Food irradiation is a process exposing food to ionizing radiations resulting in reduced storage losses, extended shell life and/or improved microbiological and parasitological safety of foods. Therefore, analytical methods are necessary to control irradiated food products by legal labs, ensuring enforcement of accurate labelling regulations. This publication describes a method for the specific detection of food which had been treated with ionizing radiations. The presented PCR method—working with endogenous DNA—is based on asymmetric PCR, where the two primers have different concentrations. The detection takes place with the aid of a TaqmanTM probe. The observed amplification efficiency, respectively, the obtained Ct values distinguish between irradiated and non-irradiated garlic samples. The detection limit can be estimated to approximatively 250 Gy. Experiments with heat treated garlic samples do not indicate a radiation treatment showing that this method is indeed specific for the detection of radiation treatment. As a conclusion, the presented real-time PCR method concerning the endogenous DNA is useful for sensitive and specific detection of irradiated garlic in routine analysis as well as a screening method.

To elucidate the capability of laboratories to determine allergen contents, an international interlaboratory trial was conducted using meat products spiked with 12 allergens. The measurement uncertainty was calculated independent of the applied method simulating realistic situations when comparing analysis certificates from different laboratories. The measurement uncertainty was revealed to be in the best cases +/-100%, in the worst cases quantification exhibited a measurement uncertainty of higher than 200% making quantitative analysis impossible. The measurement uncertainty seemed to depend on the analyte and assays used.

In routine analysis screening methods based on real-time PCR (polymerase chain reaction) are most commonly used for the detection of genetically modified (GM) plant material in food and feed. Screening tests are based on sequences frequently used for GM development, allowing the detection of a large number of GMOs (genetically modified organisms). Here, we describe the development and validation of a tetraplex real-time PCR screening assay comprising detection systems for the regulatory genes Cauliflower Mosaic Virus 35S promoter, Agrobacterium tumefaciens nos terminator, Cauliflower Mosaic Virus 35S terminator and Figwort Mosaic Virus 34S promoter. Three of the four primer and probe combinations have already been published elsewhere, whereas primers and probe for the 35S terminator have been developed in-house. Adjustment of primer and probe concentrations revealed a high PCR sensitivity with insignificant physical cross-talk between the four detection channels. The sensitivity of each PCR-system is sufficient to detect a GMO concentration as low as 0.05% of the containing respective element. The specificity of the described tetraplex is high when tested on DNA from GM maize, soy, rapeseed and tomato. We also demonstrate the robustness of the system by inter-laboratory tests. In conclusion, this method provides a sensitive and reliable screening procedure for the detection of the most frequently used regulatory elements present in GM crops either authorised or unauthorised for food.

Milk products like yogurt, flavoured milk-drinks, curd and cheese may be composed of milk different from cow, namely of ruminant species like sheep and goat. Such products experience an increasing demand in Europe and are recognised as healthy and naturally finished specialities. To verify declared milk compositions in these dairy products, two different quantitative multiplex PCR systems have been evaluated in a comparison test with eleven participating laboratories employing two unknown, traditionally manufactured cheeses with different degrees of ripening to determine milk fractions from cow, ewe and goat. Precision and accuracy was investigated by calibration to dilutions of DNA mixtures and to homologous matrix-adapted reference cheeses, respectively. As expected, independent of the particular method, best inter- and intra-laboratory accuracy has been achieved through the use of homologous reference cheese standards. Furthermore, it has been shown that cheese ripening and the concomitant DNA degradation exert an inverse effect on the method’s sensitivity and performance characteristics. Additionally, a broad market survey of different milk products demonstrated its applicability as an efficient analytical tool for food control laboratories to challenge the authenticity of milk and its products from small ruminants.

The quantification of meat proportions in raw and boiled sausage according to the recipe was evaluated using three different calibrators. To measure the DNA contents from beef, pork, sheep (mutton), and horse, a tetraplex real-time PCR method was applied. Nineteen laboratories analyzed four meat products each made of different proportions of beef, pork, sheep, and horse meat. Three kinds of calibrators were used: raw and boiled sausages of known proportions ranging from 1 to 55% of meat, and a dilution series of DNA from muscle tissue. In general, results generated using calibration sausages were more accurate than those resulting from the use of DNA from muscle tissue, and exhibited smaller measurement uncertainties. Although differences between uses of raw and boiled calibration sausages were small, the most precise and accurate results were obtained by calibration with fine-textured boiled reference sausages.

Wasabi (commonly described as Japanese horseradish, Eutrema wasabi syn. Wasabia japonica) has gained substantial attractiveness in recent years because of its characteristic flavour as ingredient in Japanese-style food products. Wasabi rhizomes are expensive compared to roots of common horseradish (Armoracia rusticana). A quantitative analytical method for the detection of wasabi plant is required for official food control authority laboratories to detect potential frauds. This paper presents a real-time PCR method allowing the detection and semi-quantification of wasabi (Eutrema wasabi syn. Wasabia japonica) in complex food matrices. The wasabi-specific primers and the TaqMan fluorescent probe are targeted at the multi-copy gene of the enzyme myrosinase. This method was found to be specific for wasabi and did not show any cross-reactivity with 24 food-relevant plant species, including 20 members of the Brassicaceae family. Because of using the multi-copy gene myrosinase, the sensitivity is very high with less than about 1 pg wasabi DNA per PCR. This real-time PCR method was applied to verify the correct declaration of 10 commercially available products containing wasabi according to the declared ingredients or the product description (wasabi powders, pastes, dressing, and snacks): 6 samples showed positive PCR results and in 4 samples it was not possible to detect any wasabi DNA. The reasons could be the lack of the wasabi plant material or the destruction of wasabi DNA during food processing. As a conclusion, the presented quantitative real-time PCR method is useful for sensitive and selective detection of wasabi in food products in routine analysis.

Nowadays many foods of plant origin with allergenic potential are analysed in foodstuffs by real-time PCR often in a multiplex manner [1]. These results are difficult to express in weight/weight units especially when composed food is analysed. This new method is able to determine contents of allergens in mass per cent based on a modified method of multiple standard addition with a simple mathematical analysis. It allows the quantitative analysis of an analyt in the range of 0.01 to 10 %

Quantitative PCR methods for the determination of beef, pork, chicken and turkey proportions in sausage were tested in an interlaboratory trial. Twelve different laboratories analysed six meat products each made of different compositions of beef, pork, chicken and turkey. Two kinds of calibrators were used: sausages of known proportions of meat and DNA from muscle tissue. Results generated using calibration sausages were more accurate than those resulting from the use of muscle tissue DNA. Regardless of the method used (either multiplex or single PCR), when using calibration sausages, it was always possible to quantify the proportions of meats in the unknown samples (in the range of 0.5–80%) with high precision and accuracy.

According to the EU and Swiss legislation, food has to be labelled for allergens to enable allergic consumers to avoid such food and its products. To provide efficient and reliable methods, two novel quantitative multiplex real-time polymerase chain reaction systems were developed and validated. They simultaneously determine DNA of peanut, hazelnut, celery, soy, egg, milk, almond and sesame, respectively. The tests exhibit good specificity and sensitivity in the range of 0.01%. Due to low DNA amounts, lower sensitivities for egg and milk were obtained. First comparisons of ELISA results with PCR results suggest a qualitative accordance, but a low correlation of quantitative results.

The performance of quantitative PCR-methods for the determination of beef and pork fraction in sausage was tested in an interlaboratory trial. Twelve different laboratories analysed four sausages of different composition of beef and pork by using four sausages of known fraction of meat as calibrators. Although different PCR-methods were applied, the precision of all results was better than 16% and the trueness better than 25%. The main reason for the good performance is the use of common calibrators emphasizing the importance of the quality of calibrators for molecular analysis. Thus, we conclude, that PCR-based detection methods are suitable for quantitative control of meat fractions in sausages.