Inactivation of Staphylococcus aureus by high hydrostatic pressure in saline solution and meat slurry with different initial inoculum levels

• The inactivation rate of Staphylococcus aureus by HHP was different in sterile saline and minced pork.
• The inactivation of S. aureus under the experimental conditions applied was described by Weibull model.
• Combination of HHP and nisin gave a greater inactivation than individual treatment.

The effect of high hydrostatic pressure (350–550 MPa, 3–12 min) and initial inoculum levels (102–106 CFU/mL (CFU/g)) on Staphylococcus aureus at room temperature in saline solution and meat slurry were investigated, and the Weibull model was used to describe the inactivation of S. aureus in both media. The results showed that the reduction of S. aureus was enhanced with increasing the pressure level and the pressure holding time in both media. The inactivation rate of S. aureus increased with increasing the initial inoculum level in saline solution, whereas 104 CFU/g of initial inoculum caused the higher log-reduction of S. aureus than the other two initial inoculum levels in meat slurry. Regression coefficients (R2), root mean square (RMSE) values and residual plot suggested that the Weibull model produced a good fit to the data. However, the shape factor (n) was not significantly dependent on the pressure and initial inoculum level. Multiple linear regression was further used to describe the effect of pressure and log initial inoculum level on the scale factor (b) values. Based on the primary and secondary models, the inactivation of S. aureus in the both two media was predicted satisfactory by the tertiary model. In addition, 3 log-reduction of S. aureus was obtained by the combination treatment of HHP (350 MPa for 6 min) and nisin (500 ppm), which has met Food Safety Standard on Quick Frozen Flour and Rice Products for microorganism in the People's Republic of China.