Amphiphilic O(Phe-r-Glu) oligopeptides randomly polymerized via papain exhibiting a pH-insensitive emulsification property

Natural amino acid polymers have been wide-used as bio-compatible emulsion stabilizers . In this study, Amphiphilic O(Phe- r -Glu)s were synthesized through the papain-catalyzed random polymerization of L -phenylalanine and L -glutamate with the major degree of polymerization value of 6–7. The polymerization yield was increased by more than 35 % using choline to reduce the energy barrier for the amino substrates to form the tetrahedral intermediate with the catalytic triad. The squalene/water emulsions stabilized by O(Phe- r -Glu) nanoparticles were pH-insensitive at pH 1–12. The investigation of mechanism found the combined effects of steric hindrance , electrostatic repulsion and the viscosity of the emulsion contributed to the stability of the emulsion droplets. Under acidic condition, the layers of O(Pho- r -Glu)s particle aggregates formed around the emulsion droplets and the higher viscosity of emulsion mainly contributed to the stability of emulsions . At basic condition, the strong electrostatic repulsion between emulsion droplets covered by the negatively charged O(Pho- r -Glu) particles and the steric hindrance contributed mainly to the prevention of the coalescence of emulsion droplets. The application of enzymatically synthesized amphiphilic peptides in emulsion, along with tunable performance through the polymerization of amino substrates, is in line with the sustainable development requirements in fields such as pharmaceuticals, food and cosmetics.