Thermal resistance of Listeria monocytogenes and Salmonella spp. in liquid egg white

Survival of a five-strain mixture of Listeria monocytogenes and a six-strain mixture of Salmonella enteritidis, S. typhimurium, and S. senftenberg (not 775W) in liquid egg white was determined by a submerged-vial technique at 51.5 degrees C and 53.2 degrees C with 0.875% added H2O2 and at 55.5 degrees C, 56.6 degrees C, and 57.7 degrees C with no additions. Survival at a range of pH values at 56.6 degrees C also was determined. Surviving bacteria were counted on tryptic soy agar and results expressed as D-values; log-unit reductions in counts in 3.5 min or 6.2 min were calculated from these D-values. Plate pasteurization of commercially broken egg white (pH 8.8) inoculated with a single strain of L innocua or S. senftenberg also was performed. Heating under currently approved pasteurization conditions, 51.5 degrees C for 3.5 min with hydrogen peroxide, 55.6 degrees C for 6.2 min, or 56.7 degrees C for 3.5 min, resulted in a less than 3-log unit reduction of viable Salmonella spp. and a less than 0.5-log unit reduction of L. monocytogenes. At 53.2 degrees C with peroxide, plate pasteurization resulted in a 3.44-log unit reduction of S. senftenberg in 3.5 min. At 57.7 degrees C with no peroxide, the D-value for Salmonella spp. was 0.78 min when heated in submerged vials, and plate pasteurization reduced viable numbers by 3.64 log units in 3.5 min. Destruction of Listeria under these conditions was still less than 1 log unit. Variation in the pH of the egg white from 7.8 to 9.3 resulted in D-values for Salmonella spp. at 56.6 degrees C of 3.60 min to 1.08 min, respectively. D-values for L. monocytogenes under these conditions ranged from 10.4 min at pH 7.8 to 20.9 min at pH 9.3. The reduced heat sensitivity of Salmonella spp. at lower pH values should be considered in reevaluating pasteurization procedures