TRANSGENE DETECTION BY PCR IN SOYBEAN PRODUCTS USED TO PRODUCE FOODS

Abstract

International regulations on trade and marketing of transgenic organisms demand their detection in foodstuffs. In this study, three
methods for gDNA isolation were tested in sources of soybean protein derived ingredients in foodstuffs. The methods were: A) Homogenization in 1 % SDS-guanidine-HCl and phenol:chloroform:isoamyl alcohol extraction, B) homogenization in 1 % SDS-β-mercaptoethanol with saline precipitation; and C) Homogenization in CTAB and cloroform:isoamyl alcohol extraction. All methods included digestion with Streptomyces griseus protease. The purity of the isolated DNA was measured by the A_260/280 nm ratio and the quality evaluated by the PCR detection of the β-conglycinine constitutive gene and a fragment of 35S CaMV promoter to identify transgenic crops. The gDNA isolated with the CTAB showed the best results in terms of extraction and amplification of both gene fragments, even in highly processed soybean protein ingredients. Moreover, the CTAB method was useful to detect transgenic material in final foodstuffs. From the 12 analyzed samples, seven were positive to the 35S promoter and β-conglycinine gene, four negative to the 35S promoter and only in one case none of the genes were detected.