Effect of temperature on the growth of Staphylococcus aureus in ready-to-eat cooked rice with pork floss

Cooked rice with pork floss (CRPF) wrapped in dried seaweed is one of the most popular ready-to-eat (RTE) foods in many Asian countries, particularly in Taiwan. The products are susceptible to Staphylococcus aureus contamination and temperature abuse during manufacturing, distribution, and storage. The objective of this study was to examine the effect of temperature on its growth in RTE CRPF for use in risk assessment and prevention of staphylococcal food poisoning (SFP). Inoculated CRPF samples were stored at 4, 12, 18, 25, and 35°C, and the change in the populations of S. aureus during storage were analyzed using three primary models to determine specific growth rate (μ_max), lag-phase duration (λ), and maximum population density (y_max). The Ratkowsky square-root and Huang square-root (HSR) models were used as the secondary models to describe the effect of temperature on μ_max, and a linear and an exponential regression models were used to describe the effect of temperature on λ and y_max, respectively. The model performance was evaluated by the root mean square error (RMSE), bias factor (B_f), and accuracy factor (A_f) when appropriate. Results showed that three primary models were suitable for describing the growth curves, with RMSE ≤ 0.3 (log MPN/g). Using μ_max obtained from the Huang model, the minimum growth temperature (T_min) estimated by the HSR model was 7.0°C, well in agreement with the reported T_min. The combination of primary and secondary models for predicting S. aureus growth was validated by additional growth curves at 30°C, which showed that the RMSE was 0.6 (log MPN/g). Therefore, the developed models were acceptable for predicting the growth of S. aureus in CRPF under likely temperature abuse conditions and can be applied to assess the risk of S. aureus in CRPF and design temperature controls to reduce the risk of SFP.