Enhanced Stability of O/W Pickering Emulsions Driven by Interfacial Adsorption of Whey Protein Nanogels

Whey protein is valued for its health and emulsifying benefits, yet its intrinsic instability limits its effectiveness as an emulsifier under food processing conditions. To address the need for physically stable emulsions, this study developed O/W Pickering emulsions stabilised by nanogel WPI (GWEs) and investigated their stability under common food processing conditions, including thermal treatment, pH adjustment, and cold storage. For comparison, emulsions stabilised by non-heated (NWEs) and heat-treated WPI (HWEs) were also prepared. The results showed that while the oil droplet size of GWEs (12.2 ± 1.16 µm) was comparable to NWEs (13.6 ± 0.26 µm), HWEs exhibited significantly larger droplets (18.0 ± 0.16 µm). GWEs demonstrated the highest protein adsorption at the oil–water interface (68.7%). TEM further revealed that whey nanogels achieved nearly full monolayer coverage of oil droplets. By contrast, only partial protein coverage and exposed interfaces were observed in NWEs and HWEs. Additionally, GWEs exhibited superior stability under food processing conditions, with minimal changes in emulsion capacity, droplet size, viscosity, and flow behaviour when subjected to heat (up to 90 °C), acidification (pH down to 3), and storage for up to 3 days, confirming the potential of nanogel WPI as an advanced stabiliser in emulsion-based formulations.