Quantification of the thermal history of insects in foods using real-time PCR-based DNA fragmentation analysis

A major challenge faced by the food industry is the contamination of food by insects. Once an insect is found in a food product, it is important to determine how it entered the food. Given that the thermal history of insects provides a clue to unraveling this mystery, in this study, we have developed a novel real-time PCR-based DNA fragmentation analysis method to quantify the thermal history of insects found in foods. We selected two species of cockroaches (Periplaneta fuliginosa and Blattela germanica) as investigative targets because cockroach contamination often causes significant economic losses in the food industry. A set of real-time PCRs was designed for each species to amplify the species-specific regions of 18S ribosomal DNA at approximate 100 and 300 bp. The degree of DNA fragmentation was evaluated using the differences between the amplification curves for the 100- and 300-bp sequences. We observed that the degree of DNA fragmentation was quantifiable when the insect was heated to >100 degrees C. Therefore, we determined whether cockroaches contaminate retort foods during the manufacturing or household consumption stages. This novel analytical method is expected to improve food safety and product reliability by identifying the cause of insect contamination.