THERMAL-RESISTANCE OF SALMONELLA SPP AND LISTERIA-MONOCYTOGENES IN LIQUID EGG-YOLK AND EGG-YOLK PRODUCTS

The effectiveness of various pasteurization procedures in destroying L isteria monocytogenes and Salmonella enteritidis in liquid egg product s was evaluated. Survivor studies were performed on individual strains of L. monocytogenes and L. innocua in commercially broken raw egg yol k samples after heating at 61.1, 63.3, and 64.4 degrees C using submer ged vials, and on Salmonella spp. at 60.0, 61.1, and 62.2 degrees C. S urviving bacteria were enumerated on TSA and results expressed as D-va lues. The influence of a(w)-lowering ingredients such as salt and suga r on thermal resistance in yolk was investigated using a five-strain m ixture of L. monocytogenes or a mixture of Salmanella spp. (four strai ns of S. enteritidis, one strain each of S. senftenberg and S. typhimu rium) at 61.1 degrees C to 66.7 degrees C. At 61.1 degrees C (present minimum temperature for pasteurization of plain egg yolk), a 7-log-uni t reduction of Salmonella took 1.4 to 2.4 min, whereas a 7-log-unit re duction of L. monocytogenes took 4.9 to 16.1 min The D-value for L. mo nocytogenes at 64.4 degrees C increased from 0.44 min in plain yolk to 8.26 min after a 21.5-min lag (total time to achieve I-log-unit reduc tion was 30.7 min) in yolk with 10% salt and 5% sugar, and 27.3 min af ter a 10.5-min lag (total time 37.8 min for 1-log-unit reduction) in y olk with 20% salt. The D-value for Salmonella in egg yolk at 64.4 degr ees C was <0.2 min, but when 1O% salt was added, the D-value was 6.4 m in. A(w)-lowering solutes in liquid egg yolk increased the thermal res istance of Salmonella and L. monocytogenes.