Assay of ochratoxin A in wine and beer by high-pressure liquid chromatography photodiode array and gas chromatography mass selective detection

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.

Design and synthesis of target-responsive aptamer-cross-linked hydrogel for visual quantitative detection of ochratoxin A

A target-responsive aptamer-cross-linked hydrogel was designed and synthesized for portable and visual quantitative detection of the toxin Ochratoxin A (OTA), which occurs in food and beverages. The hydrogel network forms by hybridization between one designed DNA strand containing the OTA aptamer and two complementary DNA strands grafting on linear polyacrylamide chains. Upon the introduction of OTA, the aptamer binds with OTA, leading to the dissociation of the hydrogel, followed by release of the preloaded gold nanoparticles (AuNPs), which can be observed by the naked eye. To enable sensitive visual and quantitative detection, we encapsulated Au@Pt core-shell nanoparticles (Au@PtNPs) in the hydrogel to generate quantitative readout in a volumetric bar-chart chip (V-Chip). In the V-Chip, Au@PtNPs catalyzes the oxidation of H2O2 to generate O2, which induces movement of an ink bar to a concentration-dependent distance for visual quantitative readout. Furthermore, to improve the detection limit in complex real samples, we introduced an immunoaffinity column (IAC) of OTA to enrich OTA from beer. After the enrichment, as low as 1.27 nM (0.51 ppb) OTA can be detected by the V-Chip, which satisfies the test requirement (2.0 ppb) by the European Commission. The integration of a target-responsive hydrogel with portable enrichment by IAC, as well as signal amplification and quantitative readout by a simple microfluidic device, offers a new method for portable detection of food safety hazard toxin OTA.

Ochratoxin A in Chinese dried jujube: method development and survey

A method was developed for the determination of the mycotoxin ochratoxin A in dried jujube (Zizyphus jujuba Miller) using alkaline methanolic extraction, immunoaffinity column clean-up (IAC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) determination. The limit of detection (LOD) was 0.01 μg kg(-1) and limit of quantification (LOQ) was 0.03 μg kg(-1). The average recoveries were 82%, 98% and 115% at 5, 0.5 and 0.1 μg kg(-1) spiked levels with relative standard deviations (RSD) of 2.9%, 5.2% and 9.2% accordingly. The method showed good linearity for both solvent standard calibration and matrix-matched standard calibration with correlation coefficients of 0.9998 and 0.9997 respectively. The intra-day precision RSD was 3.3% and the inter-day precision RSD was 4.0%. In addition, there was almost no matrix interference in LC-MS/MS detection after the IAC clean-up process. The proposed analytical set-up was successfully used to test 20 samples that were collected from local markets and stores. The results showed that all the samples were positive and the amount of OTA ranged from < 0.01 to 0.18 μg kg(-1), with a mean level of 0.14 μg kg(-1). In spite of the high positive rate, samples with this level would not cause significant health effects after consumption.

Amplified fluorescent aptasensor through catalytic recycling for highly sensitive detection of ochratoxin A

This paper describes a novel approach utilizing nano-graphite-aptamer hybrid and DNase I for the amplified detection of ochratoxin A (OTA) for the first time. Nano-graphite can effectively quench the fluorescence of carboxyfluorescein (FAM) labeled OTA specific aptamer due to their strong π-π; stacking interactions; while upon OTA addition, it will bind with aptamer to fold into an OTA-aptamerG-quadruplex structure, which does not adsorb on the surface of nano-graphite and thus retains the dye fluorescence. Meanwhile, the G-quadruplex structure can be cleaved by DNase I, and in such case OTA is delivered from the complex. The released OTA then binds other FAM-labeled aptamers on the nano-graphite surface, and touches off another target recycling, resulting in the successive release of dye-labeled aptamers from the nano-graphite, which leads to significant amplification of the signal. Under the optimized conditions, the present amplified sensing system exhibits high sensitivity toward OTA with a limit of detection of 20nM (practical measurement), which is about 100-fold higher than that of traditional unamplified homogeneous assay. Our developed method also showed high selectivity against other interference molecules and can be applied for the detection of OTA in real red wine samples. The proposed assay is simple, cost-effective, and might open a door for the development of new assays for other biomolecules. This aptasensor is of great practical importance in food safety and could be widely extended to the detection of other toxins by replacing the sequence of the recognition aptamer.

Exposure assessment to ochratoxin A in Chinese wine

A rapid, sensitive, reproducible, and inexpensive method of high-performance liquid chromatography with fluorescence detection after an anion-exchange solid-phase extraction cleanup step for the analysis of ochratoxin A (OTA) in Chinese wine was developed. The average recovery rate and the average RSD of recovery were 97.47% and about 4%. The relative standard deviations of both the interday and intraday precision were 6.7 and 12.6%, respectively. The limits of detection and quantitation were determined to be 0.01 and 0.03 μg/L, respectively. A total of 223 samples from the major wine-producing areas of China were analyzed for OTA. OTA was detected at levels of 0.01-0.98 μg/L. The mean was 0.15 μg/L. Then, participants as representative inhabitants were invited to answer the designed questionnaire about the quantity and frequency of wine consumption. All data were simulated by the point evaluation for the risk assessment of OTA contamination from wine. Those results indicated that daily intake (DI) of OTA for the average adult consumer varies between 0.86 and 1.08 ng/kg bw per week, which was lower than all the reference standards. However, the DI value (4.38-5.54 ng/kg bw per week) in the high percentile (97.5) was slightly above 5% PTWI (100 ng kg(-1) week(-1)) of the JECFA. In conclusion, OTA exposure from Chinese wine has no risk of harm. This research will provide the scientific basis for determining the maximum limit of OTA content in Chinese wine.

Label-free photoelectrochemical immunosensor for sensitive detection of Ochratoxin A

A general label-free photoelectrochemical (PEC) platform was manufactured by assembly of CdSe nanoparticles (NPs) sensitized anatase TiO2-functionalized electrode via layer-by-layer (LBL) strategy. CdSe NPs were assembled on anatase TiO2-functionalized electrode through dentate binding of TiO2 NPs to -COOH groups. Ascorbic acid (AA) was used as an efficient electron donor for scavenging photogenerated holes under visible-light irradiation. The photocurrent response of the CdSe NPs modified electrode was significantly enhanced as a result of the band alignment of CdSe and TiO2 in electrolyte. Ochratoxin A (OTA), as model analyte, was employed to investigate the performance of the PEC platform. Antibodies of OTA were immobilized on CdSe sensitized electrode by using the classic 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride coupling reactions between -COOH groups on the surfaces of CdSe NPs and -NH2 groups of the antibody. Under the optimized conditions, the photocurrent was proportional to OTA concentration range from 10pg/mL to 50ng/mL with detection limit of 2.0pg/mL. The employed PEC platform established a simple, fast and inexpensive strategy for fabrication of label-free biosensor, which might be widely applied in bioanalysis and biosensing in the future.

Natural occurrence, analysis, and prevention of mycotoxins in fruits and their processed products

Mycotoxins are small toxic chemical products formed as the secondary metabolites by fungi that readily contaminate foods with toxins in the field or after harvest. The presence of mycotoxins, such as aflatoxins, ochratoxin A, and patulin, in fruits and their processed products is of high concern for human health due to their properties to induce severe acute and chronic toxicity at low-dose levels. Currently, a broad range of detection techniques used for practical analysis and detection of a wide spectrum of mycotoxins are available. Many analytical methods have been developed for the determination of each group of these mycotoxins in different food matrices, but new methods are still required to achieve higher sensitivity and address other challenges that are posed by these mycotoxins. Effective technologies are needed to reduce or even eliminate the presence of the mycotoxins in fruits and their processed products. Preventive measures aimed at the inhibition of mycotoxin formation in fruits and their processed products are the most effective approach. Detoxification of mycotoxins by different physical, chemical, and biological methods are less effective and sometimes restricted because of concerns of safety, possible losses in nutritional quality of the treated commodities and cost implications. This article reviewed the available information on the major mycotoxins found in foods and feeds, with an emphasis of fruits and their processed products, and the analytical methods used for their determination. Based on the current knowledge, the major strategies to prevent or even eliminate the presence of the mycotoxins in fruits and their processed products were proposed.

Rapid method for the determination of multiple mycotoxins in wines and beers by LC-MS/MS using a stable isotope dilution assay

A "dilute and shoot" method for the liquid chromatography-tandem mass spectrometric (LC-MS/MS) determination of multiple mycotoxins (aflatoxins B1, B2, G1, G2, ochratoxin A (OTA), fumonisins (F) B1 and B2, zearalenone, deoxynivalenol, T-2 toxin, and HT-2 toxin) in wines and beers has been developed and validated. Separation was accomplished using ultrahigh-performance liquid chromatography (UHPLC) with <10 min analysis time. Mycotoxins were detected by dynamic multiple reaction monitoring (MRM) in positive electrospray ionization mode. Due to matrix effects, (13)C-uniformly labeled mycotoxins were added to the sample extracts prior to LC-MS/MS analysis. With external calibration, recoveries were 18-148% for white wines, 15-118% for red wines, and 20-125% for beers, at three spiking levels. The (13)C-labeled internal standards compensated for matrix effects effectively, with overall recoveries of 94-112% for white wines, 80-137% for red wines, and 61-131% for beers, with greater recoveries for FB1 and FB2, at three spiking levels. The relative standard deviation was <20% for all analytes in the wines and beers. This method was applied to a USDA-funded nationwide survey of domestic and imported wines and beers for the determination of OTA and extended to include other mycotoxins.

Effect of yearly conditions and management practices on ochratoxin A production in Sultana Seedless vineyards

Sun drying of seedless grapes (Vitis vinifera cv. Sultanina) is widely practised in the western Aegean Region providing Turkey with a significant share in the world trade of sultanas. Research was initiated in 1998 to determine the incidence of ochratoxin A (OTA), to identify the major factors resulting in contamination and to develop techniques to reduce or prevent contamination. This paper assesses OTA formation in five experimental vineyards located in Manisa province of Turkey between 1998 and 2003. The cultural practices recorded were tillage (type and timing), fertilisation, plant protection, irrigation, trellising, pruning, GA(3) application, harvest maturity and date, and drying practices (type of drying yard, dipping into alkaline solution, length of drying period). In the experimental vineyards, no OTA was found at veraison. OTA levels in grapes harvested at fresh maturity ranged between <LOD and 8 ng g(-1), whereas in dried sultanas they were between <LOD and 35 ng g(-1). The frequency of OTA-positive samples increased in dried grapes compared with fresh. The number and timing of tillage, number of damaged berries, and removal of damaged/infected berries prior to sun drying were identified as the major good practices that may contribute to the reduction of OTA in sultanas.

Determination of Patulin and Ochratoxin A using HPLC in apple juice samples in Saudi Arabia

Although, Patulin and Ochratoxin are produced by the same genera of molds, however, Patulin was the most extensively studied mycotoxins in apple juice and no reports have explored the presence of Ochratoxin A in the apple juice. Therefore, the objective of this study was to explore the presence of Patulin and Ochratoxin A in apple juice in Saudi Arabian market of Jeddah. Potato dextrose agar(PDA) was used to detect fungal contamination. Patulin was determined using HPLC equipped with a UV detector set at 276 nm. Also, HPLC with fluorescence detector was set at 333 and 420 nm as excitation and emission wavelength, respectively,was used for Ochratoxin A separation. All samples of apple juice were free from fungi and yeasts. The Patulin (PAT) was detected in only one type out of 17 types (5.88%) with a concentration of 152.5 ppb, (305%) increased compared with the maximum permitted level (50 ppb). However the occurrence of Ochratoxin A (OTA) in apple juice samples was discovered in 5 types out of 17 types (29.41%). The concentration of OTA ranged from 100 to 200 ppb reaching 5-10-folds compared with the permissible limits (20 ppb).

Mycotoxins in grapes and wine in Europe: occurrence, factors affecting the occurrence and related toxicological effects

In 2006, the European Commission has established maximum levels for ochratoxin A in wine and grape products, using occurrence data up to 2001 and toxicity data up to 2006. This paper presents an up-to-date overview of the occurrence of mycotoxins in grapes and wine produced in Europe in the period 1995-2010. In addition, for the most frequently occurring mycotoxins, factors influencing the occurrence, and the toxicological effects are presented. To evaluate possible trends in occurrence, contamination data were grouped into three periods of time, i.e. 1995-1999, 2000-2006 and 2007-2010. Most of the available contamination data on mycotoxins in grapes and wine refer to ochratoxin A, but occurrence data on this toxin from 2006 onwards are very limited. The occurrence of ochratoxin A is higher in the southern European countries than in the northern countries, and higher in red and sweet wines as compared to white wines. Fumonisins occur frequently, but in low concentrations. Data on the natural occurrence of Alternaria toxins are not available. The most important factors that influence ochratoxin A contamination of grapes and wine include: temperature and relative humidity in the month before harvesting the berries, the type of wine (maceration), and the percentage of damaged berries before vinification. Applying good agricultural practices in the vineyard, including minimizing damaged berries and chemical or biological control of the fungi, are the best methods to limit mycotoxin formation in grapes and wine. Ochratoxin A, Alternaria toxins and fumonisins are toxic to animals. These toxins are of concern to human health, but clear evidence on their relationship with human disease is not available yet. Therefore, more research in this area would be desirable.

LC-MS/MS multi-analyte method for mycotoxin determination in food supplements

A multi-analyte method for the liquid chromatography-tandem mass spectrometric determination of mycotoxins in food supplements is presented. The analytes included A and B trichothecenes (nivalenol, deoxynivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, neosolaniol, fusarenon-X, diacetoxyscirpenol, HT-2 toxin and T-2 toxin), aflatoxins (aflatoxin-B(1), aflatoxin-B(2), aflatoxin-G(1) and aflatoxin-G(2)), Alternaria toxins (alternariol, alternariol methyl ether and altenuene), fumonisins (fumonisin-B(1), fumonisin-B(2) and fumonisin-B(3)), ochratoxin A, zearalenone, beauvericin and sterigmatocystin. Optimization of the simultaneous extraction of these toxins and the sample pretreatment procedure, as well as method validation were performed on maca (Lepidium meyenii) food supplements. The results indicated that the solvent mixture ethyl acetate/formic acid (95:5, v/v) was the best compromise for the extraction of the analytes from food supplements. Liquid-liquid partition with n-hexane was applied as partial clean-up step to remove excess of co-extracted non-polar components. Further clean-up was performed on Oasis HLB cartridges. Samples were analysed using an Acquity UPLC system coupled to a Micromass Quattro Micro triple quadrupole mass spectrometer equipped with an electrospray interface operated in the positive-ion mode. Limits of detection and quantification were in the range of 0.3-30 ng g(-1) and 1-100 ng g(-1), respectively. Recovery yields were above 60% for most of the analytes, except for nivalenol, sterigmatocystine and the fumonisins. The method showed good precision and trueness. Analysis of different food supplements such as soy (Glycine max) isoflavones, St John's wort (Hypericum perforatum), garlic (Allium sativum), Ginkgo biloba, and black radish (Raphanus niger) demonstrated the general applicability of the method. Due to different matrix effects observed in different food supplement samples, the standard addition approach was applied to perform correct quantitative analysis. In 56 out of 62 samples analysed, none of the 23 mycotoxins investigated was detected. Positive samples contained at least one of the toxins fumonisin-B(1), fumonisin-B(2), fumonisin-B(3) and ochratoxin A.

Ochratoxin a: general overview and actual molecular status

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium fungi that structurally consists of a para-chlorophenolic group containing a dihydroisocoumarin moiety that is amide-linked to L-phenylalanine. OTA is detected worldwide in various food and feed sources. Studies show that this molecule can have several toxicological effects such as nephrotoxic, hepatotoxic, neurotoxic, teratogenic and immunotoxic. A role in the etiology of Balkan endemic nephropathy and its association to urinary tract tumors has been also proved. In this review, we will explore the general aspect of OTA: physico-chemical properties, toxicological profile, OTA producing fungi, contaminated food, regulation, legislation and analytical methods. Due to lack of sufficient information related to the molecular background, this paper will discuss in detail the recent advances in molecular biology of OTA biosynthesis, based on information and on new data about identification and characterization of ochratoxin biosynthetic genes in both Penicillium and Aspergillus species. This review will also cover the development of the molecular methods for the detection and quantification of OTA producing fungi in various foodstuffs.

Alternatives for sample pre-treatment and HPLC determination of Ochratoxin A in red wine using fluorescence detection

Ochratoxin A is a mycotoxin widely studied due to its nephrotoxic, immunotoxic, teratogenic and carcinogenic effects. The European Commission has fixed maximum limits for Ochratoxin A in wines and in other foods. In order to determine Ochratoxin A levels in red wine, the present paper contrasts and discusses the results of a systematic study of analytical parameters for sample pre-treatment using different immunoaffinity cartridges as well as C-18 cartridges with three solvent combinations. The direct injection of wine into two types of C-18 chromatographic columns (conventional packed column and monolithic column) is evaluated as screening method. In all cases, the analysis was carried out using HPLC with fluorescence detection. The results show statistical differences when 3 types of immunoaffinity columns were used, while higher recoveries were obtained for C-18 cartridges using acetonitrile as extraction solvent. Repeatability and accuracy of immunoaffinity and C-18 sample pre-treatment were statistically comparable (alpha=0.05). Their sensitivity was also comparable, although more favorable detection limits were obtained using the immunoaffinity treatment (0.01 microg L(-1)) in comparison with C-18 treatment (0.09 microg L(-1)). Considering the maximal allowed concentration of Ochratoxin A in wine (2.00 microg L(-1)), both methods are suitable for its determination in wine. Both methods were applied to determine this toxin in 154 wine samples, and the quantitative results demonstrated statistic comparability (alpha=0.05). These results were also confirmed from the qualitative point of view using a GC-MS method. To find an easy screening method, based on a recent publication, a monolithic HPLC column and 2 conventional packed columns were tested for Ochratoxin A determination in real wine samples by direct injection, without previous clean-up. The results show that this procedure is not useful at the concentration levels usually found in wine and although shorter time is required when using the monolithic columns even with the chromatographic analysis. Finally, based on the results, it was concluded that the combination of C-18 cartridges with conventional particle packed columns and HPLC-FLD is the most appropriate alternative for Ochratoxin A analysis in wine. Indeed, considering cost, sensitivity and selectivity, this method can be used in broad prospective programs.

An overview of conventional and emerging analytical methods for the determination of mycotoxins

Mycotoxins are a group of compounds produced by various fungi and excreted into the matrices on which they grow, often food intended for human consumption or animal feed. The high toxicity and carcinogenicity of these compounds and their ability to cause various pathological conditions has led to widespread screening of foods and feeds potentially polluted with them. Maximum permissible levels in different matrices have also been established for some toxins. As these are quite low, analytical methods for determination of mycotoxins have to be both sensitive and specific. In addition, an appropriate sample preparation and pre-concentration method is needed to isolate analytes from rather complicated samples. In this article, an overview of methods for analysis and sample preparation published in the last ten years is given for the most often encountered mycotoxins in different samples, mainly in food. Special emphasis is on liquid chromatography with fluorescence and mass spectrometric detection, while in the field of sample preparation various solid-phase extraction approaches are discussed. However, an overview of other analytical and sample preparation methods less often used is also given. Finally, different matrices where mycotoxins have to be determined are discussed with the emphasis on their specific characteristics important for the analysis (human food and beverages, animal feed, biological samples, environmental samples). Various issues important for accurate qualitative and quantitative analyses are critically discussed: sampling and choice of representative sample, sample preparation and possible bias associated with it, specificity of the analytical method and critical evaluation of results.

Ochratoxin a: comparison of extraction methods from grapes and quantitative determination by different competitive enzyme-linked immunosorbent assay kits

The European Community has recently established a maximum limit for ochratoxin A (OTA) concentration in grapevine products, but many practical difficulties remain concerning the establishment of optimum cost-effective methods of quantification. The performance of four extraction procedures and three commercial competitive enzyme-linked immunosorbent assays (cELISAs) for grapes were compared. Results differed for the extractions and the cELISA kits. The advantage of using immunoaffinity columns (IACs) in the extraction was the excellent detection limit, which was between 0.06 and 0.0075 ng ml(-1) depending on the cELISA kit used. Despite lower sensitivity (between 1.2 and 0.15 ng ml(-1) depending on the cELISA kit), an extraction method in liquid phase, which was simple and inexpensive, was confirmed as suitable for quantifying OTA at levels estimated to be dangerous for human health. Two of the three cELISA kits produced satisfactory results. When these two cELISAs were coupled with IAC extraction, the lower quantification limits were 0.010 and 0.0075 ng ml(-1), respectively, and the dynamic ranges were 50 and 27, respectively. The most reliable procedures were then compared with the reference method, high-performance liquid chromatography plus fluorescent detection coupled with an IAC. The results were very similar, although the cELISAs generally provided slightly higher values than did the chromatography method. The IAC method coupled with the cELISA was four times more sensitive than was the IAC method coupled with the chromatography method. The cELISA detection techniques were excellent alternatives to the already established chromatographic protocols, especially for mass screening and for determining concentrations of OTA as low as 0.010 ng ml(-1).