Abstract: In order to explore the predictive bactericidal effect of ultrasound-assisted steam treatment on Escherichia coli on the eggshell surface and the mechanism of bacterial damage and death, a kinetic model for the sterilization of E. coli on the eggshell surface by ultrasound-assisted steam treatment was constructed. By controlling the concentration of bacterial suspension used to artificially contaminate eggshells, the sterilization efficiencies of E. coli by ultrasound, steam and their combination were evaluated and compared with that using the sodium hypochlorite immersion method, commonly used in commercial sterilization. The Linear, Weibull, Log-Logistic and Modified Gompertz models were used to fit the inactivation curve of E. coli by ultrasound-assisted steam treatment, and the damage degree of cell morphology and the leakage of cell contents before and after sterilization were measured. The results showed that after 180 s of 150 W ultrasonic pretreatment and 3 s of steam treatment, the logarithm of the total number of E. coli decreased from 6.26 to 2.04 with a mortality rate of 67%. The sterilization process of ultrasound-assisted steam treatment was better fitted to the nonlinear dynamic model, while the Weibull model was more suitable to describe the dynamic process of sterilization with increasing ultrasonic intensity and steam treatment time. In addition, the combined treatment destroyed the ultrastructure of E. coli and the external structure of its cells, resulting in cytoplasm leakage and changes in the permeability of the membrane. Therefore, ultrasound-assisted steam treatment could aggravate the deformation and damage of bacteria, leading to bacterial death. The experimental results provide a theoretical basis for the inactivation of E. coli on the eggshell surface. According to the results of egg quality during storage, this method has broad application prospects in the production of clean eggs.

Key words: eggshell; ultrasound-assisted steam treatment; sterilization; microorganism