In this study, we examined 78 powdered spice products for wheat contamination, using enzyme-linked immunosorbent assay (ELISA) to detect wheat proteins and polymerase chain reaction (PCR) to detect wheat DNA, as notified by the Japanese Ministry of Health, Labour and Welfare. Wheat protein was detected in 22 of the 78 samples, and wheat DNA was detected in 2 of these 22 samples. In addition, to ascertain the influence of PCR inhibitors, we screened the 22 samples for plant DNA. Plant DNA was not detected in 11 of the 22 samples. Therefore, we assumed that polysaccharides and/or phenolic compounds in the spice samples were responsible for inhibiting the PCR amplifications. Subsequently, using a modified PCR procedure, Ampdirect® plus, plant DNA was detected in all 22 samples, while wheat DNA was detected in 15 samples. These results suggest that commercial powdered spice products are contaminated with wheat. Ampdirect® plus can overcome the probable PCR inhibition, which is caused by the presence of other contaminants in the extracted DNA solution, and can easily be applied in food testing. Therefore, this method can be used to detect the presence of wheat and other allergens in processed food.
