Method for determining an electrochemical signature of a liquid

Abstract

The invention relates to a method for determining an electrochemical signature of a liquid, the method comprising a step, referred to as a current variation measurement step, consisting in measuring the variation in current in the liquid using a working electrode during a potential sweep carried out using a differential pulse voltammetry technique, the pulses of which each have an amplitude of between 5 mV and 200 mV and a duration of between 1 ms and 60 ms, the potential step of which is between 1 mV and 30 mV, and the sweep speed of which is between 5 mV.s-1 and 50 mV.s-1.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for determining the electrochemical signature of a liquid

[0003] technical field

[0004] The present invention relates to a method for determining an electrochemical signature of a liquid, a device for determining an electrochemical signature of a liquid, and a use of an electrochemical signature of a liquid determined by said method to determine at least one characteristic of said liquid.

[0005] Prior art

[0006] The ability to analyze the reducing molecule composition of a wine and its associated redox state allows the winemaker or wine producer to obtain information regarding the nature and quantity of reducing molecules present in the wine. This enables them to monitor the condition and quality of their wine throughout the winemaking process, right up to bottling, and to adapt their practices as needed.

[0007] The analysis of a wine's reducing molecule composition is generally carried out using methods that combine chromatographic separation with spectrophotometric detection. However, such methods are cumbersome, slow, and expensive. They are therefore limited to oenological laboratories.

[0008] The reducing molecule composition of wine can also be analyzed by electrochemical measurement. For example, the "NomaSense PolyScan" portable analyzer from the company "Vinventions" allows for real-time measurement of the quantity of polyphenolic compounds present in grape must and wine, without prior preparation of the sample. This measurement is performed with a disposable, screen-printed carbon paste electrode, based on linear sweep voltammetry (LSV). The use of such a disposable screen-printed electrode has several drawbacks.Indeed, this results in a relatively high measurement cost and problems with measurement reproducibility and robustness, particularly due to the fragility and small size of the electrode and the less-than-ideal quality and activity of the carbon. Furthermore, such an analyzer exhibits low selectivity. In fact, it only provides a binary response regarding the composition of reducing molecules, as it can only discriminate between and therefore detect two families of compounds present in the sample being analyzed: on the one hand, easily oxidizable compounds (also called "EasyOx"), such as caffeic acid or gallic acid, and on the other hand, total polyphenols (also called "PhenOx").Furthermore, this binary response cannot be obtained directly by the user but requires pre-analysis by a specialist or comparison with a proprietary database of the company "Vinventions". Moreover, such an analyzer requires depositing a very small volume of the sample to be analyzed onto the disposable screen-printed electrode, typically a droplet, for example, of approximately 20 pL. Such a small sample volume is extremely susceptible to oxidation by the surrounding air, which means that the analysis may have limitations in terms of reliability.

[0009] There remains a need to further improve the performance of existing methods and devices for the electrochemical analysis of the reducing molecule composition of a liquid, such as wine or grape must, particularly in terms of sensitivity, selectivity, robustness, reproducibility, portability and ease of implementation.

[0010] Description of the invention

[0011] The invention aims to address this need and, according to a first aspect, relates to a method for determining the electrochemical signature of a liquid, in particular the signature of the redox equilibrium of a liquid. The method comprises a step, called the "current variation measurement step," consisting of measuring the variation of the electrochemical current in the liquid using a working electrode during a potential sweep performed by a pulsed differential voltammetry technique. The pulses of this technique have an amplitude between 5 mV and 200 mV and a duration between 1 ms and 60 ms, a potential step between 1 mV and 30 mV, and a sweep speed of 5 mV / s. -1 and 50 mV.s- 1

[0012] Preferably, the step of measuring the current variation consists of measuring the variation of an electrochemical current.

[0013] The step of measuring the variation of the current during a potential sweep can allow a volt-amperogram to be obtained.

[0014] The voltammeter diagram may contain one or more peaks, preferably two, three, four, or five peaks, or even more. Each peak may correspond to a family of molecules, in particular a family of reducing molecules.

[0015] The said voltammeter can constitute the electrochemical signature of the liquid, in particular the signature of the redox equilibrium of the liquid.

[0016] The method according to the invention is particularly advantageous because the voltamgram is obtained directly by the user after the current variation measurement step. Unlike existing methods and devices for analyzing the reducing molecule composition of a liquid, a preliminary analysis by a specialist or a comparison with a database is not necessary to obtain the voltamgram.

[0017] Compared with other types of voltammetry, such as cyclic voltammetry (also called CV for Cyclic Voltammetry) or linear voltammetry (also called LSV for Linear Sweep Voltammetry), the use of differential pulse voltammetry (also called DPV for Differential Pulse Voltammetry) can improve the sensitivity and selectivity of the measurement and thus allow the discrimination of several families of molecules, especially reducing ones, in particular at least three families of molecules, or even four or five families of molecules, especially reducing ones.

[0018] Furthermore, pulsed differential voltammetry is implemented with parameters, such as pulse amplitude, pulse duration, potential step and scan speed, whose values ​​are optimized to obtain improved selectivity and thus allow discrimination of several families of molecules, including reducing molecules, in particular at least three families of molecules, or even four or five families of molecules, including reducing molecules.

[0019] In the present invention, "redox equilibrium signature of a liquid" means the voltamgram obtained at the stage of measuring the variation of the current, or the qualitative and quantitative composition in reducing molecules of a liquid at a given instant, in particular determined from the voltamgram obtained at the stage of measuring the variation of the current.

[0020] In the present invention, "pulses" means potential jumps.

[0021] In the present invention, "potential step" means potential sampling.

[0022] In the present invention, "pulse amplitude" means the height of the potential jumps. Preferably, the pulses have a rectangular or square shape, preferably rectangular.

[0023] The pulses can each have an amplitude between 5 mV and 100 mV, preferably between 5 mV and 50 mV.

[0024] The pulses can each have a duration of between 5 ms and 50 ms, preferably between 10 ms and 50 ms.

[0025] The potential step can be between 1 mV and 10 mV, preferably between 2 mV and 10 mV.

[0026] The scan speed can be between 10 mV.s -1 and 50 mV.s -1 .

[0027] Potential scanning can be performed in the direction of increasing potentials. This means that the current variation measurement step consists of measuring the change in current produced by the oxidation of reducing molecules present in the liquid.

[0028] Potential scanning can be carried out in the direction of increasing potentials between 0 V and +2 V, preferably between 0 V and +1.5 V, more preferably between 0 V and +1.2 V, with respect to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl, or even with respect to a reference electrode Ag / AgCl, 1 M KCl or 1 M NaCl.

[0029] The pulses can have the same amplitude and / or the same duration.

[0030] The working electrode is preferably a conventional electrode, in particular made of vitreous carbon or gold, preferably made of vitreous carbon, in particular of flat or cylindrical shape.

[0031] Compared to the use of single-use electrodes, the use of a conventional working electrode, in particular made of vitreous carbon or gold, preferably vitreous carbon, is particularly advantageous because this working electrode is reusable for several dozen, or even hundreds, of current variation measurements, thus reducing the cost associated with each measurement.

[0032] Moreover, compared to the use of single-use electrodes, the use of a conventional working electrode, in particular made of vitreous carbon or gold, preferably vitreous carbon, allows for a measurement that is more reliable, reproducible and robust.

[0033] The working electrode may be a planar electrode, particularly with an active surface of disk, rectangular, or square geometry; a spherical electrode; a cylindrical electrode; or a conical electrode. The working electrode may have an active surface comprising vitreous carbon or gold, particularly polycrystalline gold, preferably vitreous carbon.

[0034] For example, the working electrode is a conventional glassy carbon electrode of flat shape, specifically with a disc having a diameter of 3 mm.

[0035] In a preferred embodiment, the working electrode has an active surface comprising vitreous carbon and the potential sweep is carried out in the direction of increasing potentials between 0 V and +1.5 V, preferably between 0 V and +1.2 V, relative to an Ag / AgCl, 3M KCl or 3M NaCl reference electrode, or even relative to an Ag / AgCl, 1M KCl or 1M NaCl reference electrode.

[0036] In the present invention, the term "active surface of the working electrode" refers to the portion of the working electrode that is effectively available for faradaic electrochemical reactions. In other words, it is the portion of the working electrode across whose surface electrons can be transferred between the working electrode and the molecules present in the liquid.

[0037] The step of measuring the variation in current can be carried out using the working electrode and a reference electrode, and in particular a counter electrode.

[0038] Preferably, the reference electrode is an Ag / AgCl, 3M KCl or 3M NaCl reference electrode, or even an Ag / AgCl, 1M KCl or 1M NaCl reference electrode.

[0039] Preferably, the counter electrode has an active surface area greater than or equal to the active surface area of ​​the working electrode. This can help to avoid limiting the faradaic processes that take place on the working electrode.

[0040] Preferably, the counter electrode is a counter electrode made of platinum, carbon or stainless steel, more preferably platinum or carbon.

[0041] The liquid can be contained in a container.

[0042] Preferably, the working electrode is introduced inside the container so as to be in contact with the liquid, in particular so that its active surface is immersed in the liquid.

[0043] Preferably, the reference electrode and the counter electrode are introduced inside the container so as to be in contact with the liquid.

[0044] The container can be an open container such as, for example, a beaker or a bottle, or a closed container such as, for example, a vat, a cask, a barrel or a keg.

[0045] Preferably, the closed container has an opening, in particular a resealable one, in its wall to allow the introduction of the working electrode, and in particular the reference electrode and the counter electrode, into said closed container. The liquid may be aqueous or hydroalcoholic.

[0046] The liquid can be a food liquid, preferably a beverage, more preferably a fruit-based beverage, including fermented or unfermented, including sparkling or unfermented.

[0047] The liquid food can be chosen from:

[0048] - grape must;

[0049] - wine, especially red, white or rosé, including sparkling or still wine;

[0050] - fruit juices, including citrus fruits, apples, pineapples, lemons, limes;

[0051] - concentrates based on fruit juice or crushed fruit;

[0052] - malted beverages, such as beer, including alcoholic and non-alcoholic versions;

[0053] - cider, perry, including sparkling or still;

[0054] - chouchen;

[0055] - vinegar, especially food or household vinegar;

[0056] - honey;

[0057] - a honey solution, in particular an aqueous honey solution;

[0058] - a propolis solution, in particular an aqueous propolis solution, especially an aqueous culture medium in which propolis is dissolved; and

[0059] - one of their mixtures.

[0060] Preferably, the food liquid is wine or grape must.

[0061] In a preferred embodiment example, the wine or grape must is untreated, in particular by dilution or pH modification, for example by adding an acidic solution, a basic solution and / or a buffer solution, especially before or during the current variation measurement step.

[0062] In other words, the method according to the invention can allow the determination of an electrochemical signature of a wine or grape must, without it being necessary to treat said wine or grape must before or during the step of measuring the variation of the current, which is particularly advantageous.

[0063] Indeed, wine is a complex matrix containing approximately 1,000 identified molecules, including phenolic compounds, acids, tannins, proteins, sulfur compounds such as sulfites, metals, and more. Therefore, when wine or grape must is analyzed without any dilution or processing, the wine's true chemical environment (pH, conductivity, ionic strength, etc.) is preserved, resulting in an electrochemical signal that is more representative of the analyzed sample. Furthermore, the inventors demonstrated that the voltamgram obtained by DPV of an undiluted wine shows more defined peaks and a better signal-to-noise ratio compared to the voltamgram obtained by DPV of the same wine diluted (see Figure 8). This reflects the preservation of the matrix's physicochemical properties (pH, conductivity, viscosity, sulfite content, etc.).These factors directly influence the faradaic currents obtained, the peak potentials, and the electrode stability. Therefore, omitting a dilution step on the analyzed matrix avoids altering the chemical and acid-base equilibria, as well as the redox behavior of certain molecules present in wine, particularly the electroactive compounds in wine, which tend to interact strongly with each other. Furthermore, omitting a dilution step significantly reduces analytical bias (contamination).

[0064] Regarding treatments by modifying pH, it should be noted that pH directly influences the sensory perception and organoleptic qualities of the wine. It is also a key factor in microbiological stability: for pH > 5 the wine becomes microbiologically unstable, sulfur dioxide loses effectiveness and these pH values ​​are outside the spectrum of oenological practices regulated by the OIV (International Organisation of Vine and Wine).

[0065] Advantageously, the wine or grape must is not treated by dilution or modification of pH by adding a basic solution and / or a buffer solution.

[0066] In a preferred embodiment example, the wine or grape must has a pH between 2.8 and 4.5, preferably between 3 and 4.

[0067] The process may include a step of stabilizing the current of the working electrode, before the step of measuring the variation of the current.

[0068] The stabilization step of the working electrode current is carried out by placing it at the open circuit potential (also called OCP for Open Circuit Potential in English).

[0069] The open circuit potential corresponds to an exchange current i = 0 A, but not necessarily to a potential E = 0 V.

[0070] The duration of the current stabilization step of the working electrode can be between 1 sec and 60 sec, preferably between 5 sec and 30 sec.

[0071] The process may include a step of activating the working electrode, before the step of measuring the variation of the current, and in particular before the step of stabilizing the current of the working electrode.

[0072] Activating the working electrode can improve the activity of its active surface, thereby enhancing the sensitivity and selectivity of the measurement. This activation can be achieved by mechanically polishing the electrode and then applying a low-pressure plasma at room temperature.

[0073] Alternatively, the working electrode activation step is implemented by applying a potential sweep during cyclic voltammetry in a cleaning solution, specifically in a first cleaning solution and then in a second cleaning solution, in which the active surface of the working electrode is immersed.

[0074] The first cleaning solution can be a basic detergent solution, having in particular a pH between 10 and 14.

[0075] The basic detergent solution may contain ethylenediaminetetraacetic acid (also called EDTA for Ethylene Diamine Tetraacetic Acid in English), for example at a concentration between 10 mM and 100 mM.

[0076] The second cleaning solution can be a hydrogen peroxide solution, with a concentration between 5 and 100 mM.

[0077] Potential scanning can be performed between -2 V and +2 V, preferably between -1.5 V and +1.5 V, using an Ag / AgCl, 3M KCl or 3M NaCl reference electrode, or even using an Ag / AgCl, 1M KCl or 1M NaCl reference electrode.

[0078] Potential scanning can be performed at a potential scanning rate of between 10 mV.s -1 and 200 mV.s -1 , preferably between 25 mV.s 1 and 100 mV.s' 1 .

[0079] The process may include a step, called the "measurement step of the area of ​​at least one peak" consisting of measuring on the voltammeter graph obtained in the current variation measurement step, the area of ​​at least one peak present, in particular the area of ​​each of the peaks present.

[0080] In the present invention, by "measure on the voltammeter obtained in the step of measuring the variation of the current, the area of ​​at least one peak present", we mean to measure the area under the curve of said voltammeter at the level of at least one peak present, that is to say the area located between the axis of the abscissa and the curve of said voltammeter at the level of at least one peak present, for example by integration.

[0081] The peak area measurement step can consist of measuring on the voltamgram obtained in the current variation measurement step, the area of ​​the peak present between +0.1 V and +0.45 V, the area of ​​the peak present between +0.45 V and +0.75 V, the area of ​​the peak present between +0.75 V and +1.2 V and the total area of ​​the voltamgram between +0.1 V and +1.2 V, relative to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl, or even relative to a reference electrode Ag / AgCl, 1M KCl or 1M NaCl. On the voltammeter obtained at the current variation measurement stage, the peak present between +0.1 V and +0.45 V relative to an Ag / AgCl, 3M KCl or 3M NaCl reference electrode, or even relative to an Ag / AgCl, 1M KCl or 1M NaCl reference electrode, may correspond to a family of molecules, including reducing ones, including caffeic acid, gallic acid, ellagic acid, caftaric acid, resveratrol, catechin and / or epicatechin.

[0082] On the voltammeter obtained at the current variation measurement stage, the peak present between +0.45 V and +0.75 V relative to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl, or even relative to a reference electrode Ag / AgCl, 1M KCl or 1M NaCl, may correspond to a family of molecules, particularly reducing ones, including in particular syringic acid, ellagic acid, fertaric acid, ferulic acid, galangin and / or ascorbic acid.

[0083] On the voltammeter obtained at the current variation measurement stage, the peak present between +0.75 V and +1.2 V relative to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl, or even relative to a reference electrode Ag / AgCl, 1M KCl or 1M NaCl, may correspond to a family of molecules, particularly reducing ones, including vanillic acid, gallic acid, coumaric acid, coutaric acid, pinocembrin, apigenin, chrysin, resveratrol, catechin and / or epicatechin.

[0084] The invention also relates, according to another aspect, to a device for determining the electrochemical signature of a liquid, in particular the signature of the redox equilibrium of a liquid, notably for implementing the process as defined above, the device comprising:

[0085] - a working electrode having an active surface comprising vitreous carbon or gold, in particular polycrystalline gold, preferably vitreous carbon,

[0086] - a reference electrode, in particular an Ag / AgCl, 3M KCl or 3M NaCl reference electrode, or even an Ag / AgCl, 1M KCl or 1M NaCl reference electrode,

[0087] - a counter electrode, in particular made of platinum, carbon or stainless steel, preferably platinum or carbon,

[0088] - a potentiostat,

[0089] - a container holding the liquid.

[0090] In the present invention, "potentiostat" means any electronic device capable of imposing at least one potential change on an electrode in solution and measuring at least one induced electrochemical current change. The container may be an open container, such as a beaker or a bottle.

[0091] Alternatively, the container is a closed container, such as for example a vat, a cask, a barrel or a keg.

[0092] Preferably, the closed container has an opening, in particular a resealable one, provided in its wall so as to allow the introduction of the working electrode, the reference electrode and the counter electrode into said closed container.

[0093] The invention also relates, according to another aspect, to the use of an electrochemical signature of a liquid, in particular a signature of the redox equilibrium of a liquid, in particular of a wine or grape must, determined by a process as defined above, to determine at least one characteristic of said liquid, in particular of said wine or said grape must.

[0094] At least one characteristic of said liquid, in particular said wine or said grape must, may be:

[0095] - a characteristic related to its color, for example red, white or pink;

[0096] - a characteristic relating to its grape variety or varieties;

[0097] - a characteristic related to his / her age;

[0098] - a characteristic related to its sugar content;

[0099] - a characteristic related to its tannin content;

[0100] - a characteristic relating to its gas content, particularly carbon dioxide; and / or

[0101] - a characteristic related to its tendency to oxidize.

[0102] Brief description of the figures

[0103] [Fig. 1] Figure 1 shows examples of voltammetry obtained by cyclic voltammetry (Figure 1 A) and by pulsed differential voltammetry according to the method according to the invention (Figure 1 B).

[0104] [Fig. 2] Figure 2 represents an example of potential variation as a function of time during a potential sweep carried out by a pulsed differential voltammetry technique according to the method according to the invention (Figure 2A) and examples of voltamgrams obtained by pulsed differential voltammetry by varying the pulse amplitude (Figure 2B), pulse duration (Figure 2C), potential step (Figure 2D) and sweep speed (Figure 2E).

[0105] [Fig. 3] Figure 3 represents examples of voltammetry obtained by pulsed differential voltammetry according to the method according to the invention with a working electrode whose active surface comprises vitreous carbon or polycrystalline gold for a white wine (Figure 3A) and a red wine (Figure 3B).

[0106] [Fig. 4] Figure 4 shows examples of volt-amperograms obtained according to the method according to the invention for a white wine, a rosé wine, a red wine and a sparkling wine.

[0107] [Fig. 5] Figure 5 represents examples of voltammetry obtained by pulsed differential voltammetry according to the method according to the invention for red wines (Figure 5A) and white wines (Figure 5B) produced from different single grape varieties.

[0108] [Fig. 6] Figure 6 represents examples of voltammetry obtained by pulsed differential voltammetry according to the method according to the invention for a red wine (Figure 6A) and a white wine (Figure 6B) during their oxidation in air.

[0109] [Fig. 7] Figure 7 represents examples of voltammetry obtained by pulsed differential voltammetry according to the method according to the invention for the same red wine depending on its vintage of production.

[0110] [Fig. 8] Figure 8 represents examples of voltammetry obtained by pulsed differential voltammetry for a white wine (Figure 8A) and a red wine (Figure 8B) according to the process of the invention or according to comparative processes comprising a sample dilution step (1:25 or 1:400).

[0111] Examples

[0112] Figure 1 shows a comparison of electrochemical analyses on untreated white and red wines during a potential sweep performed in the direction of increasing potentials between 0 V and +1.2 V, by cyclic voltammetry (sweep rate: 10 mV.s). -1 (Figure 1A) and by pulsed differential voltamperometry (scan rate: 50 mV.s -1 ; pulse amplitude: 5 mV; pulse duration: 50 ms; potential step: 5 mV).

[0113] The analyses are carried out in 20 mL samples of untreated white wine and untreated red wine, in a three-electrode configuration consisting of a working electrode whose active surface includes vitreous carbon (disc-plane electrode of 3 mm diameter), a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0114] Figure 2 shows an example of the variation of potential over time during a potential sweep performed by a pulsed differential voltammetry technique according to the method of the invention (Figure 2A). Figure 2A indicates the shape of the pulses, and what the pulse amplitude (ESAUT), pulse duration (ÎSAUT), and potential step (EPAS) represent.

[0115] Figure 2 also shows a comparison of electrochemical analyses on an untreated red wine during a potential sweep carried out in the direction of increasing potentials between 0 V and +1.2 V, by pulsed differential voltamperometry, by varying:

[0116] - the pulse amplitude between 10 mV and 200 mV (scan speed: 50 mV.s 1 ; pulse duration: 50 ms; potential step: 5 mV) (Figure 2B),

[0117] - pulse duration between 5 ms and 200 ms (scan speed: 50 mV.s 1 for pulse durations of 5 ms, 10 ms, 30 ms and 50 ms, 25 mV.s -1 for a pulse duration of 100 ms and 12.5 mV.s -1 for a pulse duration of 200 ms; pulse amplitude: 30 mV; potential step: 5 mV) (Figure 2C),

[0118] - the potential step size between 1 mV and 30 mV (scan speed: 10 mV.s -1 for a step size of 1 mV, otherwise 50 mV.s -1; pulse amplitude: 30 mV; pulse duration: 50 ms) (Figure 2D), and

[0119] - the slew rate between 5 mV.s -1 and 50 mV.s -1 (pulse amplitude: 30 mV; pulse duration: 50 ms; potential step: 5 mV) (Figure 2E).

[0120] Each analysis begins with a stabilization step of the working electrode current before the pulses are applied. To do this, the equilibrium potential (or open-circuit potential) of the working electrode is applied to the analyzed sample for 10 seconds before the pulses are applied.

[0121] The analyses are carried out in 20 mL samples of untreated red wine, in a three-electrode configuration consisting of a working electrode whose active surface includes vitreous carbon (3 mm diameter disc-plane electrode), a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0122] Figure 3 shows a comparison of electrochemical analyses on an untreated white wine (Figure 3A) and an untreated red wine (Figure 3B), during a potential sweep performed in the direction of increasing potentials between 0 V and +1.5 V with respect to an Ag / AgCl, 3M KCl reference electrode (scan rate: 10 mV / s). -1), by pulsed differential voltammetry, with a working electrode whose active surface comprises vitreous carbon or polycrystalline gold (disk-plane electrodes of the same diameter 3 mm). The parameters of the pulsed differential voltammetry technique used are: pulse amplitude: 50 mV; pulse duration: 10 ms; potential step: 2 mV.

[0123] The analyses are carried out in 20 mL samples of untreated white wine and untreated red wine, in a three-electrode configuration consisting of a working electrode whose active surface includes vitreous carbon or polycrystalline gold (disc-plane electrodes of the same diameter 3 mm), a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0124] Figure 4 shows a comparison of electrochemical analyses on an untreated white wine, an untreated rosé wine, an untreated red wine and an untreated sparkling wine, during a potential sweep carried out in the direction of increasing potentials between 0 V and + 1.5 V with respect to an Ag / AgCl, 3M KCl reference electrode (scan rate: 50 mV.s' 1 ), by pulsed differential voltamperometry.

[0125] The parameters of the pulsed differential voltamperometry technique used are: pulse amplitude: 30 mV; pulse duration: 50 ms; potential step: 5 mV.

[0126] The analyses are carried out in 20 mL samples of untreated white wine, untreated rosé wine, untreated red wine and untreated sparkling wine, in a three-electrode configuration consisting of a working electrode whose active surface includes vitreous carbon (disc-plane electrode of 3 mm diameter), a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0127] Figure 5 shows a comparison of electrochemical analyses on untreated (A) red wines or untreated (B) white wines (each wine corresponds to a single grape variety), by pulsed differential voltammetry during a potential sweep carried out in the direction of increasing potentials between 0 V and +1.2 V with respect to an Ag / AgCl, 3M KCl reference electrode (scan rate: 10 mV / s) -1) with a working electrode whose active surface contains vitreous carbon (disc-flat electrode of 3 mm diameter).

[0128] The parameters of the pulsed differential voltamperometry technique used are: potential step: 2 mV; pulse amplitude: 50 mV; pulse duration: 10 ms.

[0129] The analyses were performed each time on 20 mL of untreated wine, in a three-electrode configuration consisting of the working electrode, a platinum counter electrode (platinum grid), and a reference electrode (Ag / AgCl, 3M KCl). Figure 6 shows a comparison of electrochemical analyses on untreated (A) red and (B) white wines (each wine corresponds to a blend of grape varieties) during their oxidation in air (D0: day the bottle was opened; D15: after 15 days of contact with ambient air; D30: after 30 days of contact with ambient air), by pulsed differential voltamperometry during a potential sweep carried out in the direction of increasing potentials between 0 V and +1.2 V with respect to an Ag / AgCl, 3M KCl reference electrode (sweep rate: 50 mV·s). -1 ) with a working electrode whose active surface contains vitreous carbon (disc-flat electrode of 3 mm diameter).

[0130] The parameters of the pulsed differential voltamperometry technique used are: potential step: 5 mV; pulse amplitude: 30 mV; pulse duration: 50 ms.

[0131] The analyses are carried out each time in 20 mL of untreated wine, in a three-electrode configuration consisting of the working electrode, a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0132] Figure 7 shows a comparison of electrochemical analyses on the same red wine according to its vintage (Grand Cru Classé of the Pessac-Léognan appellation), performed by pulsed differential voltammetry during a potential sweep carried out in the direction of increasing potentials between 0 V and +1.2 V with respect to an Ag / AgCl, 3M KCl reference electrode (sweep rate: 10 mV / s). -1) with a working electrode whose active surface contains vitreous carbon (disc-plane electrode of 3 mm diameter).

[0133] The parameters of the pulsed differential voltamperometry technique used are: potential step: 2 mV; pulse amplitude: 50 mV; pulse duration: 10 ms.

[0134] The analyses are carried out each time in 20 mL of untreated wine, in a three-electrode configuration consisting of the working electrode, a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

[0135] Figure 8 represents a comparison of electrochemical analyses obtained for a white wine (Figure 8A) and a red wine (Figure 8B) according to the process of the invention or according to comparative processes comprising a dilution step (1:25 or 1:400).

[0136] The measurements are performed by pulsed differential voltamperometry during a potential sweep carried out in the direction of increasing potentials between 0 V and +1.2 V relative to an Ag / AgCl, 3M KCl reference electrode (sweep rate: 10 mV.s -1 ) with a working electrode whose active surface comprises vitreous carbon (disc-plane electrode of 3 mm diameter). The parameters of the pulsed differential voltamperometry technique used are: potential step: 2 mV; pulse amplitude: 50 mV; pulse duration: 10 ms.

[0137] The analyses are carried out each time in 20 mL of wine either untreated or treated by dilution with a buffer solution composed of a mixture of water-ethanol (12%) and tartaric acid (pH 3.4), in a three-electrode configuration consisting of the working electrode, a platinum counter electrode (platinum grid) and a reference electrode (Ag / AgCl, 3M KCl).

Claims

DEMANDS 1. A method for determining the electrochemical signature of a liquid, the method comprising a step, called the "current variation measurement step", consisting of measuring the change in current in the liquid using a working electrode, during a potential sweep performed by a pulsed differential voltammetry technique, the pulses of which each have an amplitude between 5 mV and 200 mV and a duration between 1 ms and 60 ms, a potential step between 1 mV and 30 mV, and a sweep speed between 5 mV / s -1 and 50 mV.s -1 said liquid being untreated wine or grape must.

2. Method according to claim 1, the potential sweep being carried out in the direction of increasing potentials between 0 V and +2 V, preferably between 0 V and +1.5 V, more preferably between 0 V and +1.2 V, relative to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl.

3. Method according to claim 1 or 2, the pulses having identical amplitude and / or identical duration.

4. A method according to any one of the preceding claims, the working electrode having an active surface comprising vitreous carbon or gold, preferably vitreous carbon.

5. A method according to any one of the preceding claims, the liquid being contained in a container and the working electrode being introduced inside the container so that its active surface is immersed in the liquid.

6. Method according to claim 5, the container being an open container such as for example a beaker or a bottle, or a closed container such as for example a vat, a drum, a barrel or a cask.

7. A method according to any one of the preceding claims, comprising a step, referred to as the "measurement step of the area of ​​at least one peak," consisting of measuring, on the voltammeter graph obtained in the current variation measurement step, the area of ​​at least one peak present 8. Method according to claim 7, the step of measuring the area of ​​at least one peak consisting of measuring on the voltamgram obtained in the step of measuring the variation of the current, the area of ​​the peak present between +0.1 V and +0.45 V, the area of ​​the peak present between +0.45 V and +0.75 V, the area of ​​the peak present between +0.75 V and +1.2 V and the total area of ​​the voltamgram between +0.1 V and +1.2 V, with respect to a reference electrode Ag / AgCl, 3M KCl or 3M NaCl.

9. Device for determining the electrochemical signature of a liquid, in particular for implementing the process according to any one of the preceding claims, comprising: - a working electrode having an active surface comprising vitreous carbon or gold, preferably vitreous carbon, - a reference electrode, in particular an Ag / AgCl, 3M KCl or 3M NaCl electrode, - a counter electrode, in particular made of platinum or carbon or stainless steel, preferably platinum or carbon, - a potentiostat, - a container holding the liquid; said liquid being untreated wine or grape must.

10. Device according to claim 9, the container being an open container, such as for example a beaker or a bottle.

11. Device according to claim 9, the container being a closed container, such as for example a tank, a drum, a barrel or a cask, and having an opening, in particular a resealable one, provided in its wall so as to allow the introduction of the working electrode, the reference electrode and the counter electrode into said container.

12. Use of an electrochemical signature of an untreated wine or grape must, determined by a process according to any one of claims 1 to 8, to determine at least one characteristic of said wine or grape must.

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