Peptide and protein emulsifiers

There has recently been a growing attention towards peptide and protein molecules as potential bioemulsifiers for the stabilization of foams and emulsions, thanks to their innate tendency towards interfacial adsorption. Additionally, peptides and proteins are biodegradable and biocompatible, making them less toxic if compared to traditional emulsifiers. This chapter provides a comprehensive overview of the different classes of peptide, protein and mixed protein–polysaccharide emulsifiers and discusses the emulsification mechanisms of these systems. In essence, peptide-mediated emulsification can occur either via traditional surfactant-like mechanism, where amphiphilic molecular peptide chains adsorb at the biphasic interface forming ‘spherical micelles’, or through peptide self-assembly into higher secondary structure (α-helices or β-sheets) with the formation of amphiphilic nanofibrous structures adsorbing at the interface. Moreover, peptides can self-assemble in the continuous aqueous phase forming nanofibrous network of viscous hydrogels that enhance system stability. On the other hand, emulsion stabilization by proteins is mainly achieved through either electrostatic repulsion or steric stabilization. The various characterization techniques for emulsification and interfacial stabilization will be visited throughout this chapter, focusing on structural, mesoscopic and macroscopic characterization of these systems.