29G-29 |
Thermal resistance of heat-, cold-, and starve-injured Salmonella in ground turkey |
A. M. WESCHE1, B. P. Marks2, and E. T. Ryser1. (1) Dept. of Food Science & Human Nutrition, Michigan State Univ., 2100 S. Anthony Hall, East Lansing, MI 48824-1225, (2) Dept. of Agricultural Engineering, Michigan State Univ., 210 A.W. Farrall Hall, East Lansing, MI 48824-1323 Exposing Salmonella to heat, cold and starvation stress in meat processing environments can induce sublethal injury that may lead to increased thermal tolerance during cooking. Under these conditions, safe harbor guidelines for cooking may result in incomplete destruction of salmonellae and production of an unsafe product. This study assessed the impact of heat, cold and starvation stress on the thermal resistance of Salmonella in irradiated ground turkey. A six-strain Salmonella cocktail was subjected to heat shock (30 min / 54oC), cold shock (2 h / 4oC, and starvation stress (10 d in phosphate buffer at 4oC), harvested by centrifugation and inoculated into irradiated ground turkey. D-values at 60oC were calculated for stressed cells and an unstressed control using trypticase soy agar with 0.6% yeast extract (TSA-YE) and xylose lysine deoxycholate (XLD) agar for recovery of healthy + injured and healthy cells, respectively. Treatments yielded cocktails that contained 89.0% heat-shocked, 44.7% cold-shocked, and 67.7% starved cells, respectively. D-values for the heat-shocked cocktail (0.63 min on TSA-YE, 0.34 min on XLD) were significantly higher (p<0.05) than for the unshocked control (0.41 min on TSA-YE, and 0.17 min on XLD), whereas D-values for the cold-shocked and starved cocktails were not significantly different from the unshocked control. For each treatment, differences between TSA-YE and XLD were significant, indicating that the population of healthy cells alone is not as thermotolerant as the entire population of healthy and injured cells Heat shock increased thermal resistance as expected. However, starvation decreased thermal resistance of healthy cells with cold shock unable to provide a protective effect. As the difference between the two media was greater for starvation than for the unshocked control, starvation may be thermally protective. Consequently, the product history and physiological state of Salmonella should be considered when developing safe harbor guidelines for cooking.
Session 29G, Food Microbiology: General
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