The 2015 FDA Preventive Controls for Human Foods Rule requires firms to validate pathogen-reduction steps. Some thermal processes, such as pistachio roasting, are not yet well-characterized with respect to the impact of product and process variables on Salmonella lethality. The objective was to quantify and model the effects of product and process factors on Salmonella lethality for in-shell pistachios. In-shell pistachios were inoculated with Salmonella Enteritidis PT30 (~8.5 log CFU/g), and thermally treated at various levels of temperature, process humidity, and product moisture, under dry and presoaked conditions. Salmonella survivors, moisture content, and aw were quantified at six time points during each treatment, targeting a cumulative lethality of ~3-5 log. Increasing product temperature or process dew point increased Salmonella inactivation rates (P < 0.05). For dry and presoaked treatments, analyzed separately, initial product water activity did not affect inactivation rates (P > 0.05). However, when comparing dry against presoaked treatments, inactivation rates were greater (P < 0.05) for the presoaked pistachios. Models were developed to quantify Salmonella inactivation in pistachios as a function of product temperature, moisture, and process humidity. These models successfully described the effect of these variables on Salmonella inactivation and are the first published attempts to model pathogen reduction in low-moisture products as a function of multiple dynamic variables. Based on these findings, the impact of product and process factors on Salmonella inactivation in pistachios must be considered when designing and validating industrial thermal processes for pathogen reduction.
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