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. senft enberg (not 775W) in liquid egg white was determined by a submerged-vi al technique at 51.5 degrees C and 53.2 degrees C with 0.875% added H2 O2 and at 55.5 degrees C, 56.6 degrees C, and 57.7 degrees C with no a dditions, Survival at a range of pH values at 56.6 degrees C also was determined. Surviving bacteria were counted on tryptic soy agar and re sults 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 o f commercially broken egg white (pH 8.8) inoculated with a single stra in of L. innocua or S. senftenberg also was performed. Heating under c urrently approved pasteurization conditions, 51.5 degrees C for 3.5 mi n 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. monocytog enes. At 53.2 degrees C with peroxide, plate pasteurization resulted i n a 3.44-log unit reduction of S. senftenberg in 3.5 min. At 57.7 degr ees C with no peroxide, the D-value for Salmonella spp. was 0.78 min w hen heated in submerged vials, and plate pasteurization reduced viable numbers by 3.64 log units in 3.5 min. Destruction of Listeria under t hese 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 fo r 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 s pp, at lower pH values should be considered in reevaluating pasteuriza tion procedures.