Reversed-phase liquid chromatographic method for the determination of ochratoxin A in wine

Determination of ochratoxin A in coffee and tea samples by coupling second-order multivariate calibration and fluorescence spectroscopy

A new method to quantify the mycotoxin ochratoxin A (OTA) in coffee and tea samples is proposed based on second-order multivariate calibration and excitation-emission fluorescence matrix (EEFM) data. Experimental conditions were optimized by studying the effect of pH and various organized media on the fluorescence signal of OTA. For each analysed matrix (coffee grains and tea leaves), several sample pretreatments and calibration methods (external or standard addition) and data processing by chemometric models (e.g., parallel factor analysis/PARAFAC and multivariate curve resolution-alternating least squares/MCR-ALS) were evaluated and discussed. The MCR-ALS algorithm provided an adequate fit to the data for both samples, while PARAFAC was satisfactory only for the tea samples. Regarding the figures of merit, the limits of detection were in the range of 0.2-0.3 ng mL^-1; furthermore, low relative prediction errors, between 2% and 4%, were achieved in both the fortified and real samples. Accordingly, the proposed methodology was applied to analyse fortified roasted and green coffee and real tea leaf samples. Satisfactory recoveries were achieved (ranging from 92 to 110%), and the obtained concentrations were in agreement with the values obtained by the reference method (based on high-performance liquid chromatography with fluorescence detection/HPLC-FLD). In addition, all samples contained OTA levels lower than the maximum permissible levels. Finally, the proposed strategy allows the use of green analytical chemistry principles; for instance, the use of organic solvents and the generation of waste products were significantly lower than for similar analytical methods reported in the literature.

Aptamer assisted ultrafiltration cleanup with high performance liquid chromatography-fluorescence detector for the determination of OTA in green coffee

One of the most common mycotoxin contaminating feed and foodstuffs is Ochratoxin A (OTA). OTA has a chronic toxic effect and proved to be mutagenic, nephrotoxic, teratogenic, immunosuppressive, and carcinogenic. Aptamer with their specific affinity for OTA was used in this paper to create an analytical technique. Several methods have been reported for the determination of OTA in foods. However, most of these methods could not be applied to a complex food as green coffee because the interfering native fluorescent products made the quantification very difficult. In this work, we mixed two separations based techniques to identify and quantify OTA in green coffee. Aptamer assisted ultrafiltration as separation technique based on the size of molecules was applied to separate the free OTA, the quantification of OTA was established by a high-performance liquid chromatography (HPLC-FD) with a limit of detection (LOD) of 0.05 ng/mL for OTA. Artificially contaminated green coffee displayed a good range of OTA recoveries up to 97.7%. This method can be applied to the quantitative determination of OTA in green coffee at levels below the maximum levels proposed by the European Commission for green coffee. It also confirm that aptamers can be used as biorecognition element in diagnostic assays with commercial application for mycotoxin analysis.

Ochratoxin A in the Portuguese Wine Market, Occurrence and Risk Assessment

Ochratoxin A (OTA) is mainly found in cereals and cereal-based foodstuffs, but also in wine. Being one of the most consumed alcoholic drinks in Portugal and one of the main sources of human exposure to OTA, wine monitoring and exposure studies are essential. The analytical methodology consisted of the direct injection of the filtered samples into the liquid chromatograph, equipped with fluorescent detection (LC-FLD). Linearity was adequate, both in mobile phase and in matrix-matched solutions, with R² values higher than 0.997. The limits of detection were 0.08 and 0.39 µg/L for white and red wine, respectively and recoveries were above 91.9%. One hundred wine samples acquired on the Portuguese market were investigated. In 5 samples the OTA was detected, with the red wine presenting higher frequency of contamination. Regarding the risk to human health it was observed that the estimated weekly intake (EWI) is considerably lower than the established tolerable weekly intake (TWI).

Complexes of the Mycotoxins Citrinin and Ochratoxin A with Aluminum Ions and their Spectroscopic Properties

The sensitive detection of the mycotoxin citrinin (CIT) utilizing its fluorescence requires approaches to enhance the emission. In this respect, we studied the complexation of CIT and ochratoxin A (OTA) with Al³⁺ in methanol using absorption and fluorescence spectroscopy. In this context, an isocratic high performance liquid chromatography (HPLC) method using a polymer column and a fluorescence detector was also developed that enables the separation of the metal ion complexes from the free ligands and non-complexed Al³⁺. CIT and OTA showed distinct changes in their absorption and fluorescence properties upon Al³⁺-coordination, and the fluorescence of CIT was considerably enhanced. Analysis of the photometrically assessed titration of CIT and OTA with Al³⁺ using the Job plot method revealed 1:2 and 1:1 stoichiometries for the Al³⁺ complexes of CIT (Al:CIT) and OTA (Al:OTA), respectively. In the case of CIT, only one β-diketone moiety participates in Al³⁺ coordination. These findings can be elegantly exploited for signal amplification and provide the base to reduce the limit of detection for CIT quantification by about an order of magnitude, as revealed by HPLC measurements using a fluorescence detector.

Molecularly Imprinted Solid Phase Extraction in a Syringe Needle Packed with Polypyrrole-encapsulated Carbon Nanotubes for Determination of Ochratoxin A in Red Wine

A novel micro-solid phase preconcentration (μSPP) device is developed by electrochemically depositing molecularly imprinted polypyrrole (MIPPy) over carbon nanotubes (CNTs) packed inside a 22-gauge syringe needle. The ochratoxin A (OTA) template is removed with 1% triethylamine (TEA) in 20:80 v/v acetonitrile—ammonia buffer (20 mM NH4Cl/NH3, pH 9.2). This syringe needle is used to extract trace OTA in a red wine sample, and the preconcentrated OTA is eluted with 1% (v/v) TEA in 20:80 v/v acetonitrile—ammonia buffer (20 mM NH4Cl/NH3, pH 9.2). The eluate is analyzed by high performance liquid chromatography (HPLC) with fluorescence detection (FD). The results demonstrated a significantly selective enrichment of OTA at sub-ppb levels in the presence of red wine matrix components. Using a sample volume of 0.5mL red wine for preconcentration, it is possible to determine OTA down to a detection limit of 0.04 ng/mL (at 3σB) or a quantification limit of 0.10 ng/mL (at 10σB). The total MIPPy/CNTs-μSPP-HPLC-FD analysis took only 40min, including a μSPP time of 30min, elution time of 20 s, and HPLC analysis time of 10 min. This needle can be reused and hence readily adapted in an autosampler for the processing of multiple samples in series.

Accurate determination of ochratoxin A in Korean fermented soybean paste by isotope dilution-liquid chromatography tandem mass spectrometry

Ochratoxin A (OTA), a naturally occurring mycotoxin, has been frequently detected in doenjang, a traditional fermented soybean paste, when it is fermented under improper conditions. Reliable screening of OTA in traditional fermented soybean paste (doenjang) is a special food-safety issue in Korea. Our laboratory, the National Metrology Institute of Korea, established an isotope dilution-liquid chromatography tandem mass spectrometry (ID-LC/MS/MS) method as a higher-order reference method to be used for SI-traceable value-assignment of OTA in certified reference materials (CRMs). (13)C20-OTA was used as an internal standard. Sample preparation conditions and LC/MS measurement parameters were optimised for this purpose. The analytical method was validated by measuring samples fortified with OTA at various levels. Repeatability and reproducibility studies showed that the ID-LC/MS/MS method is reliable and reproducible within 2% relative standard deviation. The analytical method was applied to determine OTA in various commercial doenjang products and home-made doenjang products.

Cross-reactivity of antibodies with phenolic compounds in pistachios during quantification of ochratoxin A by commercial enzyme-linked immunosorbent assay kits

Ochratoxin A (OTA), a nephrotoxic mycotoxin, naturally occurs in wide range of agricultural commodities. Typical screening of OTA involves various enzyme-linked immunosorbent assay (ELISA) methods. Pistachio (Pistacia vera L.) is a rich source of phenolic compounds that may result in a false positive due to structural similarities to OTA. The present study investigated the cross-reactivity profiles of phenolic compounds using two commercial ELISA test kits. High-performance liquid chromatography was used to confirm the concentration of OTA in the pistachio samples and compared with the results obtained from ELISA. When the degree of interaction and 50 % inhibitory concentration of phenolic compounds were determined, the cross-reactivity showed a pattern similar to that observed with the commercial ELSIA kits, although quantitatively different. In addition, the degree of interaction increased with the increasing concentration of phenolic compounds. The ELISA value had stronger correlations with the content of total phenolic compound, gallic acid, and catechin (R(2) = 0.757, 0.732, and 0.729, respectively) compared with epicatechin (R(2) = 0.590). These results suggest that phenolic compounds in pistachio skins may cross-react with the OTA antibody and lead to a false positive or to an overestimation of OTA concentration in ELISA-based tests.

Further aspects of ochratoxin A-cation interactions: complex formation with zinc ions and a novel analytical application of ochratoxin A-magnesium interaction in the HPLC-FLD system

Ochratoxin A (OTA) is a mycotoxin produced by different Aspergillus and Penicillium species. Since its mechanism of action is not fully understood yet, it is important to gain further insight into different interactions of OTA at the molecular level. OTA is found worldwide in many foods and drinks. Moreover, it can also be detected in human and animal tissues and body fluids, as well. Therefore, the development of highly sensitive quantitative methods for the determination of OTA is of utmost importance. OTA most likely forms complexes with divalent cations, both in cells and body fluids. In the present study, the OTA-zinc interaction was investigated and compared to OTA-magnesium complex formation using fluorescence spectroscopy and molecular modeling. Our results show that zinc(II) ion forms a two-fold higher stable complex with OTA than magnesium(II) ion. In addition, based on the enhanced fluorescence emission of OTA in its magnesium-bound form, a novel RP-HPLC-fluorescence detector (FLD) method was also established. Our results highlight that the application of magnesium chloride in alkaline eluents results in an approximately two-fold increase in sensitivity using the HPLC-FLD technique.

Reliable and simple detection of ochratoxin and fumonisin production in black Aspergillus

To date, edible fungi such as black Aspergillus (Aspergillus niger aggregates) have been considered as safe. However, it has recently been reported that some strains have a mycotoxin biosynthetic capability, and this capability must be evaluated to determine the safety of edible fungi. In this study, we assessed the ability of mycotoxin production in A. niger aggregates isolated from various Korean foods using multiplex PCR and high-performance liquid chromatography (HPLC) analyses. Multiplex PCR and HPLC analyses of 32 A. niger aggregates showed that ochratoxin and fumonisin were produced only by strains exhibiting positive PCR patterns with ochratoxin and fumonisin biosynthesis genes. However, several strains did not produce mycotoxins, even though they contained mycotoxin biosynthesis genes. Using multiplex PCR pattern and HPLC analyses, we selected Aspergillus strains that do not produce mycotoxins, which will contribute to the development of safer fermented foods.

A new validated HPLC-FLD method for detecting ochratoxin A in dry-cured meat and in blue cheese

In the present study, a fast and sensitive method for the quantification of ochratoxin A in two lipidicproteic food matrices has been developed. In particular, the sample preparation procedure has been optimized for dry-cured meat products and blue cheeses and tested for several validation parameters (LOD, LOQ, recovery, repeatability and within-laboratory precision). The procedure has been then applied to several dry-cured meat products and blue cheeses from the market.Ochratoxin A has been occasionally found in dry-cured and smoked ham from the market and the contamination occurred both in the outer and in the inner part of the products. Concerning the blue cheese, the occurrence of ochratoxin A is reported for the first time: OTA was occasionally found at low levels (0.1-3 μg/kg) in commercial samples of Roquefort from France and Gorgonzola from Italy, opening a new issue for risk assessment and quality control.

Molecularly imprinted polymers for ochratoxin a extraction and analysis

Molecularly imprinted polymers (MIPs) are considered as polymeric materials that mimic the functionality of antibodies. MIPs have been utilized for a wide variety of applications in chromatography, solid phase extraction, immunoassays, and sensor recognition. In this article, recent advances of MIPs for the extraction and analysis of ochratoxins are discussed. Selection of functional monomers to bind ochratoxin A (OTA) with high affinities, optimization of extraction procedures, and limitations of MIPs are compared from different reports. The most relevant examples in the literature are described to clearly show how useful these materials are. Strategies on MIP preparation and schemes of analytical methods are also reviewed in order to suggest the next step that would make better use of MIPs in the field of ochratoxin research. The review ends by outlining the remaining issues and impediments.

Review of secondary metabolites and mycotoxins from the Aspergillus niger group

Filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread food and feed contaminants known but they are also some of the most important workhorses used by the biotechnological industry. The Nigri section consists of six commonly found species (excluding A. aculeatus and its close relatives) from which currently 145 different secondary metabolites have been isolated and/or detected. From a human and animal safety point of view, the mycotoxins ochratoxin A (from A. carbonarius and less frequently A. niger) and fumonisin B(2) (from A. niger) are currently the most problematic compounds. Especially in foods and feeds such as coffee, nuts, dried fruits, and grape-based products where fumonisin-producing fusaria are not a problem, fumonisins pose a risk. Moreover, compounds such as malformins, naptho-gamma-pyrones, and bicoumarins (kotanins) call for monitoring in food, feed, and biotechnology products as well as for a better toxicological evaluation, since they are often produced in large amounts by the black aspergilli. For chemical differentiation/identification of the less toxic species the diketopiperazine asperazine can be used as a positive marker since it is consistently produced by A. tubingensis (177 of 177 strains tested) and A. acidus (47 of 47 strains tested) but never by A. niger (140 strains tested). Naptho-gamma-pyrones are the compounds produced in the highest quantities and are produced by all six common species in the group (A. niger 134 of 140; A. tubingensis 169 of 177; A. acidus 44 of 47; A. carbonarius 40 of 40, A. brasiliensis 18 of 18; and A. ibericus three of three).

Reduction of ochratoxin a levels in red wine by bentonite, modified bentonites, and chitosan

Adsorption method may play an important role to remove ochratoxin A (OTA) from wine by bentonite (B), nonylammonium bentonite (NB), dodecylammonium bentonite (DB), KSF-montmorillonite (KSF), and chitosan bead (CB). The optimum conditions of OTA adsorption from synthetic solutions were revealed at room temperature and pH 3.5. The adsorption equilibria of B and NB were almost established within 120 and 240 min, respectively. DB, KSF, and CB had about 90 min of equilibration time. The adsorption efficiency carried out in the synthetic OTA solution did not change remarkably when the amounts of adsorbents were 25 mg for bentonite, DB, and KSF and 100 mg for NB and CB. Furthermore, 25 mg of adsorbents was used at all adsorption studies in synthetic solution. The adsorption isotherm was fitted with mostly a Freundlich equation with respect to the correlation coefficients. The adsorption data were evaluated using Langmuir and Freundlich equations having Kf values ranging from 0.011 to 9.5 with respect to correlation coefficients (R2 = 0.900-0.977). DB and KSF have the highest adsorption capacity for OTA in synthetic solutions. In wine, the removal of OTA was succeeded at a percentage of 60-100 by KSF and CB. Furthermore, the highest adsorption capacity of OTA for red wine was obtained by using 250 mg of KSF, which caused less damage to the nature of wine and also low adsorption of polyphenols and anthcyans.

Quantitative analysis of ochratoxin A in wine and beer using solid phase extraction and high performance liquid chromatography-fluorescence detection

A reliable and accurate method is described for the quantitative analysis of ochratoxin A (OTA) in wine and beer. The method involves the use of disposable non-polar polymeric and aminopropyl solid-phase extraction cartridges to isolate the mycotoxin from alcoholic beverages. Extracts were subsequently analysed using reverse-phase high-performance liquid chromatography-fluorescence detection with post column ammoniation to improve the limit of detection. The precision of the method determined at three levels in both wine and beer was less than 5% (RSD). Standard addition studies in both wine and beer showed that the recovery of OTA varied between 90 and 106% over a concentration range of 0.016-1.284 microg l-1. The detection and quantification limits were shown to be better than 0.004 (S/N = 3) and 0.016 microg l-1 (S/N = 10) for both beer and wine.

Determination of ochratoxin A in dry-cured meat products by a HPLC–FLD quantitative method

A fast and sensitive method for the quantification of the mycotoxin ochratoxin A (OTA) in dry-cured meat products has been developed, which does not require a clean-up step, by HPLC with an alkaline mobile phase (pH 9.8). Validation procedures for specificity, trueness, ruggedness, stability, recovery and repeatability were performed. The decision limit (CC alpha) and the decision capability (CC beta) were calculated at 1.10 and 1.23 microg/kg, respectively. The procedure was applied to representative dehydration levels of dry-cured meat samples.

Trace mycotoxin analysis in complex biological and food matrices by liquid chromatography–atmospheric pressure ionisation mass spectrometry

Mycotoxins are toxic secondary metabolites produced by filamentous fungi that are growing on agricultural commodities. Their frequent presence in food and their severe toxic, carcinogenic and estrogenic properties have been recognised as potential threat to human health. A reliable risk assessment of mycotoxin contamination for humans and animals relies basically on their unambiguous identification and accurate quantification in food and feedstuff. While most screening methods for mycotoxins are based on immunoassays, unambiguous analyte confirmation can be easily achieved with mass spectrometric methods, like gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS). Due to the introduction of atmospheric pressure ionisation (API) techniques in the late 80s, LC/MS has become a routine technique also in food analysis, overcoming the traditional drawbacks of GC/MS regarding volatility and thermal stability. During the last few years, this technical and instrumental progress had also an increasing impact on the expanding field of mycotoxin analysis. The aim of the present review is to give an overview on the application of LC-(API)MS in the analysis of frequently occurring and highly toxic mycotoxins, such as trichothecenes, ochratoxins, zearalenone, fumonisins, aflatoxins, enniatins, moniliformin and several other mycotoxins. This includes also the investigation of some of their metabolites and degradation products. Suitable sample pre-treatment procedures, their applicability for high sample through-put and their influence on matrix effects will be discussed. The review covers literature published until July 2006.

Determination of Ochratoxin A in wine at sub ng/mL levels by solid-phase microextraction coupled to liquid chromatography with fluorescence detection

Solid-phase microextraction (SPME), using a polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber, interfaced with liquid chromatography-fluorescence detection (LC-FD) has been applied to the determination of Ochratoxin A (OTA) in wine samples. Compared to the most widely adopted extraction/clean-up procedure based on immunoaffinity columns (IAC), the solventless extraction is simpler and cost-effective, requiring the simple immersion of the fiber in diluted wine samples. Furthermore, a fast LC separation is achieved under isocratic conditions. The linear range investigated in wine was 0.25-8 ng/mL; at fortification levels of 0.5 and 2 ng/mL, within-day intra-laboratory precision (repeatability) values, expressed as RSD%, were 5.9 and 5.1, respectively, whereas between days (n = 4) precision was 8.5 and 7.1%, respectively. The limit of detection (LOD) at a signal-to-noise (S/N) ratio of 3 was 0.07 ng/mL; the limit of quantification (LOQ) calculated at S/N = 10 was 0.22 ng/mL, well below the European regulatory level of 2 ng/mL. The potential of the method has been demonstrated by the analysis of a number of different wine samples.

Assay of ochratoxin A in grape by high-pressure liquid chromatography coupled on line with an ESI–mass spectrometry

In this paper, we propose a method for detection of ochratoxin A (OTA) in grapes by using nano-reversed-phase high-performance liquid chromatography-electrospray ionization-mass spectrometry (nano-RP-HPLC-ESI-MS). The method is rapid, highly sensitive and reproducible. OTA is extracted preferably from the entire acinus, rather than must; using chloroform at long incubation time period, lyophilized, resolubilized in acetonitrile (AcCN) and injected onto a reversed phase capillary or analytical column. Capillary columns are the method of choice because it requires a reduced amount of injected sample and consequently the chloroform necessary for OTA extraction, which is a toxic agent. This method gives a detection limit of femtog/ml, without resorting to an immunoaffinity clean-up or concentration, which makes it by far superior to any other method reported. Moreover, by using MS as a detection method it is possible, in the case of a complex matrix, to measure its molecular mass and to confirm the presence of OTA by MS-MS, which cannot be done by fluorescent detection. The method has a high sample extraction throughput (24/h) and has adequate precision (between batch C.V. <8%) and sensitivity (limit of detection (LOD)=1 pg/g; limits of quantification (LOQ)=2 pg/g) for OTA measured.

Recent advances in mycotoxin determination in food and feed by hyphenated chromatographic techniques/mass spectrometry

Mycotoxins are fungal toxins produced by molds, which occur universally in food and feed derivatives, and are produced under certain environmental conditions in the field before harvest, post-harvest, during storage, processing, and feeding. Mycotoxin contamination is one of the most relevant and worrisome problem concerning food and feed safety because it can cause a variety of toxic acute and chronic effects in human and animals. In this review we report the use of mass spectrometry in connection with chromatographic techniques for mycotoxin determination by considering separately the most diffuse class of mycotoxins: patulin, aflatoxins, ochratoxin A, zearalenone, trichothecenes, and fumonisins. Although the selectivity of mass spectrometry is unchallenged if compared to common GC and LC detection methods, accuracy, precision, and sensitivity may be extremely variable concerning the different mycotoxins, matrices, and instruments. The sensitivity issue may be a real problem in the case of LC/MS, where the response can be very different for the different ionization techniques (ESI, APCI, APPI). Therefore, when other detection methods (such as fluorescence or UV absorbance) can be used for the quantitative determination, LC/MS appears to be only an outstanding confirmatory technique. In contrast, when the toxins are not volatile and do not bear suitable chromophores or fluorophores, LC/MS appears to be the unique method to perform quantitative and qualitative analyses without requiring any derivatization procedure. The problem of exact quantitative determination in GC/MS and LC/MS methods is particularly important for mycotoxin determination in food, given the high variability of the matrices, and can be solved only by the use of isotopically labeled internal standards or by the use of ionization interfaces able to lower matrix effects and ion suppressions. When the problems linked to inconstant ionization and matrix effects will be solved, only MS detectors will allow to simplify more and more the sample preparation procedures and to avoid clean-up procedures, making feasible low-cost, high-throughput determination of mycotoxins in many different food matrices.

Evolution of ochratoxin A content from must to wine in Port Wine microvinification

To study the evolution of ochratoxin A (OTA) content from must to wine during the making of Port Wine, grapes from the five most common varieties of Port Wine were harvested and combined in equal percentages in order to perform microvinifications. Three sets of assays were studied: a blank (A), where the most common Port Wine-making process was used; in the second (B), a solution of OTA was added to the initial must; in the third (C), the grapes were aspersed with an inoculating solution of OTA-producing fungi. Samples were collected, in duplicate, on four different occasions throughout the process. The influence of the addition of SO2 to the must was also assessed in each set. The quantification of OTA was based on the standard reference method for wines (European Standard prEN 14133), which includes clean-up via immunoaffinity columns and HPLC with fluorescence detection. The limits of detection were 0.076 microg/l for wine and 0.114 microg/l for must. The method was validated by assessing the precision, accuracy and by obtaining an estimate of the global uncertainty. Overall, the levels of OTA observed during the vinifications dropped by up to 92%, and no grapes used in this work were contaminated naturally.

Polypyrrole modified stainless steel frits for on-line micro solid phase extraction of ochratoxin A

Polypyrrole (PPy) was electrochemically synthesized on stainless steel frits as a sorbent for the micro solid phase extraction (muSPE) of ochratoxin A (OTA). Using 20 microl of standard solution under a fast flow rate of 0.5 ml/min, 80% recovery of OTA was achieved in the concentration range from 0.1-10 pg/mul. This good recovery was achieved within a short residence time of 1.2 s. A binding capacity of 1 ng OTA was estimated for each PPy-modified frit, or 2 ng OTA for two frits in series. The bound OTA could be pulsed eluted (PE) with 20 microl of 1% triethylamine in acetonitrile. On-line coupling of this PPy-on-a-frit and PE technique to high performance liquid chromatography (HPLC) was straightforward. On-line muSPE-PE-HPLC results clearly demonstrated the capability of PPy-on-a-frit to bind OTA in the presence of red wine, beer, and orange juice components.