Michelangelo Pascale

Determination of ochratoxin A in wine by means of immunoaffinity column clean-up and high-performance liquid chromatography.

A new and accurate method to quantify ochratoxin A (OA) in table wine has been developed. The method uses commercial immunoaffinity columns for clean-up and high-performance liquid chromatography (HPLC) with fluorescence detection for quantification of the toxin. Wine was diluted with a solution containing 1% polyethylene glycol (PEG 8000) and 5% sodium hydrogencarbonate, filtered and applied to an OchraTest immunoaffinity column. The column was washed with a solution containing sodium chloride (2.5%) and sodium hydrogencarbonate (0.5%) followed by water. OA was eluted with methanol and quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 333 nm, emission wavelength 460 nm) using acetonitrile-water-acetic acid (99:99:2) as mobile phase. Average recoveries of OA from white, rosé and red wine samples spiked at levels from 0.04 to 10 ng/ml ranged from 88% to 103%, with relative standard deviations (RSDs) between 0.2 and 9.7%. Detection limit was 0.01 ng/ml based on a signal-to-noise ratio of 3:1. The method was applied successfully to 56 samples of red (38), rosé (8), white (9) and dessert (1) wine. The levels of OA ranged from <0.01 to 7.6 ng/ml with red wines more contaminated than rosé and white wines. A good correlation (r=0.987) was found by comparative analysis of 20 naturally contaminated samples using this method and the method of Zimmerli and Dick with better recoveries of OA and better performances for the new method. Several advantages of this method with respect to the actually available methods have been pointed out, with particular reference to red wine which appears to be the most difficult to analyze.

Determination of ochratoxin A in domestic and imported beers in Italy by immunoaffinity clean-up and liquid chromatography

A method first developed to quantify ochratoxin A in wine has been applied to the analysis of domestic and imported beers in Italy. The method uses commercial immunoaffinity columns for clean-up and high-performance liquid chromatography for quantification of the toxin. Beer was degassed, then diluted with a polyethylene glycol-sodium hydrogencarbonate solution and applied to an OchraTest immunoaffinity column. Ochratoxin A was eluted from the immunoaffinity column with methanol and quantified by reversed-phase HPLC with fluorometric detector. Average recoveries of ochratoxin A from blank beer spiked at levels from 0.04 to 1.0 ng/ml ranged from 93.8% to 100.4%, with relative standard deviations between 3.3% and 5.7%. The detection limit was 0.01 ng/ml based on a signal-to-noise ratio of 3:1. The analysis of 61 samples of domestic (10) and imported (51) beers showed ochratoxin A levels ranging from <0.01 to 0.135 ng/ml with an incidence of contamination of 50% and no substantial difference between strong and pale beers.

Determination of zearalenone in corn by means of immunoaffinity clean-up and high-performance liquid chromatography with fluorescence detection

A rapid and accurate method to quantify zearalenone in corn is described. The method uses immunoaffinity chromatography for purification and high-performance liquid chromatography (HPLC) for detection and quantification of the toxin. Corn samples were extracted with acetonitrile-water (90:10, v/v) and the extract was diluted with water (1:10, v/v) and applied to a Vicam ZearalaTest immunoaffinity column. The column was washed with water and zearalenone was eluted with methanol and quantified by reversed-phase HPLC with fluorometric detection (lambda ex = 274 nm, lambda em = 440 nm) using acetonitrile-water-methanol (46:46:8, v/v) as mobile phase. Zearalenone recoveries from the ZearalaTest column were higher than 95%, and the column can hold a maximum of 4.0 micrograms of toxin. Average recoveries of zearalenone from corn spiked at levels of 0.1-10 micrograms/g ranged from 9 to 99.5%, with relative standard deviations of < 6%. The detection limit was 3 ng/g based on a signal-to-noise ratio of 3:1. Comparative analysis of 14 naturally contaminated samples using this method and the AOAC official method 985.18 showed a reasonable correlation (r = 0.87). Advantages of the immunoaffinity method as compared to the AOAC method are discussed.

Monoclonal antibody based electrochemical immunosensor for the determination of ochratoxin A in wheat

Competitive electrochemical enzyme-linked immunosorbent assays based on disposable screen-printed electrodes have been developed for quantitative determination of ochratoxin A (OTA). The assays were carried out using monoclonal antibodies in the direct and indirect format. OTA working range, I(50) and detection limits were 0.05-2.5 and 0.1-7.5mugL(-1), 0.35 (+/-0.04) mugL(-1) and 0.9 (+/-0.1) mugL(-1), 60 and 100mugL(-1) in the direct and indirect assay format, respectively. The immunosensor in the direct format was selected for the determination of OTA in wheat. Samples were extracted with aqueous acetonitrile and the extract analyzed directly by the assay without clean-up. The I(50) in real samples was 0.2mugL(-1) corresponding to 1.6mug/kg in the wheat sample with a detection limit of 0.4mug/kg (calculated as blank signal -3sigma). Within- and between-assay variability were less than 5 and 10%, respectively. A good correlation (r=0.9992) was found by comparative analysis of naturally contaminated wheat samples using this assay and an HPLC/immunoaffinity clean-up method based on the AOAC Official Method 2000.03 for the determination of OTA in barley.

Optimization of a Fluorescence Polarization Immunoassay for Rapid Quantification of Deoxynivalenol in Durum Wheat-Based Products

A fluorescence polarization immunoassay previously described for deoxynivalenol (DON) screening in wheat was optimized for the rapid quantification of DON in durum wheat kernels, semolina, and pasta. A background signal was observed in both spiked and naturally contaminated samples, strictly depending on the testing matrix. After subtracting the background DON level for durum wheat (0.27 microg of DON per g), semolina (0.08 microg of DON per g), and pasta (0.04 microg of DON per g), an accurate quantification of DON was possible at levels greater than 0.10 microg/g for all matrices. Average recoveries from spiked samples (0.25 to 1.75 microg/g) were 98, 102, and 101% for wheat, semolina, and pasta, respectively. Comparative analyses of 35 naturally contaminated durum wheat samples, 22 semolina samples, and 26 pasta samples performed by both the fluorescence polarization method and high-pressure liquid chromatography/immunoaffinity cleanup showed a good correlation (r > 0.995). The fluorescence polarization method showed better accuracy and precision with respect to the high-pressure liquid chromatography method and is suitable for the rapid and quantitative determination of DON in durum wheat-based products at levels foreseen by existing or coming international regulations.

Determination of T-2 toxin in cereal grains by liquid chromatography with fluorescence detection after immunoaffinity column clean-up and derivatization with 1-anthroylnitrile.

1-Anthroylnitrile (1-AN) has been shown to be an efficient labelling reagent for the determination of T-2 toxin (T-2) by high-performance liquid chromatography (HPLC)-fluorescence detection. This reaction has been used to develop a sensitive, reproducible and accurate method for the determination of T-2 in wheat, corn, barley, oats, rice and sorghum. The method uses immunoaffinity columns containing antibodies specific for T-2 for extract clean-up, pre-column derivatization with 1-AN and HPLC with fluorescence detection for toxin determination. Ground cereal samples were extracted with methanol-water (80:20, v/v), the extracts were purified by immunoaffinity columns and the toxin was quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 381 nm, emission wavelength 470 nm) after derivatization with 1-AN. Recoveries from the different cereals spiked with T-2 at levels ranging from 0.05 to 1.5 microg/g were from 80 to 99%, with relative standard deviations of less than 6%. The limit of detection was 0.005 microg/g, based on a signal-to-noise ratio of 3:1.

Identification and characterization of new Fusarium masked mycotoxins, T2 and HT2 glycosyl derivatives, in naturally contaminated wheat and oats by liquid chromatography–high-resolution mass spectrometry

The presence of glucoside derivatives of T-2 and HT-2 toxins (type A trichothecene mycotoxins) in naturally contaminated wheat and oats is reported for the first time. The use of advanced high-resolution mass spectrometry based on Orbitrap technology allowed to obtain molecular structure details by measuring exact masses of main characteristic fragments, with mass accuracy lower than 2.8 ppm (absolute value). A monoglucoside derivative of T-2 toxin and two monoglucoside derivatives of HT-2 toxin were identified and characterized. The analysis of their fragmentation patterns provided evidence for glucosylation at C-3 position for T-2 toxin and at C-3 or C-4 position for HT-2 toxin. A screening for the presence of these new masked forms of mycotoxins was carried out on a set of naturally contaminated wheat and oats samples. On the basis of peak area ratio between glucoside derivatives and free T-2 and HT-2 toxins, the presence of glucoside derivatives was more likely in wheat than in oats samples. The present work confirms the widespread occurrence of trichothecene glucosides in cereal grains naturally contaminated with the relevant unconjugated toxins, thus suggesting the importance of developing suitable analytical methods for their detection. Besides toxicity studies, tracking down these new masked forms of trichothecenes along the food/feed chain would enable to collect information on their relevance in human/animal exposure to mycotoxin risk.

Rapid method for the determination of ochratoxin A in urine by immunoaffinity column clean-up and high-performance liquid chromatography

A rapid and accurate method to quantify ochratoxin A (OTA) at ppt (pg/ml) levels in urine has been developed. The method uses commercial immunoaffinity columns for clean-up and reversed phase high-performance liquid chromatography (HPLC) with fluorescence detector for quantification of the toxin. Average recoveries of OTA from human urine spiked at levels from 0.05 ng/ml to 1.0 ng/ml ranged from 88% to 93%, with relative standard deviations (RSDs) between 1% and 8%. Detection limit was 0.005 ng/ml. Out of 41 human urine samples, 25 were found positive to OTA with only one sample exceeding 0.05 ng/ml; the latter originated from a patient affected by karyomegalic interstitial nephritis. The method can be used as a rapid and non-invasive tool to assess human and animal exposure to OTA in epidemiological studies and to establish the possible role of OTA in acute animal intoxications or human end-stage renal diseases.

Improvement of detection sensitivity of T-2 and HT-2 toxins using different fluorescent labeling reagents by high-performance liquid chromatography.

T-2 and HT-2 toxins are Fusarium mycotoxins that can occur in cereals and cereal-based products. Three fluorescent labeling reagents, i.e. 1-naphthoyl chloride (1-NC), 2-naphthoyl chloride (2-NC) and pyrene-1-carbonyl cyanide (PCC), were used for the determination of T-2 and HT-2 toxins by high-performance liquid chromatography (HPLC) with fluorescence detection (FD). Pre-column derivatization of T-2 and HT-2 toxins was carried out under mild conditions (50 degrees C, 10 min) in toluene with 4-dimethylaminopyridine (DMAP) as catalyst. All fluorescent derivatives were identified and characterized by HPLC-tandem mass spectrometry (HPLC-MS/MS). Optimal stoichiometric ratios (toxin:derivatizing reagent:catalyst), linear range and repeatability of the reaction, stability and sensitivity of the derivatives were determined. A wide linear range (10-1000 ng of either derivatized T-2 or HT-2 toxin), good stability (up to 2 weeks at -20 degrees C or 5 days at room temperature) of the fluorescent derivatives and good repeatability of the reaction (RSD</=8%) were observed. Detection limits (based on a signal-to-noise ratio of 3:1) were 10.0, 6.3 and 2.0 ng for derivatized T-2 toxin and 6.3, 2.3 and 2.8 ng for derivatized HT-2 toxin with 1-NC, 2-NC and PCC, respectively. In terms of sensitivity and repeatability, PCC and 2-NC reagents showed better performance than 1-anthroylnitrile (1-AN), a previously reported labeling reagent for T-2- and HT-2 toxins. Preliminary studies also showed the applicability of PCC and 2-NC as fluorescent labeling reagents for the simultaneous determination of T-2 and HT-2 toxins in cereal grains by HPLC/FD following immunoaffinity column clean-up.

Use of cyclodextrins as modifiers of fluorescence in the detection of mycotoxins

Cyclodextrins, cyclic oligosaccharides composed of amylose subunits, are known to interact with mycotoxins. The interactions may be useful to analytical chemists by altering the properties of the mycotoxin of interest, namely the chromatographic properties, electrophoretic properties, fluorescence, or absorption of these fungal metabolites. Practical applications of these effects have been the incorporation of cyclodextrins into high-performance liquid chromatography and capillary electrophoresis methods for mycotoxin detection. Specific mycotoxins include those with a native fluorescence such as the aflatoxins, ochratoxin A (OTA) and zearalenone (ZEN) as well as those that can be rendered fluorescent through derivatization, such as T-2 toxin. The literature describing the applications of cyclodextrins in mycotoxin analysis is reviewed and an attempt to extend the use of cyclodextrins to the detection of labelled T-2 toxin is presented. Twenty cyclodextrins were evaluated for their ability to enhance the fluorescence emission of T-2 toxin derivatized with pyrene-1-carbonyl cyanide (T2-Pyr). This evaluation revealed that heptakis (2,6-di-O-methyl)-β-cyclodextrin (DIMEB), in particular, enhanced T2-Pyr fluorescence. DIMEB was used as a buffer modifier in a capillary electrophoresis-laser-induced fluorescence (CE-LIF) method for detecting T-2 in maize. Because of the effects that certain cyclodextrins have, especially under aqueous conditions, they may make useful additives for a variety of mycotoxin analytical methods.