Heat Resistance of Listeria monocytogenes Scott A and HAL 957E1 in Various Liquid Egg Products†

Abstract

The thermal destruction of Listeria monocytogenes Scott A and HAL 957E1 (an egg isolate) was determined in five liquid egg products. The egg products used were liquid whole egg (LWE), liquid whole egg with 10% NaCl (LWEN), liquid whole egg with 10% sucrose (LWES), egg yolk with 10% NaCl (EYN), and egg yolk with 10% sucrose (EYS). Each of these products was inoculated with the individual strains of L. monocytogenes at initial populations of 106 colony-forming units (CFU)/ml and exposed to temperatures of up to 70°C for various periods of time from which thermal death time (TDT) curves were constructed. The Scott A strain tended to be more heat resistant than the egg isolate, HAL 957E1. The sensitivity of both strains to heating was influenced by the type of egg product in which they were suspended. The highest rates of kill were noted in LWE, while survival was best in those products supplemented with NaCl (LWEN and EYN). For the nonsalted products, time and temperature combinations equivalent to those required for the high-temperature short-time (HTST) pasteurization of liquid egg achieved 1.7 to 4.4 log-unit reductions of L. monocytogenes populations, while reductions for the salted products were only 0.2 to 0.6 log units. These results suggest that current HTST pasteurization conditions for liquid egg will not ensure a Listeria-free product, especially with products supplemented with NaCl.