RU2442158C2 - Method of forming matrix sensors of "static electronic nose" to identify muscat aroma of grape, grape juice and raw materials - Google Patents

Abstract

FIELD: analytic chemistry.

SUBSTANCE: invention relates to analytical chemistry of food. The method includes forming of a piezoquartz resonator's matrix, which electrodes are modified by sorbents, the survey sensors, processing of sensor responses, the formation of "visual impression", besides the matrix is formed by 4 mass-sensitive piezoquartz resonators of bulk acoustic waves, which electrodes are modified by films of the sorbent with mass 9-13 mcg deposited from solutions of beeswax in chloroform, acetone in polyvinylpyrrolidone, crown ether and trioctylphosphine oxide in toluene; the sensors are arranged in a matrix at random, the responses of individual sensors is fixed at the same time for 1 min to form a visual signal in the form of the kinetic mass-aromogram.

EFFECT: increased reproducibility, reliability and accuracy of results, as well - easier and faster determination without sophisticated mathematical algorithms.

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Description

The invention relates to analytical chemistry of food products and can be used to identify nutmeg aroma and establish the organoleptic characteristics of grapes, grape juice and wine materials using a matrix of piezoelectric quartz resonators with preliminary modification of their electrodes with sorbents of various nature ("static electronic nose" system).

The closest in technical essence and reliability of the results is a method for recognizing artificial and natural orange aromas in juices and drinks using a matrix of 6 piezosensors of volumetric acoustic waves, on the electrodes of which are applied selector films from solutions of bee glue in ethanol, beeswax in chloroform, polyvinylpyrrolidone, crown ether and polystyrene in toluene [RF patent 2267780 C1, cl. G01N 33/02, publ. 01/10/2006]. Responses of individual sensors are processed using a mathematical algorithm with sequential polling of sensors during the formation of a “visual imprint” of aroma. A matrix of 6 sensors with different coatings allows you to distinguish between artificial and natural aroma of orange.

The disadvantage of this method is the use of a large number of films and sensors, a certain predetermined sequence of interrogation of the sensors during the formation of the “visual fingerprint”, which increases the analysis time and complicates the algorithm for processing the results.

An object of the invention is to develop a method for forming a matrix of mass-sensitive sensors "static electronic nose" to identify the nutmeg aroma of grapes, grape raw materials and juice, which allows to increase expressivity, reproducibility, reliability and accuracy of the results, to ensure ease of determination without complex mathematical algorithms.

The technical problem of the invention is achieved by the fact that in the method of forming a sensor matrix of a “static electronic nose” for identifying the nutmeg aroma of grapes, grape raw materials and juice, including the formation of a matrix of piezoelectric quartz resonators, the electrodes of which are modified with sorbents, polling sensors, processing sensor responses using instrument software with the methodology of "electronic nose", the formation of a "visual imprint", characterized in that the matrix is formed of 4 mass-sensitive of resonators of volumetric acoustic waves, the electrodes of which are modified with sorbent films weighing 9-13 μg from solutions of beeswax in chloroform, polyvinylpyrrolidone in acetone, crown ether and trioctylphosphine oxide in toluene, the sensors are randomly placed in the matrix, the responses of individual sensors for this raw material according to an individual algorithm for an individual algorithm fixed simultaneously for 1 min and formed as a visual signal into the kinetic mass aromatogram.

The technical result consists in increasing the accuracy, expressivity, reliability and reproducibility of the results achieved by reducing the number of sensors, their arbitrary location in the matrix and ease of determination without complex mathematical algorithms. The arbitrary arrangement of the sensors in the matrix and the sequence of their interrogation enable different combinations of their responses in a computer program for a visual image in the form of a mass aromatogram.

Figure 1 shows the kinetic mass aromatograms of the responses of a 4-touch “static electronic nose” (PVP, TOPO, CraE, PchV) in the aroma of muscat grapes (standard 1) and table grapes that do not contain a nutmeg (standard 2).

Figure 2 presents the kinetic mass aromatograms of the responses of the 4-touch “static electronic nose” (PVP, TOFO, CraE, PchV) in the aroma of grapes of various varieties: table grape variety, red berry (sample 1), table grape variety, green berry (sample 2), seedless grape varieties of raisins (samples 3-5), seedless variety of table grapes (sample 6), universal grape varieties (samples 7 and 8).

The method is implemented as follows.

1. Preparation of a static electronic nose detection device. A matrix is formed of 4 mass-sensitive piezoelectric quartz resonators (RCC) with a natural oscillation frequency of 10 MHz. Specific volumes of solutions of the following sorbents are uniformly applied to the RCC electrodes with a microsyringe: beeswax in chloroform (PchV), polyvinylpyrrolidone in acetone (PVP), crown ether (CRE) and trioctylphosphine oxide (TOPO) in toluene, followed by static evaporation of the free solvent or drying in an oven or a desiccator above the desiccant layer, and films of sorbents with a stable “zero” signal and high sorption affinity for the volatile components of the muscatel aroma of grapes were selected as selector layers. Sensors (RCC with a sorbent film) are cooled in a desiccator above a desiccant layer to 20 ± 2 ° С. The completeness of solvent removal is confirmed by the constancy of the vibration frequency of the RCC. The sensors are fixedly fixed in the cell holders of the detecting device "static electronic nose".

2. Sample preparation. Samples of grape juice are prepared by preparing and taking an average sample, which is placed in a bottle with a ground stopper or polyurethane membrane. The juice in the bottle is kept for 10-15 minutes, after saturation of the gas phase with grape flavor vapor through a polyurethane membrane, a constant volume of the equilibrium gas phase is taken with a syringe.

3. Measurement of the analytical signal "static electronic nose". The sample is quickly injected into the cell of the detecting device. At the same time, the oscillation frequency of the sensors is fixed in time intervals of 10 s for 1 min. Record the time to reach the maximum signal during the sorption of the volatile components of the aroma. To restore the modifiers, RCCs are regenerated in an oven at an operating temperature of sorbents for 2-5 minutes or the cell of the detecting device is purged for 5-7 minutes.

The responses of individual sensors are formed into a total matrix signal and processed by a computer program, the signal is visualized in the form of a kinetic mass aromatogram (“visual imprint”). Mass aromatogram is a petal diagram of the change in the frequency of oscillation of the piezoelectric quartz plates of the sensors over time during the sorption of volatile compounds. This feature is new for each type of sample, in spite of the fact that a universal program for recording sensor responses is used, since in accordance with the individual composition of the equilibrium gas phase over a sample of juice or raw materials and the nature of the films on the electrodes, the efficiency and selectivity of interaction in the system change as a consequence, the kinetics of sorption. After its analysis, a time interval (10 s) is selected to build the most informative “visual imprint” characteristic of this type of grape raw material.

The algorithm for reading signals and generating mass aromatograms, as well as the number of sensors in the matrix, are optimized to achieve maximum differences and reproducibility of analytical signals (mass aromatograms) for sample standards (tests).

The following standard tests were selected as tests:

standard 1 - freshly prepared natural juice of clary grapes;

standard 2 - freshly prepared natural juice of table grapes that do not contain a nutmeg in the aroma.

For sample standards, standard kinetic mass aromatograms of matrix responses from 4 mass-sensitive sensors obtained within 60 s were constructed (Fig. 1). Under identical conditions, juice samples of other grape varieties are analyzed. Their mass aromatograms (FIG. 2) are compared with standard mass aromatograms.

The method is illustrated by the following example.

1. Preparation of a static electronic nose detection device. A matrix of 4 sensors "static electronic nose" is formed. RCC electrodes with a natural oscillation frequency of 10 MHz are modified by uniformly applying a microsyringe of solutions of polyvinylpyrrolidone in acetone, beeswax in chloroform, trioctylphosphine oxide and crown ether in toluene to obtain a film mass of 9-13 μg, followed by static evaporation of free solvents in a desiccator or above a layer of desiccator in a desiccator layer drying cabinet at a temperature of 50 ± 1 ° C for 20 minutes Modified piezoresonators are cooled in a desiccator above the desiccant layer to 20 ± 2 ° C.

The sensors are fixedly fixed in the holders of the sealed cell of the detecting device "static electronic nose" with a volume of 50 cm ³ .

2. Sample preparation of juice samples is carried out as follows: an average juice sample is taken, weighed on a technical balance in a bottle with a ground polyurethane stopper, incubated for 15 minutes, a 5 cm ³ equilibrium gas phase is taken through a polyurethane stopper with a syringe.

3. Measurement of the analytical signal "static electronic nose". The equilibrium gas phase of the sample is injected into the cell of the detecting device with a syringe. The responses of the sensor matrix are recorded with a frequency meter or with a computer with an interval of 5 s for 60 s. Sensor signals are formed into a kinetic mass aromatogram.

RCC modifiers are regenerated in an oven at a temperature of 50 ± 1 ° С for 5 minutes. After cooling in a desiccator to 20 ± 2 ° C, they are used for subsequent determinations.

Equilibrium gas phases of various samples of grape juice: sample 1 - table grape variety (red berry); sample 2 - table grape variety (white-green berry); Samples 3-5 - seedless grape varieties of raisins; sample 6 - seedless table grape variety (green berry); sample 7, 8 — universal grape varieties with a volume of 5 cm ³ are introduced sequentially into the detection cell of the “static electronic nose” system. Kinetic mass aromatograms of aromas of analyzed samples are built. Comparison of mass aromatograms of several samples of grape juice allows you to quickly establish compliance with the selected standards. A coincidence of more than 75% indicates that the sample is identical to natural grape juice with a nutmeg aroma or natural grape juice without a nutmeg tone in the aroma.

Sample 1 meets standard 1, its muscat aroma is pronounced. Samples 2, 4, 5, and 6 correspond as much as possible to standard 1 at the level of relative error (5–10%), however, the nutmeg aroma is expressed to varying degrees (most pronounced in sample 2, much weaker in samples 4, 5, and 6, as evidenced by the value of the total analytical signal of the "static electronic nose"). Sample 3 conditionally corresponds to standard 1, the aroma has a muscat profile, but there is also a different aroma, this grape variety is an interspecific hybrid obtained from including muscat. Samples 7 and 8 do not meet any of the standards. The method is feasible.

The absence of sorption hysteresis makes it possible to repeatedly use modified resonators (the number of sorption cycles possible with the use of one modified piezoresonator is more than 100). The loss of film by weight after 100 cycles of sorption does not exceed 0.5%. The reproducibility of measurements is 10%, the duration of the analysis, including the modification of the electrodes, is 30 min; repeated measurements for one sample - 10 min, productivity - 8 measurements / h.

A comparison of the characteristics of the sensor matrices according to the prototype and the claimed solution is presented in the table. Compared with the prototype, the developed method allows to increase the productivity and accuracy of determination, the expressness of the analysis in 2-2.5 times.

Table Characteristic Prototype Proposed solution The number of sensors in the matrix 6 four Sorbents modifiers polyvinylpyrrolidone, trioctylphosphine oxide, beeswax, crown ether, bee glue, polystyrene polyvinylpyrrolidone, trioctylphosphine oxide, beeswax, crown ether The sequence of polling sensors in the formation of a mass aromatogram of odor Has the meaning Unprincipled, because sensors are being polled simultaneously Sensor polling algorithm in the matrix Simultaneous interrogation during the entire contact time of the sample and all matrix sensors Simultaneous interrogation during the entire contact time of the sample and all matrix sensors Mass aromatogram (number of signals) 72-144 48-96 Sensor Poll Expressivity 2 minutes 1 min Duration of analysis, including electrode modification 60 min 30 minutes Total Decision Time 15 minutes 10 min (single measurement) Productivity (samples / h) four 8 Correctness for multicomponent mixtures (up to 500 volatile components) Natural juice and artificial aroma are distinguishable by “visual prints”, but juices similar in nature (orange) are indistinguishable Similar in nature juices having a different flavor tone are reliably distinguishable by mass aromatograms (figure 2)

The example shown, FIGS. 1, 2 and the characteristics given in the table show that the solution to this problem is achieved by the fact that the sensor matrix of the static electronic nose detection device is formed of 4 mass-sensitive piezoresonators, the electrodes of which are modified with sorbents with different affinities for various volatile components of the grape aroma and is applicable for assessing the aroma of grapes. Identification of the nutmeg aroma of grapes, raw materials and juice is feasible if mass aromatograms are obtained using a matrix of 4 mass-sensitive sensors with a stable “zero” signal, kinetic survey of which is carried out for 60 s at a time, the arrangement of sensors in the matrix is arbitrary, and the signals form into the kinetic mass aromatogram.

Changing the experimental conditions: increasing or decreasing the number of sensors, increasing or decreasing the mass of modifier films, changing the nature of sensitive coatings, the algorithm for constructing mass aromatograms leads to a decrease in metrological reliability and sensitivity of measurements, the similarity of mass aromatograms with aroma of different tones, and the decrease in the number of measurements without updating the coatings of the resonators, as well as to disrupt the self-oscillations of the sensors and the inability to implement the method.

The developed sensor matrix of the “static electronic nose” for identifying the nutmeg aroma of grapes, raw grape and juice allows you to:

1) objectively and unambiguously identify the nutmeg aroma of grapes, raw grape and juice;

2) to increase the expressivity and performance of the determination by reducing the number of sensors in the matrix;

3) to increase the accuracy and correctness of the results of the analysis due to the lack of subjective reasons for organometry (age, habits, experience, moral attitude, olfactory memory and the base of the taster's necessary knowledge);

4) to simplify the process of organizing tastings;

5) to simplify the stage of visualization of the results in the mass-aromatogram of the responses of the sensor matrix due to the unprincipled location of the sensors in the matrix and the sequence of their survey, which significantly reduces the stage of deciding on the quality of the sample.

Claims (1)

A method of forming a sensor matrix of a “static electronic nose” for identifying the nutmeg aroma of grapes, grape raw materials and juice, including forming a matrix of piezoelectric crystals, the electrodes of which are modified with sorbents, polling sensors, processing sensor responses, forming a “visual fingerprint”, characterized in that the matrix is formed from 4 mass-sensitive piezoresonators of volumetric acoustic waves, the electrodes of which are modified with sorbent films weighing 9-13 μg from bee solutions in ska in chloroform, acetone, polyvinyl pyrrolidone, a crown ether and trioctylphosphine oxide in toluene, sensors arranged in a matrix of arbitrary individual sensors simultaneously record the response for 1 min and formed into a visual signal in kinetic mass aromatogram.

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