P1-176 Inactivation of Salmonella in Low-moisture Products at Relatively High Temperatures Using Radiofrequency-assisted Heat Treatments (RFHT)

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Rossana Villa-Rojas, Washington State University, Pullman, WA
Juming Tang, Washington State University, Pullman, WA
Mei-Jun Zhu, Washington State University, Pullman, WA
Shuxiang Liu, Washington State University, Pullman, WA
Ravi Tadapaneni, Washington State University, Pullman, WA
Roopesh Syamaladevi, Washington State University, Pullman, WA
Bradley Marks, Michigan State University, East Lansing, MI
Introduction: Salmonella outbreaks in low-moisture foods create significant need for effective pasteurization processes, but conventional thermal treatments are challenged by low thermal diffusivity of dry products. Radiofrequency (RF) energy has reportedly reduced heating time and reduced Salmonella in low-moisture products such as spices without significant quality damage.

Purpose: The goal was to assess inactivation of Salmonella Tennessee K4643 (ST) and Enteritidis PT30 (SPT30) in low-moisture products using RFHT.

Methods: Product (100 g) was inoculated (≈9 log CFU/ml) with ST or SPT30 using a lawn culture pellet re-suspended in peptone water (3 ml). Samples were equilibrated in a controlled-humidity chamber to ~0.45 aw, then isothermally (80°C) treated in aluminum cells in an oil bath (5 durations, 6 replicates), immediately cooled in ice water, serially diluted, and plated on XLT4 agar. D-values were obtained by linear regression of the survival data (log CFU/g) and used to design RFHT. Samples (~20 g ) were heated to ~80°C  in a 0.5 kW, 27 MHz RF unit and immediately transferred to an oil bath for different holding times (duplicates), then cooled, diluted, and plated as previously explained.

Results: D-values for SPT30 (5.3 ± 0.56 min, 0.93 R2) and ST (5.7 ± 0.61 min, 0.91 R2) in wheat flour were not significantly different (P > 0.05). RFHT yielded average log reductions immediately after RF treatment, after 6 min, and after 12 min holding time, respectively, of 2.02 ± 0.31, 3.09 ± 0.30, and 3.27 ± 0.39, for ST, and 3.06 ± 0.19, 4.18 ± 0.14, and 3.60 ± 0.54 for SPT30. Only the SPT30 6 min holding time lethality was significantly higher (P < 0.05) than obtained with test cells. RFHT inactivation was not statistically different (P> 0.05) between strains.

Significance: RFHT is a promising technology for Salmonella inactivation in low-moisture products, and inactivation kinetics are essential to future process design and validation.