JP6841468B1 - Quantitative method - Google Patents

Abstract

In the quantification method for quantifying histamine, a solution containing histamine is dropped onto an electrode having an enzyme membrane on which an enzyme is formed, and the histamine contained in the solution reacts with the enzyme to be decomposed, resulting in a decomposition product. It is generated (S19). Next, in the process of decomposing histamine into decomposition products by an enzyme, oxygen in the contained solution is consumed by an oxidation reaction (S21). Next, the current value of the current that flows when oxygen in the contained solution is decomposed by applying a voltage to the electrode is acquired (S23). Then, histamine is quantified based on the acquired current value (S25).

Description

The present invention relates to a method for quantifying histamine.

Various methods for quantifying histamine have been proposed. For example, in the quantification method described in Patent Document 1, histamine is quantified through the following first to sixth steps. In the first step, histamine is extracted from seafood, meat and the like. In the second step, the temperature of the histamine-containing aqueous solution containing the extracted histamine is measured. In the third step, the first virtual histamine concentration, which is stoichiometrically equal to the saturated dissolved oxygen concentration of the histamine-containing aqueous solution at the temperature measured in the second step, is obtained by referring to a table prepared in advance. In the fourth step, an enzyme having histamine oxidase activity is injected into the histamine-containing aqueous solution. In the fifth step, oxygen in the histamine-containing aqueous solution is consumed by the oxidation reaction in the process in which the enzyme reacts with histamine in the histamine-containing aqueous solution to produce imidazole acetaldehyde. After the oxidation reaction, the second virtual histamine concentration, which is stoichiometrically equal to the saturated dissolved oxygen concentration of the histamine-containing aqueous solution, is obtained based on the output signal from the oxygen sensor. In the sixth step, the concentration of histamine in the histamine-containing aqueous solution is quantified by calculating the difference between the first virtual histamine concentration and the second virtual histamine concentration.

Japanese Unexamined Patent Publication No. 10-174599

In the above method, many steps are required to quantify histamine, and the procedure is complicated. On the other hand, there is a demand for quantifying histamine with high accuracy by a simpler method.

An object of the present invention is to provide a quantification method capable of quantifying histamine with high accuracy by a simpler method.

The quantification method according to the present invention is a quantification method for quantifying histamine, in which a solution containing the histamine is applied to an electrode having at least an working electrode having an enzyme film formed by an enzyme on the surface and a counter electrode. In a decomposition step of dropping and reacting the histamine contained in the contained solution with the enzyme to decompose it to produce a decomposition product, and in a process of decomposing the histamine into the decomposition product by the enzyme in the decomposition step. A consumption step in which oxygen in the contained solution is consumed by an oxidation reaction, an acquisition step of acquiring a current value of a current flowing when the oxygen in the contained solution is decomposed by applying a voltage to the electrode, and the acquisition. The quantification step comprises a quantification step of quantifying the concentration of the histamine based on the current value acquired in the step, and a determination step of determining the film thickness of the enzyme membrane based on the quantification range of the histamine. The linear region in the first information showing the correspondence relationship between the current value and the histamine concentration for each film thickness is applied, and the current value acquired in the acquisition step and the film determined by the determination step are applied. It is characterized in that the concentration of the histamine corresponding to the thickness is specified.

In the quantification method according to the present invention, an electrode including an working electrode having an enzyme membrane on which an enzyme is formed on the surface and a counter electrode is used. Therefore, the quantification work of histamine can be facilitated as compared with the method in which the enzyme is injected into the contained solution. Moreover, since the electrodes can be used repeatedly, it is also effective in terms of cost. In addition, the concentration of histamine can be quantified according to the thickness of the enzyme membrane. Further, by determining the film thickness of the enzyme membrane based on the histamine quantification range, the optimum enzyme membrane film thickness for the histamine quantification range can be selected and applied.

In the present invention, in the acquisition step, the current value may be acquired based on the current that flows when the voltage applied to the electrode is swept. In this case, the quantification of histamine can be performed with high accuracy.

In the present invention, the enzyme may be histamine oxidase and the degradation product may be imidazole acetaldehyde. In this case, histamine is decomposed by histamine oxidase, so that oxygen in the contained solution is consumed by the oxidation reaction. Therefore, the concentration of histamine can be appropriately quantified based on the current value that fluctuates according to the amount of oxygen consumed.

In the present invention, the present invention comprises a first pre-step of mixing an ion exchanger with the contained solution to remove contaminants, and the decomposition step uses the contained solution from which the contaminants have been removed by the first pre-step. The decomposition product may be produced. In this case, the quantification of histamine can be performed with higher accuracy.

In the present invention, the ion exchanger may be an anion exchanger. In this case, the anion contaminants contained in the contained solution can be appropriately removed by the anion exchanger.

In the present invention, the present invention comprises a second pre-step of mixing a protein flocculant with the containing solution to remove the protein, and the decomposition step is the same using the containing solution from which the protein has been removed by the second pre-step. Decomposition may be produced. In this case, the quantification of histamine can be performed with higher accuracy.

In the present invention, the protein flocculant may be either polyethylene glycol or dextran. In this case, the protein contained in the contained solution can be appropriately removed by either polyethylene glycol or dextran.

In the present invention, a third pre-step of mixing a pH adjuster with the contained solution is provided, and the decomposition step produces the decomposed product using the contained solution whose pH has been adjusted by the third pre-step. May be good. In this case, the quantification of histamine can be performed with higher accuracy.

It is a figure which shows the enzyme reaction. It is a schematic diagram which shows the electrode 11, 12, 13 and the measuring part 3. It is a flowchart which shows the quantification method. It is the first graph. It is a graph which shows the measurement result for deriving the 1st graph. It is the 2nd graph in the modification. It is the 3rd graph in the modification.

Embodiments embodying the present invention will be described in order with reference to the drawings. The drawings to be referred to are used to explain the technical features that can be adopted by the present invention, and the configurations and the like of the devices described are not intended to be limited thereto, but are merely explanatory examples. The method for quantifying histamine according to the present embodiment utilizes a chemical reaction in which histamine is decomposed by the catalytic action of an enzyme, and quantifies histamine by an electrochemical method.

<Outline of quantification method>
The outline of the method for quantifying histamine will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, histamine is oxidized, deaminated and decomposed by reacting with histamine oxidase (HOD) used as an enzyme. By this reaction, imidazole acetaldehyde is produced from histamine (arrow Y11), and HOD is displaced from the oxidized form to the reduced form by the reduction reaction (arrow Y12). In addition, oxygen is decomposed by the oxidation reaction of reduced HOD (arrow Y13), and hydrogen peroxide is generated from the decomposed oxygen and water (arrow Y14). That is, in response to the decomposition reaction of one molecule of histamine by HOD, one molecule each of histamine and oxygen disappears, and one molecule each of imidazole acetaldehyde and hydrogen peroxide is produced.

As shown in FIG. 2, in the present embodiment, electrodes 11, 12, and 13 having an enzyme film 10 on which an enzyme is formed are used. The electrode 11 is the working electrode, the electrode 12 is the counter electrode, and the electrode 13 is the reference electrode. As a solution containing histamine (hereinafter referred to as "containing solution 21"), a solution prepared by dissolving a sample obtained from a living body such as fish meat in a solvent is prepared. The prepared containing solution 21 is added dropwise to the enzyme membrane 10. At this time, the histamine contained in the contained solution 21 reacts with the HOD of the enzyme membrane 10 and decomposes to produce imidazole acetaldehyde (IAA) (arrow Y21). Further, in the process of decomposing histamine by HOD, oxygen in the contained solution 21 is consumed by the oxidation reaction, and hydrogen peroxide is generated (arrow Y22).

A voltage is applied to the electrode 11 by the measuring unit 3. Oxygen remaining in the containing solution 21 permeates the enzyme membrane 10 of the electrode 11 and reaches the electrode 11. Oxygen combines with the electrons supplied from the electrode 11 and decomposes (arrow Y23).

Therefore, by electrochemically measuring the current value flowing through the electrode 11 when a voltage is applied by the measuring unit 3, the amount of decomposed oxygen, in other words, the amount of oxygen remaining in the contained solution 21 can be determined. Can be measured. The amount of oxygen remaining in the contained solution 21 decreases as the histamine contained in the contained solution 21 is decomposed by the enzymatic reaction. That is, there is a correlation between the amount of histamine contained in the contained solution 21 and the current value of the current flowing through the electrode 11 when a voltage is applied. Therefore, the concentration of histamine contained in the contained solution 21 can be quantified based on the current value measured by the measuring unit 3.

<Quantitative procedure>
The procedure for quantifying histamine will be described with reference to FIG. First, the preparation step is executed (S11). In the preparatory step, a sample is extracted from a living body such as fish meat. The sample contains histamine. By dissolving the sample in a solvent, a containing solution 21 containing histamine is prepared.

Next, as a step for removing impurities from the contained solution 21, the first pre-step is executed (S13). In the first pre-step, the anion exchanger is mixed with the containing solution 21 to remove impurities of anions in the containing solution 21. Anion exchanger is an ion-exchange resin in which an amino group has been introduced as a functional group, Cl ion, SO ₄ ions, the contaminants anions such as amino acids can be removed.

Next, as a step for removing the protein from the contained solution 21, a second pre-step is executed (S15). In the second pre-step, the protein in the containing solution 21 is removed by mixing either polyethylene glycol or dextran as a protein flocculant in the containing solution 21.

Next, as a step for adjusting the pH of the contained solution 21, a third pre-step is executed (S17). In the third pre-step, the pH of the containing solution 21 is adjusted to neutral to weakly alkaline by mixing the phosphoric acid powder as the pH adjusting agent with the containing solution 21.

Next, the electrode 11 having the enzyme membrane 10 on the surface is prepared. The containing solution 21 prepared through the first pre-step (S13), the second pre-step (S15), and the third pre-step (S17) is added dropwise to the enzyme membrane 10. As a result, the histamine contained in the contained solution 21 reacts with the HOD of the enzyme membrane 10 and is decomposed to produce imidazole acetaldehyde (S19). Further, the oxygen in the contained solution 21 is consumed by the oxidation reaction due to the HOD in which histamine is decomposed (S21).

Next, a voltage is applied to the electrode 11 by the measuring unit 3. More specifically, the measuring unit 3 sweeps the voltage applied to the electrode 11. Oxygen remaining in the containing solution 21 is decomposed to generate hydrogen peroxide. Further, the current value of the current flowing when oxygen is decomposed is measured and acquired by the measuring unit 3 (S23). More specifically, the extreme value of the current flowing during the sweep of the voltage is acquired as the current value by the measuring unit 3.

Next, histamine is quantified based on the current value obtained in the step of S23 (S25). The specific method for quantifying histamine is as follows. As shown in FIG. 4, a first graph showing the correspondence between the current value and the histamine concentration is prepared in advance. In the first graph, the x-axis defines the concentration of histamine. The y-axis defines the current value acquired by the measuring unit 3 when the voltage applied to the electrodes is swept. The histamine concentration (variable x) and the current value (variable y) have a substantially linear relationship. The function showing a straight line linearly approximated to the first graph satisfies the relation of the equation (1). However, the unit of the variable x is ppm, and the unit of the variable y is nA.
y = 51.742x-9372.2 (1)
At the time of quantification of histamine, the value of the variable x calculated when the current value acquired in the step of S23 is substituted into the variable y of the equation (1) is specified as the histamine concentration.

FIG. 5 shows the measurement results measured to derive the first graph of FIG. For the sample extracted from the raw meat of yellowfin tuna, the containing solution 21 prepared so that the concentration of histamine was 0 ppm, 50 ppm, and 100 ppm was used. The pH was approximately 7. Then, the voltage of the electrode 11 was swept from 0 mV to −800 mV under the condition of −20 mV / sec, and the current value of the current flowing through the electrode 11 at this time was measured twice each. The first graph shown in FIG. 4 is a plot of the relationship between the current value at the time of the minimum in each of the measurement results shown in FIG. 5 and the corresponding histamine concentration.

In the first graph shown in FIG. 4, the absolute value of the current value becomes smaller as the histamine concentration increases. As a result, as the concentration of histamine increases, the amount of oxygen decomposed by the oxidation reaction of the enzyme (arrow Y13, see FIG. 1) also increases (arrow Y14, see FIG. 1), and the oxygen remaining in the containing solution 21 also increases. It shows that the amount of

The above-mentioned step S25 may be executed by the measuring unit 3 or may be executed by another method. For example, the measuring unit 3 may output the acquired current value to the outside. The user may quantify histamine by referring to the equation (1) based on the output current value.

<Action and effect of this embodiment>
As described above, in the method for quantifying histamine according to the present embodiment, an electrode 11 having an enzyme membrane 10 on the surface on which HOD used as an enzyme is formed is used. Therefore, the quantification work of histamine can be facilitated as compared with the conventional method in which the enzyme is injected into the containing solution 21. Further, since the electrode 11 having the enzyme membrane 10 can be used repeatedly, the cost required for the quantification of histamine can be reduced.

The voltage required when oxygen is decomposed by applying a voltage is −1000 mV to −400 mV (see FIG. 4). On the other hand, the voltage when imidazole acetaldehyde (see FIG. 1) produced in response to histamine being decomposed by HOD is decomposed by applying a voltage is 300 to 500 mV. Further, the voltage when hydrogen peroxide (see FIG. 1) generated when oxygen is decomposed by HOD is decomposed by applying a voltage is 700 mV to 1000 mV. That is, since oxygen can be decomposed at a negative voltage, it is not affected by substances that are easily oxidized at a positive voltage. Therefore, in the quantification method of the present embodiment in which the amount of oxygen remaining in the contained solution 21 is measured by electrochemical measurement to quantify histamine, the amount of imidazole acetaldehyde or hydrogen peroxide remaining in the contained solution 21 is electrochemically measured. It is more stable and feasible than the case of quantifying histamine by measuring. Therefore, by quantifying histamine by the above method, the concentration of histamine can be quantified with high accuracy.

In the step of S23, the voltage applied to the electrode 11 is swept by the measuring unit 3, and the current value is acquired based on the current flowing at that time. By sweeping the voltage applied to the electrode 11, the current value can be obtained in consideration of the movement and diffusion of oxygen in the contained solution 21 and the enzyme membrane 10. Therefore, the quantification of histamine based on the acquired current value can be performed with high accuracy.

In the step of S25, the concentration of histamine corresponding to the current value acquired in the step of S23 is calculated as the value of the variable x calculated when the current value is substituted into the variable y of the equation (1). In this case, the concentration of histamine can be easily quantified based on the acquired current value.

Histamine oxidase (HOD) is used as an enzyme for degrading histamine. When histamine is decomposed by histamine oxidase, the oxygen in the contained solution 21 is consumed by the oxidation reaction. Histamine is also decomposed into imidazole acetaldehyde (see FIG. 1). Therefore, the concentration of histamine can be appropriately quantified based on the current value that fluctuates according to the amount of oxygen consumed.

In the first pre-step (S13), the ion exchanger is mixed with the containing solution 21 to remove impurities. In the steps S19 to S25, the contained solution 21 from which impurities have been removed is used to quantify histamine. In this case, it is possible to suppress the inhibition of histamine decomposition by enzymes by impurities, so that the quantification of histamine can be performed with higher accuracy. Further, by using an anion exchanger as the ion exchanger, impurities of anions contained in the contained solution 21 can be appropriately removed by the anion exchanger.

In the second pre-step (S15), the protein flocculant is mixed with the containing solution 21 and the protein is removed. In the steps S19 to S25, the protein-removed containing solution 21 is used to quantify histamine. In this case, it is possible to suppress the inhibition of histamine decomposition by the enzyme by the protein, so that the quantification of histamine can be performed with higher accuracy. Further, by using either polyethylene glycol or dextran as the protein flocculant, the protein contained in the contained solution 21 can be removed more appropriately.

In the third pre-step (S17), the pH adjuster is mixed with the containing solution 21 to adjust the pH to neutral to weakly alkaline. In the steps S19 to S25, the pH-adjusted containing solution 21 is used to quantify histamine. In this case, since the decomposition of histamine by the enzyme can be promoted by setting the pH to an appropriate level, the accuracy of histamine quantification can be further improved.

<Modification example>
The present invention is not limited to the above embodiment, and various modifications can be made. In the above embodiment, the measuring machine main body may be connected to the measuring unit 3. The current value measured by the measuring unit 3 may be output to the measuring machine main body. Equation (1) may be stored in the storage unit of the measuring machine main body. The CPU of the measuring machine main body may specify the histamine concentration by acquiring the current value output by the measuring unit 3 and applying the equation (1). The CPU may output the specified histamine concentration to the display unit of the measuring machine main body. Further, for example, the measuring unit 3 may output the current value of the current flowing when the voltage applied to the electrode 11 is swept to the measuring machine main body as it is. The measuring machine main body may specify an extreme value based on the current value output from the measuring unit 3. The measuring machine main body may specify the concentration of histamine by applying the specified extreme value to the formula (1).

It may be a measuring chip in which the measuring unit 3 and the electrodes 11 to 13 are integrated. The measuring chip may be used by being connected to the interface of the measuring machine main body. The measuring unit 3 may output the measured current value to the measuring instrument main body via the interface.

The current value acquired in the step of S23 does not have to be the extreme value of the current flowing during the sweep of the voltage. For example, the total amount of current flowing during a voltage sweep may be acquired as a current value. Further, the voltage applied to the electrode 11 in the step of S23 does not have to be swept. For example, the measuring unit 3 may continuously apply a voltage at which oxygen is decomposed to the electrode 11 for a certain period of time, and acquire the current value of the current flowing at that time.

The method for quantifying histamine in the step of S25 is not limited to the method using the formula (1). For example, a table showing the correspondence between the current value and the histamine concentration may be prepared in advance. In this case, histamine may be quantified by acquiring the concentration of histamine corresponding to the current value acquired in the step S23 in the table. The substance used as an enzyme for decomposing histamine is not limited to histamine oxidase, and other enzymes capable of decomposing histamine may be used.

The ion exchanger mixed with the contained solution 21 in the first previous step is not limited to the anion exchanger, and a cation exchanger may be used under the condition that the contained substance is not adsorbed. Further, both the anion exchanger and the cation exchanger may be mixed in the containing solution 21. The protein flocculant mixed in the containing solution 21 in the second previous step is not limited to polyethylene glycol and dextran, and may be other materials. The pH adjuster mixed with the contained solution 21 in the third previous step is not limited to the phosphoric acid powder, and other substances capable of making the contained solution 21 neutral to weakly alkaline may be used. Part or all of the first pre-step (S13), the second pre-step (S15), and the third pre-step (S17) may not be performed in the histamine quantification process.

In the preparation step (S11) of the quantification method, the film thickness of the enzyme membrane 10 formed on the surface of the electrode 11 may be determined based on the quantification range of histamine. The specific method for determining the film thickness is as follows.

In the second graph shown in FIG. 6, the theoretical curve showing the relationship between the concentration of histamine in the contained solution 21 and the amount of oxygen decomposed when a voltage is applied to the electrode 11 is shown in the enzyme membrane 10. It is shown for each film thickness. The larger the film thickness of the enzyme membrane 10, the larger the ratio of oxygen consumption to the concentration of histamine. Further, in the theoretical curve, as the film thickness of the enzyme membrane 10 increases, the range of the linear portion is distributed in the region where the concentration of histamine is small, and the slope becomes steeper. On the other hand, as the film thickness of the enzyme membrane 10 becomes smaller, the range of the linear portion is widely distributed to the portion where the concentration of histamine is large, and the inclination becomes gentler. When the concentration of histamine is specified using the second graph, it is preferable to use the linear portion of the theoretical curve because the concentration can be specified in more detail and accurately.

Therefore, for example, in the preparation step (S11), the smaller the value assumed as the concentration of histamine contained in the sample and the narrower the quantification range, the larger the value as the film thickness of the enzyme membrane 10 is determined. On the other hand, the larger the value assumed as the concentration of histamine contained in the sample and the wider the quantification range, the smaller the value as the film thickness of the enzyme membrane 10 is determined. Specifically, for example, when it is assumed that the quantification range of histamine is in the range 31 (about 20 to 50 ppm), the corresponding film thickness is determined based on the theoretical curve 32 having the largest film thickness. Further, for example, when it is assumed that the quantification range of histamine is in the range 33 (about 50 to 170 ppm), the corresponding film thickness is determined based on the theoretical curve 34 having the smallest film thickness.

When histamine is quantified in the step of S25, the second graph shown in FIG. 6 is used. Specifically, it is as follows. The current value acquired in the step of S23 is converted into oxygen consumption by using a predetermined function. In the second graph, the theoretical curve corresponding to the film thickness of the enzyme membrane 10 used is referred to, and the concentration of histamine corresponding to the converted oxygen consumption is specified. For example, when an enzyme membrane 10 having a film thickness corresponding to the theoretical curve 32 is used, the concentration of histamine within the range 31 (about 20 to 50 ppm) is specified using the linear portion 32A of the theoretical curve 32. Further, for example, when the enzyme membrane 10 having a film thickness corresponding to the theoretical curve 34 is used, the concentration of histamine within the range 33 (about 50 to 170 ppm) is specified by using the linear portion 34A of the theoretical curve 34. To.

As described above, the concentration of histamine can be quantified according to the film thickness of the enzyme membrane 10 based on the current value of the current flowing when the voltage is applied to the electrode 11. Therefore, even if the film thickness of the enzyme membrane 10 fluctuates, the histamine concentration can be quantified with high accuracy. Further, by determining the film thickness of the enzyme membrane 10 according to the quantitative range of histamine, the concentration of histamine can be specified by using the linear portion of the theoretical curve of the second graph. Therefore, the histamine concentration can be specified in more detail and accurately.

The third graph shown in FIG. 7 shows the relationship between the concentration of histamine in the contained solution 21 and the current value acquired by the measuring unit 3 when the voltage applied to the electrode 11 is swept, and the film thickness of the enzyme membrane 10. It is an actually measured value shown for each (1 μm, 3 μm). From the third graph, it was clarified that the current value increases as the film thickness of the enzyme membrane 10 increases, especially when the concentration of histamine is larger than about 10 ppm.

<Others>
The treatment of S19 is an example of the "decomposition step" of the present invention. The treatment of S21 is an example of the "consumption step" of the present invention. The process of S23 is an example of the "acquisition step" of the present invention. The treatment of S25 is an example of the "quantitative step" of the present invention . The process of S 11 is an example of the "determination step" of the present invention. The second graph is an example of the " first information" of the present invention.

3: Measuring unit 10: Enzyme membrane 11, 12, 13: Electrode 21: Containing solution

Claims (8)

A quantification method for quantifying histamine
A containing solution containing the histamine is added dropwise to an electrode having at least an action electrode having an enzyme membrane on which an enzyme is formed and an counter electrode, and the histamine contained in the containing solution is reacted with the enzyme. The decomposition process that decomposes and produces decomposition products,
In the decomposition step, the oxygen in the contained solution is consumed by the oxidation reaction in the process of decomposing the histamine into the decomposition product by the enzyme, and the consumption step.
The acquisition step of acquiring the current value of the current flowing when the oxygen in the contained solution is decomposed by applying a voltage to the electrode, and
A quantification step for quantifying the concentration of histamine based on the current value acquired in the acquisition step, and a quantification step .
A determination step of determining the film thickness of the enzyme membrane based on the quantitative range of histamine.
With
The quantification step is
The linear region in the first information showing the correspondence relationship between the current value and the histamine concentration for each film thickness is applied, and the current value acquired by the acquisition step and the film determined by the determination step are applied. A quantification method comprising specifying the concentration of the histamine corresponding to the thickness. In the acquisition process,
The quantification method according to claim 1, wherein the current value is acquired based on the current that flows when the voltage applied to the electrode is swept. The enzyme is histamine oxidase,
The quantification method according to claim 1 or 2 , wherein the decomposed product is imidazole acetaldehyde. A first pre-step of mixing the ion exchanger with the containing solution and removing impurities is provided.
The decomposition step is
The quantification method according to any one of claims 1 to 3 , wherein the decomposition product is produced using the containing solution from which the contaminants have been removed by the first pre-step. The quantification method according to claim 4 , wherein the ion exchanger is an anion exchanger. A second pre-step of mixing the protein flocculant with the containing solution and removing the protein is provided.
The decomposition step is
The quantification method according to any one of claims 1 to 5 , wherein the decomposition product is produced using the containing solution from which the protein has been removed by the second prior step. The quantification method according to claim 6 , wherein the protein flocculant is either polyethylene glycol or dextran. A third pre-step of mixing the pH regulator with the containing solution is provided.
The decomposition step is
The quantification method according to any one of claims 1 to 7 , wherein the decomposition product is produced using the containing solution whose pH has been adjusted by the third prior step.

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