Browsing by Author "Sousa, Mara E.B.C."
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- Analysis of honey main sugars by size-exclusion chromatographyPublication . Sousa, Mara E.B.C.; Peres, António M.; Dias, L.G.; Morais, Jorge Sá; Estevinho, Leticia M.; Machado, Adélio A.M.The main constituents of honey are sugars, mainly the monosaccharides fructose and glucose (reducing sugars), which account for 80% of the total mass, while the disaccharides (especially sucrose and maltose) represent 10%. In general, fructose predominates (giving a sweeter taste to honey than sucrose), although, in some honeys, glucose (that assigns a less sweet taste than sucrose but more than maltose) may be the main sugar. The fructose/glucose mass ratio is a parameter that allows the identification of possible adulterations of honey, by signaling abnormal levels of glucose due to the addition of commercial glucose or syrups. It also allows assessing the crystallization trend of the honey, although the glucose/water ratio provides a more accurate indication of this behavior. Therefore, for marketing purposes, the quantification of glucose and fructose in honey is a key factor for establishing its quality. This work reports the validation of a method for determination of honey sugars by SEC to be used as control in the study of their determination with an electronic tongue. A set of honey samples was provided by the Portuguese National Federation of Beekeepers to obtain a national sampling which showed the natural composition variability of Portuguese honeys. The analysis were carried out with HPLC equipment from Varian and a Supelcogel C-610H column, selected because the elution does not require organic solvents. The target compounds to analyze were glucose and fructose for which well separated peaks were found in the chromatograms, which included other two, for a mix of polyssacharides and unknown substance(s). The results of a thorough validation showed that the method can be employed for quantification of these two sugars in honey samples.
- Cyclic voltammetry: a tool to quantify 2,4,6-trichloroanisole in aqueous samples from cork planks boiling industrial processPublication . Peres, António M.; Freitas, Patrícia; Dias, L.G.; Sousa, Mara E.B.C.; Castro, Luís M.; Veloso, Ana C.A.Chloroanisoles, namely 2,4,6-trichloroanisole, are pointed out as the primary responsible of the development of musty off-flavours in bottled wine, due to their migration from cork stoppers, which results in huge economical losses for wine industry. A prevention step is the detection of these compounds in cork planks before stoppers are produced. Mass spectrometry gas chromatography is the reference method used although it is far beyond economical possibilities of the majority of cork stoppers producers. In this work, a portable cyclic voltammetry approach was used to detect 2,4,6-trichloroanisole extracted from natural cork planks to the aqueous phase during the cork boiling industrial treatment process. Analyses were carried out under ambient conditions, in less than 15 min with a low use of solvent and without any sample pre-treatment. The proposed technique had detection (0.31+/-0.01 ng/L) and quantification (0.95+/-0.05 ng/L) limits lower than the human threshold detection level. For blank solutions, without 2,4,6-trichloroanisole addition, a concentration in the order of the quantification limit was estimated (1.0+/-0.2 ng/L), which confirms the satisfactory performance of the proposed methodology. For aqueous samples from the industrial cork planks boiling procedure, intra-day repeatabilities were lower than 3%, respectively. Also,2,4,6-trichloroanisole contents in the aqueous samples determined by this novel approach were in good agreement with those obtained by GC–MS (correlation coefficient equal to 0.98), confirming the satisfactory accuracy of the proposed methodology. So, since this novel approach is a fast, low-cost, portable and user-friendly method, it can be an alternative and helpful tool for in-situ industrial applications, allowing accurate detection of releasable 2,4,6-trichloroanisole in an earlier phase of cork stoppers production, which may allow implementing more effective cork treatments to reduce or avoid future 2,4,6-trichloroanisole contaminations of wine.
- Discrimination of monofloral honeys using a potentiometric electronic tonguePublication . Sousa, Mara E.B.C.; Dias, L.G.; Peres, António M.; Estevinho, Leticia M.; Machado, Adélio A.M.There is a commercial interest in selling honey according to its color and pollen classification because the pollen content is related to the honey quality [1]. The honey color classification is expressed in the Pfund scale (mm), based on absorbance readings at 560 nm, and ranges between extra-white and dark [2]. The objective of this work is to investigate whether a potentiometric electronic tongue (Etongue) is able to classify honeys according to their three main colors (white, amber and dark) and to discriminate between monofloral honeys within each of these groups. The E-tongue had an Ag/ Agel reference electrode with double junction, and a multi-sensor device with 20 chemical sensors, based on all-solid-state electrodes with lipid polymeric membranes formed on solid supports of conducting silver. Two identical systems of multisensors were used, which allowed recording a profile of 40 signals for each sample. Honeys samples (65), provided by the National Federation of Beekeepers of Portugal, were classified according to the color (spectrophotometric method), pollen profile composition (microscopic method) and also analyzed using the E-tongue. The honeys of each group contained the following monofloral honeys: white honeys (20 samples), Lavandu/a sp. or Echium sp. ; amber honeys (30 samples), Lavandu/a sp., Echium sp., Prunus sp. or Rubus sp.; dark honeys (15 samples), Castanea sp., Erica sp. or Rubus sp. The data were treated by linear discrimination analysis (LDA) using forward stepwise variable selection and the leave-one-out cross-validation technique. Selected E-tongue signals together with LDA allowed 100%, 90% and 80% of correct classifications of monofloral honeys within the amber, white and dark groups, respectively. The results showed that the E-tongue can be used as a practical tool for discriminating monofloral honeys, though more robust classifications are expected by using different heuristic techniques for variable selection.
- Electrochemical Sensors for Assessing Antioxidant Capacity of Bee ProductsPublication . Peres, António M.; Sousa, Mara E.B.C.; Veloso, Ana C.A.; Estevinho, Leticia M.; Dias, L.G.This chapter is focused on the application of electrochemical techniques (e.g., sensors and biosensors), as the predominant methodology, to the quantification of individual or total phenolic compounds, either in standard solutions or in real matrices (e.g., plants, fruits and beverages) and their capability for assessing antioxidant activity/capacity. Specially, the potential application to evaluate antioxidant capacity of bee-hives products (e.g., propolis, honey) is addressed. Finally, the voltammetric behavior of Portuguese monofloral honeys is discussed for the first time, taking into account the expected effects of honey color and floral origin. Also, a possible relation with the expected antioxidant capacity of honeys is discussed, considering their floral origin. Works describing the use of electrochemical detection imbibed on liquid chromatographic or capillary electrophoretic configurations among other analytical methods will not be focused in this review, although their undoubtedly potentials and proved applications.
- Evaluation of an electronic tongue for honey classification according to its pollen analysisPublication . Sousa, Mara E.B.C.; Dias, L.G.; Peres, António M.; Estevinho, Leticia M.; Machado, Adélio A.S.C.Electronic tongues (ET) have attracted great interest due to its potential to obtain global Information from complex samples that could hardly be obtained by traditional instrumental methods of analysis. These multi-sensor arrays provide a huge amount of sample information which, by applying chemometric methods, allows sample identification/ classification, taste evaluation as well as, multicomponent analysis. The method of operation consists In obtaining a signal pattern which corresponds to the overall Information on the sample using chemical sensors with high stability and cross sensitivity to different species in solution. In this work, a potenclometrlc electronic tongue or taste sensor array was used. The device had 20 sensors, based on all-solid-state electrodes with lipid polymeric membranes formed on solid conducting silver supports.
- Evaluation of healthy and sensory indexes of sweetened beverages using an electronic tonguePublication . Dias, L.G.; Sequeira, Cédric Basílio; Veloso, Ana C.A.; Sousa, Mara E.B.C.; Peres, António M.Overconsumption of sugar-sweetened beverages may increase the risk of health problems and so, the evaluation of their glycemic load and fructose-intolerance level is essential since it may allow establishing possible relations between physiologic effects of sugar-rich beverages and health. In this work, an electronic tongue was used to accurately classify beverages according to glycemic load (low, medium or high load) as well to their adequacy for people suffering from fructose malabsorption syndrome (tolerable or not): 100% of correct classifications (leave-one-out cross-validation) using linear discriminant models based on potentiomentric signals selected by a meta-heuristic simulated annealing algorithm. These results may be partially explained by the electronic tongue’s capability to mimic the human sweetness perception and total acid flavor of beverages, which can be related with glycemic load and fructose-intolerance index. Finally, the E-tongue was also applied to quantify, accurately, healthy and sensory indexes using multiple linear regression models (leave-one-out cross-validation: Radj > 0.99) in the following dynamic ranges: 4.7 < glycemic load <= 30; 0.4 < fructose intolerance index <= 1.5; 32 < sweetness perception < 155; 1.3 < total acid flavor, g L-1< 8.3; and, 5.8 < well-balanced flavor. So, the proposed electronic tongue could be used as a practical, fast, low-cost and green tool for beverage’s healthy and sensory evaluation.
- Honey evaluation using electronic tongues: An overviewPublication . Veloso, Ana C.A.; Sousa, Mara E.B.C.; Estevinho, Leticia M.; Dias, L.G.; Peres, António M.Honey-rich composition in biologically active compounds makes honey a food products highly appreciated due to the nutritional and healthy properties. Food-manufacturing is very prone to different types of adulterations and fraudulent labelling making it urgent to establish accurate, fast and cost-effective analytical techniques for honey assessment. In addition to the classical techniques (e.g., physicochemical analysis, microscopy, chromatography, immunoassay, DNA metabarcoding, spectroscopy), electrochemical based-sensor devices have arisen as reliable and green techniques for food analysis including honey evaluation, allowing in-situ and on-line assessment, being a user-friendly procedure not requiring high technical expertise. In this work, the use of electronic tongues, also known as taste sensor devices, for honey authenticity and assessment is reviewed. Also, the versatility of electronic tongues to qualitative (e.g., botanical and/or geographical origin assessment as well as detection of adulteration) and quantitative (e.g., assessment of adulterants levels, determination of flavonoids levels or antibiotics and insecticides residues, flavonoids) honey analysis is shown. The review is mainly focused on the research outputs reported during the last decade aiming to demonstrate the potentialities of potentiometric and voltammetric multi-sensor devices, pointing out their main advantages and present and future challenges for becoming a practical quality analytical tool at industrial and commercial levels.
- A hybrid electronic tongue for direct classification of baby liquid foods with or without glutenPublication . Peres, António M.; Dias, L.G.; Veloso, Ana C.A.; Sousa, Mara E.B.C.; Machado, Adélio A.S.C.People suffering from celiac disease are gluten intolerant and inadvertent ingestion of gluten proteins must be avoided. Several techniques have been proposed to detect/quantify gluten proteins in foodstuffs: immunochemical methods, mass tandem spectrometry and polymerase chain reaction as well as gluten sensors [1]. Recently, a potentiometric electronic tongue (ET) with lipo/polymeric membranes has been used to detect gliadins, which are gluten proteins, in foodstuffs [2]. However, the use of these techniques requires the previous extraction of gluten proteins. This step can be a possible drawback since it is not possible to guarantee that the extraction has a 100% yield since the protein types overlap in solubility and extractability [3]. In this work, the feasibility of a hybrid multi-sensor ET, which combines repeated cross-sensitivity and ion selective sensors (Fig. 1), to discriminate gluten-free and gluten-containing liquid baby foods has been evaluated. The device was constructed using a screenprinted technique and directly applied in the liquid infant food samples. No extraction or dilution/dissolution step was required. In total, 5 “gluten-free” and 10 “glutencontaining” liquid baby foods of different flavors were purchased at local supermarkets and analyzed.
- A hybrid electronic tongue for direct classification of baby liquid foods with or without glutenPublication . Peres, António M.; Dias, L.G.; Veloso, Ana C.A.; Sousa, Mara E.B.C.; Machado, Adélio A.S.C.
- Identificação de méis monoflorais usando uma língua electrónica e metodologias de similaridadePublication . Sousa, Mara E.B.C.; Dias, L.G.; Veloso, Ana C.A.; Estevinho, Leticia M.; Peres, António M.; Machado, Adélio A.M.O preço do mel comercial depende da sua origem floral bem coma da sua cor. Em geral, o consumidor prefere meis claros [1, 2] e monoflorais, estando disposto a pagar um preço mais elevado. Assim sendo, torna-se importante o desenvolvimento de técnicas analíticas rápidas e simples capazes de garantir a conformidade da informação polínica constante do rotulo. Neste trabalho e aplicada uma Língua Electrónica potenciometrica constituída por sensores de sensibilidade cruzada na analise de meis para a identificação e classificação de meis monoflorais. Para tal, pretende-se mostrar uma aplicação pratica e direta deste sistema baseada na utilizatção de metodologias multivariadas de similaridade [3] para o tratamento de dados analíticos. Esta metodologia baseia-se no uso de meis monoflorais com elevado conteúdo do pólen predominante com padrões comparativos para o estabelecimento de um perfil típico de sinais potenciometricos (ver figura) para cada tipo de mel, nomeadamente Lavandula sp. e Castanea sp.