Nanoparticle Morphology Outweighs Antioxidant Properties in Whey Protein–Dextran Maillard Conjugates for Oxidative Stabilization of Chia Oil Powders

Abstract

Biopolymeric nanoparticles have attracted increasing attention as stabilizers and functional ingredients in food systems, mainly due to their antioxidant and interfacial properties. However, the relative contribution of nanoparticle composition and morphology to the oxidative stabilization of encapsulated chia oil remains poorly understood. In this work, whey protein isolate (WPI) and dextran (DX) conjugates were produced via the Maillard reaction and used to synthesize nanoparticles with two distinct geometries: randomly aggregated (NP-R) and spherical (NP-S). These nanoparticles, derived from WPI/DX conjugates using DX of two molecular weights (6 and 100 KDa), were employed as Pickering stabilizers for chia oil emulsions, which were subsequently spray-dried into oil powders. The oxidative stability of the powders was evaluated during 6 weeks of storage at 4 °C and 25 °C. Although WPI/DX6 conjugates exhibited higher antioxidant capacity than WPI/DX100, the oxidative stability assays revealed that nanoparticle morphology played a more decisive role than antioxidant composition. Powders stabilized with spherical nanoparticles exhibited markedly improved oxidative protection, maintaining peroxide values below Codex Alimentarius suggested limits (PV < 15 meq O2/Kg oil) after storage at 25 °C. These findings demonstrate that, beyond antioxidant capacity, nanoparticle size and geometry govern the oxidative preservation of encapsulated oil powders, offering new insights for the rational design of Pickering stabilizers in lipid-rich food systems.