High Internal Phase Emulsion Gels Stabilized by Natural Casein peptides

The surface and interfacial properties of casein-hydrolyzed peptides were evaluated using measurement of surface and interfacial tensions, surface viscosity, dynamic light scattering (DLS), and freeze-fracture transmission electron microscopy (FF-TEM). In this study, high internal oil phase emulsion (HIPE) gels were successfully prepared, using the surface and interfacial properties of casein peptides. The casein peptides exhibited surface and interfacial activities. The estimated critical micelle concentration (CMC) and γ_CMC values were 3.0 mg/mL and 47.8 mN/m, and the average size of casein peptide micelles was 13.2 ± 1.7 nm. The surface shear viscosity of an aqueous casein peptide solution at 10 mg/mL was 1603 µPa ms, which is fifteen times larger than that of sodium dodecyl sulfate (SDS, 106 µPa ms). The larger surface viscosity of casein peptide adsorbed layer could stabilize emulsions and prevent flocculation and coalescence. High internal oil phase gel emulsions were then prepared by slowly adding oil and polyisobutene into an aqueous casein peptide solution/glycerol mixture with different compositions. Based on the pseudo ternary 15 wt% aqueous casein peptide solution/polyisobutene/glycerol phase diagram, the HIPE containing the maximum 88.1 wt% (91.5 vol%) of oil is obtained by the addition of 0.36 wt% of casein peptides. The use of only a small amount of protein-hydrolyzed peptides instead of the commonly used synthetic surfactants for HIPE preparation has great advantages for the widespread application of HIPE technology.