Pickering Emulsions Loaded with Thymol and Stabilized by Mung Bean Protein/Whey Protein Isolate Nanoparticles: Stability and Functional Properties

Thymol has been granted “Generally Recognized as Safe” status by the US Food and Drug Administration. However, its application as a natural preservative is constrained by limitations such as poor water solubility and high volatility. In this study, a dual-protein complex was prepared using mung bean protein and whey protein isolate to stabilize thymol-loaded oil-in-water (O/W) Pickering emulsions. The results demonstrated that the dual-protein system was driven by hydrogen bonding, electrostatic attraction, and hydrophobic interactions. Compared to single-protein systems, the dual-protein Pickering emulsions possessed smaller droplet sizes, lower polydispersity indices, and higher surface charges and surface hydrophobicity. Additionally, the dual protein enhanced emulsifying activity, thermal stability, and 30-day storage stability. Notably, the complex formed a continuous three-dimensional porous network structure at the mung bean protein (MBP) to whey protein isolate (WPI) ratio of 50%:50%. Benefiting from this structure and high surface hydrophobicity, the 50%:50% formulation achieved the highest thymol encapsulation efficiency. In terms of functional properties, this optimized emulsion demonstrated notable antibacterial activity and antioxidant activity; it demonstrated antibacterial activity against Shewanella putrefaciens and Staphylococcus aureus. Furthermore, the IC50 value for the 50%:50% formulation was 192.25 ± 1.93 μg/mL (DPPH) and 161.74 ± 0.71 μg/mL (ABTS). In summary, the 50%:50% formulation enhanced the emulsifying activity, encapsulation efficiency, and bioactivity of the emulsion. This system provides an effective strategy for the stabilization and encapsulation of hydrophobic active compounds in emulsions.