Use of Capillary Tubes and Plate Heat Exchanger to Validate U.S. Department of Agriculture Pasteurization Protocols for Elimination of Listeria monocytogenes in Liquid Egg Products

Abstract

D-values for a five-strain cocktail of Listeria monocytogenes in five different liquid egg products (whole egg, egg yolk, egg white, egg yolk + 5% sucrose + 5% NaCl, and egg yolk + 10% NaCl) were determined using 100-μl capillary tubes. The egg products were inoculated with approximately 1 × 1010 organisms/ml and heated in capillary tubes to temperatures ranging from 53 to 69°C for various time intervals. Using a pilot scale plate heat exchanger, the U.S. Department of Agriculture (USDA) protocols for pasteurization were also evaluated using egg products inoculated with approximately 1 × 107 L. monocytogenes/ml. Results of experiments with capillary tubes suggested that all processes would result in less than the 9D process recommended by USDA. Moreover, although pasteurization with a plate heat exchanger provided greater lethality than did capillary tubes, all products still received less than a 5.4D process. Hence, these results suggest that the current USDA protocol may not be adequate to assure a large margin of safety.