Journal of Pure and Applied MicrobiologyVol. 8 No. 2

Growth Kinetic Behavior of Toxin-Producing Bacteria on Strawberries under Dynamic Temperature Conditions

Sooyeon Ahn1, Won-Il Kim2, Hwang-Yong Kim2, Se-Ri Kim, Jae-Gee Ryu2 and Yohan Yoon1*

1Department of Food and Nutrition, Sookmyung Women?s University, Seoul - 140-742, Korea. 2Microbial Safety Division, Department of Crop Life Safety, National Academy of Agricultural Science, Rural Development Administration, Suwon 441-707, Korea.

Received on 23 October 2013 and accepted on 18 December 2013

 

ABSTRACT

This study, developed mathematical models to describe the growth kinetics of toxin-producing bacteria on strawberries under dynamic temperature. Staphylococcus aureus and Bacillus cereus were inoculated on strawberry. The samples were then stored at 4-30oC. S. aureus and B. cereus were grown on mannitol-salt agar and mannitol egg-yolk polymyxin agar, respectively. The microbial data were fitted to the Baranyi model to calculate the maximum specific growth rate (?max) and lag-phase duration. The parameters were further analyzed using a polynomial model, and dynamic models were developed to simulate bacterial growth at changing temperature. The bacterial growth gradually decreased at 4 and 10oC, but increased at 15-30oC on strawberries. The secondary model showed that temperature slightly influenced the ?max values. However, the simulation showed that S. aureus and B. cereus cell counts were not altered by dynamic temperature condition, i.e., those that exist during commercial distribution of strawberries.The results imply that the initial numbers of S. aureus and B. cereus on strawberries were not changed during distribution, and thus, an initial contamination level lower than the threshold for enterotoxin production may not cause foodborne illnesses. This result can be used to determine new control measure for S. aureus and B. cereus.

Keywords : Strawberry, Toxin-producing bacteria, Dynamic model.