Low moisture foods (LMF) have been associated with numerous Salmonella outbreaks and recalls, as a result of either an insufficient pathogen lethality step or post-processing contamination. The use of a non-pathogenic surrogate microorganism, Enterococcus faecium NRRL B2354, has been proposed to be used as a Salmonella surrogate for validating thermal treatment of LMF since the use of Salmonella is prohibited in the food processing facilities. The overall goal of this study was to validate the efficacy of E. faecium as a Salmonella surrogate in validating the thermal processing of LMF products. This research goal was achieved via three specific objectives: i) to assess the influence of talc powder as a dry-inoculum carrier on thermal resistance of E. faecium in almond meal at 0.45 aw; ii) to compare the thermal resistance of E. faecium and Salmonella in almond meal, date paste, wheat flour, peanut butter, ground black pepper, and non-fat dried milk powder via standardized methodology in an interlaboratory study; iii) to determine the effect of lactose and protein content on thermal resistance of E. faecium and Salmonella in dairy powders. Log-linear and Bigelow models were used to estimate D- and z-values in this study. The findings showed that talc powder is not recommended as a dry inoculation carrier, because the presence of talc influenced the thermal resistance of E. faecium in almond meal. The interlaboratory comparison study demonstrated that E. faecium was more thermally resistant (P < 0.05) than Salmonella in the 5 out of 6 low-moisture products, and these trends were highly impacted by product composition. Standardized methodology yielded reproducible D- and z-values between laboratories. The magnitude of difference of thermal resistance between microorganisms was most substantial in nonfat dry milk powder. Lastly, the presence of lactose, but not protein content, most likely contributed to the magnitude difference of thermal resistance between E. faecium and Salmonella in dairy powders. In summary, E. faecium NRRL B-2354 can be considered as a relevant biological validation tool for thermal processing of LMF. The positive impact of this study is to support the use of E. faecium NRRL B-2354 for validation of LMF thermal pasteurization and to ultimately reduce Salmonella outbreaks and recalls linked to LMF.
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