P1-80 Determination of the Heat Resistance Characteristics of Salmonella Typhimurium in a Range of Low Aw Commodities

Monday, July 29, 2013
Exhibit Hall (Charlotte Convention Center)
Joy Gaze, Campden BRI, Chipping Campden, United Kingdom
Rob Limburn, Campden BRI, Chipping Campden, United Kingdom
Roy Betts, Campden BRI, Chipping Campden, United Kingdom
Introduction: It is known that the dry heat resistance of Salmonella enterica is greatly increased at low water activity, potentially allowing resistant populations to survive thermal decontamination processes.  This effect is known to vary among different low moisture foods, but little published information is available offering specific heat resistance data for Salmonella in these matrices.

Purpose: To determine the heat resistance characteristics of Salmonella Typhimurium ATCC 14028 in a range of low Aw foods across a 40ºC temperature range, providing data demonstrating the effect of dry heat on Salmonella in these commodities and facilitating the design of thermal decontamination treatments for such products.

Methods: Salmonella Typhimurium ATCC 14028 was subjected to dry heat treatments at 105, 115, 125, 135 and 145ºC.  Surviving cells were recovered on both Tryptone Soya Agar (TSA) and Xyline Lysine Desoxycholate Agar (XLD) to compare the recovery of stressed cells between non-selective and selective media.  Survivor curves were plotted and D- and z-values calculated.

Results: Low moisture foods investigated were whole wheat, sesame seeds, walnuts, pecan nuts, pumpkin seeds and brazil nuts.  The average z-value calculated for S. Typhimurium across the range of low Awfoods was 19.7C° (ranges: TSA 17.6-20.9 C°, XLD: 18.1-22.2C°).  TSA cells grown on  Cells recovered on TSA medium gave higher D-values across the range of temperatures and matrices than those on XLD medium.  Average D-values ranged from 176.3 minutes at 105ºC to 1.9 minutes at 145ºC.

Significance: These data suggest that for Salmonella Typhimurium ATCCC 14028 z-values remain relatively constant across the low moisture foods investigated. A greater recovery of surviving organisms is possible on non-selective media, possibly due to the inability of heat-injured cells to grow under selective pressure. D-values calculated for each matrix provide valuable heat resistance data for Salmonella Typhimurium in these commodities.