Thermal Resistance of Heat-, Cold-, and Starvation-Injured Salmonella in Irradiated Comminuted Turkey

Abstract

To investigate the effects of sublethal stress on Salmonella thermal inactivation kinetics, an eight-strain Salmonella cocktail was subjected to heat shock (30 min at 54 degrees C), cold shock (2 h at 4 degrees C), and starvation stress (10 days in phosphate buffer at 4 degrees C), harvested by centrifugation, and inoculated into irradiated comminuted turkey. Immediately after stressing, the Salmonella cocktails contained 89.1% heat-injured, 44.7% cold-injured, and 67.7% starvation-injured cells, as determined by plating on selective and nonselective media. D60 degrees C-values for the heat-shocked cocktail (0.64 min on Trypticase soy agar containing 0.6% yeast extract [TSAYE], 0.35 min on xylose lysine desoxycholate [XLD] agar) were higher (P < 0.05) than those for the unshocked control (0.41 min on TSAYE, 0.17 min on XLD), whereas D60 degrees -values for the cold-shocked cocktail (0.38 min on TSAYE, 0.17 min on XLD) were not significantly different from those for the control. Starved cells had the same D60 degrees C-value on TSAYE as did the unshocked cocktail, but the D60 degrees C-value on XLD was significantly lower (0.14 min). Although starvation and cold shock were not thermally protective, heat shock increased thermal resistance, indicating that product history and the physiological state of the Salmonella cells should be considered when developing and validating thermal processes. D60 degrees C-values observed on selective media were significantly lower than those observed on nonselective media for all stress treatments and for the control. Therefore, nonselective culture media should be used to assess the response of microorganisms to a thermal challenge when developing performance standards for lethality.

Thermal Inactivation of Salmonella Enteritidis PT 30 in Almond Kernels as Influenced by Water Activity

“…This culture was centrifuged three times for 25 min at 2,250 x g, and the pellet was washed with phosphate buffer (0.05 mM, pH 7). The cell population was adjusted to a level of 109 CFU/ml and refrigerated (4°C) for no more than 7 days before inoculation of almond kernel flour (35,42).…”

Thermal Tolerance of Acid-Adapted and Non-adaptedEscherichia coliO157:H7 andSalmonellain Ground Beef During Storage

“…A 6.5-log unit reduction of Salmonella in cooked beef and roast beef and a 7.0-log unit reduction in certain fully and partially cooked poultry products were set as performance standards for lethality, stabilization, and product handling (Weche et al, 2005). Raw meat and poultry are usually considered ideal growth media for bacteria; however, all microbial contaminants are subjected to physical, chemical, and nutritional stresses during processing (Yousef and Courtney, 2003).…”

Evaluation of Salmonella Thermal Inactivation Model Validity for Slow Cooking of Whole-Muscle Meat Roasts in a Pilot-Scale Oven

“…With the production of heat-shock proteins, cells are able to adapt and, subsequently, better survive lethal temperatures (5,7). For example, Stephens et al (15) demonstrated that slow heating (<5°C/min) increased the thermotolerance of Listeria monocytogenes, and Wesche et al (22) reported enhanced Salmonella survival at 60°C in ground turkey previously heat shocked at 43°C for 5, 30, and 60 min. Wiegand et al (23) reported that inactivation parameters based on isothermal laboratory data generally overpredicted end-point lethality outcomes for Escherichia coli 0157:H7 in whole-muscle beef roasts slow-cooked in a pilot-scale oven.…”