Abstract
Spices, including black pepper and cumin seeds, have been implicated in recent outbreaks of salmonellosis and prompted recalls of ready-to-eat products containing contaminated spices. Vacuum-assisted steam pasteurization is performed to improve the safety and quality of many low water activity products, however process parameters associated with inactivation on whole spices are not well described. The objective of this study was to determine the effectiveness of a lab-scale vacuum-assisted steam process for the inactivation of Salmonella enterica and its potential surrogate Enterococcus faecium ATCC 8459 inoculated onto the surface of whole peppercorns and cumin seeds. In addition, the effect of two inoculation preparation methods (growth on tryptic soy agar (TSA) or inclusion within a native microbiota biofilm), on the reduction of S. enterica serovars or E. faecium was compared on steam pasteurized whole black peppercorns. Spices were processed using steam under a vacuum to achieve a mean product temperature of 86.7 ± 2.8 °C for different dwell times. Salmonella inoculated using the TSA-grown method, required 83 s and 70 s respectively to achieve a 5-log reduction of Salmonella on peppercorns and cumin seeds. Longer time periods were needed to achieve a 5-log reduction of Salmonella when it was present in a native biofilm on whole peppercorns. Survivor estimations were best predicted by the Weibull models. The mean log reductions of E. faecium were 0.9 log CFU/g lower than Salmonella on whole black peppercorns inoculated using the TSA-grown cells (P = 0.0021). The mean log reductions of Salmonella and E. faecium prepared using the biofilm-inclusion method were not significantly different (P = 0.76). E. faecium log CFU/g reductions were not significantly different compared to Salmonella on whole cumin seeds (P = 0.42) indicating that while reductions are comparable the surrogate may not always provide a conservative indication of complete Salmonella elimination for all spices processed using vacuum-assisted steam.
Highlights
Spices have been used throughout history as a way to enhance the flavor in foods
There were no significant differences in the water activity for peppercorns inoculated with Salmonella or E. faecium
In comparison injection of steam during a 1-min vacuumassisted steam dwell resulted in larger reductions of Salmonella at 4.6 ± 0.2 log CFU/g on biofilm inoculated whole black peppercorns, and 7.1 ± 0.2 log CFU/g, while using TSA-grown method
Summary
Spices have been used throughout history as a way to enhance the flavor in foods. outbreaks of salmonellosis attributed to spices and increased detection of Salmonella in imported spices has prompted increased concern regarding the safety of spices (ASTA, 2011; Van Doren et al, 2013b). Vacuum-assisted steam pasteurization of spices, sometimes referred to as dry steam, allows for shorter treatment times and lower temperatures compared to dry heat application, resulting in smaller losses of volatile compounds that are integral to the aroma and flavors of spices (Molnár et al, 2018). Use of a vacuum allows the formation of steam at temperatures between 70 and 100◦C, and when steam condenses on the spice surface, heat is transferred into the target food, inactivating bacteria associated with the surface (Lilie et al, 2007). While it is desirable to identify processing parameters resulting in a 5-log CFU reduction of Salmonella on spices, the variability in packaging and processing parameters used by different commercial facilities may result in differences in steam penetration, product temperature and other variables associated with thermal reduction of the target pathogen. It is important to identify a surrogate microorganism, whose inactivation is comparable to Salmonella, for commercial facilities to validate their individual, pathogeninactivation processes
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