Monitoring Ultraviolet (UV) Radiation Inactivation of Cronobacter sakazakii in Dry Infant Formula Using Fourier Transform Infrared Spectroscopy

Cronobacter sakazakii is an opportunistic pathogen associated with dry infant formula presenting a high risk to low birth weight neonates. The inactivation of C. sakazakii in dry infant formula by ultraviolet (UV) radiation alone and combined with hot water treatment at temperatures of 55, 60, and 65 degrees C were applied in this study. UV radiation with doses in a range from 12.1 +/- 0.30 kJ/m2 to 72.8 +/- 1.83 kJ/m2 at room temperature demonstrated significant inactivation of C. sakazakii in dry infant formula (P < 0.05). UV radiation combining 60 degrees C hot water treatment increased inactivation of C. sakazakii cells significantly (P < 0.05) in reconstituted infant formula. Significant effects of UV radiation on C. sakazakii inactivation kinetics (D value) were not observed in infant formula reconstituted in 55 and 65 degrees C water (P > 0.05). The inactivation mechanism was investigated using vibrational spectroscopy. Infrared spectroscopy detected significant stretching mode changes of macromolecules on the basis of spectral features, such as DNA, proteins, and lipids. Minor changes on cell membrane composition of C. sakazakii under UV radiation could be accurately and correctly monitored by infrared spectroscopy coupled with 2nd derivative transformation and principal component analysis.