Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2009
Publication Date: 7/12/2009
Citation: Gurtler, J., Jordan, J.S., Marks, H.M., Jones, D.R., Shaw, W. 2009. Inactivation kinetics of a four-strain composite of Salmonella Enteritidis and Oranienberg in commercially-acquired liquid egg yolk. [abstract]. International Association for Food Protection. p.1. Interpretive Summary:
Technical Abstract: Introduction: Current liquid egg pasteurization requirements are based on command and control prescribed time/temperature combinations for specified egg products. Requirements are found in the Code of Federal Regulations, Title 9, Ch. III, Sec. 590.570. These standards were based on data for the inactivation of Salmonella in liquid egg products acquired prior to 1970 and are currently being reevaluated in light of recent risk assessments, which take into account changes in industrial practices such as in-line egg processing and variation in egg product formulations not represented in the current regulation. Purpose: The goal of this study was to determine the inactivation kinetics of a four-strain composite of thermally-resistant strains of Salmonella inoculated into commercially-processed liquid egg yolk. Methods: Heat-resistant Salmonella (three serovars of Enteritidis [phage types 8, 8, and 13] and one Oranienburg) were selected for resistance to 50 ug/ml nalidixic acid. Cultures were grown to stationary phase in Tryptic Soy broth at 42C, with one 24 h transfer, concentrated ten-fold by centrifugation, and resuspended in 0.1% peptone water. Each inoculum was added to liquid egg yolk and mixed thoroughly, resulting in a final population of ca. 8 log CFU/ml egg yolk. Inoculated yolk was injected into sterile glass capillary tubes, flame-sealed and heated in a water bath at 58, 60, 62, 64, and 66C. Capillary tubes were ethanol sanitized, rinsed twice in sterile water and contents were extracted. Yolk was diluted, surface plated onto Tryptic Soy agar + 0.1% sodium pyruvate and 50 ug/ml nalidixic acid and incubated at 37C for 24 h before colonies were enumerated. Results: Decimal reduction values were calculated from survivor curves with a minimum inactivation of 6 log CFU/ml at each temperature. The asymptotic D values were 2.06 min at 58C, 0.82 min at 60C, 14.4 sec at 62C, 5.73 sec at 64C and 2.15 sec at 66C. Significance: These results provide useful information that will be used by the USDA Food Safety Inspection Service for issuing new pasteurization log reduction performance standards and industry guidance rather than command and control temperature requirements.