Abstract:The effects of sterilization treatments on the microbial compositions on both the inner and outer surfaces of duck eggshells and the ratio of black to yellow salted egg yolks were investigated in this study. Duck eggs were fumigated and cleaned with different fumigants and cleaning agents, and then stored at different temperatures. Changes in the total number of bacteria on duck eggshell inner and outer surfaces before and after treatments were subsequently compared. The effects of sterilization on the microflora on duck eggshell outer surfaces were evaluated using 16S rRNA gene sequencing and PICRUSt gene function prediction. Salted duck eggs were prepared using the mud-packing method at 35 ℃, and the ratio of black to yellow salted egg yolks was calculated. The results show that fumigation significantly inhibits the migration of bacterial colonies from the outer to inner surfaces of the eggshells, effectively controlling the total number of bacteria inside the shell. Two fumigation treatments increase efficacy relative to one. Total bacteria on the outer surface can be reduced to below the detection limit by cleaning. Low-temperature storage can limit bacterial proliferation on both inner and outer eggshell surfaces over 7 days. Total bacteria numbers on both inner and outer surfaces can be significantly reduced by combining fumigation, cleaning, and low-temperature storage. These processes also inhibit bacterial migration, tightly controlling the total bacteria inside the eggshell. 16S rRNA gene sequencing demonstrates a notable reduction in the proportion of Proteobacteria and Psychrobacter on the outer surface of the shell following sterilization treatments. Additionally, PICRUSt gene function prediction indicates a significant decrease in microbial activity within pathways associated with lipid oxidation, amino acid transport, and metabolism after sterilization treatments. Sterilization also significantly reduces the ratio of black to yellow salted egg yolks. These studies illustrate that sterilization treatment effectively decreases total bacteria count on the outer surfaces of duck eggshells and inhibits the occurrence of black salted egg yolks. These findings demonstrate the importance and necessity of sterilization before duck egg processing.