Abstract
The effect of single-cycle and multiple-cycle high hydrostatic pressure (HHP) treatments on the survival of three Salmonella Enteritidis strains in chicken breast fillets was investigated. The surface of fillets was inoculated with a cocktail of three Salmonella strains at approximately 107 colony-forming units (CFU)/g, and held at 4°C for 20 hours before HHP treatments. Reduction of Salmonella counts on tryptic soy agar (TSA) by single-cycle treatments at 300 MPa and 12°C ranged from 0.58 log CFU/g for a 0-minute (no dwell time) cycle to 3.35 log CFU/g for a 20-minute cycle, whereas with 400 MPa treatments the decline ranged from 0.93 log CFU/g to more than 5 log CFU/g, respectively. The 4.8 log unit reduction in Salmonella counts on TSA achieved by a 15-minute treatment at 400 MPa should suffice to eliminate the pathogen naturally present in contaminated chicken meat. When plated on Salmonella Shigella agar (SSA), the reduction of Salmonella counts by single-cycle treatments at 300 MPa and 12°C ranged from 0.69 log CFU/g for a 0-minute cycle to 4.21 log CFU/g for a 20-minute cycle, and with 400 MPa treatments from 1.25 log CFU/g to more than 5 log CFU/g, respectively. From the comparison of Salmonella counts on SSA and TSA it was concluded that not only the lethality but also the proportion of injured Salmonella cells increased with the length of HHP treatments. The use of multiple-cycle treatments instead of single-cycle treatments of the same HHP time for the inactivation of Salmonella Enteritidis inoculated on chicken breast fillets showed to be more advantageous at 400 MPa than at 300 MPa. No recovery of injured Salmonella cells was observed when fillets treated at 300 or 400 MPa for 5 minutes were held for 72 hours at 4°C.