Thermal Resistance of Salmonella spp. and Listeria monocytogenes in Liquid Egg Yolk and Egg White

Abstract

Decimal reduction times (D values) were determined for Salmonella spp. and Listeria monocytogenes (five pooled strains per pathogen) in raw liquid egg yolk (pH 6.3) and liquid egg white (pH 8.2 versus 9.1) by using a low-volume (0.05 ml per sample) immersed sealed-glass capillary-tube procedure. For Salmonella, D values ranged from 0.087 min (at 62.2°C) to 0.28 min (at 60°C) in yolk. and from 1.00 min (at 58.3°C) to 7.99 min (at 55.1° C) in egg white (pH 8.2). For Listeria, D values ranged from 0.58 min (at 62.2°C) to 1.34 min (at 60°C) in yolk, and from 2.41 min (at 58.3°C) to 7.59 min (at 55. 1°C) in egg white (pH 9.1). Mean ZD values for Salmonella ranged from 3.54 to 4.33°C; for Listeria, ZD values ranged from 6.06 to 9.43°C. In egg white, the heat sensitivity of both pathogens was enhanced at pH 9.1, although this trend was more evident for Salmonella spp. than for L. monocytogenes over the temperature range tested. The results indicate that USDA-prescribed minimal pasteurization requirements for liquid egg yolk (equivalent to 3.9- to 22.1-D processes, on the basis of the present study) would be far more lethal to the Salmonella and L. monocytogenes strains tested than would the corresponding thermal processes for liquid egg white (equivalent to 0.7- to 2.2-D processes).