Chloroplast markers for detecting rice grain-derived food ingredients in commercial mixed-flour products

Abstract

The development of DNA techniques such as quantitative real-time PCR (qRT-PCR) has led to advancements in the field of illegal food product detection. Here, we report a PCR-based method to detect rice grain flour in commercial mixed-flour products. To select the chloroplast genes available for a rice-specific marker, we analyzed chloroplast DNA (cpDNA) polymorphisms in several gene families from five plant species, including rice, adlay, barley, maize, and wheat by using comparative sequence analysis. We found two potential rice-specific marker genes, rpoB and rpoC2, which exhibited relatively high numbers of segregating sites compared to other genes. We designed gene-specific primers for rpoB and rpoC2 on the basis of sequence differences, and identified the appropriate PCR amplification in grain flour samples derived from six Korean rice varieties using the linearity test of the qRT-PCR assay. To test the applicability of these cpDNA markers, we performed a qRT-PCR assay on total DNA obtained from different commercial food products, and successfully detected the rice-specific cpDNA region (rpoB and rpoC2) in several commercial food products that were declared to contain rice. Thus, the reported qRT-PCR assay may prove to be a useful tool for the detection of various rice flours in commercial mixed-flour products such as Sunsik.