Does duration of cooking have an effect on PCR detection of meat for forensic purposes?

Although conventional Polymerase Chain Reaction (PCR) is one of the best methods used for meat identification for forensic purpose, some samples of cooked meat presented to Veterinary Research Institute for meat species identification have not responded in conventional PCR. Objective of this research was to exclude one of the possible reasons that would have caused this problem. To identify the effect of different cooking time on Deoxyribo Nucleic Acids (DNA) extraction and PCR, beef was used as the meat type, since very often the suspicious sample is claimed to be ‘beef’. Total of 18 samples of beef from 3 different commercial sources were used. Samples (n=6) from each source were cut into equal sizes and cooked separately to minimize contamination. They were cooked at 20 min, 40 min and 60 min cooking periods by adding equal amounts of commercially available products of turmeric powder, curry powder, chillie powder, salt powder and water. Samples were kept separately until DNA extraction. Forward and reverse primers were used for DNA amplification of bovine cytochrome b gene. The samples were subjected to DNA quantification by using the nanodrop spectrophotometer. Change in absorbance by DNA samples was used to quantify the DNA samples. The results of gel electrophoresis revealed that the samples were positive in all 3 cooking conditions with bands of ~ 272 bp equivalent compared to ladder and the positive control sample. Statistical analysis of DNA quantities revealed that even though the cooking time (up to 60 min) had no effect on the extracted DNA for species identification of beef samples as mentioned above, the DNA samples extracted from beef samples at 60 minutes resulted in high absorbance values indicating possible denaturation and fragmentation of DNA.