JPH11137286A - Fermentation of lactic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for a fermentation for lactic acid needless to remove cell bodies by using a membrane separation, centrifugal separation or the like before an electrodialysis from a culture medium and capable of causing no fouling on an electrodialysis membrane. SOLUTION: This method is conducted by introducing lactic acid produced by a lactic acid fermenting apparatus 11 using a fermentable microorganism for lactic acid belonging to the genus Rhizopus into a bipolar membrane electrolytic apparatus 31 with a two-chamber system comprising a bipolar membrane BP and an anior-exchange membrane A and removing the resultant product from the system one after another.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a novel method for fermenting lactic acid. More specifically, the present invention relates to a lactic acid fermentation method capable of performing lactic acid fermentation smoothly using electrodialysis.

[0002] Lactic acid is used as a food additive in the production of sake, soft drinks, pickles, soy sauce, bread making or beer, and as an industry, in the production of leather, fiber, plastics, pharmaceuticals or pesticides. I have.

Recently, esters such as ethyl lactate and butyl lactate, which are derivatives or synthetic intermediates of lactic acid, have been widely used as highly safe solvents and cleaning agents. Furthermore, polylactic acid, which is a polymer of lactic acid, is expected to expand its use as a biodegradable polymer.

[0004]

2. Description of the Related Art As a method for separating lactic acid from lactate by electrodialysis, a bipolar membrane for separating an alkali such as sodium or ammonia by permeating the cation exchange membrane by a two-chamber method comprising a bipolar membrane and a cation exchange membrane. An electrodialysis method and a bipolar membrane electrodialysis method in which lactate or a weak base lactate is separated by permeating an anion exchange membrane by a two-chamber method comprising a bipolar membrane and an anion exchange membrane are known (Monthly Food Chemical 1996). −
6, p30-35, JP-A-8-28077).
Here, the bipolar membrane has a structure in which an anion exchange membrane and a cation exchange membrane are joined, and when subjected to electrodialysis, the anion exchange membrane side of the bipolar membrane is placed on the anode (+) side, The bipolar membrane is used such that the cation exchange membrane side of the bipolar membrane is the cathode (-) side. When an electric field is applied, water between the bonded anion and cation exchange membranes is dissociated and split to form H ^+.
And OH ^- become, say what current flows.

[0005] Further, a so-called electrodialysis fermentation in which a lactic acid fermentation apparatus and an electrodialysis apparatus are connected to sequentially remove lactic acid from the system during fermentation to increase the speed of fermentation is known from various literatures.

When the above-mentioned bipolar membrane electrodialysis method is applied to electrodialysis fermentation, a bipolar method in which alkali such as sodium or ammonia is permeated through a cation exchange membrane and separated by a two-chamber method comprising a bipolar membrane and a cation exchange membrane. Membrane electrodialysis cannot be used practically because it is impossible to separate lactic acid from the medium.

Therefore, a bipolar membrane electrodialysis method in which lactate or a weak base lactate is permeated through an anion exchange membrane and separated by a two-chamber method comprising a bipolar membrane and an anion exchange membrane is used.

However, the following technical problems have been encountered in the above-mentioned monthly food chemicals and the lactate bipolar electrodialysis described in JP-A-8-281077.

1) In general, electrodialysis fermentation using bacteria such as lactic acid bacteria and Bacillus subtilis involves electrodialysis of nutrient components and protein components secreted by cells from a lactic acid fermenter into a bipolar membrane electrodialysis device. There is a problem of fouling of the electrodialysis membrane due to deposition and scaling on the membrane. Furthermore, for these bacteria, it is necessary to remove the cells from the medium by membrane separation, centrifugation or the like before the electrodialysis, which poses a problem for industrial practical use.

2) In the batch type two-chamber bipolar electrodialysis currently used, including the above-mentioned publication, the pH of the salt chamber rises in the latter half, the movement of hydroxide ions becomes severe, and the current efficiency decreases. In particular, sodium lactate is extremely inefficient (however, ammonium lactate reduces the decrease in efficiency).

3) In the batch type electrodialysis, since the salt chamber becomes alkaline, a special alkali-resistant membrane is required for the anion exchange membrane.

4) As described in JP-A-8-281077, when the lactate of a weak base is ammonium lactate, ammonia is gasified in a salt chamber, and blisters are generated. It is necessary to strip by sending an inert gas.

5) In the batch type two-chamber bipolar membrane electrodialysis of ammonium lactate, when the pH of the salt compartment rises, ammonia molecules move due to diffusion, and permeate the membrane and enter the recovery compartment.

[0014]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel method for fermenting lactic acid by applying bipolar membrane electrodialysis to electrodialysis fermentation.

[0015] Another object of the present invention is to provide a novel method that eliminates the need for removing cells from the medium by membrane separation or centrifugation before electrodialysis, and does not cause fouling (dirt) of the electrodialysis membrane. The present invention provides a method for fermenting lactic acid.

[0016]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies on a novel lactic acid fermentation method. As a result, a lactic acid fermentation apparatus using a microorganism having a lactic acid fermentation ability belonging to the fungus Rhizopus genus In addition, by combining a two-chamber bipolar membrane electrodialysis apparatus constituted by a bipolar membrane and an anion exchange membrane, the above objects can be achieved, thereby enabling industrially advantageous electrodialysis fermentation. They have found out the facts and completed the present invention.

That is, an object of the present invention is to provide (1) lactic acid produced by a lactic acid fermentation apparatus using a microorganism belonging to the genus Rhizopus and capable of fermenting lactic acid, by using a two-chamber method comprising a bipolar membrane and an anion exchange membrane. Introduced into the electrodialysis machine,
This is achieved by a method of fermenting lactic acid, characterized in that the lactic acid is sequentially removed from the system.

Another object of the present invention is to (2) convert lactic acid produced in the lactic acid fermentation apparatus into a monovalent lactate form and then introduce the same into the two-chamber electrodialysis apparatus. This is also achieved by the lactic acid fermentation method described in (1) above.

Further, the object of the present invention is also achieved by (3) the method of fermenting lactic acid according to (2), wherein the monovalent lactate is ammonium lactate.

Further, the object of the present invention is also achieved by (4) the method of fermenting lactic acid according to (2), wherein the monovalent lactate is sodium lactate.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The lactic acid fermentation method of the present invention is characterized in that lactic acid produced by a lactic acid fermentation apparatus using a microorganism belonging to the genus Rhizopus and having a lactic acid fermentation ability is formed by a bipolar membrane and an anion exchange membrane Introduced to the room method electrodialysis machine,
It is characterized by being sequentially removed from the system.

Microorganisms having the ability to ferment lactic acid belonging to the genus Rhizopus that can be used in the present invention include, for example, Rhizopus arrhizus, Rhizopus oryzae, and the like. Since such microorganisms having lactic acid fermentation ability belonging to the genus Rhizopus can be cultured in pellets and masses, the cells can be easily separated from the culture medium before being introduced into the electrodialysis device.

Microorganisms belonging to the genus Rhizopus and capable of fermenting lactic acid, particularly Rhizopus oryzae
Then, the composition of the culture medium is simple, and it is usually sufficient to add an inorganic salt in addition to the carbon source.Therefore, the nutrients of the culture medium contained in the fermentation solution brought into the bipolar membrane electrodialysis apparatus from the lactic acid fermentation apparatus and There is no accumulation of protein components and the like secreted by microorganisms on the surfaces of the bipolar membrane and the anion exchange membrane, and no fouling of these electrodialysis membranes is observed, so that electrodialysis fermentation can be performed continuously.

That is, in such a microorganism having a lactic acid fermentation ability belonging to the genus Rhizopus, the cells of the microorganism can be easily separated from the medium, even if the cell density of the microorganism is increased by continuous fermentation or the like. Separation devices for separating and removing microbial cells before passing the fermentation solution through the electrodialysis device do not cause clogging of the electrodialysis membrane of the electrodialysis device or a significant decrease in current efficiency. It is significantly simpler than bacteria such as lactic acid bacteria and Bacillus subtilis. In order to prevent a part of the mycelium or the spores of the microorganism from flowing into the electrodialysis apparatus and to prevent the cells from being immobilized on the electrodialysis apparatus and growing therein, it is preferable to provide a sterilizer for killing the cells. In this case, the sterilization apparatus by heating is simple, but it is of course possible to use an apparatus utilizing another sterilization method.

In addition, microorganisms having lactic acid fermentation ability belonging to the genus Rhizopus also have the effect of accumulating lactic acid and inhibiting fermentation in the same manner as general lactic acid bacteria. It is clear that there is an advantage in speeding up fermentation.

The lactic acid produced in the lactic acid fermentation apparatus can be introduced into an electrodialysis apparatus in the form of free lactic acid to separate the lactic acid, but the pH of the medium in the lactic acid fermentation apparatus belongs to the genus Rhizopus. In order to maintain the optimum pH of a microorganism having lactic acid fermentation ability, the lactic acid concentration must be considerably reduced, and the current density of electrodialysis decreases. For this reason, it is preferable to add an appropriate concentration of alkali to the culture medium in the lactic acid fermentation apparatus so as to maintain the pH of the culture medium at the optimum pH of the microorganism and convert lactic acid into a monovalent lactate. In this case, the optimal pH of a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus is 7 or less, so that hydroxide ions (OH ⁻ ) preferentially permeate lactic acid even in a strong alkali such as sodium hydroxide. However, the current efficiency can be kept very high. The alkali such as ammonia and sodium circulates between the lactic acid fermenter and the electrodialyzer.

The monovalent lactate is not particularly restricted but includes, for example, alkali metal salts of lactic acid such as sodium lactate, potassium lactate and lithium lactate, and ammonium lactate. Among these, an alkali metal salt of lactic acid such as sodium lactate has the advantage that it does not permeate the membrane, although the current efficiency is lower than that of ammonium lactate. On the other hand, in the case of ammonium lactate, sodium lactate and the like do not permeate through the membrane, but slightly permeate (however, diffusion of ammonia molecules in conventional batch type two-chamber bipolar membrane electrodialysis). ), The salt chamber is always kept neutral and therefore exists as ammonium lactate and permeates through the membrane in the form of free NH ₃ , but has the advantage of good current efficiency. Which one to use is appropriately determined according to the intended use and the like. The alkali added to convert the lactic acid to the monovalent lactate form is an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like adjusted to an appropriate concentration, ammonia water, ammonia gas. Etc. can be used.

The electrodialysis fermentation method used in the present invention can be any of a batch system, a continuous system, and a repetitive batch system in which the medium is replaced with a fresh medium while leaving the cells.

Next, as one embodiment of an electrodialysis fermentation apparatus which can be used in the lactic acid fermentation method according to the present invention,
A diagram schematically showing an electrodialysis fermentation apparatus combining a lactic acid fermentation apparatus using a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus and a two-chamber electrodialysis apparatus constituted by a bipolar membrane and an anion exchange membrane. As shown in FIG.

As shown in FIG. 1, an electrodialysis fermentation apparatus 1 which can be used in the present invention is provided with a fermentation section 12 for culturing microorganisms belonging to the genus Rhizopus having a lactic acid fermentation ability in a medium and fermenting lactic acid. A lactic acid fermentation apparatus 11 comprising: a cell structure comprising a bipolar membrane BP and an anion exchange membrane A for sequentially separating and removing lactic acid from a fermentation solution introduced from the lactic acid fermentation apparatus 11 to outside the system. And a chamber-type bipolar membrane electrodialysis apparatus 31. Further, the main body of the lactic acid fermentation apparatus 11 and the two-chamber bipolar membrane electrodialysis apparatus 3
One main body is connected to a piping 16 via a fermentation liquid take-out pump 13, a cushion tank 14, and a fermentation liquid circulation pump 15.
a to 16d. Further, the cushion tank 14 and the main body of the lactic acid fermentation apparatus 11 are
In order to return a part of the fermentation solution in 4 (preferably a solution obtained by removing lactic acid from the fermentation solution) to the fermentation unit 12, the fermentation solution is connected by a pipe 16e.

In the lactic acid fermentation apparatus 11, a fermentation unit 12 and a raw material tank (not shown) are connected by a pipe (not shown) via a pump (not shown) so that lactic acid can be fermented by continuous fermentation. It may be connected. Thereby, a pump (not shown) is supplied from the raw material tank (not shown) to the fermentation unit 12.
The fermentation raw material is supplied from the piping via the.

Further, the lactic acid fermentation apparatus 11 is used to convert the lactic acid generated in the fermentation section 12 into lactate in order to maintain the optimum pH of the microorganism without lowering the current density of the electrodialysis. Equipped with a pH sensor in the fermentation unit 12
The H sensing device 17 is provided, and the fermentation unit 12 and an alkali storage tank (not shown) for ammonia or the like are connected by a pipe (not shown) via an alkali supply pump (not shown). Thereby, while monitoring the pH of the culture medium with the pH sensing device 17, the fermentation medium in the fermentation unit 12 is always in the optimal pH range for fermentation by microorganisms having lactic acid fermentation ability belonging to the genus Rhizopus (generally 4 to 8, preferably 4 to 8). In response to the change in pH, the pH of the alkaline aqueous solution is supplied into the fermentation unit 12 by operating the electromagnetic on-off valve of the alkaline supply pump or the like according to a signal from the pH sensor 17 in accordance with a change in pH. An automatic monitoring and control system may be constructed. Note that an electric conductivity sensor or a concentration sensor may be used instead of the pH sensor.

Further, the automatic pH monitoring and control system includes a rectifier 3 on the side of the two-chamber bipolar membrane electrodialyzer 31.
While monitoring a specific parameter such as the current density in Step 2, for example, even when a decrease in the current density of electrodialysis is detected, the change in the parameter is adjusted so that the concentration in the culture medium of the fermentation unit 12 becomes an appropriate concentration. In response, it is more desirable to construct the automatic pH monitoring and control system so that the alkaline aqueous solution is supplied into the fermentation unit 12 by operating the electromagnetic on-off valve or the like of the alkaline supply pump according to a signal from the rectifier 32. .

Further, as shown in FIG. 1, the fermentation section 12 has a fermentation tank
In the lower part of the fermentation tank 19, a filter member 20 such as a sintered metal filter for preventing invasion of bacteria and microorganisms is provided. Into 19,
After the medium is stirred, the air is discharged from the system through a pipe 21 through an exhaust port provided in the upper cover 18 (and after removing air pollutants through a filter having a filter member or the like as necessary). It is possible to use a so-called air-lift type reactor that exhausts gas. The fermentation section that can be used in the present invention is not limited to the above-described ones. For example, a fermentation tank of a stirring type with a normal stirring blade, or immobilization with gel beads such as carrageenan and calcium alginate, etc. A column-type reactor packed with a growing microorganism, a membrane-type reactor in which microorganisms are sealed at a high density by a membrane, and the like can be used. Various sensors are provided below the liquid surface of the culture medium inside the fermentation tank 19 of the fermentation unit 12 so as to measure the lactic acid (or lactate) concentration, the pH of the fermentation medium, or the electric conductivity as described above. Is desirably provided.

Further, a heat exchange device 22 may be provided on the outer peripheral portion of the side surface of the fermentation tank 19 constituting the fermentation section 12. The heat exchange device 22 can maintain the temperature of the culture medium in the fermentation section 12 within a growth range of a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus (generally, 30 to 35 ° C. is optimal). It is. The heat exchange device is not particularly limited, and as shown in FIG.
A method of circulating hot water or cold water as a medium can be used.

Further, in order to appropriately supply water to the fermentation section 12, a level controller 23 and a water tank (not shown) connected to the fermentation section 12 by a pipe via a water supply pump 24 are provided. A different level controller system may be provided. In the level controller system,
The change in the liquid level of the fermentation medium in the fermentation section 12 is monitored using a liquid level sensor or the like, and the input data (input signal) from the liquid level sensor is analyzed and processed by the level controller 23, and is subjected to bipolar by electrodialysis. When the level of the fermentation medium drops below a certain level due to, for example, the progress of electrolysis of water in the membrane, the output signal from the level controller 23 operates the electromagnetic on-off valve of the water supply pump 24. Then, a system may be provided that opens the fermentation unit 12 through the pipe 25 and supplies an appropriate amount of sterilized water.

On the other hand, in the two-chamber bipolar membrane electrodialyzer 31, from the anode (+) side to the cathode (-) side,
Four cells are provided as a basic unit (hereinafter, also simply referred to as a cell) composed of two chambers arranged alternately in the order of the bipolar membrane BP and the anion exchange membrane A. Each cell is
A chamber (hereinafter, also simply referred to as a salt chamber) a formed by the anion exchange membrane A of the bipolar membrane BP and the anion exchange membrane A of the electrodialysis device 31, and the cation exchange membrane side of the bipolar membrane BP and the anion exchange membrane A (Hereinafter, also simply referred to as a recovery chamber) b.

An inlet 33 for introducing a fermentation solution (including a fermentation solution taken out from the inside of the fermentation tank 19 and a fermentation solution returned by electrodialysis) is provided in each salt chamber a.
An outlet 35 for discharging the fermented liquid after electrodialysis is provided. Each inlet 33 is connected to the fermentation liquid circulation pump 15 by a branched pipe 16d. Each exit 35
Is connected to the cushion tank 14 by a pipe 34. Thereby, the cushion tank 14 can be moved from each salt room a.
From the cushion tank 14 to the fermentation liquid circulation pump 15
A circulation system is formed to circulate the fermentation liquor (including an alkali component from which lactic acid is extracted from the fermentation liquor) to the salt chamber a via the fermentation liquor.

The recovery chamber b is provided with an outlet 36 for discharging a recovery liquid containing a lactic acid component separated from the fermentation liquid through an anion exchange membrane, and an inlet 37 for introducing the recovery liquid. ing. An outlet 36 of each recovery chamber b is connected to an inlet of a recovery liquid tank 38 by a pipe 39, and an outlet of the recovery liquid tank 38 is connected to the recovery liquid circulation pump 4.
Each of the collection chambers b is connected to the entrance 37 of the collection chamber b through a pipe 41 via the same. Thereby, a circulation system for circulating the recovered liquid is formed. In addition, in the circulation system including the recovery chamber b, in which the recovery liquid is circulated, an aqueous solution of a strong acid or an aqueous solution of a salt of a strong acid is used to increase the electric conductivity of the recovery liquid and increase the current density.
It is desirable that the aqueous solution is previously charged at a concentration such that the electric conductivity is preferably 5 to 50 mS / cm. Examples of the strong acid include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and the like, and salts thereof include a sodium salt, a potassium salt, an ammonium salt, and a lithium salt.

An electrode chamber c is provided on both sides having an anode (+) and a cathode (-). And
An outlet 42 of both electrode chambers c and an inlet of the electrode solution tank 43 are connected through a pipe 44, and an outlet of the electrode solution tank 43 is connected to an inlet 47 of both electrode chambers c via an electrode solution circulation pump 45. They are connected by a pipe 46. Thus, a circulation system for circulating the electrode solution is formed. The anode (+) plate and the cathode (−) plate are connected via a rectifier 32. In addition, an aqueous solution of ammonium sulfate, sodium sulfate, aqueous sulfuric acid, aqueous ammonium chloride, aqueous sodium chloride, aqueous hydrochloric acid, or the like having an appropriate concentration is previously charged into the circulation system including the electrode chamber c to circulate the electrode liquid. It is desirable to keep it.

By operating the electrodialysis fermentation apparatus 1 having the above configuration, the inside of the fermentation tank 19 of the fermentation section 12 of the lactic acid fermentation apparatus 11 is suitable for culturing microorganisms having lactic acid fermentation ability belonging to the genus Rhizopus in the fermentation medium. Environment
The heat exchanger keeps the temperature of the fermentation tank at an appropriate temperature while circulating the hot water. The fermentation tank 19 is supplied with air from the lower part of the fermentation tank 19 through the filter member 20 to stir the fermentation medium (exhaust through the pipe 21). Adjust the pH of the internal fermentation medium while supplying an appropriate amount of alkaline aqueous solution,
Further, if necessary, lactic acid produced is converted into lactate form by continuously supplying the water and a medium component, etc., while continuing the stable culture.

Next, the fermented liquid containing the lactate that has been sufficiently subjected to lactic acid fermentation and converted is transferred from the lactic acid tank 19 of the main body of the lactic acid fermentation apparatus to the fermented liquid removing pump 13 and the cushion tank 1.
4 and pipes 16a-1 through fermentation liquid circulation pump 15
It is introduced through the inlets 33 of the four salt chambers a of the main body of the electrodialysis apparatus 31 through 6d. In addition, by performing a DC voltage between both electrodes by the rectifier 32 and performing electrodialysis, the lactic acid component in the fermentation liquor supplied to the salt chamber a permeates the anion exchange membrane A and is directed to each recovery chamber b side. Move and separate.

The recovered liquid containing lactic acid separated from the fermentation liquid is discharged from the outlet 36 of the recovery chamber b and stored in the recovered liquid tank 38 through the pipe 39. The recovery liquid in the recovery liquid tank 38 is introduced from the inlet 37 of the recovery chamber b through the pipe 41 by the recovery liquid circulation pump 40. As a result, the recovered liquid is circulated, and the lactic acid is concentrated. Then, when the lactic acid is concentrated to the desired concentration, the lactic acid is sequentially extracted from the collection liquid circulation tank 38 and the like to the outside of the system and collected.

On the other hand, the fermented liquor containing the alkali component, which is obtained by separating and extracting lactic acid from the fermented liquor in the salt room a, is returned to the cushion tank 14 through a pipe 34 from an outlet 35 of the salt room a. A part of the fermentation liquor stored in the cushion tank 14 (particularly a fermentation liquor containing an alkali component, which is separated and extracted from the fermentation liquor) is supplied to a pipe 16
e again returns to the inside of the fermentation tank 19 of the fermentation unit 12 and is recycled as an aqueous alkaline solution. Also,
Another part (in particular, a fermentation solution containing lactate taken out from the inside of the fermentation tank 19) is introduced (circulated) from the inlet 33 of the salt room a of the electrodialysis device 12 through the pipes 16c to 16d by the fermentation solution circulation pump 15. Is done.

Since the lactic acid solution separated by electrodialysis does not contain microorganisms, nonionic organic substances or high molecular compounds, sufficient purification (concentration) is performed.

The above is an explanation of one embodiment for performing the method for producing lactic acid according to the present invention using the electrodialysis fermentation apparatus having the configuration shown in FIG. 1. The present invention is not limited to the embodiment, and a conventionally known lactic acid fermentation apparatus using a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus and a two-chamber bipolar membrane electrodialysis apparatus constituted by a bipolar membrane and an anion exchange membrane can be used. Needless to say, it can be selected and used as appropriate.
Hereinafter, another general embodiment of the method for producing lactic acid according to the present invention will be described.

First, as a medium composition for culturing microorganisms which can be used in the fermentation section of the lactic acid fermentation apparatus, those used for culturing ordinary microorganisms can be used. For example, YM medium, potato Glucose medium, Gorodkova medium, sodium acetate medium, wort medium, malt extract medium, vegetable juice medium, gypsum medium, cornmeal medium, potato yeast leachate / glucose medium, Zapec medium, Sabouraud medium, oatmeal medium, synthetic mucor medium, YpSs medium, glucose / dry yeast medium,
The broth medium, yeast / malt medium, starch / inorganic salt medium, glycerin / asparagine medium, peptone / yeast / iron medium, tyrosine medium and Pridham / Gottlieb medium, and the like belong to the genus Rhizopus. Those containing nutrients that promote lactic acid fermentation by microorganisms having lactic acid fermentation ability are desirable, and
Within the range for achieving this object, it is desirable that the concentration be as low as possible (excluding the carbon source used as a raw material for lactic acid) in order to prevent fouling of the electrodialysis membrane.

Fermentation raw materials that can be used in the fermentation section of the lactic acid fermentation apparatus include microorganisms belonging to the genus Rhizopus and having a lactic acid fermentation ability. -Glucose, sucrose, lactose, D- and L-arabinose,
D-ribose, D-xylose, D-mannose, D-
Galactose, L-rhamnose, D-fructose, L
-Sorbose, maltose, lactose, melibiose, cellobiose, trehalose, raffinose, melezitose, α-methyl-D-glucoside, D-glucosamine, N-acetylglucosamine, arbutin, dextrin, soluble starch, inulin, methanol, ethanol, adnitol, erythritol , Inositol, D-mannitol, D-sorbitol, dulcitol, D-gluconate, glycerin, hexadecane and starch. In addition to these sugar sources, potassium monophosphate, potassium potassium phosphate, magnesium sulfate, sodium chloride It is desirable to add inorganic salts such as iron, ferrous sulfate, manganese sulfate, copper sulfate, manganese chloride, zinc sulfate and calcium carbonate.

In the method for fermenting lactic acid according to the present invention, optimal conditions for culturing microorganisms used for lactic acid fermentation should be set as follows.
The pH of the fermentation medium is usually adjusted to 4 to 4 by addition of alkali.
It is desirable to carry out the treatment while controlling it to be in the range of 8, preferably 5 to 7. In such a method, the lactate produced is separated from the fermentation liquor by two-chamber bipolar membrane electrodialysis, the dialyzed lactic acid component is recovered, and the dialyzed fermentation liquor is returned to the fermentation unit again using the circulation system. By controlling the pH value and electric conductivity of the entire fermentation medium including the fermentation liquid and the lactate concentration to desired set values, fermentation can be performed while maintaining high productivity without product inhibition. It is desirable to proceed.

The fermentation rate can be increased by keeping the concentration of lactate in the fermentation liquor in the fermentation section as low as possible. However, as the concentration of lactate decreases, the electric conductivity of the fermentation medium decreases. The current density and current efficiency when electrodialyzing the fermentation liquor deteriorates, the productivity of the electrodialysis device decreases, and the amount of dialysis of other components increases, leading to a decrease in selectivity. Lactate concentration in the fermentation liquor when introduced into, preferably 0.2
ON-O of the electrodialysis device so as to be about 2% by weight.
It is preferable to adjust the concentration by increasing or decreasing the voltage or current of the FF.

The control of the electrodialysis apparatus can be easily performed by measuring the electric conductivity of the fermentation medium in the fermentation section (apparatus). It is common to control electrodialysis by electric conductivity, but in the conventional electrodialysis fermentation method of lactic acid, the fermentation unit (equipment)
The lactate concentration in the fermentation liquor was measured to control the electrodialysis apparatus. However, according to the findings of the present inventors, it is possible to sufficiently estimate the lactate concentration by measuring the electric conductivity even in a fermentation medium having a large buffer capacity containing a large amount of other inorganic salts and contaminants. As can be seen, this makes it possible to control the electrodialysis fermentation with a very simple electric conductivity sensor as compared to the conventional electrodialysis fermentation method for lactic acid. Since the electric conductivity has a phase relationship with the lactate concentration, it may be an electric conductivity that corresponds to the preferable lactate concentration range of 0.2 to 2% by weight described above. It is desirable to adjust so as to fall within a range of 1 to 30 mS / cm, more preferably 5 to 15 mS / cm.

Next, regarding the selectivity of electrodialysis, when the lactic acid component is dialyzed, the inorganic salt, which is an essential component for culturing microorganisms, is also lost from the fermentation liquor by dialysis. However, in the case of batch type electrodialysis fermentation, if an appropriate amount of inorganic salt is present in the medium before the start of fermentation, fermentation can be completed without replenishing the inorganic salt to the fermentation solution in the middle. . This is presumably because the inorganic salt that was present at the beginning was taken into the cells in the early stage of fermentation, and was sufficient for one batch fermentation.

As described above, the sugar component which is the main raw material for fermentation contained in the culture medium of the fermentation section (apparatus) is D-
There are glucose, sucrose, lactose, etc.
Since these move through the anion exchange membrane from the salt chamber side to the recovery chamber side at the same time as the electrodialysis of the lactic acid component, the circulating recovery rate of the sugar component is reduced, and the selectivity is also reduced. In general, the lower the molecular weight, the more permeated the ion-exchange membrane. For example, when glucose is used as a raw material sugar component in batch electrodialysis fermentation, the charged concentration of the raw material sugar component is reduced to 1%.
When it is 0% by weight, it varies depending on the type of ion exchange membrane and the operating conditions of electrodialysis.
Wt% glucose moves to the collection chamber side. Therefore, in the case of a sugar component, the loss due to separation into the recovery chamber can be suppressed to a low level by adding the sugar component little by little during the fermentation so as to keep the concentration in the fermentation liquid always low.

When starch having a high molecular weight or dextrin which is a partial hydrolyzate thereof is used as a fermentation raw material,
It is possible to sufficiently suppress the loss of the fermentation raw material.

Further, when the electrodialysis fermentation of the present invention is continued, high-density culture of microorganisms is also possible.
To continuously or intermittently send a fresh medium to the fermentation unit (equipment) and remove and collect the generated lactic acid component by electrodialysis, so that the cells accumulate in the fermentation unit (equipment) and become dense. Therefore, higher productivity can be obtained than in the batch type.

When the cells are separated before the fermentation solution is introduced into the main body of the electrodialysis apparatus, the cells are separated by a separating device such as a cell pellet sedimentation device or a filter using a simple filter member. A method of controlling the density of bacterial cells by filtration (recovery) can be used. As the filter, since the pellet of microorganisms having lactic acid fermentation ability belonging to the genus Rhizopus easily has a diameter of 2 to 3 mm or more, a filter having a pore diameter of about 1 mm is sufficient, and is much simpler than bacteria. .

The electrodialysis / fermentation method that can be used in the present invention is not limited to the above-described embodiment, and conventionally known techniques relating to lactic acid fermentation and electrodialysis can be widely applied. Various configurations used for fermentation devices, electrodialysis devices, and the like can be used by appropriately combining them (for example, on the lactic acid fermentation device side, the material and size of the fermentation tank, the number of tanks, etc .; Then, characteristics such as material and strength of bipolar membrane and anion exchange membrane, effective membrane area, thickness, number of cells used (number of cells), cell configuration, electrode material, structure of electrodialysis tank and configuration of various members provided Such as the structure of piping and pumps, various tanks, etc. in the circulation / recovery system, and the configuration of various members, etc., and culture conditions or operating conditions (eg, temperature of the solution in each room such as fermentation solution) pH, concentration, electrode solution relates applied current, voltage, etc.) and the like, can be appropriately determined.

[0058]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 Composition shown below Glucose 100.0 g / l MgSO ₄ .7H ₂ O 0.25 g / l (NH ₄ ) ₂ SO ₄ 0.125 g / l KH ₂ PO ₄ 0.6 g / L yeast extract 0.15 g / l medium in 2 liters of Rhizopus oryzae A
HU 6537 spores were inoculated at a concentration of 2 × 10 ⁷ cells / ml and cultured with a 3 L air lift type lifter. Culture conditions were controlled at 37 ° C. and aeration at 2 l / min, and pH 5.5 with 10% aqueous ammonia from 20 hours after the start of the culture. After 160 hours, glucose in the medium was completely consumed, and the cells were dispersed in the medium in the form of pellets having a diameter of about 3 to 4 mm.

The whole amount of the pellet was sufficiently washed with sterilized water, and the entire amount of lactic acid was recovered and quantified. The lactic acid yield from glucose was 72%.

To the pellets washed with water, 2 l of a medium having the above composition was newly added, and lactic acid fermentation was carried out by an electrodialysis fermentation apparatus shown in FIG.

The electrodialyzer has a membrane area of 1.0 d.
This is a two-chamber bipolar membrane electrodialysis apparatus comprising four pairs of chambers (four cells) composed of a m ² bipolar membrane BP and an anion exchange membrane A, wherein a 1M aqueous ammonium sulfate solution is provided in an electrode chamber c, and a 0 M aqueous solution is provided in a recovery chamber. .45M aqueous sulfuric acid solution, and a Ti / Pt plate was used for the electrodes (+/-).
The operation was performed at a constant current of 5A.

The culture conditions were as follows: temperature 37 ° C., aeration 2 l / min.
After the start of the culture, the pH is controlled at 5.5 with 10% aqueous ammonia until the lactic acid concentration becomes about 20 g / l. Thereafter, the drive system (various pumps) of the electrodialyzer is operated to remove the lactic acid in the medium. The pH of the medium was kept at 5.5 by separating and removing it sequentially out of the system. The level of the culture was kept constant by installing a level controller and adding sterile water.

As a result, glucose was completely consumed in 50 hours, 116.7 g of lactic acid was recovered by electrodialysis, and the concentration of lactic acid remaining during the culture was 21 g / l.
As a result of recovering and quantifying the entire amount of lactic acid, the yield of lactic acid from glucose was as high as 85.2%.

After the experiment, when the electrodialysis apparatus was disassembled and the inner electrodialysis membrane was observed, no fouling was observed on the membrane.

Next, in Example 2 and Comparative Example 1 below,
An experiment was conducted to confirm the improvement of the current efficiency and the decrease of the transfer amount of ammonia when the pH of the salt room of the electrodialysis apparatus was controlled to be neutral or lower.

Example 2 << When the pH of the salt compartment of the electrodialysis apparatus was controlled at 5.5 >> For this reason, as a fermentation model on the lactic acid fermentation apparatus side of the present invention, the initial lactic acid concentration in the salt chamber supplied to the salt chamber of the electrodialysis apparatus was set to 1.9% by weight for both ammonium lactate and sodium lactate. Electrodialysis was performed by constantly controlling the pH of the salt chamber to 5.5 by supplying a 50% aqueous lactic acid solution to the chamber. That is, using an electrodialysis device having the following components and operating under the conditions shown in Table 1 and below,
Electrodialysis was performed on each of ammonium lactate and sodium lactate shown in Table 1. The results obtained are shown in Table 1 below.

· Two-chamber bipolar membrane electrodialysis (bipolar membrane-anion exchange membrane) · Membrane area: 1.0 dm ² × 4 cells · Recovery chamber: 300 ml of 0.5N sulfuric acid aqueous solution charged · Salt chamber pH: 50% lactic acid aqueous solution The pH of the salt room is controlled to 5.5 by addition. ・ Total voltage: 17 V ・ Electrification time: 100 minutes

[0069]

[Table 1]

Comparative Example 1 << Batch type bipolar membrane electrodialysis with no pH adjustment in the salt chamber >> This comparative example is an example of a conventional batch type bipolar membrane electrodialysis with a lactic acid bacterium. As a model of a lactate solution obtained by adjusting lactic acid by fermentation with an alkali and centrifuging, the concentration of lactic acid initially charged in a salt chamber of an electrodialyzer is set to 7.42% by weight for ammonium lactate, Was 7.95% by weight. Also,
The amount of lactic acid charged to the salt chamber was set at 0.1 for ammonium lactate.
49 mol and 0.53 mol with sodium lactate
, And electrodialysis was performed without controlling the pH of the salt room during the electrodialysis. That is, using a batch type two-chamber bipolar membrane electrodialysis apparatus having the following constitutional requirements, the operation was carried out under the conditions shown in Table 2 and the following, and the ammonium lactate and sodium lactate shown in the following Table 2 were respectively subjected to electrolysis. Dialysis was performed. The results obtained are shown in Table 2 below.

· Two-chamber bipolar membrane electrodialysis (bipolar membrane-anion exchange membrane) · Membrane area: 1.0 dm ² × 4 cells · Recovery chamber: 300 ml of 0.5N sulfuric acid aqueous solution · Salt chamber pH: no control · Total Voltage: 17V ・ Electrification time: 80 minutes

[0072]

[Table 2]

From the experimental results of Example 2 and Comparative Example 1,
As shown in Tables 1 and 2, it was confirmed that when the pH of the salt chamber of the electrodialysis device was controlled to be neutral or lower, the current efficiency was improved and the amount of ammonia transferred was reduced.

[0074]

According to the novel lactic acid fermentation method of the present invention, a two-chamber method comprising a lactic acid fermentation apparatus using a microorganism having a lactic acid fermentation ability belonging to the genus Rhizopus of a filamentous fungus, and a cell comprising a bipolar membrane and an anion exchange membrane. By combining a bipolar membrane electrodialysis device, industrially useful and practical electrodialysis fermentation is possible, and as food additives such as sake, soft drinks, pickles, soy sauce, bread making or beer, etc. Increased use in manufacturing and industrial applications such as leather, textiles, plastics, pharmaceuticals and agricultural chemicals, and further expansion of applications to highly safe solvents, detergents, biodegradable polymers, etc. Is also possible.

Further, according to the method of the present invention, monthly food chemicals (1996-6, pp. 30 to 35) and Japanese Patent Application Laid-Open No. 8-2810, which disclose technical contents close to the present invention among the prior art, are disclosed.
No. 77, etc. have excellent effects by solving the following technical problems of bipolar electrodialysis of lactate.

1) In the electrodialysis fermentation using bacteria such as general lactic acid bacteria and Bacillus subtilis, nutrient components and protein components secreted by bacterial cells contained in a medium brought into a bipolar membrane electrodialysis device from a lactic acid fermentation device are electrodialyzed. There is a problem of fouling of the electrodialysis membrane due to deposition and scaling on the membrane. Furthermore, for these bacteria, it is necessary to remove the cells from the medium by membrane separation, centrifugation or the like before the electrodialysis, which poses a problem for industrial practical use.

However, according to the present invention, long-term continuous operation is possible for the first time by the combination of the two-chamber bipolar electrodialysis and the lactic acid fermentation by a microorganism having a lactic acid fermentation ability belonging to the genus Rhizopus, and industrial application can be achieved. . This is because the medium of a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus does not require organic nutrients and the like as compared with other lactic acid fermentations, and therefore the electrodialysis membrane is not stained.

2) Therefore, in the batch type two-chamber bipolar electrodialysis currently used, including the above-mentioned publication, the pH rises in the latter half, the movement of hydroxide ions becomes severe, and the current efficiency decreases. Sodium lactate is significantly less efficient (although ammonium lactate reduces this efficiency loss).

However, in the present invention, by combining with fermentation, lactic acid is always collected at a neutral or lower level, so that the current efficiency can be kept high. For example, according to the example of JP-A-8-28077, the current efficiency is 70% in the batch type bipolar membrane electrodialysis of ammonium lactate, but easily in the bipolar membrane electrodialysis of ammonium lactate according to the method of the present invention. Current efficiency of 90% or more.

3) In the batch type electrodialysis, since the salt chamber becomes alkaline, a special alkali-resistant membrane is required for the anion exchange membrane.

However, in the method of the present invention, a general inexpensive anion exchange membrane can be used.

4) In Japanese Patent Application Laid-Open No. 8-281077, batch type electrodialysis is performed because electrodialysis fermentation using lactic acid bacteria, which is a kind of bacteria, is used as described in the example (because, This is because so-called electrodialysis fermentation has the technical problem described in 1) above. ). Therefore, it is necessary to use a weak base lactate.
However, in the case of ammonium lactate, ammonia is gasified in the salt chamber to generate blisters, and it is necessary to perform stripping by sending an inert gas to the salt chamber.

On the other hand, in the case of using an alkali metal salt of lactic acid such as sodium lactate in the method of the present invention, the above technical problems do not occur. Further, even in the case of ammonium lactate, when neutral as in the present invention, ammonia exists as a salt and there is no problem of gasification.

5) In the batch type two-chamber bipolar membrane electrodialysis of ammonium lactate, when the pH of the salt chamber rises, the ammonia molecules move by diffusion dialysis, and permeate the membrane and enter the recovery chamber.

However, in the method of the present invention, since the salt room is always kept at a neutral level or less, ammonia exists as ammonium lactate, and the transfer of ammonia by diffusion dialysis is extremely small.

[Brief description of the drawings]

FIG. 1 schematically shows an electrodialysis / fermentation apparatus combining a lactic acid fermentation apparatus using a microorganism belonging to the genus Rhizopus and having a lactic acid fermentation ability, and a two-chamber electrodialysis apparatus constituted by a bipolar membrane and an anion exchange membrane. FIG.

[Explanation of symbols]

1 ... electrodialysis fermentation equipment, 11 ... lactic acid fermentation equipment,
12: fermentation unit, 13: fermentation liquid removal pump, 14: cushion tank, 15: fermentation liquid circulation pump, 16a to 16e: piping, 17: pH sensing device, 18 ...
Fermentation tank lid, 19 ... fermentation tank,
20 ... Filter member, 21 ... Piping,
22: heat exchange device, 23: level controller, 24: water supply pump, 25
... Piping, 31 ... Two-chamber bipolar membrane electrodialyzer, 3
2 ... rectifier, 33 ... entrance of salt room,
34 ... piping, 35 ... outlet of the salt room,
36 ... Exit of collection room, 37 ... Entry of collection room,
38 ... Recovered liquid tank, 39 ... Piping,
40: Recovery liquid circulation pump, 4
DESCRIPTION OF SYMBOLS 1 ... Piping, 42 ... Exit of electrode chamber, 43 ... Electrolyte tank, 4
4 ... Piping, 45 ... Electrolyte circulating pump,
46: piping, 47: entrance of electrode chamber, BP: bipolar membrane, A: anion exchange membrane, a: salt chamber, b: recovery chamber, c ...
Electrode chamber.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shigenobu Miura 1-16-2 Miyamae, Suginami-ku, Tokyo Musashino Chemical Laboratory Tokyo Research Laboratory

Claims (4)

[Claims] 1. Lactic acid produced by a lactic acid fermentation apparatus using a microorganism having lactic acid fermentation ability belonging to the genus Rhizopus is introduced into a two-chamber bipolar membrane electrodialysis apparatus comprising a bipolar membrane and an anion exchange membrane, A method for fermenting lactic acid, which comprises sequentially removing the lactic acid from the system. 2. Lactic acid produced by the lactic acid fermentation apparatus is:
2. A monovalent lactate form, which is introduced into the two-chamber bipolar membrane electrodialysis apparatus.
A method for fermenting lactic acid according to item 1. 3. The method for fermenting lactic acid according to claim 2, wherein the monovalent lactate is ammonium lactate. 4. The method according to claim 2, wherein the monovalent lactate is sodium lactate.