Efficacy of High Hydrostatic Pressure Treatment in Reducing Escherichia coli O157 and Listeria monocytogenes in Alfalfa Seeds

The application of high hydrostatic pressure (HHP) technology as a seed decontamination technique was evaluated. Alfalfa seeds inoculated with Escherichia coli O157 and Listeria monocytogenes were airdried and subjected to independent HHP treatments of 275 to 575 MPa for 2 min or at 475 MPa for 2 to 8 min (40 °C). There were 1.4-log and 2.0-log reductions in E. coli O157 populations at 575 MPa (2 min) and 475 MPa (8 min), respectively. However, these treatments caused only 0.8-log and 1.1-log reductions in L. monocytogenes counts. Treated seeds took longer to germinate, achieving germination rate of up to 34%, whereas 95% of the control germinated. Results suggest that L. monocytogenes is more resistant to the bactericidal effects of HHP than E. coli O157. Although HHP treatments achieved a greater reduction in E. coli O157, it was at the expense of seed germination. Overall, our results indicate that although HHP treatments reduced the populations of E. coli O157 and L. monocytogenes in alfalfa seeds, they did not completely eliminate these microorganisms.