Effect of a heat-spray and heat-double spray process using radiofrequency technology and ethanol on inoculated nuts

Almonds provide a nutritious source of energy and are known to have led to positive health benefits when consumed. However, outbreaks of Salmonella spp. in raw almonds have led to reduced consumer confidence in the nut industry. Regulatory standards established by the FDA require almonds destined for consumption in the US to undergo a process treatment that reduces Salmonella spp., by 4.0 log₁₀ CFU/g. Four Generally Recognized as Safe (GRAS) surface disinfectants suchs as ethanol, hydrogen peroxide, acetic acid, and peracetic acid were tested on almonds inoculated with Enterococcus faecium NRRL B-2354. It was found that 70% ethanol has the most potential to achieve a high log₁₀ CFU/g reduction, while holding quality. The optimal spray process had the following parameters: (1) a spray quantity of 4.5% w/w (p <.05), (2) contact time of 1–30 min (3) use of 2 spray phases (p <.05). The use of radiofrequency (RF) heating and 70% ethanol in the heat-spray process achieved 5.8 log₁₀ CFU/g reductions. In this experimental mode, independent heat and spraying achieved 2.9 and 3.0 log₁₀ CFU/g reduction, which corresponds to a contribution of 50% each to the combined heat-spray process using RF heating. The RF experiments in the heat-double spray process achieved log₁₀ reductions of 6.7, 4.7, 3.8, and 3.5 log₁₀ CFU/g for almonds, pecans, pistachios, and walnuts, respectively. The implications of these findings are that both the heat-spray and heat-double spray process may become alternatives to current nut disinfection process to achieve high log₁₀ reduction.