Electronic Tongue System Research Articles

Overview of electronic tongue sensing in environmental aqueous matrices: potential for monitoring emerging organic contaminants

Emerging organic contaminants (EOC) are synthetic or naturally occurring chemicals that have the potential to enter the environment and cause known or suspected adverse ecological and human health effects. Despite not being commonly monitored, EOC are often detected in effluents and water bodies because of their inefficient removal in conventional wastewater treatment plants. There is a growing concern about the presence and impact of EOC as well as the need for reliable and effective water monitoring using sensors capable of detecting the target molecules in complex media. Due to their specificities, such as fast response times, low cost, portability and user-friendly operation, electronic tongue (e-tongue) systems present some advantages over the traditional analytical techniques (e.g., chromatographic systems) used for environmental monitoring. We reviewed e-tongue sensors, focusing on their ability for real-time environmental monitoring. A bibliometric evaluation was carried out, along with a study of the status of the existing e-tongue systems, how they worked, and their applications in different fields. The potential of e-tongue sensors to detect organic contaminants in aqueous environmental matrices is discussed, with a particular focus on EOC.

Ion Chromatographic Fingerprinting of STC-1 Cellular Response for Taste Sensing.

Taste sensing is of great importance in both the pharmaceutical and foodstuff industries, and is currently mainly based on human sensory evaluation. Many approaches based on chemical sensors have been proposed, leading to the development of various electronic tongue systems. However, this approach is limited by the applied recognition methods, which do not consider natural receptors. Biorecognition elements such as taste receptor proteins or whole cells can be involved in the development of taste sensing biosensors usually equipped with various electrochemical transducers. Here, we propose a new approach: intestinal secretin tumor cell line (STC-1) chemosensory cells were applied for taste recognition, and their taste-specific cellular response was decoded from ion chromatographic fingerprints with the use of multivariate data processing by partial least squares discriminant analysis (PLS-DA). This approach could be useful for the development of various non-invasive taste sensing assays, as well as for studying taste transduction mechanisms in vitro.

Purity detection of goat milk based on electronic tongue and improved artificial fish swarm optimized extreme learning machine

The nutritional value of goat milk is higher than that of cow milk, which is scarce and expensive. Therefore, many bad credit enterprises mix cow’s milk into goat milk and sell it as pure goat milk, which infringes on the rights and interests of consumers. The adulteration of dairy products has a long history. Many techniques have been applied for the detection of dairy products’ adulteration, but no obvious results have been achieved. The electronic tongue system, based on a virtual instrument, can provide fast detection of goat milk’s quality. The qualitative identification of different purities of goat milk by kernel principal component analysis (KPCA) has achieved 100% accuracy. By comparing the four algorithms of the optimal extreme learning machine (ELM), it was determined that the quantitative model for the prediction of adulterated goat milk, established by the improved artificial fish swarm optimized ELM method, had high prediction accuracy. The prediction set coefficient R2 was 0.998, the average absolute error (MAE) was 0.083, and the root mean square error (MSE) was 0.011. According to its unique advantages, the electronic tongue provides a new idea and method for the detection of food adulteration. As a modern intelligent sensory instrument, the electronic tongue has great potential for brand identification as well as the identification of goat milk and goat milk powder adulteration.

Novel prediction of heavy metal residues in fish using a low‐cost optical electronic tongue system based on colorimetric sensors array

AbstractFor simultaneous and quantitative prediction of three toxic heavy metal residues (Pb, Cd and Hg) in fish, the novel and low‐cost colorimetric sensors array was fabricated. Forty eight fish samples (Carassius carassius) retailed in Zhenjiang, China, were used. Inductively coupled plasma mass spectrometry was employed as the reference analytical method. The partial least square regression (PLS) and extreme learning machine (ELM) respectively were comparatively used for data modeling. Results showed that the ELM models built were better than the PLS models with correlation coefficient in the prediction set for Pb, Cd, and Hg as 0.854, 0.83, and 0.845 respectively; while, the corresponding root mean squares error were 0.102 mg/kg, 0.026 mg/kg, and 0.016 mg/kg respectively. This work demonstrates that the developed artifical gustatory system has a great potential in the simultaneous and quantitative prediction of heavy metal residues in fish and could be used perhaps for other fish products.Practical applicationsFish is an important food commodity worldwide. It is very vital to monitor heavy metals residues in raw fishes to guarantee food safety. Traditional analytical methods for heavy metals determination in fish are quite cumbersome and usually expensive. The novel low‐cost and simple colorimetric sensors array based on pyridylazo and porphyrin indicators has been developed in the present study. Results showed that, photoelectric electronic tongue based on colorimetric sensors coupled with extreme learning machine model has a great potential in the simultaneous and quantitative prediction of toxic heavy metal residues in fish.

The Relationship between Muscle Fiber Composition and Pork Taste-traits Assessed by Electronic Tongue System.

To investigate relationships of electronic taste-traits with muscle fiber type composition (FTC) and contents of nucleotides, porcine longissimus lumborum (LL), psoas major (PM), and infra spinam (IS) muscles were obtained from eight castrated LYD pigs. FTC and taste-traits in these three porcine muscles were measured by histochemical analysis and electronic tongue system, respectively. IS had significantly higher proportion of type I fibers while LL had significantly higher proportion of type IIB than other muscles (p<0.05). IS had the highest inosine monophosphate (IMP) content while LL had the lowest IMP content (p<0.05). In contrast, LL had significantly higher hypoxanthine content compared to PM and IS (both p<0.05). For taste-traits, IS had significantly higher umami and richness values but lower sourness value than LL and PM (p<0.05). Sourness and astringency values of LL were significantly higher than those of IS (p<0.05). The proportion of type IIB fiber was positively correlated with sourness and astringency but negatively correlated with saltiness. These results suggest that sourness and astringency tastes are increased with increasing proportions of type IIB fibers in porcine muscles due to increase of hypoxanthine content. These results also imply that umami and richness tastes are increased with increasing contents of type I and IIA fibers because of increased IMP content in porcine muscles.

Using various metal phthalocyanine mixed with graphite for selective electrodes of electronic tongue to classify several types of hot drink

Metal phthalocyanine (MPc) is a metal organic compound which can be formed with several metal atoms at the center. Although MPc has semiconductor property, in order to fabricate the selective electrode for cyclic voltammetry (CV) measurement, the other material with high electrical conductive materials is required to mix in order to achieve sufficient electrochemical current. In this work, graphite powder with particle size less than 20 μm from Sigma-Aldrich Pte. Ltd. was mixed with several MPc powders including cobalt, iron, zinc and manganese phthalocyanine powders in the ratio of 20:1 by weight, respectively. The mixture powder was grinded together to achieve the uniform mixing with some powder size. In order to fabricate the selective working electrodes, the mixture was fill into a hollow Teflon rod with inner copper rod at the other end. During CV measurement, the electrodes indicated the anodic and cathodic peaks at various voltage depending on the type of metal atom of MPc therefore these modified graphite electrodes are suitable to be utilized as a selective probe for electronic tongue system. To demonstrate the classification ability of this electrode array, a variety of hot drink was used including three types of coffee, cocoa and chocolate malt. The hot drink was prepared with boil water and cooled it down to 30 °C before performing the CV measurement by five electrodes. With principle analysis, the extracted feature can separate each data group of five hot drinks and even can distinguish three types of the coffee. Thus, these graphite modified electrodes can be utilized in an electronic tongue application with low cost and high stability.

Grade classification model tandem BpNN method with multi-metal sensor for rice eating quality evaluation

Evaluation of rice eating quality is increasingly important to researchers and consumers. In this paper, a novel tandem evaluation approach, which is grade classification model tandem back propagationartion neural network (BpNN) method, was developed for multi-metal sensor to predict rice eating quality. Characteristic current and potential arrays were extracted and properly processed, resulting in potential phasor plane values and current phasor plane values. The current phasor plane values were used as the input variables of grade classification model, and consequently, the classification value and grade value of sample output as well as potential phasor plane values were used in the following BpNN for score prediction. It was found that the performance of developed grade classification model tandem BpNN method was better than that of direct neural network method. The scores predicted by developed method were compared to sensory scores obtained by traditional sensory evaluation. A correlation coefficient of 0.9964, a RMSE of 0.69, a slop of 0.98 and an intercept of 1.45 were obtained. The accuracy of developed method for score prediction was 90%. Results indicated that the developed tandem evaluation approach was an efficient method for rice score prediction in electronic tongue system.

Rapid sensing of total theaflavins content in black tea using a portable electronic tongue system coupled to efficient variables selection algorithms

This study attempted to detect the total theaflavins content in black tea using a portable electronic tongue integrated with chemometric algorithms. Glassy carbon as a working electrode was used to collect the cyclic voltammetry current signals from the black tea samples. The synergy interval partial least square with competitive adaptive reweighted sampling (Si-CARS-PLS) was attempted to optimize and select the most informative current signal variables at special potentials for the prediction of the total theaflavins content in black tea. Models were optimized via cross validation. Compared with other characteristic variables selection methods, Si-CARS-PLS showed the best performance, employing only 13 variables (0.23% of the total variables), to achieve Rp = 0.8302 and RMSEP = 0.257 in the prediction set. The portable electronic tongue based on glassy carbon electrode and cyclic voltammetry combined with variable selection algorithm Si-CARS-PLS, proved a promising, rapid and cost-effective method to measure the total theaflavins content in black tea.

Laser-Induced Carbon-Based Smart Flexible Sensor Array for Multiflavors Detection.

We report a flexible sensor array electronic tongue system that is fabricated on a polymer substrate by the laser direct writing process for multiflavor detection. Electronic tongue is a sensing system that is applied to detect different elements with the same sensor array. By analyzing responses from different measurement units, it enables a cross-sensitivity, namely, the ability of the system to responding to a range of different analytes in solution without specific functionalization of sensors. In this article, a six-unit sensing array system was fabricated by a laser direct writing process. Sensing units were introduced on a flexible polyamide surface. A high surface-volume ratio porous carbon structure was created by a laser-induced carbonization process, which provides stable conductive carbon electrodes with high sensitivity. Different surface treatments, such as gold plating, reduced-graphene oxide coating, and polyaniline coating, were accomplished for different measurement units. By applying principal component analysis, this sensing system shows a promising result for the detection of multiple flavors. The detection limit for each element is about 0.1 mM for NaCl and sugar solutions. Also, it is able to detect 10-4 times diluted commercial table vinegar solution, which originally contains 5% acetic acid. The detection limit is theoretically lower than the human threshold of 10 mM for NaCl and sugar. Besides, the sensing system shows a high sensitivity and selectivity for mixed elements. By mapping the data points, the sensor system could detect flavor combinations and provide a reliable prediction of analyte concentration ratios.

Metabolic and sensory evaluation of ultrasound-assisted osmo-dehydrated kiwifruit

Abstract The aim of this work was to investigate the effect of ultrasound (US) pre-treatment on endogenous metabolic activity of kiwifruits slices subjected to osmotic dehydration (OD), measured by metabolic heat production in isothermal calorimeter, respiration rate, structure changes and cell viability. Moreover, the overall changes on minimally processed kiwifruit were also studied by means of electronic tongue system. Kiwifruit slices (10 mm thick) were treated with US in the bath at a frequency of 35 kHz for 10, 20 and 30 min. The OD process was conducted in a 61.5% sucrose solution at 25 °C for pre-established contact period of 0, 10, 20, 30, 60 and 120 min. The results showed that the application of US pre-treatment and OD process promoted the reduction of metabolic heat as a consequence of a partial loss of vitality. Moreover, US and US + OD treatment specifically impacted the structure and the chemical picture of kiwifruit samples. Industrial relevance Ultrasound treatment coupled with osmotic dehydration could be applied at industrial level in order to save time and energy for a further dehydration process. Moreover, fruit tissue treated with ultrasound treatment promoted structural modifications and chemical changes in the kiwifruit tissue, as resulted from the present study, which could be useful for the industries to design novel products with intermediate moisture content.

Electronic Tongue for Brand Uniformity Control: A Case Study of Apulian Red Wines Recognition and Defects Evaluation †.

The potentiometric electronic tongue system has been tested as a potential analytical tool for brand uniformity control of monoculture Apulian red wines (Primitivo and Negroamaro). The sensor array was composed of eight porphyrin coatings obtained by electrochemical polymerization process and was employed for both wines discrimination and quantitative detection of wine defect compounds: “off-odour” 3-(methylthio)-propanol; isoamyl alcohol fusel oil; benzaldehyde (marker of the yeast activity) and acetic acid (marker of vinegar formation). PLS-DA applied to Electronic tongue output data has permitted a correct discrimination of more than 70% of analysed wines in respect to the original brand affiliation. Satisfactory PLS1 predictions were obtained in real wine samples; with R2 = 0.989 for isoamyl alcohol and R2 = 0.732 for acetic acid. Moreover; the possibility to distinguish wine samples on the base of permitted levels of fault compounds content was shown.

Effect of dietary processed sulfur supplementation on water-soluble flavor precursors, free amino acids, and taste characteristics of pork during refrigerated storage.

A total of 60 three-way crossbred (Landrace, Duroc, and Yorkshire) pigs were divided into two groups (processed sulfur-fed pigs (SFPs) and nonprocessed sulfur-fed pigs, (NSFPs)) and used to determine the effect of supplementation with 3 g kg-1 processed sulfur on water-soluble precursors, free amino acids, and taste of meat using an electronic tongue, during refrigerated storage. Glycogen and glucose levels of SFP were significantly higher than in NSFPs. Glycogen levels decreased and glucose levels increased during storage (P < 0.001). The pH and moisture content of SFPs were higher than in NSFPs. Inosine of SFPs was higher than in NSFPs (P < 0.05). Hence, umami and richness tastes of SFPs were higher than in NSFPs and increased during storage. The total free amino acid content of both groups was not different, although it increased during storage (P < 0.001). The umami taste of water-soluble precursors was improved in meat derived from SFPs during refrigeration. The storage time and dietary supplementation with processed sulfur increased the taste components of meat. Application of an electronic tongue system can be used to distinguish the taste characteristics of different types of pork, based on differential supplementation and aging. © 2018 Society of Chemical Industry.

Solid-Contact Potentiometric Sensors and Multisensors Based on Polyaniline and Thiacalixarene Receptors for the Analysis of Some Beverages and Alcoholic Drinks.

Electronic tongue is a sensor array that aims to discriminate and analyze complex media like food and beverages on the base of chemometrics approaches for data mining and pattern recognition. In this review, the concept of electronic tongue comprising of solid-contact potentiometric sensors with polyaniline and thacalix[4]arene derivatives is described. The electrochemical reactions of polyaniline as a background of solid-contact sensors and the characteristics of thiacalixarenes and pillararenes as neutral ionophores are briefly considered. The electronic tongue systems described were successfully applied for assessment of fruit juices, green tea, beer, and alcoholic drinks They were classified in accordance with the origination, brands and styles. Variation of the sensor response resulted from the reactions between Fe(III) ions added and sample components, i.e., antioxidants and complexing agents. The use of principal component analysis and discriminant analysis is shown for multisensor signal treatment and visualization. The discrimination conditions can be optimized by variation of the ionophores, Fe(III) concentration, and sample dilution. The results obtained were compared with other electronic tongue systems reported for the same subjects.

Design and application of electronic tongue system for orange juice quality detection using internet of things

Imitating the mechanism of human taste perception, an electronic tongue (ET) system for orange juice quality detection based on internet of things was developed. The system consists of three parts: hand-held detection terminal, wireless communication system and cloud service platform. During the detection, the hand-held detection terminal was used to obtain taste “fingerprint” data from various kinds of juices based on large pulse scanning potential, and then transmitted these data to a cloud service platform through a wireless communication system, as well as the pattern recognition methods were utilized to analyze the data. Finally, the results were compared with the built-in “fingerprint” database of the beverage on the cloud platform so as to obtain the brand or adulteration information of the tested juice. In this study, the developed ET system was further used for the identification of orange juice brand and purity detection. Linear discriminant analysis (LDA) was applied to the qualitative analysis of orange juice with different brand, and the support vector machine (SVM) was used to quantitative forecast of orange juice purity. The result indicated that the LDA can effectively differentiate samples of orange juice with different brand, which the identification accuracy reached 100%; the SVM model possess a good quantitative prediction accuracy for orange juice purity with the root mean square error (RMSE) in prediction set reaching 0.0172. This system possessed the advantages of fast detection, simple operation, low cost, high stability as well as the result was easy to query.

Detection and analysis of wheat storage year based on electronic tongue and DWT-IPSO-LSSVM algorithm

Abstract: The electronic tongue system based on virtual instrument technology was used to qualitatively analyze the wheat, which achieves rapid and objective evaluation analysis of aged wheat with different storage years. In view of the complex output signal of the electronic tongue and the large amount of data, the Discrete Wavelet Transform was used to extract the eigenvalues of the original data to reduce the data dimension size. On this basis, the improved particle swarm optimization algorithm was used to optimize the parameters of Least squares support vector machine, and the analysis model of wheat storage age was established. The experiments exhibited that the DWT-IPSO-LSSVM model had better classification performances than other pattern recognition models, such as DWT-GA-LSSVM, DWT-AF-LSSVM and DWT-PSO-LSSVM. The results showed that the accuracy of the training set, the accuracy of the test set, overall classification accuracy and Kappa coefficient of the proposed combined model in this paper were 95%, 92%, 91% and 0.88 respectively. This research indicated that the electronic tongue system combined with proposed model can be used to identify and discriminate the aged wheat with different storage years. Keywords: electronic tongue, wheat storage year, discrete wavelet transform, improved particle swarm optimization, least squares support vector machine DOI:  10.33440/j.ijpaa.20190202.46.  Citation: Guo T T, Yang Z W, Miao N, Zhang X, Li Q S, Guo J, Wang Z Q. Detection and analysis of wheat storage year based on electronic tongue and DWT-IPSO-LSSVM algorithm.  Int J Precis Agric Aviat, 2019; 2(2): 19–24.

Electronic Tongue-A Tool for All Tastes?

Electronic tongue systems are traditionally used to analyse: food products, water samples and taste masking technologies for pharmaceuticals. In principle, their applications are almost limitless, as they are able to almost completely reduce the impact of interferents and can be applied to distinguish samples of extreme complexity as for example broths from different stages of fermentation. Nevertheless, their applications outside the three principal sample types are, in comparison, rather scarce. In this review, we would like to take a closer look on what are real capabilities of electronic tongue systems, what can be achieved using mixed sensor arrays and by introduction of biosensors or molecularly imprinted polymers in the matrix. We will discuss future directions both in the sense of applications as well as system development in the ever-growing trend of low cost analysis.

Dissolution studies of metamizole sodium and pseudoephedrine sulphate dosage forms − comparison and correlation of electronic tongue results with reference studies

This work reports a critical evaluation of the results of the release of active substances (APIs) from novel pharmaceutical formulations provided by an electronic tongue system (ET). Detailed dissolution studies of modified-release granules used in pharmacotherapy containing metamizole sodium and pseudoephedrine sulphate were carried out. The impact of the dissolution-modifying excipients (carmellose sodium and hypromellose) on the dissolution process as well as on the outcomes of the sensor array of ion-selective electrodes was investigated. The obtained dissolution profiles were compared and correlated with those registered during the reference studies performed according to the pharmacopoeial method. It was pointed out that the proper evaluation of the efficiency of the release modification requires the examination of dosage forms as well as physical mixtures of API and excipient. Moreover, the results obtained using potentiometric ET were complementary to the classical methodology. Their partial inconsistency, remarked during several experiments, should be interpreted with caution owing to simultaneous sensing of APIs and excipients by the sensors and their various performances (i.e. selectivity and sensitivity) towards these components.

Rapid Liquid Recognition and Quality Inspection with Graphene Test Papers.

Electronic tongue is widely applied in liquid sensing for applications in various fields, such as environmental monitoring, healthcare, and food quality test. A rapid and simple liquid‐sensing method can greatly facilitate the routine quality tests of liquids. Nanomaterials can help miniaturize sensing devices. In this work, a broad‐spectrum liquid‐sensing system is developed for rapid liquid recognition based on disposable graphene–polymer nanocomposite test paper prepared through ion‐assisted filtration. Using this liquid‐sensing system, a number of complex liquids are successfully recognized, including metal salt solutions and polymer solutions. The electronic tongue system is especially suitable for checking the quality of the foodstuff, including soft drinks, alcoholic liquor, and milk. The toxicants in these liquids can be readily detected. Furthermore, the novel material‐structure design and liquid‐detection method can be expanded to other chemical sensors, which can greatly enrich the chemical information collected from the electrical response of single chemiresistor platform.

Interaction of peptides obtained from the enzymatic hydrolysis of soybean meal with cyclodextrins: an evaluation of bitterness reduction

Enzymatic hydrolysis improves the functional and nutritional characteristics of soybean meal proteins. However, the presence of hydrophobic peptides can cause an intense bitterness to the hydrolysate, which is deleterious in terms of final product taste. In this paper we evaluate the interaction of peptides employed for the enzymatic hydrolysis of soybean meal with α-, β- and γ-cyclodextrins, aiming to reduce the bitter taste. Each cyclodextrin was added in mass fractions of 1.5, 2.0 and 2.5% in a hydrolysate of soybean meal prepared with enzyme Alcalase® 2.4 L at 1% concentration (protein/protein). In order to identify possible interactions between the components, several instrumental techniques were employed. NMR H1 spectra evidenced strong interactivities between the peptides’ aromatic and aliphatic regions and the cyclodextrins’ internal cavities. Analysis by an electronic tongue system showed that the addition of α- and β-cyclodextrins to the hydrolysate, at concentrations 1.5 and 2.0% (w/w), respectively, induced the greatest difference with regard to control hydrolysate. The difference was also sensory perceptible to untrained tasters in a bitterness ranking test, and reveal that the treatment was efficient in reducing bitterness compared to the control samples, indicating this method as a suitable approach for masking bitterness in soybean hydrolysates.

Evolution of Taste Compounds of Dezhou-Braised Chicken During Cooking Evaluated by Chemical Analysis and an Electronic Tongue System.

This paper aimed to study the time course changes in taste compounds of Dezhou-braised chicken during the entire cooking process mainly consisting of deep-frying, high-temperature boiling, and low-temperature braising steps. For this purpose, meat samples at different processing stages were analyzed for 5'-nucleotides and free amino acids, and were also subjected to electronic tongue measurements. Results showed that IMP, Glu, Lys, and sodium chloride were the main compounds contributing to the taste attributes of the final product. IMP and Glu increased in the boiling step and remained unchanged in the following braising steps. Meanwhile, decrease in Lys content and increase in sodium chloride content were observed over time in both boiling and braising steps. Intensities for bitterness, saltiness, and Aftertaste-B obtained from the electronic tongue analysis were correlated with the concentrations of these above chemical compounds. Therefore, the electronic tongue system could be applied to evaluate the taste development of Dezhou-braised chicken during processing.