Egg White Sampling and Protein Extraction

The eggs of chicken, quail, and duck were collected within 2 to 3 days after laid from the Poultry Research Center farm of Huazhong Agricultural University and used in this study. Eggs were randomly selected for sampling. Three biological replicates and 2 technical replicates were performed during the following experiments for 2-DE analysis to reduce variations. Protein extraction was performed basically according to the previously described method (Qiu et al., 2012a). Briefly, the egg white was manually separated from the egg yolk and gently homogenized at 4 °C for 30 min with a magnetic stirrer. The egg white samples were centrifuged and resuspended 3 times. The protein content was quantified using a 2-DE Quant Kit (GE Healthcare, Piscataway, NJ).