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.