Effects of Different Nitrite Concentrations from a Vegetable Source with and without High Hydrostatic Pressure on the Recovery of Listeria monocytogenes on Ready-to-Eat Restructured Ham

Sodium nitrite exerts an inhibitory effect on the growth of Listeria monocytogenes. The objective of this study was to investigate the effects of various nitrite concentrations from a vegetable source with and without high hydrostatic pressure (HHP) on the recovery and growth of L. monocyto genes on ready-to-eat restructured ham. A preconverted celery powder was used as the vegetable source of nitrite. Targeted concentrations of natural nitrite investigated were 0, 50, and 100 mg/kg. HHP treatments evaluated were 400 MPa for 4 min and 600 MPa for 1 or 4 min at 12 +/- 2 degrees C (initial temperature of the pressurization fluid). Viable L. monocyto genes populations were monitored on modified Oxford medium and thin agar layer medium through 98 days of storage at 4 +/- 1 degrees C. Populations on both media did not differ. The HHP treatment at 600 MPa for 4 min resulted in L. monocyto genes populations below the detection limit of our sampling protocols throughout the storage period regardless of the natural nitrite concentration. The combination of HHP at 400 MPa for 4 min or 600 MPa for 1 min with natural nitrite resulted in initial inhibition of viable L. monocytogenes. Ham formulations that did not contain natural nitrite allowed faster growth of L. monocytogenes than did those with nitrite, regardless of whether they were treated with HHP. The results indicate that nitrite from a vegetable source at the concentrations used in this study resulted in slower growth of this microorganism. HHP treatments enhanced the inhibitory effects of natural nitrite on L. monocytogenes growth. Thus, the combination of natural nitrite plus HHP appears to have a synergistic inhibitory effect on L. monocyto genes growth.