Inactivation of Pathogens on Peppercorns and Sunflower Kernels Using a Pilot Scale Vacuum Steam Pasteurization System

Introduction: Spices, seeds and grains are some of the low moisture foods that have been implicated in foodborne outbreaks due to Salmonella and E. coli O157:H7. It is important to investigate inactivation methods to eliminate risks due to pathogens in such foods with minimum impact on product quality and functionality. Vacuum steam pasteurization (VSP) utilizes steam under vacuum which can be operated at temperatures below 100°C. 

Purpose: We wanted to quantify inactivation of pathogens on peppercorns and sunflower kernels and also determine if E. faecium can be used as a potential surrogate for Salmonella and E. coli O157:H7 when using VSP.

Methods: Sunflower kernels were separately inoculated with Salmonella PT30, E. coli O157:H7 and Enterococcus faecium, and peppercorns were inoculated with only Salmonella PT30 directly with bacterial lawns grown on brain heart infusion agar plates and suspended in 5 ml of water. Following equilibration of a_w to initial levels, 25 g of inoculated samples were pasteurized for varying times (0.5-5.0 min) at 75, 85, 95, and 105°C in triplicate. 

Results: Treatment of peppercorns using VSP yielded greater than 5 log CFU/g reductions of Salmonella PT30 after just 30 seconds at 75°C. For sunflower kernels, average reductions of 5.09 ± 0.92 log CFU/g was observed for Salmonella PT30 after 4 minutes at 75°C, 5.40 ± 0.83 log CFU/g for E. coli O157:H7 after 1 minute at 75°C, and 5.69 ± 0.94 log CFU/g for E. faecium after 2 minutes at 85°C. However, similar log reductions (>6.0) were observed after treatment at 95 and 105°C. 

Significance: VSP can be effectively used to reduce pathogens in peppercorns and sunflower kernels at temperature as low as 75 and 85°C and E. faecium may be used as a potential surrogate for Salmonella PT30 and E. coli O157:H7 with careful considerations of treatment time and temperatures.