Development of a Radio-Frequency Technology for the Decontamination of Salmonella from Timothy Hay

Highlights After inoculation with the Salmonella spp. cocktail and E. faecium, timothy hay samples had an initial microbial load of 7.81 and 7.75 log CFU/g, respectively. After RF treatments of 165, 175, 185, and 195 s, Salmonella spp. loads were reduced to 5.80 (SD ± 0.24), 4.00 (SD ± 0.27), 1.42 (SD ± 2.01) log CFU/g with complete decontamination at 195 s. At 165 and 175 s of RF treatments, the E. faecium loads were reduced to 7.50 (SD ± 0.14) and 6.39 (SD ± 0.31) log CFU/g with complete decontamination at 185 and 195 s. There were no statistically significant changes in the iron, vitamin A, or amino acid responses; sodium levels increased, and potassium and calcium levels decreased due to increasing RF treatment duration. Abstract. The objectives of this research were: 1) to investigate the efficacy of RF heating on the decontamination of Salmonella enterica and Enterococcus faecium NRRL B-2354 in timothy hay; 2) to evaluate the suitability of E. faecium as a surrogate of Salmonella in timothy hay during RF treatment; 3) to assess the physicochemical changes after RF treatment on vitamins, amino acids, fatty acids, and trace minerals in the timothy hay. A pilot-scale parallel-plate RF heating system (6 kW, 27.12 MHz) was used to conduct this study. The electrode gap in the RF system was adjusted to 205 mm. Timothy hay was procured from a pet food manufacturing plant in Lincoln, Nebraska, at an initial moisture content (MC) of 7% to 9% (wet basis). Timothy hay samples (150 g) were inoculated with either a cocktail containing five serotypes of Salmonella enterica [Salmonella Agona (447967), Salmonella Mbandaka (698538), Salmonella Montevideo (488275), Salmonella Tennessee (K4643), and Salmonella Reading (Moff 180418)] or a broth of Enterococcus faecium then incubated at 37°C for 24 ± 2 h. Timothy hay samples were exposed to RF energy for 165, 175, 185, and 195 s. It was determined that after inoculation with the Salmonella cocktail and E. faecium, timothy hay samples had an initial microbial load of 7.81 and 7.75 log CFU/g, respectively. After RF treatments of 165, 175, 185, and 195 s, Salmonella loads (mean ± SD log CFU/g) were reduced to 5.80 ± 0.24, 4.00 ± 0.27, 1.42 ± 2.01 log CFU/g and below the level of detection, respectively. At 165 and 175 s of RF treatments, the E. faecium loads (mean ± SD log CFU/g) were reduced to 7.50 ± 0.14 and 6.39 ± 0.31 log CFU/g and below the detection level at 185 and 195 s. There was complete decontamination at 185 and 195 s. There were no statistically significant changes in the iron, vitamin A, or amino acid responses because of increasing RF treatment duration. The study demonstrated a non-chemical approach to decontaminating Salmonella and Enterococcus faecium from low-moisture foods such as pet foods. Keywords: Decontamination, Enterococcus faecium, Low moisture, Pet food, Radio-frequency, Salmonella, Timothy hay.