A specificity-enhanced time-resolved fluoroimmunoassay for zeranol employing the dry reagent all-in-one-well principle

The broad-spectrum and ultra-sensitive detection of zeranol and its analogues by an enzyme-linked immunosorbent assay in cattle origin samples

Zeranol (α-zearalanol) has been used as a growth promoter in livestock since 1969 in some non-EU countries; the residues of zeranol and its five analogues in animal origin foods may endanger human health due to their strong estrogenic and anabolic activities. Therefore, it is urgent to establish simple, rapid, real-time, broad-spectrum and high-sensitivity detection methods for the residues of zeranol and its analogues. In this study, an ultrasensitive indirect-competition enzyme-linked immunosorbent assay (ic-ELISA) was established for the rapid multi-residue detection of zeranol and its five analogues in cattle origin samples, which was based on a broad-spectrum monoclonal antibody (mAb) that specifically bound to zeranol and its analogues with high sensitivity. The half maximal inhibitory concentration (IC₅₀) values for zeranol, β-zearalanol, zearalanone, α-zearalenol, β-zearalenol, and zearalenone were 0.103, 0.080, 0.161, 0.177, 0.254, and 0.194 ng mL⁻¹, respectively, the recovery rates of cattle origin samples spiked with zeranol ranged from 79.2–104.2%, and the coefficient of variation (CV) values were less than 11.4%. Excellent correlation (R² = 0.9845) was obtained between the results of HPLC-MS/MS and ic-ELISA. In conclusion, the developed ic-ELISA could be employed as an ultrasensitive and broad-spectrum detection method for monitoring trace ZEN residues in cattle origin foods.

This paper presents a broad-spectrum and ultra-sensitive ic-ELISA method for the rapid detection of zeranol and its analogues in cattle origin samples.

A novel biosensor for the detection of zearalenone family mycotoxins in milk

In this study, a method for detecting estrogenic mycotoxin residues in milk was developed utilizing bioluminescent whole-cell biosensors. Milk products of various compositions were spiked with the estrogenic mycotoxins zearalenone and its metabolites zearalanone, alpha-zearalanol, beta-zearalanol, alpha-zearalenol and beta-zearalenol. The estrogenic response was detected by a whole-cell biosensor based on a genetically modified Saccharomyces cerevisiae strain that in the presence of an estrogenic compound produces firefly luciferase-enzyme and further light emission within a system provided with D-luciferin substrate. The results show that the yeast sensor reacts to mycotoxins with typical sigmoidal response at nanomolar concentrations. The response differs in different milk products with regard to the fat content of the milk. Due to short assay time of less than 3h and automation the approach can be used as a bioavailability and activity screening method prior to more detailed chemical analysis.

Phenolics: occurrence and immunochemical detection in environment and food

Phenolic compounds may be of natural or anthropogenic origin and be present in the environment as well as in food. They comprise a large and diverse group of compounds that may be either beneficial or harmful for consumers. In this review first a non-exhausting overview of interesting phenolics is given, in particular with regards to their presence in environment and food. For some of these compounds, beneficial, toxicological and/or optionally endocrine disrupting activities will be presented. Further, immunochemical detection and/or isolation methods developed will be discussed, including advantages and disadvantages thereof in comparison with conventional analytical methods such as HPLC, GC, MS. A short overview of new sensor-like methods will also be included for present and future application.

Development and evaluation of immunoassay for zeranol in bovine urine

A high affinity polyclonal antibody-based enzyme linked immunosorbent assay (ELISA) was developed for the quantification of zeranol in bovine urine. On the basis of urine matrix studies, the optimized dilution factors producing insignificant matrix interference were selected as 1:5 in pretreatment. In the improved ELISA, the linear response range was between 0.02 and 1 microg/ml, and the detection limit was 0.02 microg/ml for the assay. The overall recoveries and the coefficients of variation (CVs) were in the range of 82% to approximately 127% and 3.5% to approximately 8.8%, respectively. Thirty-six bovine urine samples spiked with zeranol (ranging from 0.2 to 10 microg/ml) were detected by the ELISA and liquid chromatography (LC) method, and good correlations were obtained between the two methods (R(2)=0.9643). We conclude that this improved ELISA is suitable tool for a mass zeranol screening and can be an alternative for the conventional LC method for zeranol in bovine urine.

Comparison of time-resolved fluoroimmunoassay for determining hexoestrol residues in chicken muscle tissues based on polyclonal antibodies with liquid chromatography and tandem mass spectrometry

A time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of hexoestrol (HES) residues in animal tissues. The limit of detection (LOD) was determined to be 0.02 ng g(-1) and the limit of quantification (LOQ) was less than 0.12 ng g(-1). The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of market chicken muscle tissues and confirmed by high-performance liquid chromatography and tandem mass spectrometry (LC-MS-MS). This proposed technique could be applied to routine residue analysis.

Analytical methods for the determination of zeranol residues in animal products: A review

Analytical methods for zeranol residues are reviewed. Zeranol was a widely used as an anabolic promoter, and it could give rise to very low residues in the edible tissues of food animals. Zeranol was officially banned in Europe due to safety concerns because of its potential carcinogenic and endocrine-disrupting biological activity. A few analytical methods for determination of zeranol are reported in the literature and most of the methods such as thin-layer chromatography (TLC), gas chromatography-mass spectrometry (GC/MS), high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC/MS) and immunoassay are reviewed in this paper. Specific aspects of analysing zeranol such as sample selection, sample handling, method selection and chromatographic conditions are discussed. The instrumental methods such as LC/MS and GC/MS provide sensitive and specific techniques, but are very laborious and expensive. These methods are suitable for confirmation but not for screening of large numbers of samples. A rapid, sensitive and specific assay is needed to detect positive samples in routine analysis, and immunoassay offers practical advantages over the conventional instrumental methods in rapid analysis of zeranol residues. Immunochemical methods such as enzyme-linked immunoabsorbant assay (ELISA) are simple, rapid and cost-effective, with adequate sensitivity and specificity to detect small molecules. This review can be considered as a basis for further research aimed at identifying the most efficient approaches for the analysis of zeranol.

Time-resolved fluoroimmunoassay for ractopamine in swine tissue

This study describes the development and validation of a time-resolved fluoroimmunoassay (TR-FIA) for screening ractopamine (RAC) in swine tissue. The method is based on the direct competitive-type immunoassay using europium-labeled anti-RAC monoclonal antibody as a tracer and RAC-ovalbumin as a solid-phase antigen. When RAC was spiked at levels of 1-10 microg kg(-1), recoveries ranged from 88.2 to 118.5% for swine liver and muscle with coefficients of variation from 7.1 to 20.5%. The detection limit was 0.1 microg kg(-1). The proposed TR-FIA method was applied to the determination of RAC in an actual residue study and the applicability was confirmed by liquid chromatography-tandem mass spectrometry.

Time-Resolved Fluoroimmunoassay for 19-Nortestosterone Residues in Aquaculture Tissues

A competitive time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of 19-nortestosterone (17beta-NT) residues in aquaculture tissues. The limit of detection (LOD) was determined to be 0.08 ng g-1 and the limit of quantification (LOQ) was less than 0.8 ng g-1. The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of incurred aquaculture tissues and confirmed by liquid chromatography tandem mass spectrometry (LC/MS/MS). This proposed technique could be applied to routine residue analysis.

Rapid Determination of Time-Resolved Fluoroimmunoassay for Medroxyprogesterone Acetate Residues in Pork Tissues and Comparison with Liquid Chromatography and Tandem Mass Spectrometry

A competitive time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of medroxyprogesterone acetate (MPA) residues in pork tissues. The limits of detection (LOD) was determined to be 0.06 ng g-1 and the limits of quantification (LOQ) was less than 0.8 ng g-1. The intra-assay variations were below 10% and the interassay variations ranged between 9.7 and 12.7%. The mean recoveries established at six concentration levels varied from 87.3 to 108.3%. The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of incurred pork tissues and confirmed by high-performance liquid chromatography and tandem mass spectrometry (LC-MS-MS). This proposed technique could be applied to routine residue analysis.

A monoclonal antibody-based time-resolved fluoroimmunoassay for chloramphenicol in shrimp and chicken muscle

A time-resolved fluoroimmunoassay (TR-FIA) for determination of chloramphenicol (CAP) in shrimp and chicken muscle was developed. The method was based on a direct competitive immunoassay using europium-labeled anti-CAP monoclonal antibody (MAb) and CAP-ovalbumin as coated antigen. The limit of detection was 0.05 ng g(-1) and limit of quantification was 0.1 ng g(-1). Recoveries ranged from 101.2 to 112.5% for shrimp and 104.9 to 115.3% for chicken muscle at spiked levels of 0.1-5 ng g(-1), with intra-assay and inter-assay variations 8.7-14.6 and 9.6-17.8%, respectively. The results obtained by the TR-FIA and ELISA correlated well. The established TR-FIA was validated for the determination of incurred shrimp samples and confirmed by gas chromatography with microcell electron capture detector (GC-microECD).

Prevalence of zeranol, taleranol andFusariumspp. toxins in urine: implications for the control of zeranol abuse in the European Union

There is currently little information concerning the prevalence of zeranol and taleranol in animal urine following metabolism of the naturally occurring Fusarium spp. toxins. An epidemiological study is described which involves four European Union control laboratories in which 8008 urine samples were screened for the presence of zeranol using a time-resolved fluoroimmunoassay (TR-FIA). Of these samples, 93.6% screened negative for zeranol. All samples testing positive for zeranol were then analysed with a confirmatory method. Based on the confirmatory results, the TR-FIA-positive samples were then categorized as false-positive, true-positive or 'equivocal' (zeranol/taleranol and the Fusarium spp. toxins detected). The true-positive samples represented only 0.05% of the total number of samples (n = 4). After statistical analysis, 170 of 174 equivocal samples proved to belong to a 'normal' population in which the amount of zeranol/taleranol could be related to the total amount of Fusarium spp. toxins through a linear regression with a 99% prediction interval. This suggested that the presence of zeranol in these samples might be due to in vivo metabolism of the Fusarium spp. toxins. The presence of zeranol in the four remaining 'outliers' might be attributable to zeranol abuse rather than to natural contamination. The results are of interest for control laboratories as they might provide an analytical tool to help distinguish between abuse and natural contamination in zeranol testing.

An all-in-one dry chemistry immunoassay for the screening of coccidiostat nicarbazin in poultry eggs and liver

An automated immunoassay for the detection of nicarbazin residues in poultry eggs and liver was developed. The assay was based on a novel all-in-one dry chemistry concept and time-resolved fluorometry. The analyte specific antibody was immobilized into a single microtiter well and covered with an insulation layer, on top of which the label was dried in a small volume. The extracted sample was added automatically to the dry microtiter well, and the result was available within 18 min. Due to the rapidity and simplicity, the quantitative immunoassay could also be used as a high throughput screening method. The analytical limit of detection for the assay was calculated as 0.1 ng mL(-)(1) (n = 12) and the functional limit of detection as 3.2 ng g(-)(1) for egg (n = 6) and 11.3 ng g(-)(1) for liver (n = 6) samples. The sample recovery varied from 97.3 to 115.6%. Typically, the intra-assay variations were less than 10%, and interassay variations ranged between 8.1 and 13.6%.

Rapid time-resolved fluoroimmunoassay for the screening of narasin and salinomycin residues in poultry and eggs

Anticoccidial drugs are extensively used in the poultry industry to control the infection of the single-cell protozoa of the genus Eimeria. The most commonly used coccidiostats in poultry are the polyether ionophores such as narasin and salinomycin. This paper presents a rapid and simple method for the screening of residues of these two coccidiostatic compounds in poultry and eggs. The method is based on time-resolved fluoroimmunoassay. Sample preparation of eggs consists only of one extraction and evaporation step, and a solid phase extraction step is needed only for the muscle sample preparation. Mean recoveries were 91.0% from muscle tissue and 81.1% from eggs for both narasin and salinomycin. The performance of the assay was evaluated only for narasin because salinomycin had a cross-reactivity of 100% in the assay, and the recoveries of the compounds were not significantly different (P >0.05). The limits of detection [mean + 3 x standard deviation (SD)] of narasin were 0.56 and 0.28 microg/kg, and the limits of quantification (mean + 9 x SD) were 1.80 and 0.57 microg/kg for muscle and eggs, respectively. The coefficients of variation (CV) of the interassay precision of the method, evaluated by five replicate analyses of muscle samples spiked with 2 microg/kg of narasin and egg samples spiked with 1 microg/kg of narasin, were 4.1 and 6.4%, respectively. The CVs of intra-assay precision tests, determined by 10 replicate analyses at the above-mentioned concentration levels, were 3.8 and 4.5%, respectively.

Interlaboratory ring test of time-resolved fluoroimmunoassays for zeranol and alpha-zearalenol and comparison with zeranol test kits

Many zeranol immunoassay test kits cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the evaluation and application of recently published, dry reagent time-resolved fluoroimmunoassays (TR-FIA) for zeranol and the toxin alpha-zearalenol. A ring test of bovine urine fortified with zeranol and/or alpha-zearalenol in four European Union National Reference Laboratories demonstrated that the TR-FIA tests were accurate and robust. The alpha-zearalenol TR-FIA satisfactorily quantified alpha-zearalenol in urine fortified at 10-30 ng ml(-1). The specificity-enhanced zeranol TR-FIA accurately quantified zeranol in the range 2-5 ng ml(-1) and gave no false-positive results in blank urine, even in the presence of 30 ng ml(-1) alpha-zearalenol. Zeranol TR-FIA specificity was demonstrated further by analysing incurred zeranol-free urine samples containing natural Fusarium spp. toxins. The TR-FIA yielded no false-positive results in the presence of up to 22 ng ml(-1) toxins. The performance of four commercially available zeranol immunoassay test kits was more variable. Three kits produced many false-positive results. One kit produced only one potential false-positive using a protocol that was longer than that of the TR-FIA. These TR-FIAs will be valuable tools to develop inspection criteria to distinguish illegal zeranol abuse from contamination arising from in vivo metabolism of Fusarium spp. toxins.

Development and validation of dry reagent time-resolved fluoroimmunoassays for zeranol and alpha-zearalenol to assist in distinguishing zeranol abuse from Fusarium spp. toxin contamination in bovine urine

Zeranol, an oestrogenic growth promoter in food animals, is banned within the European Union (EU). However, commercially available immunoassay kits for zeranol cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the validation of a specificity enhanced, rapid dry reagent time-resolved fluoroimmunoassay (TR-FIA) for zeranol (recovery 99%, limit of detection 1.3 ng ml(-1)) demonstrating that up to 150 ng ml(-1) of Fusarium spp. toxins in urine do not lead to false-positive results. This assay will assist EU Member States to implement Council Directive 96/23/EC, which requires states to monitor for potential abuses of zeranol. A similar TR-FIA for the Fusarium spp. toxin alpha-zearalenol, using the same sample extract, is also described (recovery 68%, limit of detection 5.6 ng ml(-1)). Only the addition of diluted sample extract is required to perform these dry-reagent TRFIAs, the results being available within 1h of extract application. The EU-funded project 'Natural Zeranol' (FAIR5-CT97-3443) will use these fluoroimmunoassays to screen bovine urine in four Member States to gather data on the seasonality of Fusarium spp. toxin contamination of urine and the incidence of zeranol screening test positives.