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P3-05 Multilaboratory Comparison of Thermal Resistance of Enterococcus faecium and Salmonella enterica in Peanut Butter

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Ian Hildebrandt , Michigan State University , East Lansing , MI
Shannon Pickens , Illinois Institute of Technology , Bedford Park , IL
Soon Kiat Lau , University of Nebraska-Lincoln , Lincoln , NE
Jeyamkondan Subbiah , University of Nebraska-Lincoln , Lincoln , NE
Nathan Anderson , U.S. Food and Drug Administration , Bedford Park , IL
Bradley Marks , Michigan State University , East Lansing , MI
Elizabeth Grasso-Kelley , Illinois Institute of Technology , Bedford Park , IL
Introduction: Enterococcus faecium NRRL B2354 has been identified a nonpathogenic surrogate for Salmonella in almond pasteurization processes. There is a critical need to characterize and validate E. faecium against Salmonella in other low-moisture foods in order to meet the industry need for a nonpathogenic surrogate for in-plant validations. Determination of thermal resistance at multiple laboratories provides additional confidence in the thermal destruction values for use in establishing food process parameters.

Purpose: This study compared the thermal resistance of E. faecium and a Salmonella enterica cocktail in peanut butter and evaluated the reproducibility of the results obtained by two laboratories.

Methods: A five-strain Salmonella cocktail and E. faecium diluted 1:1 with peanut oil and emulsified with Tween 80 were used to inoculate commercial peanut butter. Samples were equilibrated to 25% relative humidity before dissemination to two laboratories. Aluminum test cells were filled with inoculated peanut butter in a humidity-controlled chamber and isothermally treated at three temperatures in the range 85 to 100°C, depending on the organism. After treatment, samples were serially diluted and enumerated on appropriate differential agar. Using organism survival ratios, D- and z-values were calculated using Matlab nonlinear fitting tools.

Results: The D90ºC for E. faecium (21.35±0.20 min) was greater (P≤0.05) than for S. enterica (12.62±0.15 min). Differences in D-values between laboratories were significant for two temperatures, but the nominal difference remained ≤12%. The z-value (14.94±0.34 and 15.49±0.45ºC) for S. enterica was similar (P ≥0.05) between laboratories. While the z-values for E. faecium were significantly different between laboratories (12.97±0.14 and 12.23±0.14ºC); the actual difference was small (0.74°C).

Significance: Enterococcus faecium was more thermally resistant than S. enterica at each temperature evaluated. Overall, results were reproducible between laboratories; however, the instances of unattributable differences reiterate the importance of cross-laboratory validations.

Back to: Poster Session 3 – Low-water Activity Foods, Packaging, Produce, Microbial Food Spoilage, Antimicrobials, Laboratory and Detection Methods, Water
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