Alberto Escarpa

Approach to the content of total extractable phenolic compounds from different food samples by comparison of chromatographic and spectrophotometric methods

A new approach to the error sources in the spectrophotometric determination of total phenols in foods has been performed. The choice of the suitable phenolic standard and the influence of sugars and proteins as interfering compounds were carefully studied. The results obtained by the spectrophotometric method were compared with those found from the chromatographic method which was taken as reference method because it was free of interferences. The spectrophotometric method overestimates the phenolic content except in some fruit samples with a high polyphenolic content. Sugars did not show interference whereas protein showed a high influence on the total phenols at the concentration ranges found in the extracts. In green bean samples both methods gave the same total phenols when the interference was masked. This fact could constitute an useful way to find the real content of phenolics in foods.

High-performance liquid chromatography with diode-array detection for the determination of phenolic compounds in peel and pulp from different apple varieties

Quantitative analysis of phenolic compounds from four apple varieties (Golden and Red Delicious, Granny Smith and Green Reineta) using high-performance liquid chromatography with diode-array detection was carried out. For each variety, both peel and pulp were analysed. The identification of phenolic compounds was made by comparing their retention times and UV spectra with those of standards. The results revealed differences between pulp and peel in all cases studied. The highest levels of phenolic compounds were found in the peel. High levels of catechins and flavonol glycosides, especially rutin, were found in apple peels. Chlorogenic acid was the major peak in the pulp for all apple varieties studied except for Granny Smith. Significant quantitative differences between the apple varieties were also found, the Golden Delicious variety showing the lowest content of phenolic compounds and Green Reineta variety the highest. The recovery of phenolic compounds from both peel and pulp was measured in all apple varieties. The values ranged between 95 and 105%, indicating close to quantitative recovery for the method used.

Sensing colorimetric approaches based on gold and silver nanoparticles aggregation: Chemical creativity behind the assay. A review

Localized surface plasmon resonance (LSPR) is one of the most remarkable features of gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs). Due to these inherent optical properties, colloidal solutions of Au and Ag NPs have high extinction coefficients and different colour in the visible region of the spectrum when they are well-spaced in comparison with when they are aggregated. Therefore, a well-designed chemical interaction between the analyte and NPs surroundings leads to a change of colour (red to blue for Au NPs and yellow to brown for Ag NPs from well-spaced to aggregated ones, respectively) allowing the visual detection of the target analyte. These approaches have exhibited an excellent analytical performance with high sensitivities due to the strong LSPR and excellent selectivity strategically driven by the interaction analyte-NPs surroundings involving mainly electrostatic and hydrogen bond interactions as well as donor-acceptor chemical reactions, among others. In addition, this kind of colorimetric assays has received considerable attention in the analytical field because of their simplicity and low cost since they do not require any expensive or complex instrumentation. As a consequence of this, detection of molecules with a high significance in the bio-medical, clinical, food safety and environmental fields including DNA, proteins and a wide spectrum of organic molecules as well as inorganic ions have been impressively reported in the most relevant literature using these assays. This timely review offers a rational vision of the main achievements yielded in the relevant literature according to this exciting and creative analytical field.

Superhydrophobic Alkanethiol-Coated Microsubmarines for Effective Removal of Oil

We demonstrate the use of artificial nanomachines for effective interaction, capture, transport, and removal of oil droplets. The simple nanomachine-enabled oil collection method is based on modifying microtube engines with a superhydrophobic layer able to adsorb oil by means of its strong adhesion to a long chain of self-assembled monolayers (SAMs) of alkanethiols created on the rough gold outer surface of the device. The resultant SAM-coated Au/Ni/PEDOT/Pt microsubmarine displays continuous interaction with large oil droplets and is capable of loading and transporting multiple small oil droplets. The influence of the alkanethiol chain length, polarity, and head functional group and hence of the surface hydrophobicity upon the oil-nanomotor interaction and the propulsion is examined. No such oil-motor interactions were observed in control experiments involving both unmodified microengines and microengines coated with SAM layers containing a polar terminal group. These results demonstrate that such SAM-Au/Ni/PEDOT/Pt micromachines can be useful for a facile, rapid, and efficient collection of oils in water samples, which can be potentially exploited for other water-oil separation systems. The integration of oil-sorption properties into self-propelled microengines holds great promise for the remediation of oil-contaminated water samples and for the isolation of other hydrophobic targets, such as drugs.

Micromotor‐Based High‐Yielding Fast Oxidative Detoxification of Chemical Threats

Rapid field conversion of chemical weapons into non-toxic products is one of the most challenging tasks in weapons of mass destruction (WMD) science. This is particularly the case for eliminating stockpiles of chemical warfare agents (CWAs) in remote storage field locations, where the use of large quantities of decontaminating reagents, long reaction times, and controlled mechanical agitation is impossible or undesired. New efficient “clean” technologies and (bio)chemical processes are thus sought for detoxifying stored agents, counteracting nerve-agent attacks, and decommissioning chemical weapons. Environmentally friendly solutions of hydrogen peroxide, combined with suitable activators (e.g., bicarbonate), have been shown to be extremely useful for decontaminating a broad spectrum of CWAs to yield nontoxic products. These peroxide-based systems, which rely on the in situ generation of OOH nucleophiles, have recently replaced chlorine-based bleaching processes, which produce undesirable products, and have thus led to effective decontamination of the chemical agents GB (Sarin, isopropyl methylphosphonofluoridate), VX ((S)-[2-(diisopropylamino)ethyl] O-ethyl methylphosphonothioate), GD (Soman, pinacolyl methylphosphonofluoridate), and HD (sulfur mustard). Yet, such an oxidative treatment commonly requires high peroxide concentrations (20–30%; approaching a stoichiometry of 1:50), along with prolonged operation and/or mechanical agitation. Such reaction conditions are not suitable or not desired for eliminating stockpiles of CWAs in remote field settings or hostile storage locations, as large quantities of the reagents may not be transportable on military aircrafts and require special packaging and handling. The efficient elimination of chemical-weapon stockpiles in field locations thus remains a major challenge to the chemistry and defense communities. Herein, we describe a powerful strategy that is based on self-propelled micromotors, for a high-yielding accelerated oxidative decontamination of chemical threats using low peroxide levels and no external agitation. Functionalized synthetic micromotors have recently demonstrated remarkable capabilities in terms of isolation and transport for diverse biomedical and environmental applications, but not in connection to increasing the yield and speed of chemical reactions. The new motor-based method relies on the use of peroxide-driven microtubular engines for the efficient selfmixing of a remediation solution, which dramatically accelerates the decontamination process. Fluid mixing is extremely important for enhancing the yield and speed of a wide range of chemical processes, including decontamination reactions, where quiescent conditions lead to low reaction efficiency and long operations. The observed mixing, which is induced by the peroxide-driven micromotor, is analogous to that reported for the motility of E. coli bacteria, where a large-scale collective motion has been shown to enhance diffusion processes. Enhanced diffusion of passive tracers has also been observed in the presence of catalytic nanowire motors. Although the new micromotor strategy presented herein was applied to the accelerated, high-yielding, and simplified decontamination of organophosphate (OP) nerve agents, the concept could have broad implications for enhancing the efficiency and speed of a wide range of chemical processes in the absence of external agitation. The concept of the micromotor/peroxide-based decontamination of chemical threats is illustrated in Figure 1. This new strategy relies on micromotors without mechanical stirring (Figure 1A). A known number of micromotors were placed in a nerve-agent-contaminated solution, along with hydrogen peroxide (used as the oxidizing agent as well as the micromotor fuel), the peroxide activator (NaHCO3 or NaOH), and the surfactant sodium cholate (NaCh), which was essential for bubble generation. The oxidative conversion of the OP nerve agent into para-nitrophenol (p-NP) was achieved under mild quiescent conditions that involve the in situ generation of OOH nucleophiles with no external stirring (Figure 1B). The decrease in concentration of the OP [*] Dr. J. Orozco, G. Cheng, D. Vilela, Dr. S. Sattayasamitsathit, Prof. R. Vazquez-Duhalt, Dr. G. Vald s-Ram rez, Dr. O. S. Pak, Prof. J. Wang Departments of Nanoengineering and Mechanical Engineering University of California San Diego La Jolla, CA 92093 (USA) E-mail: josephwang@ucsd.edu G. Cheng, Prof. C. Kan Tsinghua University, Beijing, 100084 (China) D. Vilela, Prof. A. Escarpa University of Alcal 28871 Alcal de Henares (Spain)

Optimization strategy and validation of one chromatographic method as approach to determine the phenolic compounds from different sources

We have designed a novel working strategy to optimize a unique chromatographic method consisting of diode array detection for the analysis of the most representative phenolic compounds from different food sources. The simultaneous inclusion of standard phenolic compounds, phenolic compounds isolated from food sources and representative real extracts as an ultimate test in analysis has allowed to establish, for the first time, a unique liquid gradient to serve as an excellent medium for the investigation of phenolics in samples from different food sources. Under the optimized conditions, 21 commercially available phenolic compounds and 25 commercially unavailable phenolic structures were analyzed in less than 30 min. The chromatographic method was designed as an alternative for the provisional identification of these compounds before their full characterization. The optimized chromatographic method was carefully validated for precision and accuracy. A high reproducibility in the retention time (<2%), peak area and calibration slope (<5%) as well as recoveries higher than 95% were obtained in all cases. Consequently, the currently described method was successfully employed to study the phenolic compounds in the most representative food samples.

Nanomaterials as electrochemical detectors in microfluidics and CE: Fundamentals, designs, and applications

The different approaches for constructing nanomaterial‐based detectors for conventional CE and microchip electrophoresis are described in this review. They include three main types of nanomaterials, including carbon nanotubes, nanoparticles, and nanorods in various designs. The fundamental reasons for the enhanced detection performance of nanomaterial‐based detectors, such as higher sensitivity, improved limits of detection, and higher peak capacity, are discussed in detail. Various applications for biomedical, food, and environmental analyses are reviewed.

An approach to the influence of nutrients and other food constituents on resistant starch formation

The influence of nutrients and other food constituents, such as dietary fibre components, catechin and phytic acid, on resistant starch (RS) formation was systematically investigated. This investigation was carried out under standardized gelatinization conditions by using a high pressure autoclave (HPA). Except for insoluble dietary fibre constituents (cellulose and lignin), all the tested food ingredients reduced the formation of RS. Calcium ions, potassium ions and catechin showed the highest reduction of RS formation, while the nutrients studied (albumin, olive oil and sucrose) as well as phytic acid affected it to a lesser extent. These results were not significantly changed by varying amounts of the studied dietary components.

Fast separation of (poly)phenolic compounds from apples and pears by high-performance liquid chromatography with diode-array detection.

Polyphenolic compounds in apples and pears were analysed by HPLC on C18-modified silica. Gradient elution with phosphoric acid-methanol mixtures and phosphoric acid-acetonitrile mixtures gave complete separation of all polyphenolics of interest. The use of methanol as modifier was preferred because it provides a more rapid separation (20 min). Diode-array detection was used for the provisional identification of polyphenolic compounds not available as standards.

Microchips for CE: Breakthroughs in real-world food analysis

The well‐known complexity of food matrices is approached using CE microchips with different strategies to improve the selectivity and sensitivity of the analysis by avoiding and/or making the sample preparation as simple as possible: (i) enhancing the peak capacity in order to perform direct injection, (ii) using the microchip platform to measure one target analyte/group of analytes with or without separating other related interferences, (iii) integrating sample preparation steps on the microchip platform, and (iv) integrating new analytical tools from nanotechnology in the detection stage. New analyte separations of food significance involving DNA probes, biogenic amines, vanilla flavors, and dyes have been reported as successfully breaking new barriers in areas of high impact in the market, such as transgenic food analysis, as well as the detection of frauds and toxins. Simple microchip layouts are still the most common designs used, though sophisticated new ones are emerging. In contrast to other application areas, electrochemical detection continues to be the most common detection route, followed by LIF, though non‐conventional detection routes are also emerging, such as chemiluminescence or UV. In terms of analytical performance, the integration of calibration and quality control on a microchip platform, and remarkable accuracy and precision are being obtained using creative analytical methodologies that enhance the analytical potency of microfluidic chips for their future commercialization. This review critically states the most important advances derived from work done in the field over the past 2–3 years.