The conditions for detecting plant-derived genes and identifying plant species in health teas, supplements, and so-called health foods in the polymerase chain reaction (PCR) were examined. The results showed that the genes may not be amplified in many samples because plant fragments and supplements may contain substances that inhibit PCR. Gene amplification by PCR was realized by suppressing the effect of inhibitors through the dilution of DNA extract of samples with nuclease-free water at a certain dilution rate. On the other hand, use of the rbcLa_F/rbcL-475R primer set, which is a combination of primers indicated by the Plant Working Group and primers prepared in this study, in PCR of the rbcL region yielded a single sequence waveform with high sensitivity and accuracy, which made it possible to analyze genes with longer sequences than usual. Applying this method to the genetic analysis of weight loss (slimming type) foods enabled us to detect the genes of Senna alexandrina and Cassia alata, which are laxatives, in the foods whose plant ingredients cannot be identified morphologically.
