Synthesis of a peptide emulsifier with an amphiphilic structure.

Three kinds of peptides (H, S, and R) with 16 amino acid residues were synthesized, and their secondary structure and emulsifying properties (emulsifying activity and oil-binding property) were investigated to clarify the effects of conformational amphiphilicity. The amino acid compositions of the three peptides were the same (8 Leu and 8 Glu residues) but their sequences were different. Circular dichroism analysis showed that peptide H contained an alpha-helix at pH 5.5 but took a random structure at pH 7.0. Peptide S also contained an alpha-helix at pH 5.5, while a beta-sheet structure was predominant at pH 7.0. Peptide R took mainly a random structure at both pH 5.5 and pH 7.0. The helical properties of peptide H and peptide S were different; the alpha-helix of peptide H was amphiphilic, while that of peptide S was not. Under conditions where peptide H formed an amphiphilic alpha-helix, both the emulsifying activity and oil-binding property of the peptide significantly increased. The emulsifying properties of peptide S, which formed an amphiphilic beta-sheet at pH 7.0, were also good at that pH. We conclude that a peptide with an amphiphilic alpha-helix or beta-sheet structure has better emulsifying properties, hence a good peptide emulsifier could be designed by incorporating such a structure.