Effects of radio frequency on physicochemical properties of powdered infant formula milk as compared with conventional thermal treatment

Abstract Radio frequency (RF) has been proved effective in inactivating Cronobacter sakazakii in powdered infant formula milk (PIFM). For successful industrial application, the quality of PIFM after combined RF and hot air treatment (RF-HA) were further investigated based on 5-log inactivation of Cronobacter sakazakii as compared with hot water treatment (HW). Severer color deterioration was observed on HW treated samples. No significant difference existed on solubility (>99%) and crude protein content (about 13 g/100 g) after both treatments. Protein denaturation temperature obtained from the differential scanning calorimetry curves increased with decreasing moisture content of PIFM and RF-HA resulted in more stable protein structures. Fourier transform infrared spectrum further confirmed the development of Maillard reaction, which was weaker in RF-HA. Microstructure by scanning electron microscopy revealed more obvious particle agglomeration behavior induced by RF. Overall, higher water activity, 0.4 as the upper limit, was not good for maintenance of nutritional attributes, though conducive to sterilization. This study could provide useful information for PIFM quality evaluation and optimization of thermal pasteurization methods.