Whey protein nanoparticles obtained by water in oil emulsification followed by heating: Influence of surfactant type on the stability, rheology and interfacial properties

Abstract

Whey protein isolate (WPI) nanoparticles were synthesized through water-in-oil (W/O) emulsions followed by heating. The aqueous phase containing 12% WPI was encapsulated within the emulsion droplets. During heat treatment at 80 ◦C for 15 min, the protein underwent gelation, leading to the formation of nanoparticles with different size and morphology depending on the emulsifier used. The examined surfactants were Polyglycerol Polyricinoleate (PGPR), Sorbitan monooleate 80 (Span 80), and a 3:1 mixture of Span 80/Polyoxyethylene sorbitan monooleate (SPTW). The study focused on understanding their interactions at the oil-water interface.Emulsions were assessed for stability, size, and optical properties, with analysis via confocal microscopy and rheology, both pre- and post-heat treatment. The resulting nanoparticles were examined using scanning electron microscopy (SEM). Interface analysis revealed similar behavior between PGPR and SPTW. However, PGPR exhibited superior stability in emulsions and was the only surfactant capable of producing nanoparticles upon thermal treatment. Conversely, emulsions containing Span 80 and SPTW experienced coalescence, leading togelation of the aqueous phase and formation of large protein aggregates. These aggregates resulted in increased viscosity and elastic modulus of the heated emulsions. PGPR proved to be the only surfactant able to generate nanoparticles with a controlled size and shape, of approximately 300 nm.