentration in the filtrate after restarting the filtering step after the rinsing step is 0.1 ppm or less and the pH of the filtrate is 8.6 or less.
The structure, material, and manufacturing method of the porous membrane used in the filtration step in the soy sauce manufacturing method of the present embodiment will be described in detail below.

<Porous membrane>
The porous membrane has a field of view including the inner surface, a field of view including the outer surface of the membrane, a field of view including the outer surface of the membrane, and a field between these fields in an SEM image of a membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane. In each area of a total of 4 fields of 2 fields photographed at intervals, the total area of the resin part having an area of 1 μm ² or less is 70% or more of the total area of the resin part; , the total area of the resin parts having an area of 10 μm ² or more is 15% or less of the total area of the resin parts; the total area of the resin parts having an area of 1 μm ² or less in each region is 70% or more of the total area of the resin parts, and the total area of the resin parts having an area of 10 μm ² or more is 15% or less of the total area of the resin parts; is either In a preferred porous membrane, the total area of the resin portions having an area of 1 μm ² or less in each region is 70% or more of the total area of the resin portions, and the area is more than 1 μm ² and less than 10 μm ² . The total area of the resin portions is 15% or less of the total area of the resin portions, and the total area of the resin portions having an area of 10 μm2 ^or more is the total area of the resin portions 15% or less.

FIG. 1 is an example of a SEM image of a cross section of a porous membrane used in the filtration step in the method for producing soy sauce according to the present embodiment. Such an SEM image is a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field between these fields in the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the hollow fiber porous membrane. SEM image obtained by photographing a predetermined field of view in the area closest to the inside of the areas of the total of 4 fields of view, 2 fields of view photographed at equal intervals. be.
In each of the above regions, there is a difference in the existence distribution of the resin portion between the membrane cross section in the membrane thickness direction perpendicular to the inner surface of the hollow fiber porous membrane and the cross section parallel to the inner surface, that is, the pores The anisotropy of connectivity can be virtually ignored.
As used herein, the term “resin portion” refers to a dendritic skeleton portion of a three-dimensional network structure made of resin, which forms a large number of pores in the porous membrane. The parts shown in black in FIG. 1 are the resin parts, and the white parts are the holes.
Inside the porous membrane, communicating pores are formed that communicate with each other while bending from the inside to the outside of the membrane. The total area of the resin part having an area of 1 μm ² or less in each of the four fields of view including the surface, the field of view including the outer surface of the film, and the two fields of view taken at equal intervals between these fields of view. However, if it is 70% or more of the total area of the resin portion, the continuity of the pores is high (that is, the existence ratio of the communicating pores inside the membrane is high), and the flux of the liquid to be treated (water permeability, water permeability), high water permeability retention rate after washing, and damage to the membrane after chemical washing, which is indexed by tensile elongation at break, is reduced. However, if the ratio of the total area of the resin part having an area of 1 μm ² or less to the total area of the resin part is too high, a tree with a three-dimensional network structure composed of resin will form a large number of pores in the porous membrane. Since the skeleton portion becomes too thin, the total area of the resin portion having an area of 1 μm ² or less is maintained at 70% or more of the total area of the resin portion, while the total area is more than 1 μm ² . It is preferable that the total area of the resin part having an area is 2% or more and 30% or less of the total area of the resin part, and the total area of the resin part having an area of 10 μm ² or more is the resin more preferably 15% or less of the total area of the resin portion, and the total area of the resin portion having an area of more than 1 μm ² and less than 10 μm ² is 15% or less of the total area of the resin portion. Further, it is more preferable that the total area of the resin portions having an area of 10 μm ² or more is 2% or more and 15% or less of the total area of the resin portions. If the total area of the resin portions having an area of more than 1 μm ² is 2% or more and 30% or less of the total area of the resin portions, a dendritic skeleton portion having a three-dimensional network structure composed of resin is formed. Since it is not too thin, the strength and tensile elongation at break of the porous membrane can be appropriately maintained.

2 to 5 are SEM images of cross sections of the porous membranes used in Example 1, Example 2, Example 3, and Comparative Example 2 in the film thickness direction perpendicular to the inner surface, respectively. A field including a field including the outer surface of the film, and a total of 4 fields of view (circles 1 to 4) taken at equal intervals between these fields of view. 4 is a histogram showing the ratio (%) of the total area of resin portions having an area. In FIG. 1, the resin portion appears in the form of granules. 2 to 5 show histograms of the area ratio of each area of each granular resin portion to the total area of all the resin portions in a field of view of a predetermined size in each region. showing. Circle 1 in FIGS. 2 to 5 indicates a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view of these fields in the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane. The number of the area closest to the inside is the number of the area closest to the inside of the areas of a total of 4 fields of view of 2 fields of view photographed at equal intervals, and the circle 4 is the number of the area closest to the inside. For example, circle 1 of Example 1 is a histogram when a field of view of a predetermined size within the innermost region of the porous hollow fiber membrane of Example 1 is photographed. A method for measuring the area distribution of the resin portion in each region of the porous hollow fiber membrane will be described later.

The surface open area ratio of the porous membrane is preferably 25 to 60%, more preferably 25 to 50%, still more preferably 25 to 45%. If the surface opening ratio on the side that comes into contact with the liquid to be treated is 25% or more, clogging and deterioration of water permeability due to abrasion of the membrane surface are reduced, so filtration stability can be enhanced. On the other hand, if the surface open area ratio is high and the pore size is too large, the required separation performance may not be exhibited. Therefore, the average pore size of the porous membrane is preferably 100-700 nm, more preferably 100-600 nm. If the average pore diameter is 100 to 700 nm, the separation performance is sufficient, and pore communication can be ensured. The methods for measuring the surface open area ratio and the average pore size will be described later.

The thickness of the porous membrane is preferably 80-1,000 μm, more preferably 100-300 μm. If the film thickness is 80 μm or more, the strength of the film can be ensured.

As for the shape of the porous hollow fiber membrane, an annular single-layer membrane can be mentioned, but a multi-layer membrane having different pore diameters between the separation layer and the support layer supporting the separation layer may also be used. In addition, the membrane may have an irregular cross-sectional structure such as having projections on the inner surface and the outer surface.

(Material (material) of porous membrane)
The resin constituting the porous membrane is preferably a thermoplastic resin, more preferably a fluororesin. Examples of fluororesins include vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-monochlorotrifluoroethylene copolymer (ECTFE), hexa Those selected from the group consisting of fluoropropylene resins, and mixtures of these resins.
Thermoplastic resins include polyolefins, copolymers of olefins and halogenated olefins, halogenated polyolefins, and mixtures thereof. Examples of thermoplastic resins include polyethylene (PE), polypropylene, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride (which may contain hexafluoropropylene domains), these A mixture of These resins are excellent in handleability due to their thermoplasticity and toughness, and thus are excellent as membrane materials. Among these, vinylidene fluoride resin, tetrafluoroethylene resin, hexafluoropropylene resin or mixtures thereof, homopolymers or copolymers of ethylene, tetrafluoroethylene, chlorotrifluoroethylene, or mixtures of homopolymers and copolymers are mechanically It is preferable because it is excellent in strength and chemical strength (chemical resistance) and good in moldability. More specifically, fluorine resins such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer can be mentioned.

The porous membrane may contain up to about 5% by mass of components (impurities, etc.) other than the thermoplastic resin. For example, it includes a solvent used when manufacturing a porous membrane. As will be described later, the first solvent (hereinafter also referred to as a non-solvent), the second solvent (hereinafter also referred to as a good solvent or poor solvent), or both used as a solvent in the production of the porous membrane are included. . These solvents can be detected by pyrolysis GC-MS (gas chromatography-mass spectrometry).

The first solvent includes sebacate, citrate, acetylcitrate, adipate, trimellitate, oleate, palmitate, stearate, phosphate, and has 6 to 30 carbon atoms. and at least one selected from the group consisting of fatty acids and epoxidized vegetable oils.
In addition, unlike the first solvent, the second solvent contains sebacate, citrate, acetylcitrate, adipate, trimellitate, oleate, palmitate, stearate, phosphorus It may be at least one selected from the group consisting of acid esters, fatty acids having 6 to 30 carbon atoms, and epoxidized vegetable oils. Examples of fatty acids having 6 to 30 carbon atoms include capric acid, lauric acid, and oleic acid. Examples of epoxidized vegetable oils include epoxy soybean oil and epoxidized linseed oil.
The first solvent is a first mixed liquid in which the ratio of the thermoplastic resin to the first solvent is 20:80, and even if the temperature of the first mixed liquid is raised to the boiling point of the first solvent, the thermoplastic It is preferable that the resin is a non-solvent that does not uniformly dissolve in the first solvent.
The second solvent is a second mixed liquid in which the ratio of the thermoplastic resin to the second solvent is 20:80, and the temperature of the second mixed liquid is higher than 25 ° C. and the boiling point of the second solvent or lower. It is preferable that the solvent is a good solvent in which the thermoplastic resin is uniformly dissolved in the second solvent at that temperature.
The second solvent is a second mixed liquid in which the ratio of the thermoplastic resin to the second solvent is 20:80, and when the temperature of the second mixed liquid is 25 ° C., the thermoplastic resin It is a poor solvent in which the thermoplastic resin uniformly dissolves in the second solvent at any temperature where the temperature of the second mixed liquid is higher than 100 ° C. and below the boiling point of the second solvent. preferable.

In addition, in the filtration step in the soy sauce manufacturing method of the present embodiment, a porous hollow fiber membrane using polyvinylidene fluoride (PVDF) as a thermoplastic resin and containing a first solvent (non-solvent) is used. can be used.
In this case, the first solvent is sebacate, citrate, acetylcitrate, adipate, trimellitate, oleate, palmitate, stearate, phosphate, and has 6 carbon atoms. At least one selected from the group consisting of 30 or less fatty acids and epoxidized vegetable oils, in a first mixed solution in which the ratio of polyvinylidene fluoride to the first solvent is 20:80, the first mixing It can be a non-solvent that does not uniformly dissolve polyvinylidene fluoride in the first solvent even when the temperature of the liquid is raised to the boiling point of the first solvent. Bis-2-ethylhexyl adipate (DOA) is preferred as the non-solvent.
Moreover, the porous hollow fiber membrane may contain a second solvent different from the first solvent. In this case, the second solvent is sebacate, citrate, acetylcitrate, adipate, trimellitate, oleate, palmitate, stearate, phosphate, and has 6 carbon atoms. At least one selected from the group consisting of 30 or less fatty acids and epoxidized vegetable oils, in a second mixture in which the ratio of polyvinylidene fluoride and the second solvent is 20:80, the second mixture It is preferable that the solvent is a good solvent that dissolves polyvinylidene fluoride uniformly in the second solvent at a liquid temperature higher than 25° C. or lower than the boiling point of the second solvent. Further, in the second solvent, polyvinylidene fluoride does not uniformly dissolve in the second solvent when the temperature of the second mixed liquid is 25 ° C., and the temperature of the second mixed liquid is higher than 100 ° C. It is more preferable that polyvinylidene fluoride is a poor solvent that uniformly dissolves in the second solvent at any temperature below the boiling point of . Acetyl tributyl citrate (ATBC) is preferred as the poor solvent.

(Physical properties of porous membrane)
The initial value of the tensile elongation at break of the porous membrane is preferably 60% or more, more preferably 80% or more, still more preferably 100% or more, and particularly preferably 120% or more. A method for measuring the tensile elongation at break will be described later.

From a practical point of view, the compressive strength of the porous membrane is preferably 0.2 MPa or more, more preferably 0.3 to 1.0 MPa, still more preferably 0.4 to 1.0 MPa.

<Method for producing porous membrane>
A method for producing a porous hollow fiber membrane will be described below. However, the method for producing the porous hollow fiber membrane used in the filtration method of the present embodiment is not limited to the following production method.
The method for producing a porous hollow fiber membrane used in the filtration step in the method for producing soy sauce according to the present embodiment includes (a) a step of preparing a melt-kneaded product, and (b) supplying the melt-kneaded product to a multi-structure spinning nozzle. (c) extracting the plasticizer from the hollow fiber membrane; and (c) extracting the plasticizer from the hollow fiber membrane. When the melt-kneaded product contains an additive, the step (d) of extracting the additive from the hollow fiber membrane may be further included after the step (c).

The concentration of the thermoplastic resin in the melt-kneaded product is preferably 20 to 60% by mass, more preferably 25 to 45% by mass, still more preferably 30 to 45% by mass. If this value is 20% by mass or more, the mechanical strength can be increased, and if it is 60% by mass or less, the water permeability can be increased. The melt-kneaded product may contain additives.
The melt-kneaded product may consist of two components, a thermoplastic resin and a solvent, or may consist of three components, a thermoplastic resin, an additive, and a solvent. The solvent includes at least a non-solvent as described later.
As the extracting agent used in step (c), it is preferable to use liquids such as methylene chloride and various alcohols that do not dissolve thermoplastic resins but have high affinity with plasticizers.
When a melt-kneaded product containing no additive is used, the hollow fiber membrane obtained through step (c) may be used as the porous hollow fiber membrane. When producing a porous hollow fiber membrane using a melt-kneaded product containing an additive, after step (c), the additive (d) is extracted and removed from the hollow fiber membrane to obtain a porous hollow fiber membrane. Further steps are preferred. As the extractant in step (d), it is preferable to use hot water or a liquid that can dissolve the additives used, such as acids and alkalis, but does not dissolve the thermoplastic resin.

Inorganic substances may be used as additives. The inorganic substance is preferably inorganic fine powder. The primary particle size of the inorganic fine powder contained in the melt-kneaded product is preferably 50 nm or less, more preferably 5 nm or more and less than 30 nm. Specific examples of the inorganic fine powder include silica (including fine silica powder), titanium oxide, lithium chloride, calcium chloride, organic clay, etc. Among these, fine silica powder is preferable from the viewpoint of cost. The above-mentioned "primary particle size of inorganic fine powder" means a value obtained from analysis of electron micrographs. That is, first, a group of inorganic fine powders is pretreated by the method of ASTM D3849. After that, the diameters of 3000 to 5000 particles photographed on the transmission electron micrograph are measured, and these values are arithmetically averaged to calculate the primary particle size of the inorganic fine powder.
By identifying the elements present in the inorganic fine powder inside the porous hollow fiber membrane using fluorescent X-rays or the like, it is possible to identify the material of the inorganic fine powder present.
When an organic substance is used as an additive, a hydrophilic polymer such as polyvinylpyrrolidone or polyethylene glycol can be used to impart hydrophilicity to the hollow fiber membrane. Moreover, the viscosity of the melt-kneaded product can be controlled by using a highly viscous additive such as glycerin or ethylene glycol.

Next, the step (a) of preparing a melt-kneaded product in the method for producing a porous hollow fiber membrane of the present embodiment will be described in detail.
In the method for producing a porous hollow fiber membrane of the present embodiment, a non-solvent for a thermoplastic resin is mixed with a good solvent or poor solvent. The mixed solvent after mixing is a non-solvent for the thermoplastic resin used. When a non-solvent is used as the raw material for the membrane in this way, a porous hollow fiber membrane having a three-dimensional network structure can be obtained. Its mechanism of action is not necessarily clear, but it is thought that the crystallization of the polymer is moderately inhibited by using a solvent with a lower solubility by mixing it with a non-solvent, making it easier to form a three-dimensional network structure. . For example, non-solvents and poor or good solvents include phthalates, sebacates, citrates, acetyl citrates, adipates, trimellitates, oleates, palmitates, and stearates. , phosphate esters, fatty acids having 6 to 30 carbon atoms, various esters such as epoxidized vegetable oils, and the like.
A solvent that can dissolve a thermoplastic resin at room temperature is called a good solvent, a solvent that cannot be dissolved at room temperature but can be dissolved at high temperature is called a poor solvent for the thermoplastic resin, and a solvent that cannot be dissolved at high temperature is called a solvent. A good solvent, a poor solvent, and a non-solvent can be determined as follows.
Put about 2g of thermoplastic resin and about 8g of solvent in a test tube, heat up to the boiling point of the solvent in about 10°C increments with a test tube block heater, mix the inside of the test tube with a spatula, etc., and the thermoplastic resin A solvent that dissolves is a good solvent or a poor solvent, and a solvent that does not dissolve is a non-solvent. A substance that dissolves at a relatively low temperature of 100° C. or less is judged as a good solvent, and a substance that does not dissolve unless the temperature is raised to a temperature of 100° C. or above and below the boiling point is judged as a poor solvent.
For example, when polyvinylidene fluoride (PVDF) is used as the thermoplastic resin and acetyl tributyl citrate (ATBC), dibutyl sebacate, or dibutyl adipate is used as the solvent, PVDF is uniformly mixed with these solvents at about 200°C. Dissolve. On the other hand, when bis-2-ethylhexyl adipate (DOA), diisononyl adipate, or bis-2-ethylhexyl sebacate is used as the solvent, PVDF does not dissolve in these solvents even when the temperature is raised to 250°C.
When ethylene-tetrafluoroethylene copolymer (ETFE) is used as the thermoplastic resin and diethyl adipate is used as the solvent, the ETFE is uniformly mixed and dissolved at about 200.degree. On the other hand, it does not dissolve when bis-2-ethylhexyl adipate (DIBA) is used as a solvent.
Also, when ethylene-monochlorotrifluoroethylene copolymer (ECTFE) is used as the thermoplastic resin and triethyl citrate is used as the solvent, it dissolves uniformly at about 200°C, and when triphenylphosphite (TPP) is used, it dissolves. do not do.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these. Each physical property value in Examples and Comparative Examples was obtained by the following methods.

(1) Outer Diameter and Inner Diameter of Porous Hollow Fiber Membrane The porous hollow fiber membrane was thinly sliced using a razor in a cross section orthogonal to the length direction, and the outer diameter and inner diameter were measured with a 100x magnifying glass. . For one sample, measurements were taken at 60 cut surfaces at intervals of 30 mm for the length method, and the average value was taken as the outer diameter and inner diameter of the hollow fiber membrane.

(2) Electron microscopic photography A porous hollow fiber membrane was cut into an annular shape in a cross section perpendicular to the length direction, dyed with 10% phosphotungstic acid + osmium tetroxide, and embedded in an epoxy resin. Then, after trimming, the cross section of the sample was subjected to BIB processing to prepare a smooth cross section, which was then subjected to a conductive treatment to prepare a microscopic sample. Using the HITACHI SU8000 series electron microscope, the electron microscope (SEM) image of the cross section of the film at an acceleration voltage of 1 kV is 5,000 to 30,000 times the film thickness (thick part) cross section. A field of view including the inner surface of the membrane, a field of view including the outer surface of the membrane, and two fields of view taken at equal intervals between these fields of view, a total of 4 fields of view (circles 1 to 4 in Figures 2 to 5) was taken at a predetermined field of view. It can be measured by changing the magnification according to the average pore diameter. Specifically, when the average pore diameter is 0.1 μm or more, it is 5000 times. , 10,000 times, and 30,000 times when the average pore size is less than 0.05 μm. The size of the field of view was 2560×1920 pixels.
ImageJ was used for image processing, and the captured SEM image was subjected to threshold processing (Image-Adjust-Threshold: Otsu method (Otsu was selected)) to binarize the hole portion and the resin portion. .
Surface aperture ratio: The surface aperture ratio was measured by calculating the ratio of the resin portion and the hole portion in the binarized image.
Area distribution of resin part: Using ImageJ's "Analyze Particle" command (Analyz Particle: Size 0.10-Infinity), the size of the binarized granular resin part contained in the captured SEM image was measured. . If the total area of all the resin parts included in the SEM image is ΣS, and the area of the resin parts of 1 μm ² or less is ΣS (<1 μm ^{2 ), then ΣS (<1 μm 2 )} /ΣS is calculated to obtain 1 μm The area ratio of the resin portion having an area of ² or less was calculated. Similarly, the area ratio of the resin portion having an area within a predetermined range was calculated.
Regarding the noise removal when performing the binarization process, the resin portion with an area of less than 0.1 μm ² was removed as noise, and the resin portion with an area of 0.1 μm ² or more was analyzed. Further, noise was removed by applying median filter processing (Process-Filters-Median: Radius: 3.0 pixels).
In addition, a granular resin part cut off at the edge of the SEM image was also measured. Also, the "Include Holes" treatment was not performed. In addition, no processing was performed to correct the shape from a "snowman" shape to a "flat" shape or the like.
Mean Pore Pore Size: Measured using ImageJ's "Plugins-Bone J-Thickness" command. The space size was defined as the maximum circle size that fits into the gap.

(3) Flux (permeability, initial pure water flux)
After immersing the porous hollow fiber membrane in ethanol and repeating immersion in pure water several times, one end of the wet hollow fiber membrane having a length of about 10 cm was sealed, and an injection needle was inserted into the hollow part of the other end. 25 ° C. pure water is injected from the injection needle at a pressure of 0.1 MPa in an environment of ° C., the amount of pure water permeating from the outer surface of the membrane is measured, and the following formula:
Initial pure water flux [L/m ² /h] = 60 × (permeated water amount [L]) / {π × (membrane outer diameter [m]) × (membrane effective length [m]) × (measurement time [min] )}
The pure water flux was determined by , and the water permeability was evaluated.
The term "effective membrane length" refers to the net membrane length excluding the portion where the injection needle is inserted.

(4) Water Permeability Retention Rate During Filtration of Actual Liquid First, kiage soy sauce was heated at 70° C. for 60 minutes and pasteurized to prepare a pasteurized soy sauce stock solution.
Next, (i) pure water was put into a circulation tank, and circulation filtration was performed so that the transmembrane pressure difference was 0.05 MPa, and the permeated water was collected for 1 minute to obtain the initial water permeability.
Next, (ii) after removing the water in the piping, the heated soy sauce undiluted solution was put into the circulation tank, and circulation filtration was performed so that the transmembrane pressure difference was 0.15 MPa.
Next, (iii) after the residual liquid of pasteurized soy sauce was removed from the piping, pure water was put into the circulation tank, and the mixture was circulated and filtered so that the transmembrane pressure difference was 0.05 MPa, and washed with water.
Next, (iv) after removing the water in the pipe, the prepared chemical solution was put into the circulation vessel, and membrane circulation filtration was carried out to carry out cleaning with the chemical solution for 30 minutes. An aqueous solution obtained by mixing 0.2% by weight of sodium hypochlorite and 1% by weight of caustic soda was used as the chemical solution.
Next, (v) after cleaning with the chemical solution, remove the chemical solution from the piping, put pure water into the circulation tank, perform circulation filtration so that the transmembrane pressure difference = 0.05 MPa, and remove the permeated water that comes out. Samples were repeatedly collected at a timing of 10 L/m ² , and when the permeate had a chlorine concentration of 0.1 ppm or less and a pH of 8.6 or less, washing was terminated, and the amount of water used for rinsing was recorded. In addition, circulating filtration was continued at the same transmembrane pressure difference, and the permeated water was collected for 1 minute and used as the permeation amount, which was compared with the initial permeation amount.
Each parameter was calculated by the following formula:
Transmembrane pressure difference = {(input pressure) + (output pressure)}/2
Inner membrane surface area [m ² ] = π x (hollow fiber membrane inner diameter [m]) x (hollow fiber membrane effective length [m])
Membrane surface linear velocity [m/s]=4×(circulating water volume [m ³ /s])/{π×(membrane inner diameter [m]) ² }. All operations were performed at 25° C. and a film surface linear velocity of 1.0 m/sec.

(5) Tensile elongation at break (%)
A porous hollow fiber membrane was used as a sample, and the tensile elongation at break was calculated according to JIS K7161. The load and displacement at tensile breakage were measured under the following conditions.
Measuring equipment: Instron type tensile tester (AGS-5D manufactured by Shimadzu Corporation)
Distance between chucks: 5cm
Pulling speed: 20cm/min

(8) Sediment component ratio (X0, X1) before and after filtration of pasteurized soy sauce The sediment component was obtained by putting 20 mL of the target soy sauce in a graduated cylinder, heating it in a constant temperature bath set at 85 ° C. for 90 minutes, and then keeping it at room temperature for 5 days. After standing still, the height of the precipitated component was measured, and the height of the precipitated component before and after filtration was compared and evaluated. By comparing the height of the sediment components after standing, the ratio of sediment components present in a unit volume of soy sauce can be determined.

(9) Measurement of total nitrogen content (N0, N1) A soy sauce sample was burned in a stream of pure oxygen and further reduced, and the total nitrogen content in the sample was quantified as nitrogen gas. Total nitrogen content was calculated as a percentage of the sample volume. SUMIGRAPH NC-220F manufactured by Sumika Chemical Analysis Center Co., Ltd. was used as the measurement apparatus, the measurement method was set to METHOD "LxM", the sample amount was set to 500 µL, the reactor temperature was set to 870°C, and the reduction furnace temperature was set to 600°C. Quantitation was calculated from a calibration curve for aspartic acid.

[Example 1]
PVDF resin (manufactured by Kureha Co., Ltd., KF-W #1000) as a thermoplastic resin 40% by mass, fine silica powder (primary particle size: 16 nm) 23% by mass, and bis 2-ethylhexyl adipate (DOA) as a non-solvent 32. A melt-kneaded product was prepared using 9% by mass and 4.1% by mass of acetyl tributyl citrate (ATBC, boiling point 343° C.) as a poor solvent. The temperature of the resulting molten mixture was 240°C. The resulting melt-mixed material is passed through a spinning nozzle having a double-tube structure, and the hollow fiber-like extrudate is passed through a free running distance of 120 mm. developed. The obtained hollow fiber extrudate was taken up at a speed of 5 m/min and wound on a skein. The wound hollow fiber extrudate is immersed in isopropyl alcohol to extract and remove DOA and ATBC, then immersed in water for 30 minutes to replace the hollow fiber membrane with water, and then soaked in a 20 wt% NaOH aqueous solution for 70 minutes. C. for 1 hour, and then repeatedly washed with water to extract and remove finely divided silica to prepare a porous hollow fiber membrane.
Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a three-dimensional network structure. In addition, the membrane had a high flux (water permeability) and a high degree of communication. A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.78%, a change of less than 2%.

[Example 2]
40% by mass of ETFE resin (TL-081, manufactured by Asahi Glass Co., Ltd.) as a thermoplastic resin, 23% by mass of finely divided silica (primary particle size: 16 nm), and 32.9% by mass of bis-2-ethylhexyl adipate (DOA) as a non-solvent. % and 4.1% by mass of diisobutyl adipate (DIBA) as a poor solvent to prepare a melt-kneaded product. The temperature of the resulting molten mixture was 240°C. The resulting melt-mixed material is passed through a spinning nozzle having a double-tube structure, and the hollow fiber-like extrudate is passed through a free running distance of 120 mm. developed. The obtained hollow fiber extrudate was taken up at a speed of 5 m/min and wound on a skein. The wound hollow fiber extrudate is immersed in isopropyl alcohol to extract and remove DOA and DIBA, then immersed in water for 30 minutes to replace the hollow fiber membrane with water, and then soaked in a 20 wt% NaOH aqueous solution for 70 minutes. C. for 1 hour, and then repeatedly washed with water to extract and remove finely divided silica to prepare a porous hollow fiber membrane.
Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a three-dimensional network structure. In addition, the membrane had a high flux (water permeability) and a high degree of communication.
A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.77%, a change of less than 2%.

[Example 3]
40% by mass of ECTFE resin (Halar 901, manufactured by Solvay Specialty Polymers) as a thermoplastic resin, 23% by mass of finely divided silica (primary particle size: 16 nm), and 32% by mass of triphenyl phosphite (TPP) as a non-solvent. A melt-kneaded product was prepared using 9% by mass and 4.1% by mass of bis-2-ethylhexyl adipate (DOA) as a poor solvent. The temperature of the resulting molten mixture was 240°C. The resulting melt-mixed material is passed through a spinning nozzle having a double-tube structure, and the hollow fiber-like extrudate is passed through a free running distance of 120 mm. developed. The obtained hollow fiber extrudate was taken up at a speed of 5 m/min and wound on a skein. The wound hollow fiber extrudate is immersed in isopropyl alcohol to extract and remove TPP and DOA, then immersed in water for 30 minutes to replace the hollow fiber membrane with water, and then soaked in a 20 wt% NaOH aqueous solution for 70 minutes. C. for 1 hour, and then repeatedly washed with water to extract and remove finely divided silica to prepare a porous hollow fiber membrane.
Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a three-dimensional network structure. In addition, the membrane had a high flux (water permeability) and a high degree of communication.
A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.71%, a change of about 3%.

[Comparative Example 1]
A hollow fiber membrane of Comparative Example 1 was obtained by forming the membrane in the same manner as in Example 1 except that only ATBC was used as the solvent. Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a spherulite structure. In addition, the flux was low and the membrane had low connectivity.
A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.2%, a change of about 32%.

[Comparative Example 2]
A hollow fiber membrane of Comparative Example 2 was obtained by forming the membrane in the same manner as in Example 1, except that the finely divided silica was 0% and the solvent was only γ-butyrolactone. Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a spherulite structure. In addition, the flux was low and the membrane had low connectivity.
A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.3%, a change of about 27%.

[Comparative Example 3]
A hollow fiber membrane of Comparative Example 3 was obtained by forming the membrane in the same manner as in Example 3, except that DOA was used as the solvent. Table 1 below shows the composition, manufacturing conditions, and various physical properties of the obtained porous membrane. The resulting porous hollow fiber membrane had a spherulite structure. In addition, the flux was low and the membrane had low connectivity.
A firing process was performed. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the porous membrane was treated in the same manner, a sediment component of 1 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of sediment components by the filtration was over 99%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.25%, a change of about 29%.

[Comparative Example 4]
The soy sauce stock solution after heating was mixed with diatomaceous earth of Standard Supercell (manufactured by Celite Co., Ltd.), and filtered with a filter press manufactured by Naigai Joki Co., Ltd. so that the pressure was 1.0 MPa. 20 mL of the soy sauce after the pasteurization process was placed in a graduated cylinder, heated in a constant temperature bath set at 85°C for 90 minutes, and then allowed to stand at room temperature for 5 days. was formed. On the other hand, when 20 mL of the filtrate obtained by filtering the soy sauce after the pasteurization process with the diatomaceous earth was treated in the same manner, a sediment component of 5 mm was formed with respect to the liquid surface height of 138 mm. That is, the removal rate of the sediment component by the diatomaceous earth filtration was about 95%. The total nitrogen content of the pasteurized soy sauce before filtration was 1.77% by weight, while the total nitrogen content after filtration was 1.74%, a change of about 2%.

From the above results, it was found that a membrane with good connectivity has excellent filtration performance and chemical resistance, and has a long life.

The filtration step in the soy sauce manufacturing method according to the present invention uses a porous filtration membrane (a membrane with good communication of pores from the inside of the membrane on the side of the liquid to be treated to the outside of the membrane on the side of the filtrate. Therefore, the change in the total nitrogen content of the pasteurized soy sauce before and after filtration is low, and the sediment removal rate is high. Even when using an aqueous solution containing 0.5% to 0.5% by weight of sodium hypochlorite or 0.4% to 4% by weight of sodium hydroxide, the deterioration of the membrane is minimized. Therefore, the method for producing soy sauce according to the present invention is excellent in filtering performance and resistance to chemicals, and has a long life.

Claims (8)

The following steps:
A heating step of heating soy sauce containing a lees component to form an aggregate of the lees component; to separate the filtrate from the aggregates of the sediment component;
A method for producing soy sauce comprising
In the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane, a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field of view including the outer surface of the membrane, and photographed at equal intervals between these fields 2 In each region of a total of four visual fields, the total area of the resin portion having an area of 1 μm ² or less is 70% or more of the total area of the resin portion, and the resin has an area of 10 μm ² or more. The total area of the part is 15% or less of the total area of the resin part, and
The resin constituting the porous membrane consists of vinylidene fluoride resin (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-monochlorotrifluoroethylene copolymer (ECTFE), and a mixture of these resins. is selected from the group, and the three-dimensional network structure is formed from a melt-kneaded composition of the resin, finely divided silica, a solvent, and a poor solvent, and
X1/X0×100<5, where X0 is the sediment component ratio of the heated soy sauce before the filtering step, N0 is the total nitrogen component, X1 is the sediment component ratio of the heated soy sauce after the filtering step, and N1 is the total nitrogen component. %, and satisfies the relationship N1/N0×100≧97%,
The method for producing soy sauce, characterized by: The porous membrane has a field of view including the inner surface, a field of view including the outer surface of the membrane, and a field between these fields in the SEM image of the membrane cross section in the film thickness direction perpendicular to the inner surface of the porous membrane. Claim that the total area of the resin portion having an area of more than 1 μm ² and less than 10 μm ² in each region of a total of 4 fields of view taken at equal intervals is 15% or less of the total area of the resin part Item 1. The method according to item 1. 3. The method according to claim 1, wherein the porous membrane has a surface open area ratio of 25 to 60%. The method according to any one of claims 1 to 3, wherein said porous membrane is a hollow fiber membrane. Claim 1, further comprising a washing step of washing the inside of the porous membrane by passing or immersing a washing liquid through the porous membrane after the filtering step, wherein the washing liquid is hot water of 50°C to 90°C. 5. The method according to any one of 1 to 4. After the filtration step, it further comprises a washing step of washing the inside of the porous membrane by passing or immersing a washing liquid through the porous membrane, wherein the washing liquid is 0.05% by weight or more and 0.5% by weight or less. The method according to any one of claims 1 to 5, which is an aqueous solution containing sodium hypochlorite or 0.4% by weight or more and 4% by weight or less of sodium hydroxide. The relationship between the tensile elongation at break E0 of the porous membrane before the washing step and the tensile elongation at break E1 of the porous membrane after the washing step is E1/E0×100≧80%. The method according to 5 or 6. The tensile breaking elongation E0 of the porous membrane before the washing step and the tensile breaking elongation of the porous membrane after repeating the washing step X times (where X is an integer of 2 to 100) 7. The method according to claim 5 or 6, wherein the relationship with degree EX is EX/E0*100≧70%.

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