Development of a multiplex real-time PCR to quantify aflatoxin, ochratoxin A and patulin producing molds in foods

A multiplex real-time PCR (qPCR) method to quantify aflatoxin, ochratoxin A (OTA) and patulin producing molds in foods was developed. For this, the primer pairs F/R-omt, F/R-npstr and F/R-idhtrb and the TaqMan probes, OMTprobe, NPSprobe and IDHprobe targeting the omt-1, otanpsPN and idh genes involved in aflatoxin, OTA and patulin biosynthesis, respectively, were used. The functionality of the developed qPCR method was demonstrated by the high linear relationship of the standard curves constructed with the omt-1, otanpsPN and idh gene copies and threshold cycle (Ct) values for the respective producing molds tested to quantify aflatoxin, OTA and patulin producing molds. The ability of the optimized qPCR protocol to quantify producing molds was evaluated in different artificially inoculated foods (fruits, nuts, cereals and dry-ripened meat and cheese products). Efficiency values ranged from 81 to 110% in all inoculated foods. The detection limit was between 3 and 1logcfu/g for aflatoxin, OTA and patulin producing molds. The developed multiplex qPCR was shown be an appropriate tool for sensitive quantification of growth of toxigenic fungi in foods throughout the incubation time. Thus, the multiplex qPCR is a useful, rapid and efficient method to quantify simultaneously aflatoxin, OTA and patulin producing molds in food products.

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.

Mycobiota and mycotoxin producing fungi from cocoa beans

The present study reports on the natural mycobiota occurring in cocoa beans, paying special attention to the incidence of fungal species that are potential producers of mycotoxins. The results show that predominant fungi were different species of the genus Aspergillus belonging to section Flavi and Nigri. Of the 214 strains of Aspergillus section Flavi collected from cocoa beans, 120 were identified as A. flavus and 94 as A. tamarii. Of Aspergillus section Nigri 138 strains were isolated, with 132 belonging to A. niger aggregate and 6 to A. carbonarius species. Potential ability to produce aflatoxins (AFs) B1, B2, G1 and G2, cyclopiazonic acid (CPA) and ochratoxin A (OTA) was studied by isolate culture followed by HPLC analysis of these mycotoxins in the culture extracts. Results indicated that 64.1% and 34.2% of the A. flavus strains produced AFs and CPA, respectively. Most of the A. flavus strains presented moderate toxigenicity with mean levels of AFs ranging from 100 ng g(-1) to 1000 ng g(-1). All the CPA-producing strains of A. flavus were highly toxigenic producing >30 microg g(-1) of CPA. Furthermore, 98% of A. tamarii strains produced CPA and over 50% of them were highly CPA toxigenic. With respect to OTA-producing fungi, a high percentage of black aspergilli strains (49.2%) were able to produce OTA. Additionally, most of the OTA-producing isolates were of moderate toxigenicity, producing amounts of OTA from 10 microg g(-1) to 100 microg g(-1). These results indicate that there is a possible risk factor posed by AFs, CPA and OTA contamination of cocoa beans, and consequently, cocoa products.

Approach for ochratoxin A fast screening in spices using clean-up tandem immunoassay columns with confirmation by high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS)

An approach for ochratoxin A (OTA) fast cost-effective screening based on clean-up tandem immunoassay columns was developed and optimized for OTA detection with a cut-off level of 10 microg kg(-1) in spices. Two procedures were tested and applied for OTA detection. Column with bottom detection immunolayer was optimized for OTA determination in Capsicum ssp. spices. A modified clean-up tandem immunoassay procedure with top detection immunolayer was successfully applied for all tested spices. Its main advantages were decreasing of the number of analysis steps and quantity of antibody and also minimizing of matrix effects. The total duration of the extraction and analysis was about 40 min for six samples. Chilli, red pepper, pili-pili, cayenne, paprika, nutmeg, ginger, white pepper and black pepper samples were analyzed for OTA contamination by the proposed clean-up tandem immunoassay procedures. Clean-up tandem immunoassay results were confirmed by HPLC-MS/MS with immunoaffinity column clean-up. Among 17 tested Capsicum ssp. spices, 6 samples (35%) contained OTA in a concentration exceeding the 10 microg kg(-1) limit discussed by the European Commission. All tested nutmeg (n=8), ginger (n=5), white pepper (n=7) and black pepper (n=6) samples did not contain OTA above this action level.

Fitness for purpose – Ochratoxin A analytical developments

Laboratory accreditation involving third party auditing, the use of validated methods and participation in laboratory proficiency testing are essential elements for laboratory quality assurance in relation to ochratoxin A (OTA) analysis. A number of methods, mainly based on liquid chromatography (LC) with fluorescence detection (FD), coupled with immunoaffinity column or solid phase extraction cleanup, have been collaboratively validated and adopted as official standards for OTA determination in a variety of foods, including cereals, coffee, wine and beer. Enzyme-linked immunosorbent assays (ELISA) kits are widely used as screening methods for the occurrence of OTA in food. Novel technologies using anti-OTA antibodies (electrochemical immunosensors, fluorescence polarisation, lateral flow devices, enzyme-based flow through membranes, and surface plasmon resonance biosensors) have been proposed for rapid analysis of OTA in food and beverages, and may be applied for in situ measurements. Validation of these immunochemical methods and commercial kits is required. Liquid chromatography-mass spectrometry represents an adequate alternative to LC-FD particularly in the area of multi-mycotoxin analysis. OTA specific molecularly imprinted polymers are currently considered for cleanup as a potential and cheaper alternative to immunoaffinity or solid-phase extraction sorbents.