Adjusting processing parameters in an entry-level commercial dehydrator to achieve a 5-log reduction of salmonella during the cooking step

Abstract

The U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) guidance encourages jerky processors to use a single lethality step that will achieve a 5-log reduction of Salmonella. Many processors rely on internal temperature-time combinations recommended in this guidance. However, the efficacy of convective heating is highly dependent on relative humidity (RH). RH recommendations are vague because of variability in processing conditions and limited available data. This study was conducted to establish processing conditions for an entry-level commercial dehydrator (Harvest Saver R5A) to achieve a 5-log reduction of Salmonella. Unseasoned, unmarinated top round beef strips (65 mm thick) were inoculated with Salmonella (.7 log CFU/g) and processed with the chamber temperature set to 82.28C for a total cook time of 60 min with the intake closed (closed oven). Modifications (product load and fan speed) were made in subsequent trials to improve lethality. After incubation at 378C for 24 to 48 h, surviving Salmonella populations were enumerated on tryptic soy agar. In trial A, the maximum fan speed (2.5 m/s) with 30 kg of product resulted in 45 to 48.5% RH at 60 min, and a 5-log reduction of Salmonella was achieved in only 35.5% of the meat samples (54 of 152 samples). Increasing the product load by 40% (42 kg; trial B) increased RH in the chamber (57 to 85%) and resulted in improved lethality; a 5-log reduction was achieved in 95.0% of samples (131 of 138 samples). Because samples with reduced lethality were located on the windward side of the chamber, the fan speed was reduced (0.9 m/s; trial C1) to increase the RH, resulting in a 5-log reduction in 100% of the samples (138 of 138 samples). A replicate trial (trial C2) was conducted, and a 5-log reduction again was achieved in 100% of the samples. All trials exceeded recommendations by the FSIS; however, adequate Salmonella reduction was achieved only when the RH was .65% throughout. Product load and fan speed are practical parameters for processors to manipulate to increase the RH in closed systems and thus improve Salmonella lethality.