Inactivation of Salmonella enterica and Enterococcus faecium on Whole Black Peppercorns and Cumin Seeds Using Steam and Ethylene Oxide Fumigation

Abstract

Current methods to reduce the native microbiota and potential pathogens on spices include steam treatments and ethylene oxide (EtO) fumigation. The objectives of this research were to identify the effectiveness of a lab-scale steam apparatus and a commercial EtO process on the inactivation of Salmonella enterica or Enterococcus faecium NRRL B-2354 inoculated whole black peppercorns and cumin seeds.

Peppercorns and cumin seeds were inoculated with Salmonella or Enterococcus and processed in a lab-scale steam apparatus at 16.9 PSIA and two references temperatures (165°F and 180°F) and in a commercial ethylene oxide fumigation chamber using a standard commercial EtO fumigation process. Cells were enumerated by serial dilution and plating onto TSA with a thin overlay of selective media.

Inoculation preparation influenced inactivation of Salmonella on peppercorns with greater reductions reported for TSA-grown cells compared to within a biofilm. To achieve an assured 5-log reduction of TSA-inoculated Salmonella on peppercorns exposure for 125s and 100s at 165°F and 180°F, respectively is required. For cumin seeds temperatures of 165°F for 110s were needed or 65s at 180°F to assure 5 log reduction. EtO fumigation significantly reduced both microorganisms on both spices (p<0.05), however significant variation existed between bags in the same process run. Reductions of Enterococcus were comparable or less than that of Salmonella under the majority of conditions, however a direct linear relationship cannot be used to compare the microbes. This study demonstrates that the effectiveness of Enterococcus faecium NRRL B-2354 as a surrogate for Salmonella can vary between spices and processes.