99A-16
Detection of transgenic sequences by PCR in alkaline cooked corn Mexican products
A. GÁLVEZ1, C. Fong1, C. Luis1, R. Madrid1, J. Plasencia2, and M. Quirasco1. (1) Food Chemistry and Biotechnology, National Autonomous University of Mexico, Fac. Química. Conjunto E, Lab. 312. Ciudad Universitaria., Mexico City, 04510, Mexico, (2) Biochemistry, National Autonomous University of Mexico, Fac. Química. Conjunto E, Lab. 101. Ciudad Universitaria, Mexico City, 04510, Mexico
Corn is the staple food in Mexico and Central America, where an alkaline treatment (nixtamalization) is applied in order to obtain dough suitable for tortilla making and for preparing corn snacks. It is generally considered that nixtamal conditions are stringent enough to prevent further detection of DNA.
Our objective was to assess the suitability of PCR detection of transgenic sequences in traditional alkaline treated corn based foods, as well as in snacks, canned grains and corn cobs.
DNA extraction was performed using the DNAzol reagent followed by purification with isopropanol. End-point PCR was performed using primers designed to anneal with the CamV35S public sequence, followed by nested reactions. Restriction analyses and sequencing of amplicons were performed in order to confirm amplified sequences. Controls for the experiments were tortillas and snacks spiked with Starlink corn, made in the laboratory, at concentrations varying from 0.1 to 10%.
Analyses were made with end point PCRs where the limit of detection for CamV35S was 0.0002% in raw grains. Even though most of the products were nixtamalized, cooked on hot plate (200°C) and/or deep fried (198°C), the transgenic sequence was readily detected in samples of canned corn grains, frozen cobs, as well as in nixtamalized products: tortillas, fried tortilla chips, fried dough chips, either commercial or experimental ones. Some results are shown in Figure 1 for amplicons and their restriction analysis with Asp700. An important DNA degradation was observed due to alkaline and thermal treatments, but still the primers designed were able to amplify products of approximately 200pb.
Since previous results showed that thermal treatments are more relevant for DNA degradation than the alkaline treatment, it can be considered that PCR analysis is a very sensitive and useful tool for detecting transgenic sequences even in highly processed foods.
Session 99A, Biotechnology: General
2:00 PM - 5:30 PM, Thursday PM Room Hall N-1