Electrochemical determination of gallic acid in food matrices using novel materials.

Gallic acid (GA), as an endogenous polyphenol, has shown many different important properties that have influenced its use in the food and pharmaceutical industry. These properties include its antioxidant, anti-cancer, anti-tumor, anti-HIV and anti-ulcerogenic activities. The most commonly used GA determination techniques have been the spectrophotometric and chromatographic techniques. However, these techniques have shown some drawbacks; they are expensive, labour intensive, time-consuming and are not suitable for in-situ measurements. Electrochemical methods using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at inert glassy carbon electrode (GCE) or carbon paste electrodes (CPE) have also been used in the determination of GA. However, despite their easy application and fast result generation, their sensitivity and selectivity have been relatively inadequate for the analysis of GA found in beverages and pharmaceutical products. The aim of this study is therefore to investigate and develop novel nanomaterials-based electrochemical sensors for determination and analysis of GA that is fast, sensitive, cost-effective and selective. In this study, the detection of GA in red and white wines was achieved using CV, through the development of carbon-based working electrodes modified with graphene oxide nanoparticles and other metal oxide nanoparticles. The synthesised metal oxide nanoparticles were characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and Zetasizer (for particle size analysis). Meanwhile, characterisation of the developed electrodes was carried out using CV, DPV and electrochemical impedance spectroscopy. The electrochemical effects of the electrodes were analysed. This thesis presents the results of a novel graphene oxide nanocolloids-SiO2 nanoparticles combination used for the electrochemical determination of GA. The results show enhanced peak currents, with high sensitivity and selectivity. The anodic peak current was enhanced from 241 µA (for the bare GCE) to 411 µA (for the modified GCE) - with a limit of detection (LOD) of 2.09 x 10-6 mol L-1, within a concentration range of 6.25 x 10-6 to 1.0 x 10-3 mol L-1. The thesis also proposes that there is a synergistic effect between SiO2 nanoparticles and graphene oxide nanocolloids in the determination of GA. Synthesised amorphous zirconium oxide nanoparticles were used for the modification of a carbon paste electrode and used for the determination of GA. The electrode modification enhanced the electrochemical activity of GA, with increased sensitivity and selectivity. The modified electrode produced an enhanced anodic peak from 260 µA (for the bare electrode) to 451 µA (for the modified electrode) - with an LOD of 1.24 x 10-7 mol L-1, within a range of 1 x 10-6 to 1.0 x 1 x 10-3 mol L-1. The thesis additionally makes a novel proposal for the interaction and effect of the amorphous zirconia nanoparticles on the graphite in the CPE. Zinc oxide nanoparticles and cobalt oxide nanoparticles were also used individually for the modification of carbon paste electrodes. The modified electrodes showed an enhanced effect on GA oxidation. This enhanced effect was an increase in anodic peak current from 261 µA to 414 µA, when the CPE was modified. The LOD produced by the ZnO nanoparticles-modified CPE was 1.86 x 10-7 mol L-1, within a concentration range of 1 x 10-3 to 5 x 10-2 mmol L-1. Meanwhile, the effect of scan rate and the effect of pH show that the electrodes were more effective in acidic pH, and that the GA-electrode interaction was an adsorption-controlled process. Cobalt oxide nanoparticles were also synthesised, characterised and used for the modification of CPE. The modified electrode produced an enhanced anodic peak current from 302 µA (for the bare CPE) to 404 µA (for the modified electrode). The LOD of the modified electrode was studied and found to be 1.52 x 10-6 mol L-1, at a concentration range of 1 x 10-4 to 1 x 10-3 mol L-1. The modified electrodes were successfully used for the determination of GA in real samples of red and white wine. Based on the electrochemical activities of the different electrodes made, the Zirconium dioxide nanoparticles-modified carbon paste electrode seems to have produced the best results. The zirconium dioxide-modified CPE showed increased sensitivity and better limit of detection for GA

Dietary Polyphenols and Neuroprotection

As editors of this book our aim was to collect new data from experienced authors in order to further advance the knowledge on the protective effects of polyphenols’ intake, e.g., when included in the human diet, to modulate cellular functions and pathways associated with neurodegenerative diseases.Fruits and vegetables are the richest source of polyphenols in the regular human diet. Most of these molecules possess high antioxidant capacity, as well as several other important activities that can affect human health, among which anti-inflammatory properties and the potential ability to modulate different cell-signalling pathways seem to be the most important. Neurodegenerative diseases are among the main causes of death worldwide and, in most of them like Alzheimer’s or Parkinson’s, neurodegeneration occurs long before the onset of first symptoms, where a large population of brain neurons are already lost. Besides neurons, glial cells like astrocytes and microglia, are involved in oxidative and neuroinflammatory pathological pathways, making them interesting targets for neuroprotective strategies. Polyphenols are promising candidates for those strategies, either as prophylactic substances or as therapeutic molecules.In this book, several research papers and two reviews explore the chemical properties of naturally occurring polyphenols and some new possibilities for the therapeutical and/or prophylactic roles of these molecules on neurodegeneration and neurodegenerative diseases

Rapid separation of phenolic flavourings by liquid chromatography and nanomolar electrochemical detection at a boron-doped diamond electrode

In recent years, there has been considerable research focus on natural plant phenolics. They are present as key contributors to the flavour of food and beverages and are also proven to function as antioxidants, providing a wide range of physiological properties including anti-cancer, anti-inflammatory and anti-microbial. Their investigation and detection in plants, food and beverages require the development of rapid, selective and sensitive analytical methods. In this thesis, an overview of plant secondary metabolites, their classification and physiological properties are given. The characteristics of the boron-doped diamond (BDD) electrode and the coupling of liquid chromatography (LC) with electrochemical detection (ECD) are also described. This work focuses on determining the phenolic analytes that are associated with the distinct flavour of whiskey. Initially, the whiskey is analysed using direct electroanalysis at a Nafion-modified BDD electrode. Inclusion complexation with cyclodextrins (CDs) and peak deconvolution reveals guaiacols, phenols and cresol isomers as the phenolic molecular fingerprint of whiskey. Pre-concentration with Nafion on the electrode surface results in a 5-fold decrease in the limit of detection (LOD) compared to the bare BDD electrode. The electro-oxidation mechanisms of the analytes are also investigated with cyclic voltammetry (CV). To specifically determine the flavour contributing analytes and to differentiate whiskey based on geographical origin, detection at the BDD electrode is preceded by chromatographic separation with a C18 core-shell column. Significantly higher concentrations of the phenolic compounds are determined in Islay whiskey, attributed to its unique production process. The detection limit (S/N = 3) of guaiacol with LC-ECD is 5 nM, 80-fold lower than that obtained with LC-ultraviolet (UV) detection (2 µM). Attention was then turned to the separation and detection of gallic acid (GA) and ellagic acid (EA) in whiskey. GA and EA are present in the oak casks used for maturation and so their presence can be used as markers of authentic whiskey. Chromatographic separation using a reversed-phase (RP) C18 column with gradient elution is followed by amperometric detection at a BDD electrode. LODs of 60 and 200 nM are obtained for GA and EA, respectively, with the highest concentrations of both acids found in a 14-year-old whiskey. Rapid and sensitive analytical methods are required for the detection of spoilage metabolites in the food and beverage manufacturing industries. In beverages, guaiacol may be present as a result of microbial metabolism, resulting in the formation of a medicinal off-odour with subsequent financial implications. LC-ECD at a BDD electrode provides LODs of 10-30 nM for guaiacol and its phenolic precursors. Notably, separation is achieved within 60 s, providing a rapid alternative to traditional microbiological culturing methods. The outcomes presented represent an advancement in the separation and selective sensing of phenolic analytes, and are of importance in the food and beverage sectors

Spectroelectrochemical determination of the antioxidant properties of carpobrotus mellei and carpobrotus quadrifidus natural products

Philosophiae Doctor - PhDSouth African Carpobrotus species have been found to contain hydrolysable tannins,various flavonoids e.g. rutin and hyperoside, phytosterols and aromatic acids which have a diverse range of pharmacological properties including antimicrobial and, antioxidant activities. The main aim of the thesis was to determine the natural products in C. mellei and C. quadrifidus using chromatographic techniques and electrochemical analysis. The antioxidant activity of both Carpobrotus species was determined by using a superoxide dismutase (SOD) biosensor. ESI-LC-MS was used to separate and determine flavonoids in C. mellei and C. quadrifidus. 8 flavonoid compounds: catechin, epicatechin, epicatechin-epicatechin, coumarylquinic acid, isorhamnetin, quercetin-hexose (hyperoside), rutin and myricetin-deoxyhexose were identified. Cyclic and square wave voltammetry were used to detect flavonoids from C. mellei and C. quadrifidus. Catechin was detected in the ethyl acetate extract of C. mellei and C. quadrifidus. The oxidation potential of the plant extracts were observed at +150.6 mV to +1072.6 mV. The oxidation mechanism proceeds in sequential steps, related to the catechol moiety, -OH groups in C ring and the resorcinol group. The oxidation process of the catechol moiety involves a two electron - two proton reversible reaction and forms o-quinone. This occurs first at low potential and is a reversible reaction. The hydroxyl group in the C ring and resorcinol group oxidise there after and undergo an irreversible reaction. UV-vis and FTIR spectroscopy were used to confirm the presence of catechin in the ethyl acetate extract of both plants.UV-visible spectroelectrochemistry confirmed the oxidation process of catechin at constant potential. Since C. mellei and C. quadrifidus were confirmed to contain flavonoids by ESI-LC-MS and electrochemical analysis, the antioxidant activity was further investigated using a SOD biosensor. The superoxide dismutase (SOD) enzyme was immobilised with 1% Nafion on a platinum electrode. Detection limit and sensitivity of the SOD biosensor were found to be 0.03918 μmol L-1 and 1.44 μA(μmol L-1)-1, respectively. The results showed that C. mellei and C. quadrifidus have antioxidant activity, with relative antioxidant capacity (RAC) of 24% and 42%, respectively. May 200

Novel nanomaterials for lab on chip devices development: application to food system and their effect on the oxidative stress in cell cultures

This Doctoral Thesis has been formed in two well-defined areas within the field of design and development of electrochemical sensors, using nanomaterials with high analytical performance in terms of sensitivity, selectivity and reproducibility. On the one hand, the properties of transition metal chalcogenides as new nanomaterials were explored with the aim of developing new high-performance electrochemical sensors. The transition metal chalcogenides are formed by triatomic sheets with the general formula MX2, where M is a transition metal and X is a chalcogenide (S, Se or Te) and where, in turn, M is arranged in a plane surrounded by two others of X linked by covalent bonds. Each of these sheets is held by Van der Waarls forces, facilitating their exfoliation in individual layers by simple methods. First, the ultrasound-assisted exfoliation of transition metals of group VI (MoS2, WS2, MoSe2 and WSe2) was carried out. Subsequently, they were characterized by scanning electron microscopy, Raman spectroscopy, and electrochemical techniques. Next, the electrocatalytic properties of these nanomaterials in the oxidation of polyphenolic compounds, chosen for this purpose for their high antioxidant capacity, were studied. These nanomaterials demonstrated excellent resistance to sensor passivation, one of the limiting factors in the application of electrochemical techniques in the analysis of complex samples. Ultimately, its analytical application to the determination of endogenous polyphenolic compounds in complex food matrices was demonstrated. On the other hand, electrochemical sensors were developed for the in-situ detection of hydrogen peroxide in cell cultures as a marker of oxidative stress. To this end, electrodes based on high-performance nanomaterials were designed and developed aimed at electrochemical sensitivity and selectivity (Carbon Black and Prussian Blue) for the selective detection and quantification of hydrogen peroxide in a cellular model of Parkison's disease. Likewise, an on-chip platform with similar analytical performance was developed to develop cell cultures, detect hydrogen peroxide under conditions of oxidative stress, as well as evaluate the antioxidant effect of exogenous polyphenolic compounds on oxidative stress levels

Novel nanomaterials for lab on chip devices development: application to food system and their effect on the oxidative stress in cell cultures

Esta Tesis Doctoral se ha configurado en dos áreas bien definidas dentro del ámbito del diseño y desarrollo de sensores electroquímicos, empleando nanomateriales con altas prestaciones analíticas en términos de sensibilidad, selectividad y reproducibilidad. Por una parte, se exploraron las propiedades de los calcogenuros de metales de transición como nuevos nanomateriales con el objetivo de desarrollar nuevos sensores electroquímicos de altas prestaciones. Los calcogenuros de metales de transición están formados por láminas triatómicas con fórmula general MX2, donde M es un metal de transición y X un calcogenuro (S, Se o Te) y donde a su vez M se dispone en un plano rodeado por otros dos de X unidos mediante enlaces covalentes. Cada una de estas láminas se encuentran unidas mediante fuerzas de Van der Waarls, facilitando su exfoliación en capas individuales mediante métodos sencillos. En primer lugar, se llevó a cabo la exfoliación asistida por ultrasonidos de metales de transición del grupo VI (MoS2, WS2, MoSe2 y WSe2). Posteriormente, se caracterizaron mediante microscopía electrónica de barrido, espectroscopía Raman y técnicas electroquímicas. Seguidamente, se estudiaron las capacidades electrocatalíticas de estos nanomateriales en la oxidación de compuestos polifenólicos, elegidos para tal fin por su elevada capacidad antioxidante. Estos nanomateriales, demostraron una excelente resistencia a la pasivación del sensor, uno de los factores limitantes de la aplicación de las técnicas electroquímicas en el análisis de muestras complejas, constituyendo este hallazgo uno de los resultados más relevantes obtenidos. En último término, se demostró su aplicación analítica a la determinación de compuestos polifenólicos endógenos en matrices complejas de alimentos. Por otra parte, se desarrollaron sensores electroquímicos para la detección in-situ de peróxido de hidrógeno en cultivos celulares como marcador de estrés oxidativo. Para ello, se diseñaron y desarrollaron electrodos basados en nanomateriales de altas prestaciones dirigidos a la sensibilidad y selectividad electroquímicas (Carbon Black y Prussian Blue) para la detección y cuantificación selectiva de peróxido de hidrógeno en un modelo celular de enfermedad de Parkison. Asimismo, se desarrolló una plataforma on-chip con prestaciones analíticas similares para desarrollar cultivos celulares, detectar peróxido de hidrógeno en condiciones de estrés oxidativo, así como evaluar el efecto antioxidante de compuestos polifenólicos exógenos en los niveles de estrés oxidativo

NANOFIBERS: TAILOR-MADE APPLICATIONS FOR THE FOOD AND BEVERAGE INDUSTRY

Attualmente, l\u2019industria alimentare, per meglio rispondere alle attese dei consumatori, diversifica l\u2019offerta con nuovi prodotti alimentari, risultato della continua ricerca e dell\u2019innovazione tecnologica. L\u2019applicazione di nuovi processi di produzione e l\u2019impiego di materiali innovativi, hanno aumentato la variet\ue0 di alimenti disponibili e apportato dei miglioramenti rivelandosi molto promettenti per la futura produzione alimentare. In particolare, le nanotecnologie forniscono materiali quali nanoparticelle, nanoemulsioni, membrane porose, ecc., capaci di migliorare alcune delle principali operazioni unitarie quali la filtrazione, il packaging, i sistemi di controllo analitico nonch\ue9 alcune delle caratteristiche dei prodotti quali la stabilit\ue0, il sapore, l\u2019aroma, ecc. Tra le diverse forme di nanostrutture, particolare attenzione hanno ricevuto i materiali nanofibrosi, sviluppati mediante la tecnica di elettrofilatura (electrospinning). Questa tecnica, consente di produrre a partire da polimeri biologici e sintetici membrane nanostrutturate caratterizzate da un elevato rapporto superficie/massa, una elevata porosit\ue0 e resistenza meccanica. I materiali nanofibrosi possono combinare i vantaggi dei nanomateriali particolati come le nanoparticelle, con quelli dei laminati polimerici come film o membrane. In questa tesi si sono studiate le potenzialit\ue0 delle nanofibre in tre campi di applicazioni alimentari: (i) sensori destinati al controllo di qualit\ue0 degli alimenti, (ii) sistemi di incapsulamento/rilascio per la formulazione di ingredienti attivi o materiali di packaging e (iii) membrane di separazione per il filtraggio di bevande. La strategia metodologica seguita ha utilizzato un approccio ready-to-use e non proof-of-concept, con campioni, materiali e condizioni operative, il pi\uf9 possibile reali. Di conseguenza la tesi \ue8 stata strutturata in tre capitoli, corrispondenti ai campi di applicazioni sopra elencati. In particolare il capitolo 1, descrive l\u2019applicazione delle membrane nanofibrose poliammidiche per aumentare la selettivit\ue0 e specificit\ue0 di sensori elettrochimici usati per l\u2019analisi di matrici alimentari anche complesse. Il capitolo 2, esplora l\u2019utilizzo delle nanofibre per incapsulare e rilasciare in modo controllato specie chimiche bioattive (quali composti fenolici antiossidanti e composti volatili antimicrobici). Infine, il capitolo 3 studia l\u2019impiego delle membrane nanostrutturate per filtrare bevande (quali succo di mela) e per rimuovere selettivamente i suoi polifenoli amari. Ognuna delle applicazioni specifiche rappresenta un contributo scientifico distinto ed \ue8 un singolo risultato della tesi.The increasing demand for food that are more nutritious, safe, affordable, pleasant and healthy is the driving force of product and process innovation in the food and beverage industry. Nanotechnology offers a way to meet such demands through the design of materials that are able to improve the performance in some of the most relevant operations of this industry (such as filtration, preservation and quality control), as well as some important characteristics of the products (such as stability, flavour, nutritional quality, etc.). Among the nanomaterials developed for practical purposes, electrospun nanofibrous materials, produced from synthetic and bio- polymers have received great attention by virtue of their fabrication simplicity through the electrospinning technique and their special nano-related features that include large surface-to-mass ratio, very high porosity, enhanced mechanical resistance and improved responsive capacity to changes in the surrounding atmosphere compared to conventional configurations of the same polymer or polymer blend. Nanofibrous materials can combine the advantages of particulate nanomaterials like nanoparticles with the advantages of polymeric laminate materials like films or membranes. In this thesis, we will demonstrate the potentialities of nanofibers in three spheres of food-related applications: (i) sensors aimed at food quality control, (ii) as encapsulation/release systems for active ingredients or packaging materials and (iii) as separation membranes for beverage filtration. The methodological strategy that will be followed, intends to be as close as possible to the ready-to-use approach, rather than to the proof-of-concept study, by using more realistic samples, materials and testing conditions. The thesis is thus structured in three chapters, each one devoted to the above mentioned technological sphere. In particular, chapter 1 will investigate the application of polyamidic nanofibrous membranes for increasing selectivity and specificity in electrochemical sensing of complex foodstuffs. Chapter 2 will explore the use of nanofibers for encapsulation and controlled release of bioactive chemical species (such as antioxidant phenolic compounds and antimicrobial volatiles). Finally, chapter 3 will descrive the use of nanostructured membranes for the filtration of beverages (in particular of apple juice) and for selectively removing bitter polyphenols. Every tailor-made application developed represents a separate scientific contribution and is an individual deliverable of the thesis

Nuevas estrategias electrocinéticas y nuevas aportaciones a la detección electroquímica en microchips de electroforesis capilar basadas en el empleo de nanotubos de carbono y otras nanoestructuras

Premio Extraordinario de Doctorado 2012El trabajo se ha centrado en la exploración de las posibilidades analíticas de los microchips de electroforesis capilar con detección electroquímica (microEC-DE) en el campo alimentario y, de una manera más concreta, en el análisis de alimentos funcionales que tanto interés suscita en la industria alimentaría. Antioxidantes naturales (polifenoles), vitaminas e isoflavonas han sido determinados en una gran variedad de alimentos y suplementos dietéticos debido a sus beneficios para nuestra salud (propiedades anticarcenogénicas y protectoras contra distintas enfermedades). El trabajo desarrollado estos cuatro años se puede dividir en dos grandes bloques; el primero, que corresponde al desarrollo de metodologías que mejoraran el análisis alimentario mediante el uso del microEC-DE proponiéndose un nuevo concepto denominado "calibración integrada" con el cual se mejoró tanto el rendimiento analítico como la precisión y exactitud del método y, un segundo bloque, que consistió en la exploración del uso de nanomateriales (nanotubos de carbono y nanohilos) como detectores electroquímicos en el sistema microfluídico dando lugar a enormes mejoras en los límites de detección y en la eficacia de la separación electroforética

Preparation, Physico-Chemical Properties and Biomedical Applications of Nanoparticles

Nowadays, the impact of nanotechnology on applications in medicine and biomedical sciences has broader societal and economic effects, enhancing awareness of the business, regulatory, and administrative aspects of medical applications. The selected papers included in the present Special Issue gives readers a critical, balanced and realistic evaluation of existing nanomedicine developments and future prospects, allowing practitioners to plan and make decisions.The topics of this book covers the use of nanoparticles and nanotechnology in medical applications including biomaterials for tissue regeneration, diagnosis and monitoring, surgery, prosthetics, drug delivery systems, nanocarriers, and wound dressing. I would like to express my gratitude to all contributors to this issue, who have given so much of their time and effort to help create this collection of high quality papers

Phenolic Compounds: Extraction, Optimization, Identification and Applications in Food Industry

Interest has grown regarding natural plant extracts in food and beverage applications, their vital role in the food industry, and their therapeutic use against diseases. The protective effects of healthy diets are partially due to the variety of plant metabolites, particularly phenolic compounds, which are considered the most important class of compounds that originates from plant-derived metabolites. Phenolics are well renowned for their possession of a wide array of remarkable biological properties. This Special Issue (SI) aims to gather the most recent contributions concerning their chemistry, extraction methods, and analytical techniques, applications, and biological activities. This Special Issue of Processes, entitled “Phenolic Compounds: Extraction, Optimization, Identification and Applications in Food Industry”, gathers the recent work of leading researchers in a single collection, covering a variety of theoretical studies and experimental applications and focusing on the extraction, identification, and industrial applications. The advances presented in the contributions in this SI have significantly helped to accomplish this target. In addition to research articles, the Special Issue features two reviews that cover a range of topics highlighting the versatility of the area. The topics covered in this SI include advanced methodologies for the isolation, purification, and analysis of phenolics from food, food waste, and medicinal plants; biological activities and mechanisms of action; health benefits from in vivo evaluation; and the development of novel phenolics-based nutraceuticals and functional ingredients