Stability and recovery of maize DNA during food processing

The identification and quantification of food ingredients based on DNA detection depends strictly on DNA stability during the food preparation treatment and on the efficiency of DNA recovery. Investigations into DNA stability carried out on polenta by real time PCR revealed that after 65 min of processing the amplifiable DNA decreased to 40% of the amount detectable before processing. Four commercial kits for DNA extraction were compared with the hexadecyltrimethyl ammoniumbromide (CTAB)-based method for DNA extraction from different maize foodstuffs: flour, canned maize, corn chip snacks, cheese corn puff snacks, chocolate corn flakes and an infant formula having a maize flour ingredient. The methods were evaluated for recovered DNA quality and yield by agarose gel electrophoresis, PCR and real time PCR targeting of the maize zein gene. No detectable DNA could be extracted from the chocolate corn flakes, whereas highly degraded DNA was extracted from all the other materials tested except flour which yielded high quality DNA. Among the methods tested, CTAB, the Wizard method and Wizard Magnetic DNA Purification System kits gave the highest DNA yields. The overall data indicate that quantitative detection of ingredients in processed food. products may not reflect the original amount of DNA due to DNA degradation and low yield of DNA recovery.