ε-Polylysine/Sodium Alginate Bilayer-Modified Nanoliposomes Enhancing the Stability and In Vitro Bioavailability of Epigallocatechin Gallate

Epigallocatechin gallate (EGCG) represents the key phenolic compound in green tea, which has been verified to possess various biological effects but suffers from low stability and poor bioavailability. To address these issues, EGCG-loaded nanoliposomes (ELs) were screened and prepared using an ethanol injection–calcium acetate gradient (EtOH-CAG) method. An encapsulation efficiency of 94.61% was achieved, involving a particle size of 118.6 nm and a polydispersity index (PDI) of 0.23. Via layer-by-layer assembly, nanoliposomes modified with either ε-polylysine (ε-PL) monolayer (ELP) or ε-polylysine/sodium alginate (SA) bilayer (ELPA) exhibited substantially improved stability. Moreover, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermal analysis confirmed the effective loading of EGCG and the successful decoration of ε-PL and SA. Molecular docking analyses of dual ligands further characterized the surface modification mechanism, which was primarily mediated by hydrogen bonding and electrostatic interactions. ELPA maintained robust stability under conditions including 200 mM salt concentration, a pH range of 4–10, temperatures up to 55 °C, and a 25-day storage duration. The modified systems showed considerably enhanced cellular uptake without causing cytotoxicity. Collectively, the developed ε-PL/SA bilayer nanoliposomes offer an eco-friendly, efficient strategy to enhance EGCG stability and in vitro bioavailability in functional food applications.