Determination of Cry9C protein in processed foods made with StarLink corn

StarLink (Aventis CropScience US) hybrid corn has been genetically modified to contain a pesticidal protein, Cry9C, which makes it more resistant than traditional varieties to certain types of corn insect pests. Unlike other varieties of genetically engineered corn, the U.S. Environmental Protection Agency authorized the use of StarLink corn for animal feed and industrial use only, not for human consumption. However, some Cry9C-containing corn was mistakenly or inadvertently comingled with yellow corn intended for human food use. Because corn containing the Cry9C construct was not approved for human use, the U.S. Food and Drug Administration considers food containing it to be adulterated. Consequently, this regulatory violation resulted in hundreds of recalls of corn-based products, such as taco shells, containing cry9C DNA. Detecting the novel protein in StarLink corn is an emerging issue; therefore, there is no standardized or established analytical method for detecting Cry9C protein in processed foods. We developed a procedure for quantitation of Cry9C protein, with validation data, in processed food matrixes with a limit of quantitation at 1.7 ng/g (ppb), using a commercial polyclonal antibody-based Cry9C kit that was intended for corn grain samples. Intra- and interassay coefficients of variation were 2.8 and 11.8%, respectively. Mean recoveries were 73 and 85% at 2 and 5 ng/g Cry9C fortifications, respectively, for 19 control non-StarLink corn-based matrixes. Our data demonstrate only 0-0.5% of Cry9C protein survived the processing of tortilla chips and soft tortillas made from 100% StarLink corn, resulting in levels from below the detection limit to 45 ppb.