Purpose: Determine the thermal processing parameters (D- and z-values) for C. sakazakii and Salmonella spp. in NDM and validate radiofrequency dielectric heating (RFDH) system for decontamination of NDM.
Methods: High-heat (HH) and low-heat (LH) NDM were separately inoculated with a 5-strain cocktail of either C. sakazakii or Salmonella spp., transferred to thermal death time (TDT) disks and held at 75, 80, 85 or 90°C for 0 to 80 min. Surviving populations of the organisms were determined by plating on tryptic soy agar. Three replications were conducted and linear regression was used to determine the D- and the z-values. The inoculated NDM was heated using an RFDH system and held at specific temperatures in a convection oven to validate the RFDH system.
Results: The D-values of C. sakazakii or Salmonella spp. were similar within the HH- or LH-NDM at respective temperatures using TDT disks and RFDH combined with convection oven used for the holding period; except for Salmonella spp. in HH-NDM at 85°C. D-values of C. sakazakii and Salmonella spp. varied from 23.00 to 26.25 min at 75°C, 7.52 to 13.75 min at 80°C, 6.03 to 8.68 min at 85°C, and 3.05 to 5.82 min at 90°C. The z-values of C. sakazakii or Salmonella spp. in HH- or LH-NDM were similar using TDT disks and RFDH.
Significance: Radio frequency heating can be used as a post-process lethality treatment for NDM prior to the packaging; however, the effect of RFDH on the functional properties of NDM should be evaluated to enhance adoption by the dry milk industry.