A DNA extraction and purification method using an ion-exchange resin type kit for the detection of genetically modified papaya in processed papaya products

Papaya (Carica papaya LINNAEUS) is cultivated worldwide. The fruit is affected by the papaya ringspot virus (Gonsalves, Tripathi, Carr, & Suzuki, 2010). Genetically modified (GM) papaya line 55-1, having resistance to the papaya ringspot virus, was developed by Cornell University, the University of Hawaii and the Upjohn Company (Fitch, Manshardt, Gonsalves, Slightom, & Sanford, 1992), and has been cultivated in Hawaii since 1998. As of 2010, line 55-1, which includes cultivars such as Rainbow and SunUp (the dominant cultivar grown in Hawaii), accounts for more than 70% of Hawaii's papaya acreage (Gonsalves et al., 2010). Line 55-1 is commercially grown and consumed in Hawaii and the rest of the United States. The Canadian government approved the import of line 55-1 in 2003, and the Food Safety Commission of Japan approved its import in 2010. Furthermore, GM papaya line 63-1 was developed by Cornell University and Hawaii University, GM papaya line X17-2 was developed by University of Florida, GM papaya Huanong No. 1 was developed by South China Agricultural University. The molecular characterization and the method for the detection of Huanong No. 1 papaya were reported by Guo et al. (2009). Three lines of GM papaya were approved for growing and commercialization in each country where GM papaya was developed. However those GM papayas were unauthorized in Japan. The European Union, Japan and Korea have enforced mandatory GM labeling regulations for approved GM foods, and the import of any unauthorized GM food has been prohibited. Another GM papaya having resistance to the papaya ringspot virus YK strain (PRSV-YK) was recently detected in commercially processed food in Japan, as well as in papaya seeds imported from Taiwan (Nakamura et al., 2011). To date, the cultivation of unauthorized GM papaya resistant to PRSV-YK has not been allowed by the Cartagena Protocol, an international agreement regulating the international movement of GM organisms. Thus, the cultivation and use of GM papaya resistant to PRSV-YK as food has been limited, and it cannot be imported into Japan (MAFF, 2011; MHLW, 2011).

Therefore, detection methods for the authorized line 55-1, unauthorized line 63-1, line X17-2, Huanong No. 1 papaya and PRSV-YK resistant papaya are required to ensure the reliability of food labeling, and to monitor the presence of the unauthorized GM papaya in Japan. A qualitative detection method for line 55-1, using a PCR test and a histochemical assay, has been developed (Akiyama et al., 2002; Goda, Asano, Shibuya, Hino, & Toyoda, 2001; Wakui et al., 2004; Yamaguchi et al., 2006). A method for the extraction and purification of genomic DNA from fresh papaya, by a simple operation in a short time, has been established (Ohmori et al., 2008). However, there are no suitable methods for the extraction and purification of DNA from processed papaya products, which could be used for the detection of GM papaya. Hence, a method to extract and purify DNA from processed papaya products is required.

In the present study, we developed a method for the detection of GM papaya, using an ion-exchange resin type kit to extract and purify DNA from processed papaya products, such as dried papaya, canned papaya and papaya jam.