Efficacy of vacuum steam pasteurization for inactivation of Salmonella PT 30, Escherichia coli O157:H7 and Enterococcus faecium on low moisture foods

- Low aw foods were inoculated with Salmonella PT 30, E. coli O157:H7 and E. faecium.
- Inoculated foods were exposed to vacuum steam pasteurization.
- > 5 log reduction of pathogens on flaxseed and sunflower seeds at 75 °C
- > 5 log reduction of Salmonella on peppercorns at 75 °C and milled flaxseed at 85 °C
- E. faecium can be used as a surrogate for both Salmonella PT 30 and E. coli O157:H7.

Low moisture foods such as nuts, spices, and seeds have been implicated in several outbreaks due to Salmonella or E. coli O157:H7 contamination. Such foods may be consumed raw, and can be used as ingredients in other food products. While numerous thermal inactivation studies have been conducted for Salmonella on nuts, studies on other seeds and grains are minimal. Product water activity can influence the thermal resistance of pathogens, where thermal resistance increases as water activity decreases, leading to a requirement for higher temperatures and longer exposure times to achieve significant reduction of pathogen numbers. Vacuum steam pasteurization uses steam under vacuum, which can be operated at temperatures above and below 100 °C. The objective of this study was to determine the efficacy of vacuum steam pasteurization for inactivation of pathogens on whole flaxseed, quinoa, sunflower kernels, milled flaxseed and whole black peppercorns. The use of E. faecium as a potential surrogate for Salmonella and E. coli O157:H7 in vacuum steam pasteurization was also evaluated. Pasteurization for 1 min at 75 °C yielded average log reductions of 5.48 ± 1.22, 5.71 ± 0.40 and 5.23 ± 0.61 on flaxseed, 4.29 ± 0.92, 5.89 ± 0.26 and 2.39 ± 0.83 on quinoa, and 4.01 ± 0.74, 5.40 ± 0.83 and 2.99 ± 0.92 on sunflower kernels for Salmonella PT 30, E. coli O157:H7 and E. faecium, respectively. Similarly, on milled flaxseed and black peppercorns average log reductions of 3.02 ± 0.79 and 6.10 ± 0.64 CFU/g were observed for Salmonella PT 30 after 1 min of treatment at 75 °C but, on average, > 6.0 log reductions were observed after pasteurization at 85 °C. Our data demonstrate that vacuum steam pasteurization can be effectively used to reduce pathogens on these low moisture foods at temperature as low as 75 and 85 °C, and that E. faecium may be used as a potential surrogate for Salmonella PT 30 and E. coli O157:H7.