Inactivation of Salmonella on Particulate Foods using Superheated Steam (SHS)

Abstract

Salmonella outbreaks and recalls on raw or minimally decontaminated tree nuts and spices have recently brought the issue to sterilize this pathogen before distribution to the market. The objective of this study was to investigate a reduction efficacy of superheated steam (SHS) treatment on Salmonella enterica serovar Typhimurium and Enteritidis on the surfaces of particulate foods such as raw almond kernels, pecans halves and black peppercorns. When homogeneously cocktailed Salmonella serotypes on particulate foods were treated with saturated steam (SS) at 100˚C and SHS at 120, 140, 160 and 180˚C with 3 m s-1 of steam velocity, treating black pepper, pecans and almonds with either 160˚C SHS for 6, 13, 15 s or 180˚C SHS for 3, 13, 8 s respectively could reduce the inoculated Salmonella populations less than 1 log CFU g-1 (the detection limit

average 6.3 log reduction) without specific changes in quality of the foods. To see the effect of thermal resistance value of each serotype of Salmonella on the reduction efficacy, raw almond kernels which are inoculated with Salmonella cocktails of the two serotypes at various mixing ratios were treated with 100˚C SS to 180˚C SHS of 3 m s-1 for 1 s to 45 s. It was observed that the more the ratio of the serotype Typhimurium in the Salmonella cocktail was, the more sterilizing effect of SHS was. This could be contributed to the low thermal resistance of the serotype. The survivor curves of the Salmonella were fitted with the first-order model and Weibull model. The Weibull model provided better fit of the results. The calculated t_R (analogous in the meaning of classical D value) and z values explained the reduction efficacy of Salmonella on particulate foods well enough. In conclusion, these results suggest that the SHS ≥160˚C could serve an effective method to prevent Salmonellosis for particulate formed tree nuts and spices without quality deterioration.