Immunoaffinity column clean-up prior to thin-layer chromatography for the determination of aflatoxins in various food matrices

In situ sample cleanup during immunoassay: a simple method for rapid detection of aflatoxin B, in food samples

A strategy for rapid in situ elimination of interfering substances that are present in extracts of food samples during assay is described in this article. The novel feature of this method is that the sample purification is carried out as a part of the assay, and a separate sample cleanup step is not required. The assay procedure involves the sequential addition of standard or sample, cleaning solutions, and aflatoxin B1-horseradish peroxidase conjugate (AFB1-HRP) over antibody-spotted zones of a membrane, and 3,3'-diaminobenzidine was used as the substrate for visualization. We have determined that trifluoroacetic acid and propionic acids at concentrations of 100 mM are highly effective for cleaning groundnut, wheat, corn, and poultry feed samples and that NaHCO3 (100 mM) is successful in cleaning processed soybean. In all cases, subsequent washing was performed with phosphate-buffered saline solution to facilitate the removal of traces of adhering interfering substances. A batch of 12 samples can be analyzed within 8 min either by visual comparison of the color intensity (inversely related to the analyte concentration) of a sample spot with those of reference standards or, more precisely, by densitometry. The method was tested for the analysis of AFB1 in groundnut, wheat, corn, processed soybean, chili, and poultry feed. The detection limit obtained was 5 microg/kg, except for chili, where it was 10 microg/kg. The average recoveries from different noninfected food samples spiked with AFB1 at concentrations of 5 to 100 microg/kg were between 99 and 105%. The values obtained for infected corn and groundnut samples correlated well with the estimates obtained by high-pressure liquid chromatography. The absence of a sample extraction step reduces the cost and labor involved in the assay. The method may be potentially applicable to the assay of other mycotoxins and environmental pollutants.

Determination of aflatoxins in medicinal herbs by HPLC. An efficient method for routine analysis

A fast and easy to perform method for the routine determination of aflatoxins in medicinal herbs was developed. The described method involves a single-step extraction with a non-chlorinated solvent, an immunoaffinity clean-up and HPLC with fluorescence detection. Whilst assays with naturally contaminated and with spiked samples of several herbs showed that the recoveries were somewhat low and dependent on the kind of sample and the degree of grinding, the intra-batch reproducibility was good, allowing a reliable quantitation by the standard-addition method. Good linearity, repeatability and accuracy were demonstrated in assays involving several medicinal herbs. The limit of quantitation was of the order of 0.05-0.1 ng/g, being dependent of the species analysed, and the method required no tedious concentration or back-extraction steps.

Determination of aflatoxins in foodstuffs employing fluorometric method

Results from the examination of total aflatoxins in foodstuffs are presented Determination of the aflatoxins was done employing rapid and reliable method based on immunnosorbent columns clean-up and measurement of the aflatoxins by fluorometer (Vicam, USA). Quantification and detection limits of the method were 1.0 and 0.1 ppb respectively. This method is especially suitable when laboratories are dealing with big number of samples. 20% of the samples were found to content total aflatoxins over MRL (5 g/kg). The positive samples were further analysed with TLC as a confirmatory method, whereby over 95% of positive samples where confirmed by TLC technique. Application of this rapid aflatoxin method significantly simplifies their analysis, especially when laboratories are dealing with big number of samples.

Joint IDF-IUPAC-IAEA(FAO) interlaboratory validation for determining aflatoxin M1 in milk by using immunoaffinity clean-up before thin-layer chromatography

A collaborative study was conducted under the auspices of the International Dairy Federation (IDF), the International Union of Pure and Applied Chemistry (IUPAC) and the International Atomic Energy Agency (IAEA), a collaborative Food and Agricultural Organization (FAO) body fully to validate a method combining immunoaffinity clean-up to thin-layer chromatography for the determination of aflatoxin M(1) in milk. Work was done in order to afford those laboratories not equipped with high-performance liquid chromatography, mainly from developing countries, with a simplified but fully validated method as an alternative to the European validated immunoaffinity-high performance liquid chromatography method published as an EN ISO Standard 14501, February 1999. The validation study was carried out on samples of aflatoxin M(1)-contaminated milk and milk powder at levels close to the tolerable level of 0.5 microg l(-1) as recommended by the Codex Alimentarius and to the regulatory level of 0.05 microg l(-1) as laid down by the European Commission. Fourteen laboratories representing 11 countries participated in the trial. The relative standard deviations for repeatability and reproducibility based on raw data were in the range 27-48 and 35-54%, respectively. The recovery rate varied from 32 to 120%. The mishandling of two crucial steps of the protocol such as matrix sample reconstitution and extract evaporation could explain the wide variation of the recovery rate. For this reason, data were then corrected for recovery. Consequently, the relative standard deviations for repeatability and reproducibility were recalculated after correction for recovery and were in the range 26-54 and 34-53%, respectively. The method will be published as a standard ISO/DIS 14674--IDF 190.

Limited survey for the presence of aflatoxins in foods from local markets and supermarkets in Valencia, Spain

Aflatoxin B1 (AFB1), B2 (AFB2), G1 (AFG1) and G2 (AFG2) were extracted by matrix solid-phase dispersion with C18 silica and acetonitrile as the eluting solvent, analysed by liquid chromatography with fluorescence detection and confirmed by liquid chromatography with mass spectrometry using an electrospray interface in 58 samples grouped as cereals, dried fruits, herbs and spices, pulses, snacks, and nuts and nut products collected from local markets and supermarkets in Valencia, Spain. All samples analysed by the proposed method were previously studied with an enzyme-linked immunosorbent assay as a screening protocol for the fast detection of mycotoxins. The samples containing residues (3/58) were hazelnut (0.42 and 0.52 microg kg(-1) for AFB1 and AFG1, respectively), nut cocktail (0.29 and 0.47 microg kg(-1) for AFB1 and AFG1, respectively) and pinhol (0.30 microg kg(-1) for AFG1). Such values were below the legislated maximum residue levels for the European Union.

A combinatorial approach to obtain affinity media with binding properties towards the aflatoxins

In our work we performed a combinatorial solid-phase synthesis in aqueous medium to prepare peptide libraries from which to select an amino acid sequence with binding properties towards aflatoxins. We used polystyrene beads, functionalised with carboxylic groups as solid support and eight amino acids as monomers. During the first step 64 different sequences of two amino acids were prepared by exploiting the principles of combinatorial chemistry; then the binding properties of all sequences towards aflatoxin B(1 )were checked. We determined binding constants towards aflatoxin B(1) and towards aflatoxins B(2), G(1) and G(2). Results were promising, so we prepared a new library by using the selected dipeptide as the starting solid phase. After selecting the best tetrapeptide sequences, we determined binding constants towards the quoted aflatoxins. We obtained binding constants ( K>10(4) M(-1)) similar to those shown by human serum albumin for similar compounds. Preliminary studies on an extraction column were promising for the development of an SPE system and for its application in food matrices.

Immunoaffinity column clean-up and thin layer chromatography for determination of ochratoxin A in green coffee

An immunoaffinity clean-up-based method for determining ochratoxin A (OTA) in green coffee aiming at one-dimensional thin layer chromatography (TLC) analysis was established. OTA was extracted with a mixture of methanol and aqueous sodium hydrogen carbonate solution, purified through an immunoaffinity column, separated on normal or reversed-phase (RP) TLC plates and detected and quantified by visual and densitometric analysis. The linear equation of the standard calibration curve by densitometric analysis gave R(2) > 0.999 (0.04-84 ng). The mean recovery (R) of OTA from spiked samples (1.8-109 microg kg(-1)) by densitometric and visual analyses were 98.4 and 103.8%, respectively. The relative standard deviations (RSD) for densitometric and visual analysis varied from 1.1 to 24.9% and from 0.0 to 18.8%, respectively. The RSD for naturally contaminated samples by densitometry (three levels of contamination, n = 3) varied from 11.1 to 18.1%. The correlation (R(2)) between high-performance liquid chromatography (HPLC) and densitometry, and between visual and densitometric analysis for spiked samples were > 0.99. The limit of detection (LOD) of the method was 0.5 microg kg(-1) for normal TLC. Toluene-ethyl acetate-88% formic acid (6:3:1 v/v/v) and acetonitrile-methanol-water-glacial acetic acid (35:35:29:10 v/v/v/v) were regarded as the suitable TLC solvents for eluting both standards and samples on normal and RP TLC plates, respectively. Toluene-acetic acid (99:1 v/v) was chosen as the spotting solvent among several others for giving the best sensitivity and resolution of OTA on TLC plates as well as the best recovery of OTA from standard and sample extract residues. Preliminary studies were carried out to investigate the reuse of the immunoaffinity column and the interference of caffeine in the OTA recovery.