Complex Food Samples Research Articles

A Novel Magnetic Molecular Imprinted Polymer for Selective Extraction of Zearalenone from Cereal Flours before Liquid Chromatography-Tandem Mass Spectrometry Determination.

Zearalenone (ZEN) is a nonsteroidal estrogenic mycotoxin produced by various Fusarium species and commonly occurring in corn and other cereals. Even though its acute toxicity is low, still the estrogenic activity of ZEN and metabolites is a matter of concern. In this work, a new magnetic molecularly imprinted polymer (mMIP) for the selective extraction of ZEN from cereal flours is presented. The mMIP was synthesized previously using quercetin as dummy template, and here we wanted to test its applicability to complex food samples. Analyte determination was carried out by high-performance liquid chromatography coupled to tandem mass spectrometry. The selectivity of the mMIP and the main validation method parameters were assessed. In particular, even in samples as complex as cereals, matrix effect was negligible. Although the mMIP showed cross-selectivity towards both ZEN-related and quercetin-related compounds, nonetheless ZEN recovery was > 95% for the two lower spiking levels, and the quantification limit was 0.14 ng g−1, i.e., ca. 500 times lower than the maximum limit fixed for most cereals by European law. Therefore, the material, also in comparison with a commercial sorbent, appears suitable for the application in food analysis, also to isolate ZEN at trace levels.

Interlaboratory studies on chlorinated paraffins: Evaluation of different methods for food matrices

Short-chained chlorinated paraffins (SCCP) and medium-chained chlorinated paraffins (MCCPs) are two of the main groups currently used to classify chlorinated paraffins (CPs). Since only SCCPs have been restricted by the Stockholm Convention, a robust but selective analysis with comparable results especially for SCCPs, but also for all other CPs is needed to ensure official controls to enforce future resulting food legislation. Failing that, expansion of the legislation towards total CP or to include MCCPs and other main groups needs to be considered. A survey taken amongst official and private laboratories in the EU and beyond revealed a large variety of methods currently in use or in planning stages for CP analysis. In June 2017, spiked samples of coconut fat were sent to 27 registered participants from 18 countries for an interlaboratory study. In July 2018, lard samples spiked with CPs, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were sent to 13 registered participants from 11 countries. In both cases, more than 55% of participants had a satisfactory overall performance (AZ2<3, σ = 25%). The greatest challenge seemed to be correct quantification of SCCP and MCCP mixtures, hinting at future problems with the through biodegradation much more complex food samples. Of the wide variety of methods being used, GC-MS based methods were favoured. Both HRMS and LRMS methods were able to perform satisfactorily. Identified influencing factors included choice of instrument, choice of standards and data processing strategy. These factors need to be further investigated in future interlaboratory studies.

Sensitive analysis of trace macrolide antibiotics in complex food samples by ambient mass spectrometry with molecularly imprinted polymer-coated wooden tips

In this article, an ambient mass spectrometric method with molecularly imprinted polymer (MIP)-coated wooden tips was developed for sensitive analysis of trace macrolide antibiotics in complex food samples. A novel solid-phase microextraction (SPME) probe was prepared, via the modification of a layer MIP coating (with roxithromycin as template molecule) on the surface of wooden tips. The obtained MIP-coated wooden-tip SPME probe can be applied directly to enrich trace macrolide antibiotics from complex food samples, with enrichment factors of 244–1604, 72–370, and 12–82 folds for analysis of five investigated macrolide antibiotics in drinking water, honey, and milk samples, respectively. After extraction, a high voltage and some spray solvent were applied on the loaded SPME probe to desorb and ionize analytes enriched on the probe surface for electrospray ionization mass spectrometric (ESI-MS) analysis under ambient and open-air conditions. The method showed good linearity, with correlation coefficient values (r2) no less than 0.9904, and the calibration function was verified via Mandel's fitting test (p > 0.063). The limits of detection were in the range of 0.003–0.05, 1.1–5.1, and 1.9–15.8 ng/g for analysis of drinking water, honey, and milk samples, respectively. Recoveries of the five targeted macrolide antibiotics in honey and milk samples ranged from 73.4% to 98.1%, with the standard deviations no higher than 8.6%. As a result, MIP-coated wooden-tip ESI-MS method could be feasibly used as a sensitive method for determination of trace macrolide antibiotics in complex food samples.

Recent trends in analytical methods for water-soluble vitamins

In this review, recent advances in the analysis of water-soluble vitamins (WSVs) have been reported considering the advantages and disadvantages of various extraction, separation and detection techniques, commonly used for their quantification. Acid hydrolysis, enzyme treatment, SPE based methods and some other extraction methods have been discussed. Particular attention has been devoted to the analytical techniques based on liquid chromatography and electrophoresis. Furthermore, suitability and selectivity of hydrophilic interaction liquid chromatography (HILIC) for WSVs has been discussed in detail. Problems related to these techniques and their possible solutions have also been considered. Special focus has been given to the applications of liquid chromatography (since 2014-2019) for the simultaneous analysis of WSVs and their homologous in complex food samples.

One-step membrane protected micro-solid-phase extraction and derivatization coupling to high-performance liquid chromatography for selective determination of aliphatic aldehydes in cosmetics and food

Aliphatic aldehyde is a type of important organic material and precursor. However, some of them have been proved danger or harmful to health, especially those are occurred in food and cosmetics. Here, we reported a rapid and efficiency one-step membrane protected micro-solid-phase extraction and derivatization (μ-SPE-D) method for selectively determination of trace aliphatic aldehydes in complex cosmetic and food samples by coupling to high-performance liquid chromatography (HPLC). In this method, one-step extraction and derivatization strategy reduced the sample preparation time; membrane protected solid-phase extraction technology eliminated matrix interference; and the efficient sorbent mono-(6-(diethylenetriamine)-6-deoxy)-beta-cyclodextrin- ploy(styrene-divinylbenzene-methacrylic acid) (NH2-β-CD-Poly(St-DVB-MAA)) guaranteed the selective adsorption of aliphatic aldehydes. The sorbent, NH2-β-CD-Poly(St-DVB-MAA), was prepared via chemical fabrication and optimized carefully. The μ-SPE device, and extraction and derivatization conditions were optimized. The mechanism of extraction and derivatization was also discussed. While coupling to HPLC, the method detection limits were as low as 0.024–2.5 μg/L, and the method quantification limits were 0.081–7.6 μg/L with relative standard deviations (RSDs) in the range of 2.2–7.7%. Finally, this membrane protected μ-SPE-D-HPLC was successfully applied to the real sample analysis. In cosmetics analysis, aliphatic aldehydes were found and quantified in the range of 9.0–750.2 μg/kg, and the recoveries were in the range of 81.7–114.9% with RSDs less than 8.3% from toner and moisturizer samples. Meanwhile, aliphatic aldehydes were found and quantified in the range of 1.3–31.3 μg/kg, and the recoveries were in the range of 80.8–114.4% with RSDs less than 7.1% from fried food samples. Our results proved that only 5 min was needed for extraction and derivatization processes. Furthermore, the method detection limits of formaldehyde were an order of magnitude less than literature reports which reveal excellent selectivity of this membrane protected μ-SPE-D-HPLC method.

Rapid determination of kappa-carrageenan using a biosensor from immobilized Pseudomonas carrageenovora cells.

A potentiometric whole cell biosensor based on immobilized marine bacterium, Pseudomonas carrageenovora producing κ-carrageenase and glycosulfatase enzymes for specific and direct determination of κ-carrageenan, is described. The bacterial cells were immobilized on the self-plasticized hydrogen ion (H+)-selective acrylic membrane electrode surface to form a catalytic layer. Hydrogen ionophore I was incorporated in the poly(n-butyl acrylate) [poly(nBA)] as a pH ionophore. Catalytic decomposition of κ-carrageenan by the bienzymatic cascade reaction produced neoagarobiose, an inorganic sulfate ion and a proton. The latter was detectable by H+ ion transducer for indirect potentiometric quantification of κ-carrageenan concentration. The use of a disposable screen-printed Ag/AgCl electrode (SPE) provided no cleaning requirement and enabled κ-carrageenan detection to be carried out conveniently without cross contamination in a complex food sample. The SPE-based microbial biosensor response was found to be reproducible with high reproducibility and relative standard deviation (RSD) at 2.6% (n = 3). The whole cell biosensor demonstrated a broad dynamic linear response range to κ-carrageenan from 0.2–100 ppm in 20 mM phosphate buffer saline (PBS) at pH 7.5 with a detection limit at 0.05 ppm and a Nernstian sensitivity of 58.78±0.87 mV/decade (R2 = 0.995). The biosensor showed excellent selectivity towards κ-carrageenan compared to other types of carrageenans tested e.g. ι-carrageenan and λ-carrageenan. No pretreatment to the food sample was necessary when the developed whole cell biosensor was employed for direct assay of κ-carrageenan in dairy product.

Detection of viable but nonculturable Vibrio parahaemolyticus in shrimp samples using improved real-time PCR and real-time LAMP methods

Accurate and highly sensitive detection of viable but nonculturable (VBNC) Vibrio parahaemolyticus is crucial for preventing seafood-related outbreaks. The VBNC state may occur due to bacterial susceptibility to cold shock during food storage. Propidium monoazide (PMA) has been widely applied to detect VBNC foodborne pathogens. In this study, we developed and compared real-time PCR (qPCR) and real-time LAMP (qLAMP) methods combined with an improved propidium monoazide (PMAxx) to detect pathogenic VBNC V. parahaemolyticus. The designed primers and probes were determined to be highly selective for V. parahaemolyticus strains. The combined PMAxx-qPCR method, requiring 100 min, demonstrated a quantification limit of 10.5 colony-forming units (CFU)/mL in pure culture and 28 CFU/g in raw shrimp respectively, which were 10-fold lower than the PMAxx-qLAMP method (45min). When testing mixtures containing different ratios of VBNC to dead V. parahaemolyticus, PMAxx-based methods were notably superior at distinguishing between VBNC and dead bacteria when VBNC cell concentrations were low. Therefore, PMAxx is an effective means for improving the detection and quantification of VBNC V. parahaemolyticus by qPCR and qLAMP. Pretreatment with PMAxx was shown to be suitable for detection of VBNC V. parahaemolyticus in complex food samples, including raw shrimp.

Analysis of Selected Endocrine Disrupters Fraction Including Bisphenols Extracted from Daily Products, Food Packaging and Treated Wastewater Using Optimized Solid-Phase Extraction and Temperature-Dependent Inclusion Chromatography.

The aim of this research is to demonstrate the concept and ability for the fast and preliminary screening of complex food and environmental samples for the presence of endocrine disrupters fractions, consisting of low-molecular mass micropollutants, particularly various bisphenols (A, B, C, E, F, S, Z, AF, AP, BP and FL). The developed analytical protocol for this research requires two main steps: (i) optimized solid phase extraction (SPE) for selective isolation, purification and pre-concentration of target fraction, and (ii) selective temperature-dependent inclusion chromatography for samples analysis via a HPLC-UV-VisDAD system using isocratic elution and internal standard quantification approach. The chromatographic experiment revealed that both β-CD and its hydroxypropyl derivative strongly interact with selected bisphenols. This is in contrast to the steroids and PAHs molecules investigated previously, where a strong interaction with β-cyclodextrin was observed. Integrated areas derived from acquired chromatographic profiles for each individual sample were used as the simple classification variable enabling samples comparison. We demonstrated that the proposed analytical protocol allows for fast estimation of EDC fractions in various daily use products, food and environmental samples. The materials of interest were selected due to the presence in surface water ecosystems of their residues, and finally, in raw wastewater including rice bags, plastic bags, cloths, sanitary towels, fish baits and various plastic foils from food products. Treated sewage water released directly to the environment from a municipal treatment plant (Jamno, Koszalin) was also investigated. It has been demonstrated that a whole range of low-molecular mass compounds, which may be detected using UV-Vis detector, can easily be emitted from various in daily use products. The presence of micropollutants in treated wastewater, water ecosystems and plastic waste utilization via technological wastewater treatment processes must be addressed, especially in terms of microplastic-based pollutants acting as endocrine disrupters. It is hoped that the proposed simple analytical protocol will be useful for fast sample classification or selection prior to advanced targeted analysis involving the more accurate quantification of specific analytes using e.g., mass spectrometry detectors.

Zero background and triple-signal amplified fluorescence aptasensor for antibiotics detection in foods

It's important to eliminate matrix interference for accurate detecting antibiotic residues in complex food samples. In this study, we designed a zero-backgrounded fluorescence aptasensor to achieve on-site detection of antibiotic residues, with chloramphenicol (CAP) as representative analyte. Moreover, a three stir-bars assisted target recycling system (TSBTR) was designed to achieve triple signal amplification and increase the sensitivity. The bars included one magnetic stir-bar modified with two kinds of long DNA chains, and two gold stir-bars modified with Y shape-duplex DNA probes respectively. In the presence of CAP, the target could recurrently react with the probes on the bars and replace a large amount of long DNA chains into supernatant. After then, the bars were taken out and SYBR green dye was added to the solution. The dye can specifically intercalate into the duplex structures of DNA chains to emit fluorescence while not emitting a signal in its free state. Under the optimized experimental conditions, a wide linear response range of 5 orders of magnitude from 0.001 ng mL−1 to 10 ng mL−1 was achieved with a detection limit of 0.033 pg mL−1 CAP. The assay was successfully employed to detect CAP in food samples (milk & fish) with consistent results with ELISA's. High selectivity and sensitivity were attributed to the zero background signal and triple signal-amplification strategy. Moreover, the detection time can be shortened to 40 min due to that three signal amplified process can occur simultaneously. The fluorescent aptasensor was also label- and enzyme-free. All these ensure the platform to be rapid, cost-effective, easily-used, and is especially appropriate for detection antibiotics in food safety.

A nanocomposite consisting of graphene oxide, zeolite imidazolate framework 8, and a molecularly imprinted polymer for (multiple) fiber solid phase microextraction of sterol and steroid hormones prior to their quantitation by HPLC.

A method is described for multiple monolithic fiber solid-phase microextraction of five sterol and steroid hormones from complex food samples. A composite was prepared from graphene oxide, a metal-organic framework (ZIF-8) and a molecularly imprinted polymers was deposited on a single thin fiber. Four thin fibers were combined to obtain a fiber bundle. The nanocomposite was characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The parameters affecting the extraction were optimized by Box-Behnken design. Following elution with methanol, the analytes progesterone, testosterone, β-sitosterol, cholesterol and campesterol were quantified via HPLC. Response is linear in the 0.01-1000μgL-1 concentration range, and limits of detection range from 3 to 5ngL-1. The method was successfully applied to the determination of the five analytes in spiked samples of white meat, egg yolks and vegetables. The relative mean recoveries ranged from 95.0% to 101.0%. Graphical abstract Schematic presentation of a monolith molecularly imprinting polymer (MIP) fiber fabrication for solid phase microextraction (SPME) of sterol and steroid hormones. The fiber was synthesis using graphene oxide and metal-organic framework, ZIF-8, composite by imprinting technique and progesterone as template. Four fibers were combined to obtain a fiber bundle. Then, multiple fiber solid-phase microextraction was employed for determination of analytes by coupling with HPLC/UV detection.

Genomically Informed Strain-Specific Recovery of Shiga Toxin–Producing Escherichia coli during Foodborne Illness Outbreak Investigations

Next-generation sequencing plays an important role in the characterization of clinical bacterial isolates for source attribution purposes during investigations of foodborne illness outbreaks. Once an illness cluster and a suspect food vehicle have been identified, food testing is initiated for confirmation and to determine the scope of a contamination event so that the implicated lots may be removed from the marketplace. For biochemically diverse families of pathogens such as Shiga toxin-producing Escherichia coli (STEC), the ability to detect specific strains may be hampered by the lack of a universal selective enrichment approach for their recovery against high levels of background microbiota. The availability of whole genome sequence data for a given outbreak STEC strain prior to commencement of food testing may provide food microbiologists an opportunity to customize selective enrichment techniques favoring the recovery of the outbreak strain. Here we demonstrate the advantages of using the publicly available ResFinder tool in the analysis of STEC model strains belonging to serotypes O111 and O157 to determine antimicrobial resistance traits that can be used in formulating strain-specific enrichment media to enhance recovery of these strains from microbiologically complex food samples. The improved recovery from ground beef of model STEC strains with various antimicrobial resistance profiles was demonstrated using three classes of antibiotics as selective agents, suggesting the universal applicability of this new approach in supporting foodborne illness investigations.

Facile construction of magnetic core-shell covalent organic frameworks as efficient solid-phase extraction adsorbents for highly sensitive determination of sulfonamide residues against complex food sample matrices.

Integration of advanced sample pretreatment techniques, with the involvement of functional nano/micro-materials as adsorbents, is of great importance and value for food-safety precise inspection. For now, the major demands for functional adsorbents are ease of fabrication, fast adsorption and separation performance, low toxicity, robustness, and reusability. In the present work, core–shell structured magnetic covalent organic frameworks (COFs) that employed Fe3O4 microspheres as the magnetic core and TpBD COFs as the adsorption shell have been successfully constructed as efficient solid phase extraction (SPE) adsorbents for complex food sample analysis. In favor of the combination of magnetic separation and effective preconcentration, the proposed magnetic COF-SPE method gave a rapid detection performance of the simultaneous detection of ten sulfonamide residues as well as high sensitivity, with detection limits in the range of 0.28–1.45 μg L−1 under the optimized experimental conditions. The Fe3O4@TpBD core–shell adsorbents also demonstrated good stability, robust SPE preconcentration ability, excellent determination recovery, and good reusability. The applicability of the developed SPE method was well demonstrated by real sample analysis, with the recoveries ranging from 82–94%. Through this example, it was believed that the new emerging porous nano/micro-materials, like COFs, metal–organic networks, or hybrid structures, would play more and more important roles as functional materials in food-safety inspection, especially for highly efficient determination of targets against complicated food sample matrices.

Nanochannel-Confined Graphene Quantum Dots for Ultrasensitive Electrochemical Analysis of Complex Samples.

Herein, we present an electrochemical sensing platform based on nanochannel-confined graphene quantum dots (GQDs) that is able to detect a spectrum of small analytes in complex samples with high sensitivity. Vertically ordered mesoporous silica-nanochannel film (VMSF) is decorated on the supporting electrode, conferring the electrode with excellent antifouling and anti-interference properties through steric exclusion and electrostatic repulsion. The synthesized GQDs with different functionalities are confined in the nanochannels of VMSF through electrophoresis, serving as the recognition element and signal amplifier. Without the usual need of tedious pretreatment, ultrasensitive and fast detection of Hg2+, Cu2+, and Cd2+ (with limits of detection (LOD) of 9.8 pM, 8.3 pM, and 4.3 nM, respectively) and dopamine (LOD of 120 nM) in complex food (Hg2+-contaminated seafood), environmental (soil-leaching solution), and biological (serum) samples are realized as proof-of-concept demonstrations.

A Fluidic Device for Immunomagnetic Separation of Foodborne Bacteria Using Self-Assembled Magnetic Nanoparticle Chains.

Immunomagnetic separation has been widely used for the separation and concentration of foodborne pathogens from complex food samples, however it can only handle a small volume of samples. In this paper, we presented a novel fluidic device for the specific and efficient separation and concentration of salmonella typhimurium using self-assembled magnetic nanoparticle chains. The laminated sawtooth-shaped iron foils were first mounted in the 3D-printed matrix and magnetized by a strong magnet to generate dot-array high gradient magnetic fields in the fluidic channel, which was simulated using COMSOL (5.3a, Burlington, MA, USA). Then, magnetic nanoparticles with a diameter of 150 nm, which were modified with the anti-salmonella polyclonal antibodies, were injected into the channel, and the magnetic nanoparticle chains were vertically formed at the dots and verified using a fluorescence inverted microscope. Finally, the bacterial sample was continuous-flow injected, and the target bacteria could be captured by the antibodies on the chains, followed by gold standard culture plating to determine the amount of the target bacteria. Under the optimal conditions, the target bacteria could be separated with a separation efficiency of 80% in 45 min. This fluidic device could be further improved using thinner sawtooth-shaped iron foils and stronger magnets to obtain a better dot-array magnetic field with larger magnetic intensity and denser dot distribution, and has the potential to be integrated with the existing biological assays for rapid and sensitive detection of foodborne bacteria.

A Phenolphthalein-Dummy Template Molecularly Imprinted Polymer for Highly Selective Extraction and Clean-Up of Bisphenol A in Complex Biological, Environmental and Food Samples.

A molecularly imprinted polymer (MIP) for highly selective solid-phase extraction (SPE) of bisphenol A (BPA) was prepared using phenolphthalein (PP) as the novel dummy template by bulk polymerization. A particle diameter distribution of 40–60 μm, a specific surface area of 359.8 m2·g−1, and a total pore volume of 0.730 cm3·g−1 for the prepared PP-imprinted polymer (PPMIP) were obtained. Good selectivity and specific adsorption capacity for BPA of the prepared PPMIP were also demonstrated by the chromatographic evaluation and sorption experiments. The PPMIP as a SPE sorbent was evaluated for the selective extraction and clean-up of BPA from complex biological, environmental, and food samples. Meanwhile, an accurate and sensitive analytical method based on the PPMIP-SPE purification procedure coupled with high performance liquid chromatography-diode array detector (HPLC-DAD) detection has been successfully developed for the rapid determination of BPA from these samples, with detection limits of 1.3 ng·mL−1 for bovine serum and milk, 2.6 ng·mL−1 for human urine and edible oil, 5.2 ng·mL−1 for soybean sauce, and 1.3 ng·g−1 for sediment. The BPA recoveries at two different spiking levels were in the range of 82.1–106.9%, with relative standard deviation (RSD) values below 7.7%.

Magnetic covalent organic frameworks based on magnetic solid phase extraction for determination of six steroidal and phenolic endocrine disrupting chemicals in food samples

A simple and rapid magnetic covalent organic frameworks based on magnetic solid phase extraction method was proposed for effective determination of six steroidal and phenolic endocrine disrupting chemicals in meat samples. Fluorescence labeling combined with high performance liquid chromatography fluorescence detection was used to quantify endocrine disrupting chemicals. Covalent organic frameworks could be a wonderful choice as sorbent for endocrine disrupting chemicals enrichment due to its characteristics of large specific surface area, great structure stability and functional properties. In this work, COF(TpBD) was chosen as functionalized groups to be grafted onto the surface of Fe3O4 microspheres via one-step surface fabrication strategy. The parameters affecting the extraction efficiency were investigated in detail. The adsorption equilibrium was achieved within 5 min. Under the optimized conditions, the obtained Fe3O4@COF(TpBD) materials showed excellent extraction performance for endocrine disrupting chemicals with high sensitivity (1.4–8.7 μg L−1 for LODs and 4.6–29.0 μg L−1 for LOQs) and good linearity (R ≥ 0.9986). Determination of endocrine disrupting chemicals in meats was achieved using the proposed method. Furthermore, the method, validated on spiked meats (including chicken, pork and shrimp), showed satisfactory accuracy, with average recoveries in the 89.6–108.9% range and relative standard deviations ≤6.3%. Additionally, two kinetic models were investigated to recognize the target analytes adsorption mechanism onto Fe3O4@COF(TpBD) materials, and the results indicated that the pseudo-second-order model was the most suitable in describing the adsorption kinetics of endocrine disrupting chemicals on the Fe3O4@COF(TpBD) materials. The proposed method was proved to be feasible for the determination of endocrine disrupting chemicals in complex food samples.

Molecularly imprinted covalent organic polymers for the selective extraction of benzoxazole fluorescent whitening agents from food samples.

Molecularly imprinted covalent organic polymers were constructed by an imine-linking reaction between 1,3,5-triformylphloroglucinol and 2,6-diaminopyridine and used for the selective solid-phase extraction of benzoxazole fluorescent whitening agents from food samples. Binding experiments showed that imprinting sites on molecularly imprinted polymers had higher selectivity for targets compared with those of the corresponding non-imprinted polymers. Parameters affecting the solid-phase extraction procedure were examined. Under optimal conditions, actual samples were treated and the eluent was analyzed with high-performance liquid chromatography with diode-array detection. The results showed that the established method has a wide linearity, satisfactory detection limits and quantification limits, and acceptable recoveries. Thus, this developed method possesses the practical potential for the selective determination of benzoxazole fluorescent whitening agents in complex food samples.

Characterization of secondary metabolites from green cocoa beans using focusing-modulated comprehensive two-dimensional liquid chromatography coupled to tandem mass spectrometry

Proanthocyanidins as well as other secondary metabolites present in green cocoa beans were studied thanks to a new method involving the use of on-line comprehensive two-dimensional liquid chromatography coupled to tandem mass spectrometry (LC × LC-MS/MS). In order to enhance the performance of previously developed methodologies, the use of different modulation strategies were explored. Focusing modulation clearly allowed the attainment of higher resolving power and peak capacity compared to non-focusing modulation set-ups. Moreover, the use of active modulation by the addition of a make-up flow efficiently helped to compensate for the solvent strength mismatch produced between dimensions. The optimized method was useful to successfully describe the secondary metabolite composition of green cocoa that was characterized by the presence of 30 main compounds, including 3 xanthines, 2 flavan-3-ols and 24 oligomeric procyanidins with a degree of polymerization up to 12. The obtained results showed that the proanthocyanidins found in the cocoa beans were exclusively B-type procyanidins. The existence of (epi)catechin subunits linked to sugar or galloyl moieties was not observed. The developed method produced a good separation of secondary metabolites allowing an improvement with respect to the available methodologies for the analysis of a complex food sample such as cocoa metabolites in terms of speed of analysis, resolution and peak capacity.

Heparin-stabilized gold nanoparticles-based CUPRAC colorimetric sensor for antioxidant capacity measurement

Sensing of total antioxidant capacity (TAC) as an integrated parameter showing the collective action of various antioxidants is an important challenge in food, biochemical and drug analysis. A novel heparin-stabilized gold nanoparticles (AuNPs)-based ‘cupric reducing antioxidant capacity’ (CUPRAC) colorimetric sensor was designed for TAC measurement. Heparin, a sulfated polysaccharide, was both the reducing and stabilizing agent for distinct negatively-charged AuNPs synthesis. The stabilized AuNPs were added to the copper(I)-neocuproine (Cu(I)-Nc) solution formed from the reaction of Cu(II)-Nc with antioxidants, and the absorbance of the resulting Cu(I)-Nc-AuNPs (Cu(I)-Nc cationic chelate electrostatically adsorbed on gold nanoparticles) was measured at 455 nm. As opposed to other similar AuNPs-based sensors, the proposed nano-sensor exhibited excellent (1000-fold) tolerance toward inert electrolytes without aggregation. The linear range was wider than that of conventional CUPRAC, with lower LOD (0.2 µM for trolox) and higher molar absorptivity (8.36 × 104 M−1 cm−1 for quercetin). The ‘trolox equivalent antioxidant capacity’ (TEAC) values and activity order for a number of antioxidants were in accordance with those of the reference CUPRAC assay. Antioxidant additions to black tea extract gave recoveries of 93–97% and RSD 2–6%. This green sensor significantly reduced reagent consumption, and operated in complex food samples with a simple, reliable and robust methodology.

Tandem HILIC-RP liquid chromatography for increased polarity coverage in food analysis.

Comprehensive non-targeted analysis of food products normally requires two complementary chromatographic runs to achieve maximum compound coverage. In this study, we present a sensitive tandem-LC method, which combines RP and HILIC separation in a single run. The setup consists of a C18 trap column and two subsequently coupled analytical columns (HILIC and C18) which are operated in parallel. First, hydrophobic compounds are retained on the RP trap column while rather hydrophilic compounds are directly transferred onto a HILIC phase. Next, the pre-fractionated sample composition is analyzed by HILIC or RP chromatography, respectively. The presented setup allows individual and independent gradient elution as well as interfacing with mass spectrometry. The performance of the method has been proven by means of food relevant standards and analysis of complex food samples (e.g. red wine, meat extract). The simple and robust setup provides high flexibility in the selection of column combinations and does not require sophisticated instrumental setups or software. The method significantly increases the covered polarity range compared to classical one-dimensional chromatography. Our results indicate that tandem LC is a valuable and universal tool in the non-targeted screening of various types of complex food samples.