SDS-PAGE Profile of Ovalbumin Isolated from Native Chicken (Gallus gallus domesticus) Egg White by Sequential PEG 6000 and Isoelectric Precipitation

Ovalbumin is the predominant protein in chicken egg white, constituting approximately 54–60% of total egg white protein, and is of considerable interest in food science, immunology, and pharmaceutical research. This study describes a sequential purification protocol for ovalbumin from native chicken (Gallus gallus domesticus) egg white using polyethylene glycol 6000 (PEG 6000) precipitation followed by isoelectric precipitation. Four isolation replicates were conducted: N1 and N2 each used pooled egg white from two eggs, while N3 and N4 each used a single egg, accounting for the observed volume differences across replicates. Egg white was pre-treated with phosphate buffer (0.02 M, pH 6.5) and 0.1 M NaCl, then subjected to 18% (w/v) PEG 6000 precipitation at 10 °C to remove co-precipitating proteins. The ovalbumin-enriched supernatant (F1) was subsequently precipitated at pH 4.5 ± 0.05 to yield an isoelectric supernatant (F2) and ovalbumin precipitate (F3). Protein concentrations estimated by OD280 spectrophotometry demonstrated notable enrichment in F3 fractions (3.04–25.19 mg/mL). SDS-PAGE analysis (10% polyacrylamide, Laemmli system) confirmed the presence of a dominant protein band at approximately 43–46 kDa in F3, co-migrating with commercial ovalbumin reference, consistent with the known molecular weight of ovalbumin (~45 kDa). Densitometric inspection of gel images suggested that the ~45 kDa band accounted for 75–85% of total lane integrated optical density in valid replicates, indicating effective enrichment. These findings support the sequential PEG-isoelectric precipitation approach as an accessible and efficient method for ovalbumin enrichment from native chicken egg white.