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Title: THERMAL RESISTANCE OF SALMONELLA SPP. AND LISTERIA MONOCYTOGENES IN LIQUID EGG YOLK AND EGG YOLK PRODUCTS

Author
item PALUMBO MARY S - DELAWARE VALLEY COLLEGE
item BEERS SHARON M - DELAWARE VALLEY COLLEGE
item Bhaduri, Saumya
item Palumbo, Samuel

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Liquid egg products, used by the food service industry and food processors, are pasteurized to destroy harmful bacteria. Current guidelines are based on the destruction of Salmonella, a principal disease-causing organism associated with foods. However, the recent concern about Listeria monocytogenes in products of animal origin coupled with its heat resistance and its ability to grow in refrigerated foods prompted a reexamination of pasteurization requirements. The heat resistance of five individual strains of L. monocytogenes and six strains of Salmonella were determined in liquid egg yolk. We also examined the effects of ingredients such as salt and sugar on the heat resistance of these disease-causing bacteria in liquid egg yolk. These ingredients reduced the amount of water available for bacterial growth, and thus increased the refrigerated shelf-life of the egg product. However, these ingredients salso increased the heat resistance of the bacteria. These data are useful to regulatory agencies and industry in updating pasteurization guidelines for processing liquid egg products.

Technical Abstract: The effectiveness of various pasteurization procedures in destroying Listeria monocytogenes and Salmonella enteritidis in liquid egg products was evaluated. Survivor studies were performed on individual strains of L. monocytogenes, L. innocua, and Salmonella spp. in commercially broken raw egg yolk samples at 61.1, 63.3, and 64.4 C using the submerged ampule technique. Surviving bacteria were counted on TSA and results expressed as D-values. The influence of aw-lowering ingredients such as salt and sugar on thermal resistance in yolk was investigated using a five-strain mixture of L. monocytogenes or a six-strain mixture of Salmonella spp. at temperatures between 61.1 C and 66.7 C. At 61.1 C (present minimum temperature for pasteurization of plain egg yolk), a 7 log reduction of Salmonella took 1.4 to 2.4 min, whereas a 7 log reduction of L. monocytogenes took 4.9 to 16.1 min. The D-value for L. monocytogenes at 64.4 C increased from 0.44 min in plain yolk to 8.26 min after a 21.5 min time lag (total time to achieve 1-log reduction was 30.7 min) in yolk with 10% salt and 5% sugar, and 27.3 min after a 10.5 min time lag (total time 37.8 min for 1-log reduction) in yolk with 20% salt. The D-value for Salmonella in egg yolk at 64.4 C was <0.2 min, but when 10% salt was added, the D-value was 6.4 min. Aw-lowering solutes in liquid egg yolk increased the thermal resistance of Salmonella and L. monocytogenes.