A real-time polymerase chain reaction (PCR) method for the detection of wasabi (Eutrema wasabi) in foods

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.