|LU, KUAN HUNG - National Taiwan University|
|SHEEN, YI JYAN - National Taiwan University|
|HUANG, TSUI PING - National Taiwan University|
|KAO, SHU-HUI - National Taiwan University|
|CHENG, CHUN LUNG - Council Of Agriculture|
|Hwang, Cheng-An - Andy|
|SHEEN, LEE YAN - National Taiwan University|
Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2019
Publication Date: 11/28/2019
Citation: Lu, K., Sheen, Y., Huang, T., Kao, S., Cheng, C., Hwang, C., Sheen, S., Huang, L., Sheen, L. 2019. Effect of temperature on the growth of Staphylococcus aureus in ready-to-eat cooked rice with pork floss. Food Microbiology. 89:103. https://doi.org/10.1016/j.fm.2019.103374.
Interpretive Summary: Pork floss onigiri (PFO, or rice ball with pork) is susceptible to the contamination of Staphylococcus aureus that leads to staphylococcal food poisoning. This study examined the growth of S. aureus in PFO at 4, 12, 18, 25, and 35 degrees Celsius, and the growth curves were used to develop growth models of S. aureus in PFO. The models were successfully developed and validated, and they can be used to predict the growth of S. aureus in PFO under the likely temperature abuse conditions for designing time and temperature controls to reduce the risk of staphylococcal food poisoning.
Technical Abstract: Pork floss onigiri (PFO), a Japanese-style rice ball containing pork floss, mayonnaise, and dried seaweed, is one of the most popular ready-to-eat (RTE) foods in Taiwan. The product is susceptible to contamination by Staphylococcus aureus and temperature abuse during manufacturing, distribution, and storage. This study aimed to develop mathematical models to predict the growth of S. aureus in PFO under temperature abuse conditions for assessing potential staphylococcal poisoning and designing processing and distribution controls. PFO samples inoculated with S. aureus were stored at 4, 12, 18, 25, and 35 degrees Celsius. The populations of S. aureus during storage were determined and the growth curves were analyzed using three primary models, namely Huang, Baranyi, and reparamerized Gompertz models to obtain the growth kinetic parameters, including specific growth rate (µmax), lag-phase duration ('), and maximum population density (Ymax). The Ratkowsky square-root and Huang square-root models were used as the secondary models to describe the effect of temperature on µmax, and a linear and an exponential regression models were used to describe the effect of temperature on ' and Ymax, respectively. The model performance was evaluated by the root mean square error (RMSE), bias factor (Bf), and accuracy factor (Af) when appropriate. Results showed that the three primary models were suitable for modeling the growth curves of S. aureus in PFO with RMSE = 0.7. Using µmax obtained from the Huang model, the minimum growth temperature (Tmin) estimated by the Huang square-root model was 7.0 degrees Celsius, which is in agreement with the reported Tmin for S. aureus (7 degrees Celsius). The combination of primary and secondary models for predicting S. aureus growth was validated by additional growth curves at 30 degrees Celsius, which showed RMSE was 0.6. Therefore, the developed mathematical models were acceptable for predicting the growth of S. aureus in PFO under the likely temperature abuse conditions and can be applied to assess the risk of S. aureus poisoning in PFO and design temperature controls to reduce the risk.