Pre-soaking of seeds enhances pressure inactivation of E. coli O157:H7 and Salmonella spp. on crimson clover, red clover, radish and broccoli seeds

The application of high hydrostatic pressure (HHP) at a level of 600 MPa at 20 °C to decontaminate crimson clover, red clover, radish and broccoli seeds inoculated with E. coli O157:H7 and Salmonella were evaluated. Salmonella was generally more pressure-resistant than E. coli O157:H7 on clover and radish seeds except on broccoli seeds where the trend was reversed. In addition, the application of HHP differentially affected seeds' germinability and the order of pressure tolerance of the seeds was such that red clover > crimson clover ≈ broccoli > radish seeds with final germination percentages ranging from 85–100% while their untreated counterparts had final germination percentages of 99–100%. Pre-soaking the different types of seeds in water for 30, 60 or 90 min at ambient temperature followed by HHP at 600 MPa for 2 or 5 min at 20 °C significantly (P < 0.05) enhanced the pressure inactivation of the inoculated pathogens. Moreover, the ability of HHP-treated seeds to germinate also varied as a function of the pre-soaking duration and the seed type. Pre-soaking radish and broccoli seeds for 30 min prior to HHP (2 or 5 min) resulted in germination percentages of ≤ 1% after 8 days of incubation. On the contrary, red clover seeds displayed higher germination potential when pre-soaked for 60 min at 20 °C prior to HPP (5 min) with final germination percentages of 94%, although their yield was substantially lower than their untreated counterparts. Red clover seeds pre-soaked for 60 min at 4 °C followed by HPP at 600 MPa for 5 min at 20 °C produced germination percentages of 91 and 95% after 3 and 8 days of sprouting compared to 99 and 100% respectively for untreated seeds. In addition, this condition did not significantly (P > 0.05) reduce the sprout yield. The treatment also resulted in a reduction of a 5 log initial load of E. coli O157:H7 and Salmonella to an undetectable level (neither pathogen was detected in 2-g seed samples after enrichment).