Comparison of three methods of DNA extraction from cold-smoked salmon and impact of physical treatments

Aims: To compare three bacterial DNA extraction procedures on cold-smoked salmon (CSS) and assess the impact on their efficiency of two physical treatments of the food matrix, ionizing irradiation and freezing. Methods and Results: As molecular methods for bacterial detection have become an important analytical tool, we compared bacterial DNA extraction procedures on CSS. Working with frozen and irradiated CSS, we obtained negative responses from samples known to be highly contaminated. Thus, we decided to study the impact of these two physical treatments on bacterial DNA extraction procedures. The efficiency of bacterial DNA extraction directly from the fish matrix suspension was measured by an rpoB PCR-based reaction. The results demonstrated that the DNeasy tissue extraction kit (Qiagen, Courtaboeuf, France) was the most efficient and reproducible method. We also showed that freezing and ionizing irradiation have a negative impact on DNA extraction. This was found probably not to be due to inhibition as the PCR reaction remained negative after adding BSA to the PCR mix reaction. Conclusions: The extraction kit was the most efficient method. Physical treatments were shown to hamper bacterial DNA extraction. Significance and Impact of the Study: Attention must be paid to molecular bacterial detection on food products subject to freezing or to ionizing irradiation.