Edible plant by-products as source of polyphenols: prebiotic effect and analytical methods.

Polyphenols with high chemical diversity are present in vegetables both in the edible parts and by-products. A large proportion of them remains unabsorbed along the gastrointestinal tract, being accumulated in the colon, where they are metabolized by the intestinal microbiota. These polyphenols have been found to have "prebiotic-like" effects. The edible plant industry generates tons of residues called by-products, which consist of unutilized plant tissues (peels, husks, calyxes and seeds). Their disposal requires special and costly treatments to avoid environmental complications. Reintroducing these by-products into the value chain using technological and biotechnological practices is highly appealing since many of them contain nutrients and bioactive compounds, such as polyphenols, with many health-promoting properties. Edible plant by-products as a source of polyphenols highlights the need for analytical methods. Analytical methods are becoming increasingly selective, sensitive and precise, but the great breakthrough lies in the pretreatment of the sample and in particular in the extraction methods. This review shows the importance of edible plant by-products as a source of polyphenols, due to their prebiotic effect, and to compile the most appropriate analytical methods for the determination of the total content of phenolic compounds as well as the detection and quantification of individual polyphenols.

Biosensors for GMO Testing: Nearly 25 Years of Research.

In the nearly two decades since genetically modified organisms (GMOs) were first commercialized, genetically engineered crops have gained ground on their conventional counterparts, reaching 185 million hectares worldwide in 2016. The technology has bestowed most of its benefits on enhancing crop productivity with two main traits currently dominating the market: insect-resistant and herbicide-tolerant crops. Despite their rapid and vast adoption by farmers worldwide, GMOs have generated heated debates, especially in European countries (EU), driven mostly by consumers concerned about safety of transgenic foods and about the potential impact on the environment. The need to monitor and to verify the presence and the amount of GMOs in agricultural crops and in food products has generated interest in analytical methods for sensitive, accurate, rapid, and cheap detection of these products. DNA biosensors have been envisioned as a novel DNA-detection technology that would one day substitute current amplification-based methods, providing hand-held, quick, and ultrasensitive gene-level detection. This review summarizes the contributions made in nearly 20 years of research regarding the application of genosensing technology for the qualitative and quantitative determination of transgenic traits.

Electrochemical enzyme biosensors based on calcium phosphate materials for tyramine detection in food samples.

Electrochemical tyrosinase biosensors for tyramine determination were developed by the immobilization of the enzyme in calcium phosphate materials (CaPs) followed by cross-linking with glutaraldehyde. Tyramine was detected by the electrochemical reduction at -0.1V of the o- enzymatically-formed dopaquinone. Three different CaPs were explored as immobilization systems, monetite, brushite and brushite cement. Biosensors based on brushite matrices provide better analytical properties than the monetite one. Compared to brushite, a 10-fold increase of sensitivity was obtained with the brushite cement-based biosensor, which highlights the effect of brushite crystal formation in the presence of the enzyme in the biosensor performance. Several variables involved in the enzyme immobilization method such as glutaraldehyde cross-linking time, PPO/brushite ratio and thickness of the brushite-enzyme film were investigated. Furthermore, the effects of pH and temperature on biosensor performance were also optimized. Brushite cement-PPO-GA biosensor resulted in a reliable, highly sensitive, fast, inexpensive and easy analytical method for tyramine detection. Under optimal conditions (time of 15min, a ratio of 1.0 and 50µg of the brushite-enzyme mixture, 20°C and pH 6,0), a linear range of 5.8 × 10-7 to 1.6 × 10-5, sensitivity 1.50 × 103mAM-1 cm-2, detection limit, 4.85 × 10-8M and a response time, 6s were obtained. The suitability of the proposed biosensor to determine the tyramine content in cheese samples has been explored. The mean analytical recovery of added tyramine in gouda and brie cheeses were found to be 95.5±5.8 and 96.9±7.5 respectively. A study of the tyramine content evolution over the course of a week under inadequate storage showed the importance of monitoring the degradation of certain foods.

Electrochemical genosensors in food safety assessment.

The main goal of food safety assessment is to provide reliable information on the identity and composition of food and reduce the presence of harmful components. Nowadays, there are many countries where rather than the presence of pathogens, common public concerns are focused on the presence of hidden allergens, fraudulent practices, and genetic modifications in food. Accordingly, food regulations attempt to offer a high level of protection and to guarantee transparent information to the consumers. The availability of analytical methods is essential to comply these requirements. Protein-based strategies are usually employed for this purpose, but present some limitations. Because DNA is a more stable molecule, present in most tissues, and can be amplified, there has been an increasing interest in developing DNA-based approaches (polymerase chain reaction, microarrays, and genosensors). In this regard, electrochemical genosensors may play a major role in fulfilling the needs of food industry, such as reliable, portable, and affordable devices. This work reviews the achievements of this technology applied to allergen detection, species identification, and genetically modified organisms testing. We summarized the legislative framework, current design strategies in sensor development, their analytical characteristics, and future prospects.

Detección de alérgenos de cacahuete mediante un sensor de ADN / Detection of peanut allergens by a DNA sensor

En el presente trabajo se propone un genosensor electroquímico para la detección de un segmento de ADN que codifica parte de la proteína alergénica Ara h 2 del cacahuete. El genosensor se basa en un ensayo tipo sándwich, el analito hibrida con dos secuencias de bases, una de ellas inmovilizada sobre un electrodo de oro serigrafiado, formando una monocapa autoensamblada. La optimización del dispositivo se realizó utilizando la metodología de Superficies de Respuesta. La máxima respuesta se encontró para concentraciones de sonda de captura y agente bloqueante, 1 mM y 2,5 mM respectivamente

In the present work an electrochemical genosensor for detecting a DNA segment encoding part of the allergenic protein peanut Ara h 2 is proposed. Genosensors is based on a sandwich assay format, the analyte hybridized with two base sequences, one immobilized onto a screen printed gold electrode, forming a self-assembled monolayer. The optimization of the device was performed using Response Surface Methodology. The maximum response was found to be 1 µM of capture probe concentration and 2,5 mM of blocking agent concentration

Diseño de un genosensor electroquímico para la detección indirecta de gluten en alimentos / Electrochemical genosensor for indirect wheat gluten detection in food

Se propone un nuevo genosensor electroquímico para la detección de una secuencia específica de ADN que codifica un fragmento inmunogénico de la Alfa-2-gliadina, proteína del gluten de trigo responsable de la celiaquía. El diseño del genosensor se basa en la formación de una monocapa autoensamblada de sonda de captura y un agente bloqueante, mercaptohexanol, sobre electrodos de oro serigrafiados. Se eligió un ensayo tipo sándwich, utilizando una sonda indicadora marcada con biotina y el conjugado estreptavidina-fosfatasa alcalina como molécula de marcaje. La detección del analito se basó en la medida de la corriente de oxidación del 1-naftol, producto formado por la hidrólisis enzimática del 1-naftil-fosfato, mediante voltamperometría de pulso diferencial. Se investigaron y optimizaron los parámetros implicados en la composición de la fase sensora mediante voltametría cíclica, encontrándose como relación óptima sonda de captura: mercaptohexanol 2 microM:9 mM. Con el objetivo de minimizar las adsorciones inespecíficas, se optimizaron las concentraciones de sonda indicadora y conjugado enzima-estreptavidina, especies involucradas en la fase de medida, obteniéndose como valores óptimos 1 microM y 1,075x10-3 g/L respectivamente. El genosensor propuesto presentó una respuesta lineal entre 20 y 250 nM(AU)

A new electrochemical genosensor has been developed for the detection of a specific DNA sequence that encodes for an immunogenic fragment of Alpha-2-gliadin, protein of gluten wheat that plays an important role in celiac disease. The genosensor is based on a mixed self-assembled monolayer consisting on a capture probe and a diluent molecule, mercaptohexanol, both immobilized on screen-printed gold electrodes. A sandwich-type hybridization assay was selected, using a signaling-DNA probe labeled with biotin and streptavidin-alkaline phosphatase as a reporter molecule. Detection of DNA gluten is based on the measurement of the oxidization current of 1-naphthol, product formed by Alpha-naphthyl phosphate enzymatic hydrolysis, by differential pulse voltammetry. Parameters involved in the sensing phase were investigated and optimized by cyclic voltammetry. The optimal capture probe to mercaptohexanol ratio was found to be 2 micreM:9 mM. In order to minimize unspecific adsorptions, both signaling probe and enzyme-streptavidin conjugate concentrations (measurement phase parameters) were optimized (1 micreM and 1.075·10-3 g/L respectively). A linear response from 20 nM to 250 nM is obtained with the proposed genosensor(AU)

Biosensor amperométrico para la medida de galactosa compuesto por microgeles de poliacrilamida / Amperometric biosensor based on polyacrylamide microgels for galactose determination

La galactosemia es uno de los errores innatos del metabolismo más frecuentes. Su presentación clínica en niños no tratados puede ser severa, a veces mortal; su diagnóstico es relativamente simple y su tratamiento es muy sencillo y efectivo. Esto ha hecho que en los últimos años se hayan propuesto nuevos diseños de biosensores para la determinación de galactosa basados en galactosa oxidasa. El objetivo del trabajo consistió en la inmovilización de galactosa oxidasa (GlOx) en micropartículas de poliacrilamida (PAA), sintetizadas a partir del método de emulsión concentrada, y su utilización como material biológico de un nuevo biosensor amperométrico para la determinación de galactosa. Para preparar los biosensores de galactosa se depositaron las micropartículas con galactosa oxidasa sobre la superficie de un electrodo de platino y se cubrieron con una membrana de diálisis. Las micropartículas se caracterizaron mediante un analizador de partículas Galai Cis-1, microscopía electrónica de barrido, difracción de rayos X y calorimetría de barrido diferencial. La temperatura de transición vítrea (Tg) de los microgeles de poliacrilamida disminuyó al encapsular en su interior galactosa oxidasa. Se estudió la influencia de distintos factores, tales como grado de reticulación, pH y temperatura en la respuesta del biosensor. Las condiciones óptimas se corresponden a un grado de reticulación del 7%, 40º C y pH 7,0. El sistema de inmovilización propuesto apenas modifica la actividad enzimática, pero parece proteger a la enzima aumentando el intervalo de temperatura en el que es activa

Galactosemia is one of the natural errors of the metabolism more frequent, its clinical representation in children not treated can be severe, sometimes mortal; its diagnostic is relatively simple and its treatment is very easy and effective. Hence, in last years new biosensors design for galactose determination based on galactose oxidase has been proposed. The aim of this work consists of the immobilization of galactose oxidase (GlOx) in polyacrylamide microparticles, using the concentrated emulsion method, and their use as biological material of a new amperometric biosensor for galactose determination. For preparing the galactose biosensors, microparticles with galactose oxidase were deposited on the surface of a platinum electrode and covered with a dialysis membrane. Microparticles were characterized by a Galai Cis-1 particle analyzer system, scanning electron microscopy, X-rays diffraction and differential scanning calorimetry. The presence of galactose oxidase decreases the transition temperature (Tg) of the polyacrylamide microgels. The influence of several experimental factors, such as crosslinking content, pH and temperature, on the biosensor response was investigated. The optimal performance of the biosensor takes place for a cross-linking of 7.0%, 40ºC and pH 7.0. The proposed immobilization system almost does not modify the enzyme activity, but seems to protect to the enzyme because an increase of the temperature range in which the enzyme is active is observed