Effect of Salt Concentrations on the High Pressure Inactivation of Listeria monocytogenes

Introduction: National and international health agencies have recommended a significant reduction in daily intake of sodium by reducing the amount of NaCl in foods, specifically processed meats. One role of NaCl in processed meat is to decrease a_w, thereby inhibiting microbial growth. Thus, sodium reduction could increase the risk of survival and growth of spoilage and pathogenic microorganisms on these products. Therefore, alternate processing technologies to improve safety of sodium reduced foods are necessary.

Purpose: Examine the effect of salt types and concentrations on high pressure inactivation of L. monocytogenes in ground chicken.

Methods: Ground chicken formulated with three salt types (NaCl, KCl, CaCl₂), three salt concentrations (0, 1.5, 2.5%) and inoculated to 10⁸ CFU/g with a four-strain cocktail of L. monocytogenes were subjected to four pressure treatments (0, 100, 300, 600 MPa) and two durations (60, 180 s) in an experiment with factorial design. Surviving cells were enumerated by plating on modified Oxford agar and analyzed by factorial ANOVA using mixed model.

Results: Pressure treatments at 100 or 300 MPa did not significantly (P < 0.0001) reduce L. monocytogenes populations. At 600 MPa, salt types, concentrations and duration of pressure treatment all had a significant effect on L. monocytogenes populations. Formulations with increasing concentrations of NaCl or KCl, showed significantly lower reduction in L. monocytogenes, while with CaCl₂ formulations, increase in concentration resulted in a significantly higher reduction. For instance, increase in NaCl concentration from 0 to 1.5 and 2.5% resulted in a reduction of 6.16, 2.52 and 1.34 log CFU/g, respectively, when exposed to 600 MPa for 60 s. In case of CaCl₂, increase from 0 to 1.5 and 2.5% resulted in a reduction of 6.16, 7.38 and 7.77 log CFU/g, respectively.

Significance: The results demonstrate that high pressure processing is a viable process to improve microbial safety of sodium reduced foods.