Research -Interaction of Gaseous Chlorine Dioxide and Mild Heat on the Inactivation of Salmonella on Almonds

The interactive effects of mild heat and gaseous chlorine dioxide (ClO₂) on populations of Salmonella on almonds were studied. Almonds, dip inoculated with a two-strain cocktail of attenuated Salmonella Typhimurium, were treated with three concentrations of ClO₂ at ambient temperature (ca. 22°C), and at 45, 50, 55, and 60°C for 4 h and with more than 90% relative humidity. Concentrations of ClO₂ during treatments were measured, and populations of Salmonella were determined following treatments. Results demonstrated that ClO₂ at concentrations of more than 4 mg/L and ambient temperature only reduced populations of Salmonella by 1.46 log CFU/g. With increasing treatment temperature, the efficacy of gaseous ClO₂ increased. At 55 and 60°C, >1 mg/L ClO₂, and a 4-h treatment time, >4 log CFU/g Salmonella was inactivated. Reductions greater than 4 log of the bacterium by gaseous ClO₂ at 55°C were confirmed using a three-strain cocktail of pathogenic Salmonella. Overall, results demonstrated that mild heating is necessary for gaseous ClO₂ to achieve more than 4 log CFU/g inactivation of Salmonella on almonds.

• ClO₂ applied at ambient temperature achieves less than 2-log reductions of Salmonella.

• Mild heat and ClO₂ have a synergistic effect on the reduction of Salmonella.

• Surrogate Salmonella Typhimurium and pathogenic Salmonella behave similarly to ClO₂ and heat.