Application of High Hydrostatic Pressure to Eliminate Listeria monocytogenes from Fresh Pork Sausage

Ground pork patties were inoculated separately with 109 CFU/g each of three strains of Listeria monocytogenes obtained from the National Animal Disease Center (NADC). Inoculated patties were packaged under vacuum and treated at 414 megapascals (60,000 lb/in2) for up to 60 min by high hydrostatic pressure (HHP). Survivors were determined by surface plating onto modified Oxford agar and trypticase soy agar with yeast extract, as well as by the most probable number method using Listeria enrichment broth. Average D values ranged from 1.89 to 4.17 min, depending on the strain, with the most virulent strain (reported by the NADC) having the highest D value. We tested the usefulness of applying a mild heat treatment at 50°C, simultaneously with HHP, to lower these values. Average D values ranged from 0.37 to 0.63 min, depending on the strain. Thus, a 10-log10 reduction could be achieved even in the most pressure-resistant strain of L. monocytogenes by a 6-min application of heat and HHP. Shelf life studies were also conducted, with spoilage levels reached after 5 days of storage at 4°C for controls versus 28 days for treated samples. Sensory evaluation of uninoculated grilled patties showed that panelists could not distinguish between those treated by heat and HHP and untreated controls (P < 0.05). Thus, treatment by HHP in combination with mild heating can be used successfully to produce safer, longer-lasting fresh pork without affecting quality.