In this study, the release of free fat acids (FFA) from and the digestion characteristics of curcumin nanoemulsions constructed using whey protein isolate (WPI)-(-)-epigallocatechin-3-gallate (ECGG) graft copolymers with 3% and 4% grafting degrees as emulsifiers were investigated during in vitro simulated digestion and compared with those of curcumin nanoemulsions stabilized by WPI. It was found that binding to EGCG might cause the unfolding of WPI, and the interfacial film thickness of the WPI-EGCG stabilized emulsion increased by 31.6 nm compared with that of the WPI stabilized emulsion. The WPI-EGCG complex stabilized emulsion had a smaller particle size dispersion and average particle size than the WPI stabilized emulsion and was therefore more stable and superior in promoting lipid digestion. After 120 minutes of intestinal digestion, the final release rate of FFA from the nanoemulsion stabilized with 4% WPI-EGCG was 85.13%. Also, the graft treatment improved the bioaccessibility of curcumin encapsulated in the system.

To reveal the difference in the oil/water interfacial behavior of nanoemulsions prepared separately with three emulsifiers, octenyl succinic anhydride (OSA)-modified starch, Tween-80/Span-80 (T/S80), and lecithin, this study employed a rheometer and a contact angle meter to analyze the shear rheological properties and interfacial adsorption dynamics of the emulsion systems. Furthermore, molecular dynamics simulation was utilized to delve into the underlying mechanisms of their microscopic oil/water interfacial behavior. The findings revealed that OSA exhibited the lowest interfacial tension at the oil/water interface, while T/S80 demonstrated the highest diffusion rate within the oil/water interfacial layer. This was primarily attributed to the carbon chain-based structure of T/S80, which facilitated its dispersion in water. The number of hydrogen bonds formed between the OSA-modified starch-stabilized emulsion and water molecules was the largest, approximately 1300, indicating stronger hydrophobic effect and explaining why the emulsion droplets were the closest to a sphere in shape. OSA-modified starch and T/S80 molecules tended to form van der Waals force with water molecules. In contrast, the two carbon chains of lecithin, with glycerol as its backbone, showed a more diverse range of weak interactions because of their mutual repulsion.