Multiplex real-time PCR using SYBR® GreenER™ for the detection of DNA allergens in food

Multiplex DNA detection of food allergens on a digital versatile disk

The development of a DNA microarray method on a digital versatile disk (DVD) is described for the simultaneous detection of traces of hazelnut ( Corylus avellana L.), peanut ( Arachis hypogaea ), and soybean ( Glycine max ) in foods. After DNA extraction, multiplex PCR was set up using 5'-labeled specific primers for Cor a 1, Ar h 2, and Le genes, respectively. Digoxin-labeled PCR products were detected by hybridization with 5'-biotinylated probes immobilized on a streptavidin-modified DVD surface. The reaction product attenuates the signal intensity of the laser that reached the DVD drive used as detector, correlating well with the amount of amplified sequence. Analytical performances showed a detection limit of 1 μg/g and good assay reproducibility (RSD 8%), suitable for the simultaneous detection of the three targeted allergens. The developed methodology was tested with several commercially available foodstuffs, demonstrating its applicability. The results were in good agreement, in terms of sensitivity and reproducibility, with those obtained with ELISA, PCR-gel agarose electrophoresis, and RT-PCR.

Detection of allergenic ingredients using real-time PCR: a case study on hazelnut (Corylus avellena) and soy (Glycine max)

Compliance with the European allergen labeling legislation (Directive 2007/68/EC) is only possible when coupled with appropriate methods to detect allergens in food. The aim of the current study was to develop new real-time PCR assays for the detection of hazelnut and soy and evaluate these assays via comparison with commercially available kits. Although the new assays were not as sensitive as the commercial qualitative assays, they proved to be more specific. Moreover, the cross-reactivity study indicated contamination of some of the food products used with either hazelnut or soy, which presents a risk for the allergic consumer. The assays were able to quantify as few as 5-15 genome copies. This unit, used to express analytical results for allergen detection by means of PCR, needs to be converted to a unit expressing the amount of allergenic ingredient in order to be informative. This study emphasizes that the use of real-time PCR for allergen quantification is complicated by the lack of appropriate reference materials for allergens.

Comparison of DNA extraction methods and development of duplex PCR and real-time PCR to detect tomato, carrot, and celery in food

Traceability is of particular importance for those persons who suffer allergy or intolerance to some food component(s) and need a strict avoidance of the allergenic food. In this paper, methodologies are described to fingerprint the presence of allergenic species such as carrot, tomato, and celery by DNA detection. Three DNA extraction methods were applied on vegetables and foods containing or not containing the allergens, and the results were compared and discussed. Fast SYBR Green DNA melting curve temperature analyses and duplex PCR assays with internal control have been developed for detection of these allergenic vegetables and have been tested on commercial foods. Spiking food experiments were also performed, assessing that limits of detection (LOD) of 1 mg/kg for carrot and tomato DNA and 10 mg/kg for celery DNA have been reached.

A novel SERRS sandwich-hybridization assay to detect specific DNA target

In this study, we have applied Surface Enhanced Resonance Raman Scattering (SERRS) technology to the specific detection of DNA. We present an innovative SERRS sandwich-hybridization assay that allows specific DNA detection without any enzymatic amplification, such as is the case with Polymerase Chain Reaction (PCR). In some substrates, such as ancient or processed remains, enzymatic amplification fails due to DNA alteration (degradation, chemical modification) or to the presence of inhibitors. Consequently, the development of a non-enzymatic method, allowing specific DNA detection, could avoid long, expensive and inconclusive amplification trials. Here, we report the proof of concept of a SERRS sandwich-hybridization assay that leads to the detection of a specific chamois DNA. This SERRS assay reveals its potential as a non-enzymatic alternative technology to DNA amplification methods (particularly the PCR method) with several applications for species detection. As the amount and type of damage highly depend on the preservation conditions, the present SERRS assay would enlarge the range of samples suitable for DNA analysis and ultimately would provide exciting new opportunities for the investigation of ancient DNA in the fields of evolutionary biology and molecular ecology, and of altered DNA in food frauds detection and forensics.

Multiplex, quantitative, ligation-dependent probe amplification for determination of allergens in food

Legislation requires labeling of foods containing allergenic ingredients. Here, we present a robust 10-plex quantitative and sensitive ligation-dependent probe amplification method, the allergen-multiplex ligation-dependent probe amplification (MLPA) method, for specific detection of eight allergens: sesame, soy, hazelnut, peanut, lupine, gluten, mustard, and celery. Ligated probes were amplified by polymerase chain reaction (PCR), and amplicons were detected using capillary electrophoresis. Quantitative results were obtained by comparing signals with an internal positive control. The limit of detection varied from approximately 5 to 400 gene copies, depending on the allergen. The method was tested using different foods spiked with mustard, celery, soy, or lupine flour in the 1-0.001% range. Depending on the allergen, sensitivities were similar or better than those obtained with qPCR. The allergen-MLPA method is modular and can be adapted by adding probe pairs for other allergens. The DNA-based allergen-MLPA method will constitute a complementary method to the traditional protein-based methods.