JP7590715B2 - Sensor cleaning solutions containing amphiphiles - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies ▲1▼December 9, 2018 Presentation at the 2018 (Heisei 30) Kyushu Branch Academic Conference of the Japan Society of Applied Physics ▲2▼December 8, 2018 Publication of the 2018 (Heisei 30) Kyushu Branch Academic Conference of the Japan Society of Applied Physics https://annex. jsap. or. jp/kyushu/conf. html ▲3▼May 29, 2019 ISOEN presentation ▲4▼May 26, 2019 ISOEN publication

This invention relates to a cleaning solution containing an amphiphilic substance.

An amphiphilic substance is a general term for molecules that have both a "hydrophilic group" that is compatible with water (aqueous phase) and a "lipophilic group" (hydrophobic group) that is compatible with oil (organic phase) in the same molecule. Examples include surfactants, as well as biological molecules such as phospholipids and amphiphilic polymers.

Taste sensors have been developed as sensors that use these amphipathic substances. Bitter and astringent substances are highly hydrophobic, and are compatible with the hydrophobic groups of amphipathic substances, and have the property of binding strongly to each other (hydrophobic bonding). Taking advantage of this hydrophobic bonding property, the inventors of the present application have developed taste sensors such as bitter and astringent taste sensors. A taste sensor is a molecular membrane sensor in which the membrane potential changes depending on the components in a solution when immersed in a sample, and the bitterness or astringency of the components in the solution can be detected relatively by measuring the membrane potential.

During taste testing, bitter and astringent substances in the sample are strongly adsorbed to these sensors. In order to repeatedly use the sensors during taste testing, it is necessary to wash away the bitter and astringent substances adsorbed to the sensor and return it to its original state. Such a washing solution must be optimized for washing away the bitter and astringent substances (adsorbed substances) adsorbed to the molecular membrane of the sensor.

As mentioned above, in order to carry out taste tests (taste tests), the inventors have developed a taste sensor that uses a molecular membrane made of lipids, which are amphipathic substances, and this is disclosed in Patent Documents 1 to 4 and Non-Patent Document 1. Patent Document 1 discloses a "taste sensor and its manufacturing method," and describes the importance of lipids as taste sensors. Patent Document 2 also describes the composition of "lipid membranes" that present lipid membranes that are highly selective for bitterness and astringency. Patent Document 3 discloses a "molecular membrane for taste tests," and presents the composition of lipid membranes that are highly selective for sourness, saltiness, and umami. In addition, lipid membranes for the common sweetness of sucrose and fructose have been presented at academic conferences as "highly sensitive sweetness sensor using lipid polymer membranes" in Non-Patent Document 1.

Patent Document 4 discloses an effective method for cleaning these lipid membranes. In this cleaning method, the cleaning solution is mainly composed of an organic solvent such as ethanol, an acid, an alkali, and a salt. A common detergent is a surfactant such as sodium lauryl sulfate, which is an amphipathic substance. However, surfactants have the risk of changing the characteristics of the sensor or destroying the sensor in the following two ways. One is that the surfactant binds to the amphipathic substance contained in the sensor, and the other is that the surfactant peels off the amphipathic substance contained in the sensor from the sensor. Therefore, Patent Document 4 proposes optimizing cleaning by using an organic solvent such as ethanol, an acid, an alkali, and a salt without using a surfactant.

Patent No. 2578370 Patent No. 4395236 Patent No. 4520577 Patent No. 4516879

"Highly sensitive sweetness sensor using lipid polymer membranes" Journal of the Japanese Society for Taste and Odor 14(3), pp. 629-632 (2007)

Bitter and astringent substances form strong hydrophobic bonds with the sensor, which means that cleaning the sensor takes a long time. The cleaning solution must meet the following two conditions:

-Do not damage the sensor.

- Effectively remove hydrophobic substances (bitter substances, astringent substances, etc.) adsorbed to the sensor from the sensor.

The measurement process of a taste sensor consists of the time to measure the taste sample and the time to clean the sensor. Since the cleaning time takes up two-thirds of the total time, the measurement time can be significantly reduced by shortening the cleaning time. Therefore, there is a demand for an effective cleaning solution that contributes to shortening the cleaning time for taste sensors.

According to the embodiment,
A cleaning solution for cleaning a taste sensor membrane that detects at least one taste substance selected from salty, sour, bitter, sweet, umami, and astringent tastes , comprising :
The taste sensor membrane is composed of a lipid polymer membrane composed of a polymer material, a lipid, and a plasticizer,
The lipid includes a first amphiphilic substance composed of a lipid molecule group having a hydrophobic region extending in a longitudinal direction of an atomic array and a hydrophilic region present in a portion of the longitudinally extending atomic array,
The lipid-polymer membrane has a matrix surface that accommodates the lipid molecular group,
A cleaning solution used in a taste sensor system in which a taste substance is detected based on a change in sensor membrane potential caused by electrostatic and hydrophobic interactions acting between the taste sensor membrane and the taste substance , and the taste sensor membrane is then cleaned,
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance contains a negatively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs the sensor responsive substance has a positive charge, the cleaning solution is composed of a water-soluble second amphipathic substance that has a positive charge,
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance contains a positively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs this sensor responsive substance has a negative charge, the cleaning solution is characterized in that it is composed of a water-soluble second amphipathic substance that has a negative charge.

Further, according to the embodiment,
The cleaning solution is characterized in that the second amphiphilic substance contained in the cleaning solution has a positive charge, has a hydrophilic group such as a COOH group or a POOH group, and is acidic.

Further, according to the embodiment,
The cleaning solution according to claim 1, wherein the lipid molecular group contains at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group.

Further, according to the embodiment,
the cleaning liquid is an aqueous solution containing 0.05 to 0.2% by mass of a surfactant,
For a taste sensor in which the lipid membrane is positively charged, the lipid membrane contains only a surfactant having a positive charge;
For a taste sensor in which the lipid membrane is negatively charged, there is provided a cleaning solution according to claim 1, which contains only a surfactant having a negative charge .

FIG. 1 is a schematic diagram illustrating a taste sensor system including a sensor membrane capable of evaluating taste, which is used to verify the examples. 2A is a front view showing a schematic perspective of a portion of a sensor probe in the taste sensor system shown in FIG. 1, and FIG. 2B is a front view showing a schematic perspective of a portion of a reference electrode probe in the taste sensor system shown in FIG. 1. FIG. 2 is a schematic diagram for explaining the composition and chemical structure of a sensor film used in the sensor system shown in FIG. 1. 2 is a flowchart showing a process of taste measurement in the taste sensor system shown in FIG. 1 . 2 is a schematic diagram showing the change in sensor output over time and the change in charge in a lipid-polymer membrane in a taste measurement performed by the taste sensor system shown in FIG. 1 . FIG. 4 is a flow chart showing a cleaning solution evaluation process in the taste sensor system shown in FIG. 1 according to an embodiment. 2 is a graph showing response value characteristics over time from a sensor electrode and a reference electrode to a standard solution and a sample solution measured by the taste sensor system shown in FIG. 1 .

The following describes the embodiment with reference to the drawings.

The cleaning solution according to the embodiment has been developed based on the knowledge of the following inventors:

When the charge of the first amphipathic substance contained in the taste sensor (sensor membrane) and the charge of the second amphipathic substance contained in the cleaning solution are made the same, the two are electrically repelled, preventing the second amphipathic substance in the cleaning solution from being adsorbed onto the sensor. This has led to the discovery that the sensor is not affected by the cleaning solution. Furthermore, it has been discovered that a cleaning effect can be obtained by the second amphipathic substance.

As mentioned above, an amphiphilic substance is a general term for molecules that have both a "hydrophilic group" that is compatible with water (aqueous phase) and a "lipophilic group" (hydrophobic group) that is compatible with oil (organic phase) in the same molecule. Examples of amphiphilic substances include surfactants, as well as biological molecules such as phospholipids and amphiphilic polymers.

Table 1 below shows the optimal relationship between the charge of the sensor, the first and second amphiphilic substances contained in the cleaning solution, and the charge of the sensor's responsive substance. This is a relationship that provides a cleaning effect and does not affect the sensor characteristics.

Note 1: Iso-α acids, which give beer its bitter taste, and tannic acid, which gives red wine its astringency. Note 2: Quinine hydrochloride, which gives medicine its basic bitter taste. If the polarity of the electric charge of the bitter and astringent substance (sensor's response substance) is opposite to that of the second amphiphilic substance contained in the cleaning solution, it will be electrically attracted to the second amphiphilic substance in the cleaning solution and will form hydrophobic bonds with each other. This can be expected to have a cleaning effect in which the bitter and astringent substance (sensor's response substance) adsorbed on the sensor is separated from the first amphiphilic substance of the sensor.

Examples of the hydrophilic group portion of the amphiphilic substance include quaternary ammonium type, alkylamine type, and pyridine type, which are positively charged, and carboxylic acid type, sulfonic acid type, sulfate type, and phosphate type, which are negatively charged, and the hydrophobic group of the amphiphilic substance (first and second amphiphilic substance) includes carbon chains and benzene rings. If the amphiphilic substance is highly hydrophobic, it is poorly soluble in water and is used as a sensor material (lipid membrane containing the first amphiphilic substance). Here, the lipidic substance of lipid 17B (lipidic substance containing the first amphiphilic substance) has a lipidic molecule group having a hydrophobic portion and a hydrophilic portion present in a part of the atomic arrangement extending in the longitudinal direction, and the lipid membrane for the taste sensor is configured to have a matrix on the surface that can accommodate the lipidic molecule group. The lipid membrane for the taste sensor has a structure in which at least a portion of the lipid molecule group is accommodated within the lipid membrane matrix with the hydrophilic sites arranged on the surface, and is capable of detecting at least two tastes among salty, sour, bitter, sweet, and umami. The lipid molecule group also contains at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group. Specific examples of materials for this sensor have already been disclosed in Patent Documents 1 to 4 and Non-Patent Document 1.

On the other hand, if the hydrophilicity is strong, it dissolves in water and is used as a cleaning agent (cleaning solution containing the second amphipathic substance). Negatively charged second amphipathic substances are shown in Tables 2-1, 2-2, and 2-3 below, and positively charged second amphipathic substances are shown in Tables 3-1 and 3-2. Some amphipathic substances have both positive and negative hydrophilic groups, and if the negative group is a carboxylic acid group or a phosphoric acid group, the carboxylic acid group and the phosphoric acid group do not dissociate under acidic conditions, resulting in an amphipathic substance (second amphipathic substance) that is only positively charged. An example of this is shown in Table 4. When the second amphipathic substances shown in Table 4 are used as materials for cleaning solutions, the pH of the cleaning solution is made acidic and the substance is used as a positively charged substance.

[Taste sensor system]
Prior to describing the examples, a taste sensor system used to verify the examples will be described.

<Taste detection process in taste sensor system>
FIG. 1 shows a taste sensor system. In this taste sensor system, a container 10 is prepared for individually storing a reference solution, a sample solution, a cleaning solution, etc., and a reference electrode probe 11 and one or more taste sensor probes 15 shown in FIG. 2 are supported by an arm mechanism (not shown) that can move up and down so that they can be inserted and removed into the container 10. This taste sensor system employs a CPA (Change of membrane Potential caused by Adsorption) measurement method, and a sensor membrane (a lipid membrane containing a first amphiphilic substance) that detects each taste quality is prepared, and a taste sensor probe 15 equipped with each sensor membrane is prepared. Here, the taste qualities include umami, sourness, saltiness, sweetness, astringency, and bitterness. Therefore, a taste sensor probe 15 equipped with a sensor membrane corresponding to each taste quality is prepared.

As shown in FIG. 2A, the taste sensor probe 15 has a sensor membrane (a lipid membrane containing a first amphipathic substance) 17 for detecting a corresponding taste quality fixed around the through-hole of the tube 16. The surface of the sensor membrane 17 is arranged so as to be exposed inside the container 11, and the opposite surface of the sensor membrane 17 is exposed to a conductive internal liquid contained in the tube 16. One example of this internal liquid is a 3.3 M KCl saturated AgCl solution. A sensor electrode 19 is inserted and arranged inside the tube 16, and the tip of the sensor electrode 19 is immersed in the conductive internal liquid so as to face the sensor membrane 17. The electrode 19 is connected to a voltage detector 20 via a lead wire 19A.

As shown in FIG. 2(B), the reference electrode probe 11 is composed of a tubular glass tube 13 whose tip opening is sealed with a liquid-tight porous ceramic 18. The glass tube 13 is filled with a conductive internal liquid, similar to the sensor, and the reference electrode 12 is immersed in this conductive internal liquid. This reference electrode 12 is connected to the voltage detector 20 via a lead wire 12A.

In the measurement method of the embodiment, the change in membrane potential due to electrostatic/hydrophobic interactions acting between the sensor membrane and the taste substance is output as a voltage signal. The voltage detector 20 detects the voltage between the reference electrode 12 and the sensor electrode 19 for the reference solution and the sample solution, and detects the change over time from when the probes 12, 15 are immersed in the reference solution and the sample solution. The detected voltage signal is converted into a digital voltage signal by the A/D converter 22, and the digital voltage signal is sent to the calculation device 23 and stored in the memory 23A. The calculation device 23 calculates the change over time of the sensor voltage Vr in the reference solution and the response voltage Vs in the sample solution as a response value (Vs-Vr) and stores it in the memory 23A.

The memory 23A stores the response value (relative value: Vs-Vr) as data on the first taste response value, and the first taste response value (relative value: Vs-Vr) is compared with known data in the calculation device 23 to quantify the taste quality of the sample liquid, which is then output to the output device 24 for use in judging the taste, etc.

As will be explained later, when measuring high-intensity sweeteners, the response value (relative value: Vs-Vr) is detected as the first taste, and then the probes 12, 15 are immersed in a reference solution and washed with the reference solution. Then, the voltage Vr' between the reference electrode 12 and the sensor electrode 19 relative to the reference solution is detected, and the differential voltage (CPA value: Vr'-Vr) is calculated as the aftertaste response value and stored in memory 23A as the aftertaste response value. The probes 12, 15 are then washed and used again for taste testing.

The taste sensor membrane (lipid membrane containing a first amphipathic substance) 17 is composed of a lipid polymer membrane as shown in FIG. 3. As shown in the schematic structure of FIG. 3, the sensor membrane 17 according to the embodiment is composed of PVC (polyvinyl chloride) 17A as a polymer material, lipid (lipid containing a first amphipathic substance) 17B that adjusts the flexibility and hydrophobicity of the membrane, and plasticizer 17C that adjusts the charge and hydrophobicity of the membrane.

Here, the lipidic substance of lipid 17B (lipidic substance including the first amphipathic substance) has a molecular structure with a hydrophobic portion in which the atomic arrangement extends longitudinally and a hydrophilic portion at or near one end of the hydrophobic portion. That is, the lipidic substance has a lipidic molecular group having a hydrophobic portion and a hydrophilic portion present in a portion of the atomic arrangement extending longitudinally, and the lipid membrane for the taste sensor is configured to have a matrix on its surface that can accommodate the lipidic molecular group. The lipid membrane for the taste sensor has a structure in which at least a portion of the lipidic molecular group is accommodated in the lipid membrane matrix so that the hydrophilic portions are arranged on the surface, and is capable of detecting at least two tastes among salty, sour, bitter, sweet, and umami. The lipidic molecular group also includes at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group.

In the examples, bitter sensor C00 is described as the first sensor, and this first sensor has the composition shown in Table 5 below. Similarly, bitter sensor BT0 is described as the second sensor, and this first sensor has the composition shown in Table 5 below.

The lipid 17B and the plasticizer 17C are fixed and supported by PVC (polyvinyl chloride) 17A. When the sensor membrane 17 is exposed to a taste solution (aqueous solution) 28 containing a taste substance, electrostatic interaction and hydrophobic interaction occur between the lipid polymer membrane 17B and the taste substance in the sample aqueous solution (sample liquid) 28 containing the taste substance, changing the membrane potential of the sensor membrane 17. More specifically, as an example, in the salty taste sensor membrane 17, a negative membrane potential is generated by the negative charges 34 of the negatively charged lipid and ion rejector, and when Na ions are present in the sample aqueous solution, they are taken up by the sodium ionophore 30 in the membrane, and the positive charges 36 of Na change the membrane potential in the positive direction. In the sensor membrane 17 for high-intensity sweeteners, a positive membrane potential is generated by the positively charged lipid, and when a negatively charged high-intensity sweetener is present in the sample liquid, it is adsorbed to the sensor membrane, changing the membrane potential in the negative direction. This change in the membrane potential of the sensor membrane 17 is detected by the sensor electrode 19, and the difference with the potential of the reference electrode 12 is output in response as a voltage signal.

The taste measurement based on the sensor membrane 17 in the sensor system shown in FIG. 1 is specifically performed according to the procedure shown in FIG. 4, and the sensor output (voltage change) shown in FIG. 5(A) is obtained. The sensor output (voltage change) shown in FIG. 5(A) corresponds to the action of negative charges on the sensor membrane 17 in the reference solution 30 and the aqueous solution to be measured (so-called sample solution 28) in FIG. 5(B), (C), (D), and (E). In FIG. 5(C) to FIG. 5(E), the rectangles indicate negative charges 34 of bitter or astringent substances (hydrophobic substances), and the circles indicate negative charges 36 of sour, salty, or umami substances (hydrophilic substances), and the arrows indicate the movement of these negative charges toward or away from the sensor membrane 17. These changes in the membrane potential of the sensor membrane 17 are detected by the sensor electrode 19, and the difference with the potential of the reference electrode 12 is output in response as a voltage signal as shown in FIG. 4.

Taste measurement in the sensor system shown in Figure 1 is specifically carried out according to the procedure shown in Figure 4. When starting taste measurement, a reference solution is first prepared, and a test aqueous solution (so-called sample solution 28) to which a predetermined additive has been added as the target of taste measurement is also prepared. The reference solution, the test aqueous solution (so-called sample solution 28) and a cleaning solution (cleaning solution containing a second amphipathic substance) are each stored in different containers 10 and preparation for measurement is completed. Thereafter, the reference electrode probe 11 and the taste sensor probe 15 are immersed in the reference solution, and the reference value voltage Vr between the reference electrode 12 and the sensor electrode 19 is measured and stored in memory 23A (S1). An example of a reference solution 30 prepared for taste measurement is a solution in which 30 mM KCI is added with 0.3 mM tartaric acid (30 mM KCI + 0.3 mM tartaric acid), and examples of a test solution (so-called sample solution 28) prepared for taste measurement include quinine hydrochloride, iso-α acid, etc., as described later.

This reference voltage Vr is compared with the previously measured reference voltage to check whether it is within the reference range. If the difference between the previously measured reference voltage Vr and the currently measured reference voltage Vr is within a predetermined value during the comparison, the process proceeds to the next step S2. If the difference between the previously measured reference voltage Vr and the currently measured reference voltage Vr is not within a predetermined value, step S1 is executed again to measure the reference solution again. When measuring the reference solution for the first time, step S1 is repeated a predetermined number of times and averaged to determine the reference value Vr, which is then stored in the memory 23A (S1). Here, since the reference solution 30 does not contain the charge of the object to be measured, the potential of the sensor film 17 is maintained constant, and a baseline voltage is output from the reference electrode 12 and the sensor electrode 19. Next, the reference electrode probe 11 and the taste sensor probe 15 are immersed in the solution to be measured (sample solution), and the sample voltage Vs between the reference electrode 12 and the sensor electrode 19 is measured and stored in the memory 23A (S2).

This measurement produces a sensor output as shown in Fig. 5. As shown in Fig. 5(B), the negative charges 34 of bitter or astringent substances (hydrophobic substances) and the negative charges 36 of sour, salty or umami substances (hydrophilic substances) are moved so as to be adsorbed to the high-intensity sweetener sensor membrane 17 at a positive potential, so that the potential of the sensor membrane 17 is greatly reduced from time t1 as shown in Fig. 5(A), and a sample voltage Vs is output between the reference electrode 12 and the sensor electrode 19. The sample voltage Vs is compared with a reference voltage Vr, and the difference voltage between the sample voltage Vs and the reference voltage Vr is calculated as a sample response value (relative value: ΔV=Vs-Vr) (S3).
Here, the response value (relative value: ΔV=Vs−Vr) corresponds to the first taste at high sweetness intensity.

Then, the reference electrode probe 11 and the taste sensor probe 15 are again immersed in the reference liquid 30 and the sensor membrane 17 is washed with the reference liquid 30.

As the sensor membrane 17 is washed with the reference solution 30 from time t2, the negative charges 36 of the sour, salty or umami substances (hydrophilic substances) are moved (dispersed) into the reference solution 30 so as to be separated from the sensor membrane 17, as shown in FIG. 5(D). Therefore, the potential of the sensor membrane 17 is slightly increased to a potential where only the negative charges 34 of the bitter or astringent substances (hydrophobic substances) remain. The output voltage between the reference electrode 12 and the sensor electrode 19 is changed to a sensor output Vr' that corresponds to a potential where only an aftertaste remains. This reference value voltage Vr' is measured and stored in memory 23A (S4).

Then, the difference voltage between the reference voltage Vr' and the reference voltage Vr (CPA value: ΔV' = Vr' - Vr) is calculated by the calculation device 23 as the aftertaste response value (CPA value) for the measured solution (sample solution) 28, and is stored in the memory 23A (S5).

At time t3, the reference electrode probe 11 and the taste sensor probe 15 are immersed in a cleaning solution prepared in another container 10 and washed (S6).

When the sensor membrane 17 is washed with the washing liquid, the negative charges 34 of the bitter or astringent substances (hydrophobic substances) are separated from the sensor membrane 17 and diffused into the washing liquid . Therefore, the potential of the sensor membrane 17 is changed so as to rise to the baseline reference voltage Vr over time. Thereafter, steps S1 to S4 are repeated as necessary.

When measuring the aftertaste, the reference electrode probe 11 and the taste sensor probe 15 are again immersed in the reference solution, and the reference voltage Vr' between the reference electrode 12 and the sensor electrode 19 is measured and stored in the memory 23A (S4). By measuring the potential in the reference solution again, the aftertaste response value (CPA) for the sample is also calculated by the calculation device 23 as (ΔVr' = Vr' - Vr) (S5).

After step S3 or step S5, a cleaning step shown in step S6 is performed. In this cleaning step, the reference electrode probe 11 and the taste sensor probe 15 are immersed in a cleaning solution (cleaning solution containing a second amphipathic substance) prepared in another container 10, and the reference electrode probe 11 and the taste sensor probe 15 are washed with the cleaning solution, and steps S1 to S3 or steps S1 to S5 are repeated again. In these steps, when the repetition of steps S1 to S4 reaches a predetermined number of times, for example, 5 times, the average value [ΔVaver = (ΔV1 + ΔV2 + ΔV3 + ΔV4 + ΔV5) / 5] of the response value of the differential voltage (ΔV = Vs - Vr) or/and the average value [Δ'raver = (ΔVr'1 + ΔVr'2 + ΔVr'3 + ΔVr'4 + ΔVr'5) / 5] of the CPA value (ΔVr' = Vr' - Vr) are calculated and stored in the memory 23A. After the processing of steps S1 to S6, the taste measurement of the aqueous solution to be measured (so-called sample solution 28) is completed, and if there is a new aqueous solution to be measured (so-called sample solution 28), the processing of steps S1 to S6 is carried out again. If there is no new aqueous solution to be measured (so-called sample solution 28), the processing ends after the processing of step S6. In the above-mentioned processing, the degree of the known taste value can be determined from the average value ΔVaver of the response value of the differential voltage.

In addition, in step S1, if the measurement value falls outside the predetermined range even after repeated measurements of the reference liquid, the cleaning of the taste sensor probe 15 is deemed insufficient, and the reference electrode probe 11 and the taste sensor probe 15 are immersed in a cleaning liquid (cleaning liquid containing a second amphipathic substance) prepared in the container 10, and the reference electrode probe 11 and the taste sensor probe 15 are cleaned again with the cleaning liquid. In addition, in the measurement of the reference liquid in step S1, if it is determined that the sensor membrane of the taste sensor probe 15 is not restored even by cleaning, the taste sensor probe 15 is subject to replacement and is replaced with a new taste sensor probe 15.

<Verification of cleaning in taste sensor system>
In the taste sensor system shown in FIG. 1, the verification of the cleaning of the reference electrode probe 11 and the taste sensor probe 15 is performed by preparing the taste sensor probe 15 to be verified (a sensor probe having a lipid membrane containing a first amphipathic substance) and a reference solution, and also preparing a measurement solution (so-called sample solution 28) to which a predetermined additive is added as a target for taste measurement and a cleaning solution (cleaning solution containing a second amphipathic substance) to be verified. The reference electrode probe 11 and the taste sensor probe 15 are immersed in the reference solution, and the reference value voltage Vr between the reference electrode 12 and the sensor electrode 19 is measured and stored in the memory 23A (S11). As already described, during the period R1 during which the reference electrode 12 and the sensor electrode 19 are immersed in the reference solution as shown in FIG. 7, the sensor output from the sensor is maintained at the reference value (relative value 0%). Thereafter, the reference electrode probe 11 and the taste sensor probe 15 are immersed in the measurement solution (so-called sample solution 28) and the sensor output from the sensor is detected. Since the adsorbable substance in the sample is adsorbed to the lipid membrane (lipid membrane containing the first amphipathic substance) of the sensor probe 15, the sensor outputs a sensor signal whose output level gradually increases toward a relative value of 100% as shown in period R2. After that, the reference electrode probe 11 and the taste sensor probe 15 are immersed in a cleaning solution (cleaning solution containing the second amphipathic substance) to clean the lipid membrane (lipid membrane containing the first amphipathic substance) of the taste sensor probe 15. During this cleaning period R3, the adsorbable substance escapes from the lipid membrane (lipid membrane containing the first amphipathic substance) of the sensor probe 15 into the cleaning solution (cleaning solution containing the second amphipathic substance) together with a positive or negative charge, and the lipid membrane (lipid membrane containing the first amphipathic substance) is cleaned. During this cleaning process period R3, the output from the sensor is gradually attenuated from a relative value of 100%. After cleaning, the reference electrode probe 11 and the taste sensor probe 15 are immersed again in the reference solution for period R4 to measure the output signal. When the lipid membrane (lipid membrane containing the first amphipathic substance) is ideally washed with the washing solution (washing solution containing the second amphipathic substance), the sensor output will be at a signal level of 0% (relative value) of the residual value without adsorbed substances, but a signal output of a level dependent on the proportion of remaining adsorbed substances will be output from the sensor. As the period R4 during which the sensor is immersed in the reference solution elapses, the signal level output from the sensor will reach a verification level at which it will not decrease any further. This verification level corresponds to the residual value without adsorbed substances, and the higher this level, the higher the residual rate of remaining adsorbed substances, and the lower this level, the lower the residual rate of remaining adsorbed substances. From this verification process, the optimality of the sensor material (lipid membrane containing the first amphipathic substance) and the washing agent (washing solution containing the second amphipathic substance) is verified. The verification results of the sensor material (lipid membrane containing the first amphipathic substance) and washing agent (washing solution containing the second amphipathic substance) optimal for the following embodiment will be described together with comparative examples.

[Example]
The first sensor according to the embodiment is a bitterness sensor C00, which detects acidic bitter substances (negative charge) such as iso-α acid contained in beer, and is a sensor that is positively charged. The second sensor according to the embodiment is a bitterness sensor BT0, which detects basic bitter substances (positive charge) in medicines such as quinine hydrochloride, and is a sensor that is negatively charged. The measurement was performed using the system shown in FIG. 1. The membrane potential when a bitter substance or an astringent substance is adsorbed to the sensor is detected. The measurement procedure involves measuring a reference solution instead of human saliva, which is set as the zero point. The potential change of the sensor when the sample is measured is set as the output. After measuring the sample, the sensor is washed by inserting and removing it into a cleaning solution. As described with reference to FIG. 7, if there is adsorption, the sensor does not return to the original zero point of the reference solution. The cleaning effect can be evaluated by how far it returns. If the sample is only a non-adsorbent reference solution, the position of the zero point changes, and the deterioration of the sensor due to the cleaning solution can be evaluated.

The conventional cleaning solution used in the first sensor C00 is 30% ethanol, 100 mM KCl, 10 mM KOH, and the conventional cleaning solution used in the second sensor BT0 is 30% ethanol, 100 mM HCl. The first sensor C00 is measured with 0.1% iso-α acid, and the second sensor BT0 is measured with 1 mM quinine hydrochloride, and then washed with the conventional cleaning solution for 90 seconds. It was detected that the sensor output did not return to the zero point by about 10% when using the normal cleaning solution. When 0.2% lauryldimethylaminoacetic acid (in this case, since the pH is 1, the carboxylic acid does not dissociate and the amino group is positively charged) was added to the first sensor C00 as a representative from the lists in Tables 2-1, 2-2 and 2-3, and 0.05% sodium lauryl sulfate (in this case, since the pH is 1, the carboxylic acid does not dissociate and the amino group is positively charged) was added to the second sensor BT0 as a representative from the lists in Tables 2-1, 2-2 and 2-3 in comparison with these conventional cleaning solutions, the rate of return to the zero point was suppressed by 3 to 10 times compared to the normal cleaning solutions, and a sufficient cleaning effect was observed. Furthermore, it was found that the membrane potential after immersing these sensors in each cleaning solution was constant and did not affect the sensors. The structure of sodium lauryl sulfate is as follows:
The structure of lauryldimethylamino acid is shown in Chemical Formula 1(b).

Chemical Formula 1

Conventional wisdom has it that a cleaning agent using a water-soluble amphipathic substance would destroy a sensor made of lipids, which are amphipathic substances. In this embodiment, the charges of the sensor and the amphipathic substance contained in the cleaning agent are combined to repel each other, thereby minimizing damage to the sensor. Furthermore, substances that adsorb bitter or astringent tastes to the sensor have an opposite charge to the sensor, which is also opposite to the charge of the amphipathic substance contained in the cleaning solution, so that the adsorbent and the amphipathic substance in the cleaning solution are electrically attracted to each other and tend to form hydrophobic bonds. As a result, the adsorbent and the amphipathic substance in the cleaning solution are easily adsorbed, while the amphipathic substance in the cleaning solution is water-soluble, resulting in the effect of peeling off bitter or astringent substances adsorbed to the membrane.

The present invention can be applied to cleaning solutions containing the amphiphilic substances lauryl dimethylamino acetic acid and sodium lauryl sulfate of the examples, as well as water-soluble, negatively charged amphiphilic substances shown in Tables 2-1, 2-2, and 2-3, water-soluble, positively charged amphiphilic substances shown in Tables 3-1 and 3-2, and water-soluble, positively charged amphiphilic substances with both positive and negative charges and positively charged under acidic conditions shown in Table 4.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. Furthermore, even if each component of the claims is expressed by dividing the components, or expressing a plurality of components together, or expressing them in combination, it is within the scope of the present invention. In addition, multiple embodiments may be combined, and examples composed of this combination are also within the scope of the invention.
The following is a summary of the claims originally proposed in this application.
(1) A cleaning solution for cleaning a taste sensor membrane that detects at least one taste substance selected from the group consisting of salty, sour, bitter, sweet, umami, and astringent tastes, comprising:
the taste sensor membrane is made of a lipid-polymer membrane having a matrix surface that contains a lipid molecule group, the lipid molecule group having a hydrophobic portion whose atomic arrangement extends in the longitudinal direction and a hydrophilic portion present in a portion of the atomic arrangement extending in the longitudinal direction, and the taste sensor membrane is made of a sensor that detects the taste substance based on a change in the sensor membrane potential caused by electrostatic and hydrophobic interactions acting between the taste sensor membrane and the taste substance;
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance contains a negatively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs the sensor responsive substance has a positive charge, the cleaning solution is composed of a water-soluble second amphipathic substance that has a positive charge,
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance includes a positively charged sensor responsive substance and the hydrophilic portion of the first amphipathic substance that adsorbs this sensor responsive substance has a negative charge, the cleaning solution is characterized in that it is composed of a water-soluble second amphipathic substance that has a negative charge.
(2) A cleaning solution according to (1), characterized in that the second amphipathic substance contained in the cleaning solution has a positive charge, has a hydrophilic group such as a COOH group or a POOH group, and is acidic.
(3) The cleaning solution according to (1), wherein the lipid-polymer membrane is composed of a polymer membrane, a lipid containing the first amphipathic substance, and a plasticizer.
(4) A cleaning solution according to (1), characterized in that the lipid molecule group contains at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group .
(5) A cleaning method for cleaning a taste sensor membrane that detects at least one taste substance selected from salty, sour, bitter, sweet, umami, and astringent tastes with a first cleaning liquid or a second cleaning liquid, comprising:
The taste sensor membrane comprises a lipid containing a first amphipathic substance composed of a lipid molecule group having a hydrophobic portion whose atomic arrangement extends in the longitudinal direction and a hydrophilic portion present in a portion of the atomic arrangement extending in the longitudinal direction, and is composed of a sensor membrane having a matrix surface that accommodates the lipid molecule group, and is composed of a molecular membrane sensor that detects the taste substance based on a change in sensor membrane potential due to electrostatic and hydrophobic interactions acting between the sensor membrane and the taste substance,
In the cleaning of a taste sensor membrane in which the taste substance contains a negatively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs the sensor responsive substance has a positive charge, the first cleaning solution is composed of a water-soluble second amphipathic substance that has a positive charge,
In the cleaning of a taste sensor membrane in which the taste substance includes a positively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs the sensor responsive substance has a negative charge, the second cleaning liquid is composed of a water-soluble second amphipathic substance having a negative charge,
A cleaning method characterized in that the taste sensor membrane is immersed in a test aqueous solution to which the taste substance has been added, and one of the first cleaning liquid and the second cleaning liquid is selected depending on the sensor membrane potential measured, and the taste sensor membrane is cleaned by immersing the taste sensor membrane in the selected first cleaning liquid or second cleaning liquid.
(6) A cleaning method according to (5), characterized in that the cleaned taste sensor membrane is immersed in a reference liquid for a predetermined period of time to measure the sensor membrane potential, and the cleaning liquid that brings the sensor membrane potential to a reference level is selected as the first cleaning liquid or the second cleaning liquid.
(7) The cleaning method according to (5), wherein the second amphipathic substance contained in the cleaning solution has a positive charge, has a hydrophilic group such as a COOH group or a POOH group, and is acidic.
(8) The cleaning method according to (5), wherein the lipid-polymer membrane is composed of a polymer membrane, a lipid containing the first amphipathic substance, and a plasticizer .
(9) The cleaning method according to (5), wherein the lipid molecule group contains at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group.
(10) A method for cleaning a taste sensor that detects taste based on a change in membrane potential of a lipid membrane, comprising the steps of:
the cleaning solution is an aqueous solution containing 0.05 to 0.2 mass % of a surfactant, and for a taste sensor in which the lipid membrane is positively charged, cleaning is performed with a cleaning solution containing only a surfactant having a positive charge;
For a taste sensor in which the lipid membrane is negatively charged, the taste sensor is washed with a washing solution containing only a negatively charged surfactant.
How to clean the taste sensor.

10...container, 11...reference electrode probe, 12...reference electrode, 13...glass tube, 15...taste sensor probe, 16...tube, 17...sensor membrane, 17A...PVC (polyvinyl chloride), 17B...lipid, 17C...plasticizer, 18...porous ceramic, 19...sensor electrode, 12A, 19A...lead wire, 20...voltage detector, 22...A/D converter, 23...arithmetic unit, 23A...memory, 24...output unit, 28...aqueous solution, 30...Na ionophore

Claims (4)

A cleaning solution for cleaning a taste sensor membrane that detects at least one taste substance selected from salty, sour, bitter, sweet, umami, and astringent tastes , comprising :
The taste sensor membrane is composed of a lipid polymer membrane composed of a polymer material, a lipid, and a plasticizer,
The lipid includes a first amphiphilic substance composed of a lipid molecule group having a hydrophobic region extending in a longitudinal direction of an atomic array and a hydrophilic region present in a portion of the longitudinally extending atomic array,
The lipid-polymer membrane has a matrix surface that accommodates the lipid molecular group,
A cleaning solution used in a taste sensor system in which a taste substance is detected based on a change in sensor membrane potential caused by electrostatic and hydrophobic interactions acting between the taste sensor membrane and the taste substance , and the taste sensor membrane is then cleaned,
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance contains a negatively charged sensor responsive substance and the hydrophilic site of the first amphipathic substance that adsorbs the sensor responsive substance has a positive charge, the cleaning solution is composed of a water-soluble second amphipathic substance that has a positive charge,
In a cleaning solution for cleaning a taste sensor membrane in which the taste substance includes a positively charged sensor responsive substance and the hydrophilic portion of the first amphipathic substance that adsorbs this sensor responsive substance has a negative charge, the cleaning solution is characterized in that it is composed of a water-soluble second amphipathic substance that has a negative charge. The cleaning solution according to claim 1, characterized in that the second amphiphilic substance contained in the cleaning solution has a positive charge, has a hydrophilic group such as a COOH group or a POOH group, and is acidic. The cleaning solution of claim 1, characterized in that the lipid molecular group contains at least one of a phosphate group, an amino group, an ammonium group, a hydroxyl group, and a carboxyl group, and a saturated hydrocarbon group. the cleaning liquid is an aqueous solution containing 0.05 to 0.2% by mass of a surfactant,
For a taste sensor in which the lipid membrane is positively charged, the lipid membrane contains only a surfactant having a positive charge;
2. The cleaning solution according to claim 1, wherein the cleaning solution contains only a negatively charged surfactant for a taste sensor having a negatively charged lipid membrane .

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