Method for producing mixed powder, mixed powder, powder, and powder medium

Abstract

The present invention addresses the problem of providing: a powder producing method for obtaining a powder that has excellent solubility with respect to sparingly soluble tyrosine and has a neutral liquidity (pH 6.0-8.5) when dissolved in water; said powder; and a powder medium containing the powder. A method for producing a mixed powder according to the present invention comprises: a dissolving step in which tyrosine and histidine are dissolved in a solvent to obtain a solution containing tyrosine and histidine; and a powdering step in which a mixed powder of tyrosine and histidine is obtained by drying said solution.

Description

Method for producing mixed powder, mixed powder, powder, and powder medium

[0001] The present invention relates to a method for producing a mixed powder, a mixed powder, a powder, and a powder culture medium.

[0002] Conventionally, in order to improve the solubility of a poorly soluble medium, a method has been proposed in which the medium is prepared into an aqueous solution with other components and then freeze-dried (Patent Document 1).

[0003] Special table 2018-521682 publication

[0004] In this context, the present inventors, referring to Patent Document 1, prepared an aqueous solution of poorly soluble tyrosine with another component (hereinafter also referred to as the "second component") and then freeze-dried it. However, it was found that the solubility of the resulting mixed powder was insufficient depending on the type of the second component. Furthermore, it was found that depending on the type of the second component, the resulting mixed powder became basic when dissolved in water. A basic solution is problematic because it may decompose components such as vitamins present in the medium.

[0005] In view of the above circumstances, the present invention aims to provide a method for producing a powder of poorly soluble tyrosine, which has excellent solubility and a neutral pH (pH 6.0 to 8.5) when dissolved in water, as well as the powder and a powder culture medium containing the powder.

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using histidine as the second component, and have arrived at the present invention. That is, the present inventors have found that the above-mentioned problems can be solved by the following configuration.

[0007] (1) A method for producing a mixed powder, comprising: a dissolving step of dissolving tyrosine and histidine in a solvent to obtain a solution containing tyrosine and histidine; and a powdering step of drying the solution to obtain a mixed powder of tyrosine and histidine. (2) A method for producing a mixed powder according to (1) above, wherein heating and / or alkali is used for dissolution in the dissolving step. (3) A method for producing a mixed powder according to (1) or (2) above, wherein heating is used for dissolution in the dissolving step. (4) A method for producing a mixed powder according to any of (1) to (3) above, wherein the powdering step is a step of drying the solution by spray drying and / or a step of drying the solution by heating and reducing pressure. (5) A method for producing a mixed powder according to any of (1) to (4) above, wherein the mixing ratio of histidine to tyrosine in the dissolving step is 0.5 to 10 by mass. (6) A mixed powder produced by the method for producing a mixed powder according to any one of (1) to (5) above. (7) A mixed powder of tyrosine and histidine, which, when dissolved in water at 15 to 25°C for 7 minutes, results in a solution with a pH of 6.0 to 8.5 and a tyrosine concentration of 0.3 g / L or more. (8) A powder containing tyrosine and histidine, which, when dissolved in water at 15 to 25°C so that the final tyrosine concentration is 0.35 g / L or more when completely dissolved, satisfies the following conditions: The time when water is added in an amount to achieve the final concentration is set to 0 minutes, and the solution is sampled 7 minutes later and filtered through a 0.2 μm filter, the pH of the solution is 8.5 or less and the tyrosine contained therein is at a concentration of 0.3 g / L or more. (9) A powder culture medium comprising the mixed powder or powder according to any one of (6) to (8) above.

[0008] As will be described below, the present invention can provide a method for producing a powder of poorly soluble tyrosine, which has excellent solubility and a neutral pH (pH 6.0 to 8.5) when dissolved in water, as well as the powder and a powder culture medium containing the powder.

[0009] The method for producing a mixed powder of the present invention and the mixed powder of the present invention will be described below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Each component may be used alone or in combination of two or more types. Here, when two or more types of each component are used in combination, the content of the component refers to the total content unless otherwise specified.

[0010] [1] Method for Producing Mixed Powder The method for producing a mixed powder of the present invention (hereinafter also simply referred to as "the production method of the present invention") is a method for producing a mixed powder, comprising: a dissolving step of dissolving tyrosine and histidine in a solvent to obtain a solution containing tyrosine and histidine; and a powdering step of drying the solution to obtain a mixed powder of tyrosine and histidine.

[0011] The manufacturing method of the present invention, with its configuration, is believed to be able to solve the above-mentioned problems. The reason for this is unclear, but is thought to be roughly as follows. One factor contributing to the poor solubility of tyrosine is thought to be the association (packing) of tyrosine molecules. In contrast, in the present invention, tyrosine and histidine are dissolved in a solvent and then dried, which is thought to allow the heterocyclic ring of histidine to enter between tyrosine molecules and suppress packing of tyrosine molecules. Furthermore, histidine exhibits excellent solubility. Therefore, according to the present invention, a powder in which tyrosine and highly soluble histidine are mixed at the molecular level is thought to be obtained. As a result, the mixed powder obtained by the manufacturing method of the present invention is thought to exhibit excellent solubility. This is also inferred from the fact that simply mixing tyrosine and histidine does not improve solubility.

[0012] Each step of the production method of the present invention will be described below.

[0013] [Dissolving Step] The dissolving step is a step of dissolving tyrosine and histidine in a solvent to obtain a solution containing tyrosine and histidine.

[0014] [Tyrosine] The amount of tyrosine mixed with the solvent is not particularly limited, but in order to achieve better effects of the present invention, when heating is used for dissolution, the amount is preferably 0.01 to 100 g / L, more preferably 0.1 to 10 g / L, and even more preferably 0.2 to 5 g / L; when alkali is used for dissolution, the amount is preferably 0.1 to 1000 g / L, more preferably 0.2 to 300 g / L, even more preferably 0.2 to 200 g / L, and most preferably 1 to 100 g / L.

[0015] [Histidine] The amount of histidine mixed with the solvent is not particularly limited, but in order to achieve better effects of the present invention, when heating is used for dissolution, the amount is preferably 0.01 to 1000 g / L, more preferably 0.1 to 100 g / L, and even more preferably 0.5 to 10 g / L; when alkali is used for dissolution, the amount is preferably 0.2 to 3000 g / L, more preferably 1 to 600 g / L, even more preferably 5 to 300 g / L, and most preferably 10 to 100 g / L.

[0016] [Mixing Ratio] The mixing ratio of histidine to tyrosine (mixing amount of histidine / mixing amount of tyrosine) is a mass ratio, and for reasons of superior effects of the present invention, it is preferably 0.1 to 100, more preferably 0.5 to 50, even more preferably 1 to 20, and particularly preferably 2 to 10. Hereinafter, the mixing ratio of the second component to tyrosine (mixing amount of second component / mixing amount of tyrosine) (mass ratio) will also be simply referred to as the "mixing ratio".

[0017] [Solvent] The solvent used in the dissolving step is not particularly limited, but is preferably water or a hydrophilic solvent, more preferably water, for reasons of better effects of the present invention. Furthermore, it may be solid at room temperature, as long as it is liquefied upon heating. The hydrophilic solvent is not particularly limited as long as it is a hydrophilic solvent, but specific examples include ether group-containing compounds such as tetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether, and polyethylene glycol dialkyl ether; lactone group-containing compounds such as γ-butyrolactone and γ-valerolactone; amides such as caprolactam, N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide, N-methylpyrrolidone (NMP), N-octylpyrrolidone, and pyrrolidone; Examples of the hydrophilic solvent include lactam group-containing compounds, sulfones and sulfoxides such as sulfolane (tetramethylene sulfone) and dimethyl sulfoxide (DMSO), sugars or sugar derivatives such as sucrose, glucose, fructose, and lactose, sugar alcohols such as sorbitol and mannitol, furan derivatives such as 2-furancarboxylic acid and 3-furancarboxylic acid, alcohols such as methanol, ethylene glycol, glycerol, diethylene glycol, and triethylene glycol, and phenolic compounds such as dimethoxyphenol, m-cresol, o-cresol, p-cresol, phenol, and naphthol. These hydrophilic solvents may be used alone or in combination of two or more.

[0018] [Dissolution Method] The method for dissolving tyrosine and histidine in a solvent is not particularly limited, but the use of heat and / or alkali is preferred, and the use of heat is more preferred, because it provides better effects of the present invention. Note that "using heat" means heating the solvent, and "using alkali" means adding an alkali (sodium hydroxide, etc.) to the solvent.

[0019] When heating is used for dissolution, the temperature is not particularly limited, but in order to obtain better effects of the present invention, the temperature is preferably 40 to 300° C., more preferably 40 to 200° C., and even more preferably 50 to 90° C. During dissolution, the solvent may be in a subcritical or supercritical state under pressure at or above its boiling point.

[0020] When an alkali is used for dissolution, it is preferable to set the pH of the solution to 12 or higher, because this will provide a more effective effect of the present invention. Furthermore, when an alkali is used for dissolution, it is preferable to adjust the pH to neutral using an acid (such as hydrochloric acid) after dissolution (neutralization step), because this will provide a more effective effect of the present invention. In this specification, "neutral" means a pH of 6.0 to 8.5.

[0021] When dissolving using an alkali and then adjusting the pH to neutral using an acid, the resulting solution will contain salt. It is believed that when the solution contains salt, the suppression of packing between tyrosine molecules by histidine is somewhat reduced. Furthermore, when the solution contains salt, the resulting mixed powder will also contain salt. When the mixed powder contains salt, there is a risk of an increase in osmotic pressure when dissolved in water. For these reasons, it is preferable to use heat rather than alkali for dissolution.

[0022] [Powdering Step] The powdering step is a step of obtaining a mixed powder of tyrosine and histidine by drying the solution obtained in the dissolving step described above.

[0023] [Drying Method] The method for drying the solution is not particularly limited, and specific examples include spray drying, drying by heating (e.g., 40 to 80°C) and reducing pressure (e.g., 100 mmHg or less) (e.g., drying using an evaporator), freeze drying, etc. As a method for drying the solution, a drying method other than freeze drying is preferred, and spray drying and / or drying by heating and reducing pressure is more preferred, with spray drying being even more preferred, from the viewpoints that the resulting mixed powder is highly uniform, resulting in better solubility, and the time required for drying is short.

[0024] [Mixed Powder] The mixed powder obtained by the production method of the present invention is particularly useful as a powder for a culture medium.

[0025] [2] Mixed Powder The mixed powder of the present invention is a mixed powder of tyrosine and histidine, which, when dissolved in water at 15 to 30°C (preferably 15 to 25°C) for 7 minutes, gives a solution having a pH of 6.0 to 8.5 and a tyrosine concentration of 0.3 g / L or more. The tyrosine concentration is preferably 0.3 g / L or more and 1.0 g / L or less, more preferably 0.35 g / L or more and 0.9 g / L or less, and most preferably 0.4 g / L or more and 0.7 g / L or less. The mixed powder is preferably a mixed powder obtained by the above-mentioned production method of the present invention.

[0026] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0027] [Production of Powder] Each powder was produced as follows.

[0028] Example 1

[0029] <Dissolution Step> 460 mL of distilled water, 320 mg of L-tyrosine (1.76 mmol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 544 mg of L-histidine (3.53 mmol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a 1000 mL three-neck flask equipped with a stirring blade, and the mixture was heated at 80°C for 2 hours while stirring at 300 rpm (revolutions per minute), and complete dissolution was confirmed. A supersaturated liquid was thus obtained. The resulting supersaturated liquid is also referred to as A1. A1 was stable for several hours even when returned to room temperature.

[0030] <Powdering step> The supersaturated liquid (A1) obtained in the dissolution step was placed in a 1000 mL flask. Then, it was dried by heating (50 to 60°C) and reducing the pressure (50 mmHg or less) using an evaporator. In this way, a powder was obtained. The obtained powder is also referred to as HE1. Regarding HE1 １ The composition was confirmed by H-NMR (nuclear magnetic resonance) and found to be a mixed powder of tyrosine:histidine = 1:2 (molar ratio).

[0031] Examples 2 to 4 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 1, except that the amount of L-histidine mixed in the dissolving step was changed as shown in Table 1.

[0032] Example 5 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 1, except that in the powdering step, the supersaturated liquid obtained in the dissolving step was spray-dried using a Mini Spray Dryer B-290 (manufactured by Buchi). When the supersaturated liquid was insufficient when obtaining the powder, additional supersaturated liquid was prepared and used.

[0033] Examples 6 and 7 Mixed powders of tyrosine and histidine were obtained in the same manner as in Example 5, except that the amount of L-histidine mixed in the dissolving step was changed as shown in Table 1.

[0034] Example 8 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 1, except that in the powdering step, the supersaturated liquid obtained in the dissolving step was freeze-dried for one week using a freeze dryer FDU-12AS (manufactured by AS ONE Corporation) to obtain a powder.

[0035] Example 9 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 8, except that the amount of L-histidine mixed in the dissolving step was changed as shown in Table 1.

[0036] Example 10

[0037] <Dissolution Step> 30 mL of distilled water, 2.0 g of L-tyrosine (11.0 mmol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 3.4 g of histidine (21.9 mmol) were added to a 200 mL beaker, and 3.9 g of sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was then added to adjust the pH to 12 or higher, allowing for complete dissolution. Subsequently, a 5N (normality) aqueous HCl solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to between 7 and 8. A slurry was thus obtained. The obtained slurry is also referred to as NT1.

[0038] <Powdering step> The slurry (NT1) obtained in the dissolution step was placed in a 1000 mL flask. Then, it was dried by heating (50-60°C) and reducing the pressure (50 mmHg or less) using an evaporator. In this way, a powder was obtained. The obtained powder is also called HE10. About HE10 １ The composition was confirmed by H-NMR, and it was found to be a mixed powder of tyrosine:histidine=1:2 (molar ratio).

[0039] Examples 11 and 12 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 10, except that the amount of L-histidine mixed in the dissolving step was changed as shown in Table 1.

[0040] Example 13 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 10, except that in the powdering step, the slurry obtained in the dissolving step was freeze-dried for one week using a freeze dryer FDU-12AS (manufactured by AS ONE Corporation) to obtain a powder.

[0041] Examples 14 and 15 A mixed powder of tyrosine and histidine was obtained in the same manner as in Example 13, except that the amount of L-histidine mixed in the dissolving step was changed as shown in Table 1.

[0042] Comparative Example 1

[0043] <Dissolution step> 460 mL of distilled water and 320 mg of L-tyrosine (1.76 mmol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a 1000 mL three-neck flask equipped with a stirring blade, and the mixture was heated at 80°C for 2 hours while stirring at 300 rpm, and complete dissolution was confirmed. In this way, a supersaturated liquid was obtained. The obtained supersaturated liquid is also referred to as E1.

[0044] <Powdering step> The supersaturated liquid (E1) obtained in the dissolution step was placed in a 1000 mL flask. It was then dried by heating (70°C) and reducing the pressure (50 mmHg or less) using an evaporator. In this way, a powder was obtained. The obtained powder is also referred to as T1.

[0045] Comparative Example 2 L-tyrosine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the powder in Comparative Example 2.

[0046] Comparative Example 3: A powder was obtained in the same manner as in Example 1, except that L-arginine was used instead of L-histidine in the dissolution step. The obtained powder is also referred to as T2. Regarding T2 １ The composition was confirmed by H-NMR, and it was found to be a mixed powder of tyrosine:arginine=1:1.78 (molar ratio).

[0047] Comparative Example 4: A powder was obtained in the same manner as in Example 1, except that L-phenylalanine was used instead of L-histidine in the dissolution step. The obtained powder is also referred to as T3. Regarding T2 １ The composition was confirmed by H-NMR, and it was found to be a mixed powder of tyrosine:phenylalanine=1:1.86 (molar ratio).

[0048] [Evaluation] The following evaluations were carried out for each of the obtained powders.

[0049] [Solubility] 30 mL of distilled water was placed in a 100 mL beaker and stirred with a stirrer tip, and the obtained powder was added (25°C). The amount of powder added is as shown in the "Amount Added" column in Table 1. The time of addition was set to 0 minutes, and the solubility was evaluated visually according to the following evaluation criteria. The results are shown in Table 1. In practice, AA, A, B, C, or D is preferred, AA, A, B, or C is more preferred, AA, A, or B is even more preferred, AA or A is particularly preferred, and AA is most preferred. The above-mentioned amount added was calculated from the mixing ratio so that the amount of tyrosine in the solution would be 0.44 g / L. AA: Completely dissolved within 30 seconds; A: Completely dissolved between 30 seconds and 5 minutes; B: Completely dissolved between 5 minutes and 10 minutes; C: Completely dissolved between 10 minutes and 15 minutes; D: Completely dissolved between 15 minutes and 1 hour; E: Cloudy and sediment present even after 1 hour.

[0050] [Liquid Properties] The pH of the solution obtained in the solubility evaluation was evaluated. Then, the liquid properties were evaluated according to the following evaluation criteria. The results are shown in Table 1. In practice, neutrality is preferable. Acidic: pH less than 6.0 Neutral: pH 6.0 to 8.5 Basic: pH greater than 8.5

[0051] [Overall Evaluation] An overall evaluation was made based on the evaluation results of solubility and liquid properties according to the following evaluation criteria. The results are shown in Table 1. AA: Completely dissolved within 30 seconds, liquid property is neutral. A: Completely dissolved within 5 minutes, liquid property is neutral. B: Completely dissolved within 10 minutes, liquid property is neutral. C: Completely dissolved within 15 minutes, liquid property is neutral. D: Completely dissolved within 1 hour, liquid property is neutral. E: Still cloudy after 1 hour and / or pH is other than neutral.

[0052]

[0053] In Table 1, the "composition ratio (molar ratio)" of the powder indicates the composition ratio (molar ratio) of the second component to tyrosine. １ The results were confirmed using H-NMR. In Table 1, the "salt content" of the powder indicates the salt (NaCl) content (% by mass) when the total of tyrosine and the second component is taken as 100% by mass.

[0054] As can be seen from Table 1, the mixed powders obtained by Examples 1 to 15, which are the production method of the present invention, showed excellent solubility compared to a powder obtained by dissolving only tyrosine in a solvent and drying it (Comparative Example 1), commercially available tyrosine (Comparative Example 2), and a mixed powder obtained by using phenylalanine instead of histidine (Comparative Example 4). Note that Comparative Examples 1 and 2 did not completely dissolve even after 4 hours.

[0055] Comparing Examples 1 to 15, the mixed powders obtained in Examples 1 to 9, which used heating for dissolution, showed superior solubility.

[0056] Comparing Examples 1 to 4 (comparison of embodiments differing only in the mixing ratio), the mixed powders obtained in Examples 1 to 3, in which the mixing ratio was 0.6 or greater, exhibited superior solubility. In particular, the mixed powders obtained in Examples 1 and 2, in which the mixing ratio was 1 or greater, exhibited even superior solubility. Similarly, comparing Examples 5 to 7 (comparison of embodiments differing only in the mixing ratio), the mixed powders obtained in Examples 5 and 6, in which the mixing ratio was 1 or greater, exhibited superior solubility. Similarly, comparing Examples 10 to 12 (comparison of embodiments differing only in the mixing ratio), the mixed powders obtained in Examples 10 to 11, in which the mixing ratio was 1 or greater, exhibited superior solubility. Similarly, comparing Examples 13 to 15 (comparison of embodiments differing only in the mixing ratio), the mixed powders obtained in Examples 13 to 14, in which the mixing ratio was 1 or greater, exhibited superior solubility.

[0057] A comparison between Example 1, Example 5, and Example 8 (comparison between embodiments that differ only in the drying method) shows that the mixed powders obtained in Example 1, which used an evaporator (heating and reduced pressure) for drying, and Example 5, which used spray drying, exhibited superior solubility. Among them, the mixed powder obtained in Example 5 exhibited even superior solubility. Similarly, a comparison between Example 2 and Example 6 (comparison between embodiments that differ only in the drying method) shows that the mixed powder obtained in Example 6, which used spray drying for drying, exhibited superior solubility.

[0058] As can be seen from Table 1, the mixed powder obtained by using arginine instead of histidine (Comparative Example 3) was basic when dissolved in water. Furthermore, a comparison between Example 1 and Comparative Example 4 (comparison between embodiments differing only in the type of second component) shows that the mixed powder obtained by using histidine as the second component (Example 1) exhibited superior solubility to the mixed powder obtained by using a component other than histidine as the second component (Comparative Example 4).

[0059] The mixed powder obtained by the production method of the present invention was applied to E-MEM medium (Eagle's minimum essential medium) and its solubility was evaluated as follows. Since the dissolution rate of tyrosine is extremely fast in a medium containing the tyrosine / histidine molecular mixed powder of the present invention, it can be said that it is possible to detect whether a medium contains the tyrosine / histidine mixed powder of the present invention by the method shown below.

[0060] E-MEM medium A, from which tyrosine and histidine had been removed, was mixed as shown in Table 2 and the resulting mixed powder was uniformly mixed in a mortar to obtain E-MEM medium A mixed powder. E-MEM medium A was dissolved in water at a concentration of 11.9 g / L to obtain a liquid medium.

[0061]

[0062] Using the E-MEM medium A prepared in this manner, as shown in Table 3, medium A1 was prepared as Example 16 by adding 0.4 g / L of the tyrosine / histidine = 1 / 2 (mass ratio) molecular mixed powder of the present invention to E-MEM medium A, and medium A2 was prepared as Comparative Example 5 by adding the same amounts of L-tyrosine and L-histidine alone to E-MEM medium A instead of the tyrosine / histidine molecular mixed powder used in Example 16. At room temperature (22°C), medium A1, medium A2, and stirrer chips were placed in a 50 mL container, and water was added to each to make 20 mL. Stirring was initiated at 100 rpm with the time after water addition set as 0 minutes. After 7 minutes, 1 mL was withdrawn from the slurry. The withdrawn slurry was immediately filtered through a 0.2 μm filter to obtain liquids AL1 and AL2, respectively. The tyrosine content was measured by HPLC (high performance liquid chromatography) and found to be 0.4 g / L in AL1 and 0.18 g / L in AL2. The pH of the slurry before extraction was acidic, 4 or more and less than 6.

[0063] In this example, the initial amount of tyrosine added was 0.4 g / L, which is close to the upper limit of tyrosine solubility. However, considering that the actual amount may be lower depending on the medium, and that the amount of tyrosine detected after 7 minutes does not exceed 0.3 g / L even when taking into account error in the case of powders to which tyrosine and histidine are added separately, it can be said that if the filtrate after 7 minutes exceeds 0.3 g / L, it can be considered that the tyrosine-histidine mixed powder of the present invention is contained. The tyrosine concentration is preferably 0.3 g / L or more and 1.0 g / L or less, more preferably 0.35 g / L or more and 0.9 g / L or less, and most preferably 0.4 g / L or more and 0.7 g / L or less.

[0064]

Claims

1. a dissolving step of dissolving tyrosine and histidine in a solvent to obtain a solution containing tyrosine and histidine; and a powdering step of drying the solution to obtain a mixed powder of tyrosine and histidine.

2. The method for producing a mixed powder according to claim 1 , wherein the dissolving step uses heating and / or alkali for dissolving.

3. The method for producing a mixed powder according to claim 1 , wherein the dissolving step uses heating for dissolving.

4. The method for producing a mixed powder according to claim 1 , wherein the powdering step is a step of drying the solution by spray drying and / or a step of drying the solution by heating and reducing pressure.

5. 2. The method for producing a mixed powder according to claim 1, wherein in the dissolving step, a mixing ratio of histidine to tyrosine is 0.5 to 10 in terms of mass ratio.

6. A mixed powder produced by the method for producing a mixed powder according to claim 1.

7. A mixed powder of tyrosine and histidine, which when dissolved in water at 15 to 25°C for 7 minutes, gives a solution having a pH of 6.0 to 8.5 and a tyrosine concentration of 0.3 g / L or more.

8. A powder containing tyrosine and histidine, which satisfies the following conditions when dissolved in water at 15 to 25°C so that the final concentration of tyrosine is 0.35 g / L or more when completely dissolved. Conditions: The time when water was added in an amount sufficient to achieve the final concentration was defined as 0 minutes. After 7 minutes had elapsed, the liquid was sampled and filtered through a 0.2 μm filter. The liquid had a pH of 8.5 or less and contained tyrosine at a concentration of 0.3 g / L or more.

9. A powder medium comprising the mixed powder or powder according to any one of claims 6 to 8.

10. A method for producing a mixed powder as described in claim 1, wherein when the mixed powder is dissolved in water, the resulting solution has a pH of 6.0 to 8.

5.

11. A method for producing a mixed powder as described in claim 1, wherein, when the mixed powder is dissolved in water, the tyrosine concentration in the solution obtained 7 minutes after dissolution, assuming that the time of dissolution is 0 minutes, is 0.3 g / L or more.

12. A method for producing the mixed powder described in claim 1, wherein the mixed powder is for use as a culture medium.