Effects Of Different Processing On Cronobacter Sakazakii And Quality Of Infant Formula

Infancy is the most important period of growth and development in people’s lifetime.Infant formula that simulates the composition and proportion of breast milk are the main food sources for many infants.The requirements on food safety and nutrition supplement are very rigorous.Since the 21st century,the incidents of food-borne pathogens in infant formula milk powder occur frequently,which is a great threat to infants’health.The most dangerous pathogen in infant formula is Cronobacter sakazakii which spreads the most widely and causes serious injury.Therefore,it is of great significance to study infant formula processing technology that can effectively kill Cronobacter sakazakii and maintain the stability of nutrition elements in milk formula.In this study,radio frequency dielectric heating（RFDH）and radio frequency combined with ultraviolet irradiation（RF-UVC）processing methods were selected to analyze the impact of different processing methods on the bactericidal kinetics and physicochemical properties of Cronobacter sakazakii in infant formula.Changes in structural,oxidative,and antioxidant properties ofβ-lactoglobulin induced by RF and RF-UVC were studied.In this study,the radio frequency device of 27.12 MHz,1500 W and the ultraviolet irradiation sterilization device with intensity of 11.8 W/m²were used for processing infant formula.Firstly,the infant formula inoculated uniformly with Cronobacter sakazakii was treated by radio frequency processing（80^oC,85^oC and 90^oC）and RF combined with UV-C processing to study the bactericidal kinetics of Cronobacter sakazakii under different treatments.First-order kinetic model,Weibull model and Log-logistic model were used to fit and validate the inactivation curves.The study found that combination of radio frequency and ultraviolet irradiation for 30 min（90^oC）had the best sterilization performance,the lethal logarithm is 2.56 log.The Log-logistic model has the best fitting result for either RF or RF-UVC combined treatment.Secondly,the effects of RF and RF-UVC treatment on the basic nutrients and the main vitamins in infant formula were studied.The results showed that the content of protein,carbohydrate,fat etc.decreased in RF treatment.The loss of above-mentioned basic nutrients in the RF-UVC treatment was smaller than that of RF treatment.In the study of several major vitamins under radio frequency,vitamin C,vitamin B₁,B₂,B₆,nicotinamide,Pantothenic acid had varying degrees of loss.As the temperature increases,the loss of vitamins became more serious.While RF combined with UV-C treatment can greatly reduce the loss of vitamin C,vitamin B₁,B₆ and pantothenic acid.Moreover,the atomic force microscopy was used to analyze the morphology of infant formula treated by RF.Fourier transform infrared spectrum,sulfhydryl content,surface hydrophobicity were analyzed to investigate the change of structural,oxidative,and antioxidant properties ofβ-lactoglobulin after RF combined UV-C.Results showed that the topography of infant formula after radio frequency treatment was more compact and the surface was smoother.The secondary structure and tertiary structure ofβ-lactoglobulin changed significantly after different treatments.RF-UVC treatments significantly increasedβ-sheet content.Intrinsic tryptophan fluorescence absorbance ofβ-lactoglobulin was decreased most significantly after 30 min RF-UVC treatment.RF and RF-UVC treatments affected the oxidative and anti-oxidative properties ofβ-lactoglobulin to varying degrees.These results indicated that protein structures and the anti-oxidative properties ofβ-lactoglobulin changed after these treatments with protein unfolding and exposure of hydrophobic group.