Comparison of Cronobacter sakazakii thermal death kinetics in powdered infant formula milk using hot water and combined radio frequency and hot air treatment

Abstract. Powdered infant formula milk is prone to Cronobacter sakazakii (C. sakazakii) contamination, which is fatal to infants. In order to explore effective thermal inactivation applications of powdered infant formula milk, this research studied the thermal death kinetics of C. sakazakii in powdered infant formula milk using hot water and radio frequency energy. D-values and z-values were determined for powdered infant formula milk with water activity of 0.2, 0.3 and 0.4 inoculated with approximately 10 8 CFU/g C. sakazakii vegetative cells and sealed in TDT cells which were completely immersed in a circulating water bath and held at prescribed temperatures for predetermined time periods. D-values for sample with water activity of 0.3 at 60, 65, 70 and 75 °C were 77.9, 50.3, 29.9 and 15.6 min, respectively, which were too harsh for quality retention of powdered infant formula milk because under these conditions, protein was denatured. The z-value was 21.5 °C. When inoculated powdered infant formula milk sealed in Petri dish was exposed to combined radio frequency and hot air treatment, one log reduction of C. sakazakii was obtained during come up time of 70 °C. Under such condition, quality of powdered infant formula milk was well retained. With increase of sample water activity, D and z values decreased for both treatments. This study demonstrated that radio frequency technology may serve as an effective way to inactivate C. sakazakii in packaged powdered infant formula milk.