Abstract
Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus (S. aureus) are the cause of Saphylococcal food poisoning (SFP) outbreaks. Thus, estimation of the time to detection (TTD) of SEs, that is, the time required to reach the SEs detection limit, is essential for food preservation and quantitative risk assessment. This study was conducted to explore an appropriate method to predict the TTD of SEs in cooked chicken product under variable environmental conditions. An S. aureus strain that produces staphylococcal enterotoxin A (SEA) was inoculated into cooked chicken meat. Initial inoculating concentrations (approximately 102, 103, 104 CFU/g) of S. aureus and incubation temperatures (15 ± 1, 22 ± 1, 29 ± 1, and 36 ± 1°C) were chosen as environmental variables. The counting of S. aureus colonies and the detection of SEA were performed every 3 or 6 h during the incubation. The TTD of SEA was considered a response of S. aureus to environmental variables. Linear polynomial regression was used to model the effects of environmental variables on the TTD of SEA. Result showed that the correlation coefficient (R2) of the regressed equation is higher than 0.98, which means the obtained equation was reliable. Moreover, the minimum concentration of S. aureus for producing a detectable amount of SEA under various environmental conditions was approximately 6.32 log CFU/g, which was considered the threshold for S. aureus to produce SEA. Hence, the TTD of SEA could be obtained by calculating the time required to reach the threshold by using an established S. aureus growth predictive model. Both established methods were validated through internal and external validation. The results of graphical comparison, RMSE, SEP, Af, and Bf showed that the accuracy of both methods were acceptable, and linear polynomial regression method showed more accurately.
Highlights
Staphylococcus aureus (S. aureus) is a worldwide cause of foodborne diseases
A linear polynomial regression model that describes the effects of temperature and initial inoculation concentration on the time to detection (TTD) of staphylococcal enterotoxin A (SEA) was established by stepwise regression as follows: TTD = 112.9 − 23.95Linoc − 1.677T + 0.6122T × Linoc +0.1663(Linoc)2 − 0.03133(T)2(R2 = 0.9895) (7)
The analysis of variance (ANOVA) of the linear polynomial regression model indicated that Equation (7) was significant (p < 0.01)
Summary
Staphylococcus aureus (S. aureus) is a worldwide cause of foodborne diseases. In the European Union (EU), 393 foodborne outbreaks caused by staphylococcal species were reported in 2014 (EFSA, 2014). In the US, foodborne illnesses caused by S. aureus were estimated to range from 72,341 to 529,417 (Scallan et al, 2011). According to the Notification of National Food Poison. Outbreaks in 2015 issued by the National Health Commission of P. R. China (http://www.nhfpc.gov.cn/yjb/s7859/201604/ 8d34e4c442c54d33909319954c43311c.shtml), S. aureus is one of the major causes of foodborne diseases in China
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