Efficacy of a heat-spray and heat-double spray process on inoculated nuts with Salmonella enteritidis ATCC 1045

Abstract

Due to Salmonella outbreaks in almonds, regulatory standards have been established, requiring that almonds for human consumption in North America must achieve a minimum of 4 log10 CFU/g reduction of Salmonella. This study investigated a system using a combination of heating and transient application of ethanol to reduce bacterial load. This approach used a small scale heat-spray and heat-double spray process that included a two factor block design with heat (25±2 °C and 125±2 °C) and spray levels (0,1,2); One factor design with nut levels of almonds, pistachios, pecans, and walnuts for each heat-spray and heat-double spray process; a two factor experiment included a dip contact time (5s, 1800s) and ethanol evaporation time (5 s, 1800 s). Also, to evaluate the interaction of a heat-spray process on moisture content of almonds, a two factor design with levels of heat (25±2 °C and 125 ± 2 °C) and spray (0,1) was used. Additionally, the spray evaporation rate was evaluated. The heat-spray process shows additivity, while the heat-double spray process shows synergism. The heat-double spray process on almonds achieved a 6.1 mean log10 CFU/g reduction of Salmonella that was 35% higher than that of the heat-spray. For other nuts, the heat-double spray process led to a 4.8, 3.0, and 4.0 log10 reduction for pecan, pistachio, and walnut, respectively. The dip time (p < 0.05) had a greater effect than ethanol evaporation (p > 0.05) on log10 reduction of Salmonella in almonds. By applying ethanol 70%, the moisture increases by ∼0.5% w.b., whereas applying temperature decreases moisture by ∼2% w.b. The implication of these findings is that both the heat-spray and heat-double-spray process may be alternatives to the current almond disinfection processes in achieving a high log10 reduction.