Radio frequency assisted thermal processing for pasteurization of packaged whole milk powder surrounded by oil

Abstract

The presence of Salmonella in milk powders has caused several outbreaks resulting in serious health problems and even deaths as well as significant economic loss due to recalls. The objective of this study was to investigate the effect of RF heating on the reduction of Salmonella in packaged whole milk powder surrounded by an oil medium. The thermal destruction kinetics (decimal reduction time; D-value) of Salmonella and Enterococcus faecium NRRL B-2354 (a potential surrogate of Salmonella for low moisture foods) in whole milk powder were determined at 75, 80, and 85 °C using thermal-death-time (TDT) cells, and the z-values (the temperature increase required to obtain a decimal reduction of the D-value) were calculated. The efficacy of the RF treatment was validated by heating the milk powder immersed in soybean oil by RF heating to 75 °C and holding it in a conventional oven for different time periods. A 5 log CFU/g reduction of Salmonella in whole milk powder was achieved after RF heating followed by 120 min holding in an oven at 75 °C. The water activity (aw) of whole milk powder significantly increased while its moisture content significantly decreased after RF heating followed by 120 min holding. A significant color change was observed after the treatment resulting in a 5 log CFU/g reduction of Salmonella. The results indicate that radio frequency heating combined with oil immersion can be used as a rapid method for milk powders to achieve the target temperature but a holding time of a few hours will be needed for a post-process lethality treatment.