HEAT-RESISTANCE OF LISTERIA-MONOCYTOGENES SCOTT-A AND HAL-957E1 IN VARIOUS LIQUID EGG PRODUCTS

The thermal destruction of Listeria monocytogenes Scott A and HAL 957E 1 (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 1 0% NaCl (EYN), and egg yolk with 10% sucrose (EYS). Each of these prod ucts was inoculated with the individual strains of L. monocytogenes at initial populations of 10(6) colony-forming units (CFU)/ml and expose d to temperatures of up to 70 degrees C for various periods of time fr om which thermal death time (TDT) curves were constructed. The Scott A strain tended to be more heat resistant than the egg isolate, HAL 957 E1. The sensitivity of both strains to heating was influenced by the t ype of egg product in which they were suspended. The highest rates of kill were noted in LWE, while survival was best in those products supp lemented with NaCl (LWEN and EYN). For the nonsalted products, time an d temperature combinations equivalent to those required for the high-t emperature short-time (HTST) pasteurization of liquid egg achieved 1.7 to 4.4 log-unit reductions of L. monocytogenes populations, while red uctions 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.