Survival Pattern and Toxin Production of Pathogens in Spiced and Non Spiced Fried Rice

Aims: There is no data regarding the survival rate of pathogens in party foods held at different temperature and time interval in Nigeria. Hence, the need to study the survival rate of selected food borne pathogens in Fried rice (spiced and non – spiced) served at parties, monitor toxin production and the rate at which it is produced with respect to time and holding temperature as well as determine the effect of spices on the survival of food pathogens.

Place and Duration of Study: Lagelu and Ibadan North Local Government Authority Area of Ibadan, Oyo State, Nigeria, between May 2017 and September 2017.

Methodology: We obtained 10 fried rice samples (5 spiced and 5 non- spiced) from different parties inside sterile food warmers and transferred to the Food Microbiology Laboratory. Pathogens inoculated were obtained from the culture collection unit of the Food Microbiology laboratory and they were Bacillus cereus, Staphylococcus aureus, Salmonella typhi and Escherichia coli. Inoculum size of the pathogens was determined prior to inoculation. Initial temperature of the fried rice sample was taken and after inoculation, samples were taken at an interval of 2 hours to determine the survival rate of the pathogens. Brine Shrimp Lethality (BSL) assay was used to determine the level of toxin produced.

Results: The microbial load of all pathogens inoculated increased from its initial size as the holding temperature reduces and holding time increases. For E. coli, there was an increase from 5.3 log10CFU/g to 9.3 log10CFU/g and 8.3 log10CFU/g in non–spiced fried rice and spiced fried rice, respectively, initial load for S. typhi also increase from 4.1 log10CFU/g to 9.1 and 8.4, for B. cereus and S. aureus there was an increase form 6.3 log10CFU/g to 9.0 and 8.4 for non-spiced and spiced rice respectively. Toxicity test shows that the lethal dose was high at 8 hours (LC50:1.5) which connotes that the toxicity was high at this holding time.

Conclusion: Holding cooked foods at ambient temperature for 6 h or longer without appropriate reheating constitute a major critical control point for party food. Keeping foods at the right temperatures is an essential food safety practice. Adequate knowledge and application of this by caterers will reduce the rate of food borne illness in the country.