The effect of sodium carboxymethyl cellulose (CMC), a food additive used as a thickener and emulsion stabilizer, on detection of genetically modified (GM) foods was evaluated. The addition of CMC to processed rice foods at 2% (w/w) concentration inhibited the yield of DNA in the DNA purification step by up to 40% and 70% using ion-exchange resin-type DNA purification kit and silica membrane-type DNA purification kit, respectively. The DNA yield from the rice vermicelli commodities containing CMC was significantly lower than that from the CMC-free rice vermicelli commodities. When 2% (w/w) CMC was contained in the rice flour with < 5,000 copies of transgenic genes for GM rice, the false negative rate in the real-time polymerase chain reaction detection targeting the genes was more than 10%. The CMC attenuates the DNA purification efficiency from the rice food samples, and may interfere with the GM rice testing using DNA samples prepared from processed rice foods containing CMC.
