Portable Electronic Tongue Based on Microsensors for the Analysis of Cava Wines

Pablo Giménez-Gómez, Roger Escudé-Pujol, Fina Capdevila, Anna Puig-Pujol, Cecilia Jiménez-Jorquera, Manuel Gutiérrez-Capitán
2016 Sensors  
Cava is a quality sparkling wine produced in Spain. As a product with a designation of origin, Cava wine has to meet certain quality requirements throughout its production process; therefore, the analysis of several parameters is of great interest. In this work, a portable electronic tongue for the analysis of Cava wine is described. The system is comprised of compact and low-power-consumption electronic equipment and an array of microsensors formed by six ion-selective field effect transistors
more » ... sensitive to pH, Na + , K + , Ca 2+ , Cl − , and CO 3 2− , one conductivity sensor, one redox potential sensor, and two amperometric gold microelectrodes. This system, combined with chemometric tools, has been applied to the analysis of 78 Cava wine samples. Results demonstrate that the electronic tongue is able to classify the samples according to the aging time, with a percentage of correct prediction between 80% and 96%, by using linear discriminant analysis, as well as to quantify the total acidity, pH, volumetric alcoholic degree, potassium, conductivity, glycerol, and methanol parameters, with mean relative errors between 2.3% and 6.0%, by using partial least squares regressions. Sensors 2016, 16, 1796 2 of 12 the most used beverages to test the viability of these systems [12] . Cava is a quality sparkling wine protected under a designation of origin (D.O.) in Spain, which is produced mostly in the Penedès region. Unlike most wines, sparkling wines are characterized by the presence of CO 2 in solution, which is produced by a second alcoholic fermentation, and a biological aging in contact with lees under anaerobic conditions for at least nine months in the bottle [13] . It is significant to mention the complexity of the Cava wine as a sample, given the drastic changes in the chemical composition (CO 2 , sugars, ethanol, pH, amino acids), physical properties (turbidity, density, color), and varietal aromas produced by these fermentation and aging processes [14] . Only one research group from the Universitat Autònoma de Barcelona has approached the analysis of Cava with electronic tongue systems. This group was able to classify Cava wine samples according to the content of sugar added [15] and to the aging time in bottle [16] , as well as to determine the sugar and the total dry extract by using a voltammetric electronic tongue based on modified graphite-epoxy electrodes. In another work, the use of enzyme-modified sensors in the array allowed the quantification of different phenolic indices in Rosé Cava wines [17] . However, these systems were limited to the determination of just a few parameters, so it is necessary to develop more versatile and innovative tools for the analysis of Cava wine. Most electronic tongue systems reported until now for food quality are laboratory versions [10, 11] , partly due to the use of large-sized sensors and data collection equipment. On one hand, the miniaturization of the electronic tongue has been approached by using individual wire electrodes [18] or developing integrated arrays of sensors. Usually, these arrays have a planar configuration and include layers of conductive inks or pastes sequentially deposited onto insulating and chemically-inert substrates. Depending on the thickness of these layers, integrated arrays of sensors have been fabricated by using screen-printed methods (thick-film technology) and applied as portable devices for monitoring drinking waters [19] and beer discrimination [20] . Additionally, thin-film technologies have been also used to fabricate integrated multisensor systems combined with flow injection analysis [9] and portable taste sensors [21] , both by using standard photolithographic techniques. On the other hand, an alternative to obtaining versatile portable instruments for multiparametric applications at a minimum cost is the use of commercial integrated circuits (IC), such as power supplies, analog-to-digital converters, and microcontrollers [22] . The reduced size of these systems implies reduced fabrication and maintenance costs, as well as lower power consumption. In a previous paper [23], we developed and tested a compact multisensor meter, whose electronics were fabricated according to microsensor requirements and took into account the minimum energy consumption and its portability. In this work, we have fabricated a multi-ion-selective field effect transistor (ISFET) meter able to simultaneously measure up to six ISFETs, with the same requirements of portability and low power consumption. The two compact meters have been used together to perform the multiparametric analysis with an array of microsensors fabricated with microelectronic technology. This combination supposes an advance to achieve a portable electronic tongue system. The array of microsensors was formed by one conductivity sensor, one redox potential (ORP) sensor, and two amperometric gold microelectrodes, which were measured with the multisensor meter, together with six ISFETs sensitive to pH, Na + , K + , Ca 2+ , Cl − , and CO 3 2− , measured with the multi-ISFET meter. For the data treatment, two different multivariate methods were used: linear discriminant analysis (LDA) and partial least squares (PLS). A set of 78 Cava wine samples was analyzed with the electronic tongue. The system demonstrated its reliability for Cava wines according to the aging time, as well as the quantification of some chemical parameters with high accuracy. Materials and Methods Reagents and Solutions All reagents used were of high purity, analytical grade or equivalent. All solutions were prepared with de-ionized water. For ISFET calibration, stock solutions with ionic salts with concentrations of
doi:10.3390/s16111796 pmid:27801796 pmcid:PMC5134455 fatcat:bk3d5jo3yndxxmt4ef6croc2qq