Growth of Staphylococcus aureus in cooked ready-to-eat ground fish as affected by inoculum size and potassium sorbate as food preservative

• Maximum Growth rate was independent of initial size and potassium sorbate.
• Initial size and potassium sorbate notably affected lag time during storage.
• Lag time systematically decreased with increasing inoculum size.
• RLT concept resulted in better description of Staphylococcus aureus behavior than hyperbola model.

This study was conducted to investigate the influence of inoculum size and potassium sorbate on kinetic growth of Staphylococcus aureus in cooked ready-to-eat ground fish (CGF) prevalent retail storage temperatures. Two treatment levels (with or without 0.2% potassium sorbate) and three inoculum sizes (3.0, 4.5, or 5.5 log CFU/g) were evaluated. CGF samples were inoculated and subsequently stored at 10, 15, 20, 25, 30, and 37 °C. Growth curves at each storage temperature were fitted to Baranyi model to estimate lag time (λ, hour) and maximum growth rate (log CFU/g/h). Prediction of λ was dependent on the inoculum size and potassium sorbate treatment. Two secondary λ models (relative lag time (RLT) and hyperbola) were used to describe the variability in the growth behavior of S. aureus on CGF. RLT values were higher for treated samples (3.55, 3.16, and 2.74, respectively for 3 inoculum sizes) than those obtained from untreated samples (3.49, 3.01, and 2.34) and decreased with increasing the inoculum size. Hyperbola model indicated considerable variability but no systematic trend was observed. Relative error within acceptable prediction zone was higher than 80% for overall secondary models developed. This supported that the developed models demonstrated acceptable performance under examined temperatures.