Emulsion formed in bovine serum album/anionic surfactant/H2O system under acidic condition

At neutral pH, bovine serum album (BSA) conformation is "heart-shaped", and with decreasing pH, BSA may adopt the fast "F" form below a pH of about 4, and expanded "E" form at pH lower than about 3. However, as far as we know, the researches on the interaction between protein and surfactant are all carried out at pH higher than its isoelectric point (pI, which is 4.9), which means only the information about how the "heart-shaped" BSA interacts with surfactant is understood so far. In this paper, we studied the interaction between BSA and anionic surfactant at pH lower than its pI and hope to help understand the role of protein conformation in its interaction with surfactant. We found that BSA and anionic surfactant could form emulsion only when pH value was lower than or about 3, suggesting that the "E" formed BSA was an important criterion for emulsion formation. Moreover, the emulsion formation was companied with increased α-helix content and decreased β-sheet content for BSA. In addition, the emulsion formation was closely dependent on the anionic surfactant content; only a moderate anionic surfactant could make emulsion formed.