Multivariate Optimization of Electrochemical Biosensors for the Determination of Compounds Related to Food Safety-A Review.

We summarize the application of multivariate optimization for the construction of electrochemical biosensors. The introduction provides an overview of electrochemical biosensing, which is classified into catalytic-based and affinity-based biosensors, and discusses the most recent published works in each category. We then explore the relevance of electrochemical biosensors for food safety analysis, taking into account analytes of different natures. Then, we describe the chemometrics tools used in the construction of electrochemical sensors/biosensors and provide examples from the literature. Finally, we carefully discuss the construction of electrochemical biosensors based on design of experiments, including the advantages, disadvantages, and future perspectives of using multivariate optimization in this field. The discussion section offers a comprehensive analysis of these topics.

Development of a voltammetric electronic tongue for the simultaneous determination of synthetic antioxidants in edible olive oils.

A voltammetric electronic tongue (E-tongue) is "a multisensor system, which consists of a number of low-selective sensors and uses advanced mathematical procedures for signal processing based on pattern recognition and/or data multivariate analysis such as artificial neural networks (ANNs), principal component analysis (PCA), among others". Thus, E-tongues in combination with chemometrics tools result in more accurate and selective analytical methods. In this work, we report results of a simple and reliable electroanalytical method to determine butyl hydroxyanisole (BHA), butyl hydroxytoluene (BHT) and propyl gallate (PG) in edible olive oils (EOO). Therefore, the square wave voltammetry (SWV) was used on platinum and carbon fiber disk ultramicroelectrodes (E-tongue configuration) combined with chemometrics tools to perform these studies. On the other hand, two data fusion strategies were used in order to combine electrochemical data obtained for each working electrode in the E-tongue: low-level data fusion (LLDF) and mid-level data fusion (MLDF). In addition, to reduce the dimensionality of the dataset in MLDF, the discrete wavelet transform (DWT) was used. Finally, to assert the predictive capability of the method for BHA, BHT, and PG determination in real samples, a recovery study for the antioxidants in EOO samples was performed, demonstrating the analytical accuracy of the proposed method. Moreover, from the comparison between the proposed electrochemical method with the AOAC reference method and others found in the literature in terms of the quality of the model (REP %) and the percent recovery assays (%) in different samples, our results were better than other reported previously for the simultaneous determination of BHA, BHT, and PG in real samples. Moreover, the percent recovery assays obtained with the proposed electrochemical method were in good agreement with those obtained by the chromatographic method.

Second-order electrochemical data generation to quantify carvacrol in oregano essential oils.

A novel analytical method using voltammetric second-order modeling based on multivariate curve resolution-alternating least-square (MCR-ALS) is presented for the first time for the quantitation of carvacrol (CAR) in oregano essential oils (OEO). The second-order cyclic voltammetry data were generated on the basis that CAR shows a diffusional system. Thus, the scan rate (v) was used as a second instrumental mode and cyclic voltammograms at different v were acquired for a single sample, generating the second-order data. CAR determination was performed in presence of thymol, included as a potential interferent. Results demonstrated that MCR-ALS successfully exploited the second-order advantage and the recoveries were not statistically different than 100%. The limits of detection and quantitation were estimated using the MCR-ALS which were 6.27 × 10-5°mol°L-1°and 1.90 × 10-4°mol L-1, respectively. Finally, the developed methodology was implemented to quantify of CAR in OEO samples.

Scientometric Overview of Coffee By-Products and Their Applications.

As coffee consumption is on the rise, and the global coffee production creates an excess of 23 million tons of waste per year, a revolutionary transition towards a circular economy via the transformation and valorization of the main by-products from its cultivation and preparation (Coffee Husk (CH), Coffee Pulp (CP), Coffee Silverskin (CS), and Spent Coffee Grounds (SCG)) is inspiring researchers around the world. The recent growth of scholarly publications in the field and the emerging applications of coffee by-products published in these scientific papers encourages a systematic review to identify the knowledge structure, research hotspots, and to discuss the challenges and future directions. This paper displays a comprehensive scientometric analysis based on 108 articles with a high level of influence in the field of coffee by-products and their applications. According to our analysis, the research in this field shows an explosive growth since 2017, clustered in five core applications: bioactive compounds, microbial transformation, environmental applications, biofuels from thermochemical processes, and construction materials.

Analytical determinations of luteolin.

Plants, through the photosynthesis process, produce the substances necessary for all the life cycles of nature, which are called "primary metabolites." Moreover, there are some plants that synthesize, in addition to these, other substances with more specific functions, which are known as "secondary metabolites." It is inside this group that flavonoids are located, whose main function is to protect organisms from damage caused by different oxidizing agents. Luteolin (3,4,5,7-tetrahydroxy-flavone) belongs to the sub-class of flavonoids known as flavones and is one of 10,000 flavonoids currently known, being one of the most bio-active flavonoids. Its various beneficial properties for health, together with the increasing reduction in the use of synthetic antioxidants, make the study of luteolin a very active field. Within this, the quantification of this molecule has become a subject of very special interest given that it is transversal to all fields. In this review article, we aim to give the reader a broad and deep vision of this topic, focusing on the events reported in the last 5 years and covering all possible techniques related to analytical determinations. We will discuss in terms of advantages and disadvantages between techniques, selectivity, sensitivity, costs, time consumption, and reagents as well as in the complexity of operations.

Analysis of dynamic networks based on the Ising model for the case of study of co-authorship of scientific articles.

Two computational methods based on the Ising model were implemented for studying temporal dynamic in co-authorship networks: an interpretative for real networks and another for simulation via Monte Carlo. The objective of simulation networks is to evaluate if the Ising model describes in similar way the dynamic of the network and of the magnetic system, so that it can be found a generalized explanation to the behaviours observed in real networks. The scientific papers used for building the real networks were acquired from WoS core collection. The variables for each record took into account bibliographic references. The search equation for each network considered specific topics trying to obtain an advanced temporal evolution in terms of the addition of new nodes; that means 3 steps, a time to reach the interest of the scientific community, a gradual increase until reaching a peak and finally, a decreasing trend by losing of novelty. It is possible to conclude that both methods are consistent with each other, showing that the Ising model can predict behaviours such as the number and size of communities (or domains) according to the temporal distribution of new nodes.

Determination of kinetic parameters of the enzymatic reaction between soybean peroxidase and natural antioxidants using chemometric tools.

The oxidation of eugenol, isoeugenol and vanillin natural antioxidants catalyzed by the soybean peroxidase enzyme was studied using uv-vis spectroscopy. An experimental design was used to optimize the different variables. The multivariate curve resolution method was used to obtain the profiles of antioxidant absorbance's as a function of time due to uv-vis absorption bands of both antioxidants and the enzymatic reaction product/s show a strong overlap. From these results, apparent Michaelis-Menten constants as well as the kinetic parameters k1 and k3 involved in the catalytic cycle of peroxidases were calculated. The antioxidant apparent acidity constants were also determined at different pH's from uv-vis spectrophotometric measurements. Values of k1 were (0.6 ±â€¯0.1) × 105 M-1 s-1, (2.0 ±â€¯0.2) × 105 M-1 s-1 and (7.0 ±â€¯0.5) × 106 M-1 s-1 and k3 (4.0 ±â€¯0.2) × 105 M-1 s-1, (6.0 ±â€¯0.6) × 105 M-1 s-1 and (6.0 ±â€¯0.9) × 106 M-1 s-1 for eugenol, isoeugenol and vanillin, respectively.

Development of an electrochemical method to determine phenolic monoterpenes in essential oils.

A simple, rapid and non-expensive method is proposed to determine phenolic monoterpenes such as thymol and carvacrol in essential oils of thyme and oregano. The linear sweep voltammetry based on glassy carbon electrodes was the electrochemical technique used. Thymol and carvacrol have one main oxidation peak in non-aqueous media centered at about 1.3 V vs. Ag/AgCl. The electron transfer process is mainly diffusion controlled. The calibration plots generated using the commercial standards of thymol and carvacrol were used to estimate the total content in real samples. The calibration plots were linear in the concentration range from 8.5 × 10-5 to 1.3 × 10-3 mol L-1 and 7.9 × 10-5 to 1.2 × 10-3 mol L-1 for thymol and carvacrol, respectively. Results obtained with the electrochemical method are in good agreement with those of the official method (gas chromatography). In addition, the analytical procedure does not require previous preparation of the sample or modification of the electrode surface. The electrochemical technique used is very simple to apply. Under these conditions, the methodology proposed is a good, simple and fast option to perform a quality control of essential oils.

Square wave voltammetry with multivariate calibration tools for determination of eugenol, carvacrol and thymol in honey.

The simultaneous determination of eugenol (EU), thymol (Ty) and carvacrol (CA) in honey samples, employing square wave voltammetry (SWV) and chemometrics tools, is informed for the first time. For this purpose, a glassy carbon electrode (GCE) was used as working electrode. The operating conditions and influencing parameters (involving several chemical and instrumental parameters) were first optimized by cyclic voltammetry (CV). Thus, the effects of the scan rate, pH and analyte concentration on the electrochemical response of the above mentioned molecules were studied. The results show that the electrochemical responses of the three compounds are very similar and that the voltammetric traces present a high degree of overlap under all the experimental conditions used in this study. Therefore, two chemometric tools were tested to obtain the multivariate calibration model. One method was the partial least squares regression (PLS-1), which assumes a linear behaviour. The other nonlinear method was an artificial neural network (ANN). In this last case we used a supervised, feed-forward network with Levenberg-Marquardt back propagation training. From the accuracies and precisions analysis between nominal and estimated concentrations calculated by using both methods, it was inferred that the ANN method was a good model to quantify EU, Ty and CA in honey samples. Recovery percentages were between 87% and 104%, except for two samples whose values were 136% and 72%. The analytical methodology was simple, fast and accurate.

Metabolomics and pesticides: systematic literature review using graph theory for analysis of references / Metabolómica y Pesticidas: Revisión sistemática de literatura usando teoría de grafos para el análisis de referencias

The systematic literature review presented here is designed to illustrate the role of metabonomics and metabolomics in pesticide exposure studies. The search was conducted in Thomson Reuters Web of Science (ISI Web of Knowledge) database. The references and citations for each article were downloaded for analysis. Graph theory was used to determine relevant articles and distinct relationships between classic and current research in this field through its structural characteristics. The initial network included 4423 nodes and 4978 links, from which indegree, outdegree and betweenness indicators were extracted. After preprocessing the data, the network was reduced to 415 nodes and 974 links. From this network, 80 articles with the highest score between the three indicators were extracted for review. This methodology allowed for the identification of different perspectives of metabolomic and metabonomic pesticide studies that included the mode and mechanism of action, toxicological and biological monitoring, environmental metab-olomics, metabolism, dose response and biomarkers and its role in pesticide exposure.

La revisión sistemática de literatura presentada a continuación tiene como objetivo dar a conocer el rol que han tenido la metabolómica en el estudio de la exposición a plaguicidas. La búsqueda se llevó a cabo en la base de datos Thomson Reuters Web of Science (ISI Web of Knowledge). Posteriormente, se descargaron todos los registros producto de resultado de la búsqueda y cada citación dentro de cada artículo. Estas referencias fueron analizadas mediante la teoría de grafos con el fin de identificar los artículos más relevantes, los artículos clásicos y recientes y los que presentan mayor intermediación en el tema de investigación. La red de citaciones fue construida con inicialmente con 4423 nodos (artículos) y 4978 enlaces (citaciones) a los cuales se les determinó los indicadores de grado de entrada, grado de salida y centralidad en el grafo. Posteriormente, esta red de citaciones fue procesada eliminando los artículos desconectados, reduciendo la red a 415 nodos y 974 enlaces. De esta red ya procesada se extrajeron 80 artículos que presentaron mayores indicadores de grado y centralidad. Finalmente, esta metodología permitió la identificación de diferentes perspectivas de los estudios metabolómicos y metabonómicos en la exposición a plaguicidas que incluyen estudios de modo de acción, mecanismos de acción, monitoreo biológico y toxicológico, metabolómica ambiental, metabolismo, dosis respuesta e identificación de biomarcadores.

Quantitative determination of tocopherols in edible vegetable oils using electrochemical ultra-microsensors combined with chemometric tools.

We have developed an electroanalytical method to quantify different isomers of tocopherols in edible vegetable oils. The method uses the square wave voltammetry on a carbon fiber disk ultramicroelectrode in benzene/ethanol+0.1 mol L(-1)H2SO4. Because the oxidation peaks of these natural antioxidants show an important overlapping, we have used two chemometric tools to obtain the multivariate calibration model. One method was the multivariate curve resolution-alternating least square (MCR-ALS), which assumes a linear behavior, i.e., the total signal is the sum of individual signals of components, and another nonlinear method such as artificial neuronal networks (ANNs). From the accuracy and precision analysis between nominal and estimated concentrations by both methods, we could infer that the ANNs method was a good model to quantify tocopherols in edible oil samples. Recovery percentages were between 94% and 99%. In addition, we found a difference of 1.4-6.8% between the total content of tocopherols in edible oil samples and the vitamin E content declared by the manufacturers.

Electrochemical oxidation of butein at glassy carbon electrodes.

The electrochemical oxidation of flavonoid butein is studied at glassy carbon electrodes in phosphate and citrate buffer solutions of different pH values, and 1M perchloric acid aqueous solutions by cyclic and square wave voltammetries. The oxidation peak corresponds to the 2e(-), 2H(+) oxidation of the 3,4-dihydroxy group in B ring of butein, given the corresponding quinone species. The overall electrode process shows a quasi-reversible behavior and an adsorption/diffusion mixed control at high butein bulk concentrations. At low butein concentrations, the electrode process shows mainly an adsorption control. Butein surface concentration values were obtained from the charge associated with the adsorbed butein oxidation peaks, which are in agreement with those values expected for the formation of a monolayer of adsorbate in the concentration range from 1 to 5µM. Square wave voltammetry was used to perform a full thermodynamic and kinetics characterization of the butein surface redox couple. Therefore, from the combination of the "quasi-reversible maximum" and the "splitting of the net square wave voltammetric peak" methods, values of (0.386±0.003) V, (0.46±0.04), and 2.7×10(2)s(-1) were calculated for the formal potential, the anodic transfer coefficient, and the formal rate constant, respectively, of the butein overall surface redox process in pH4.00 citrate buffer solutions. These results will be then used to study the interaction of butein, and other flavonoids with the deoxyribonucleic acid, in order to better understand the potential therapeutic applications of these compounds.

Development of an amperometric biosensor based on peroxidases to quantify citrinin in rice samples.

An amperometric biosensor based on horseradish peroxidase (EC1.11.1.7,H2O2-oxide-reductases) to determine the content of citrinin mycotoxin in rice samples is proposed by the first time. The method uses carbon paste electrodes filled up with multi-walled carbon nanotubes embedded in a mineral oil, horseradish peroxidase, and ferrocene as a redox mediator. The biosensor is covered externally with a dialysis membrane, which is fixed to the body side of the electrode with a Teflon laboratory film, and an O-ring. The reproducibility and the repeatability were of 7.0% and 3.0%, respectively, showing a very good biosensor performance. The calibration curve was linear in a concentration range from 1 to 11.6nM. The limits of detection and quantification were 0.25nM and 0.75nM, respectively. For comparison, the citrinin content in rice samples was also determined by fluorimetric measurements. A very good correlation was obtained between the electrochemical and spectrophotometric methods.

Qualitative and quantitative electroanalysis of synthetic phenolic antioxidant mixtures in edible oils based on their acid-base properties.

A simple electroanalytical method using square wave voltammetry at a Pt band ultramicroelectrode to perform a qualitative and quantitative analysis of different synthetic antioxidant mixtures permitted by official regulations in edible oils is proposed. The methodology was based on the comparison of voltammetric signals obtained in acetonitrile+0.1M (C4H9)4NF6P with those recorded in the same reaction medium when different aliquots of (C4H9)4NOH were added to allow a qualitative differentiation between antioxidants. Firstly, studies on solutions prepared from commercial reagents were carried out. Then, the results obtained were transferred to the analysis of a real matrix, i.e., an edible olive oil. From real samples spiked with a known amount of different synthetic antioxidant mixtures, we could deduce the presence of these antioxidants by comparing results obtained in the neutral medium with those obtained after the successive addition of base. The standard addition method was used to quantify the individually spiked synthetic antioxidants in the real sample. Recovery percentages were between 88% and 118%. The reproducibility was 1.5%, 3.1%, 4.1% and 4.1% in ACN+0.1M TBAHFP and 1.5%, 4.6%, 6.6% and 2.5% in Bz/EtOH (1:2)+0.1M H2SO4 for TBHQ, BHA, BHT and PG, respectively. The repeatability was 1% for PG in both media. These parameters show a good system performance.