Physicochemical Stability and Bio-Functionality of Liposome-Encapsulated Macadamia Husk Phenolic Extract

Macadamia husks are an underutilized by-product of nut processing and a rich source of phenolic compounds with strong antioxidant activity. However, their instability during processing, storage, and gastrointestinal digestion limits their application in food systems. This study aimed to encapsulate macadamia husk phenolic-rich extract (MHPE) in liposomes to improve stability, enable controlled release, and assess cytotoxicity for functional food applications. MHPE was encapsulated in soy lecithin liposomes using high-shear mixing followed by high-pressure homogenisation. Liposomes were characterized by particle size, polydispersity index (PDI), ζ-potential, encapsulation efficiency, and morphology. Cytotoxicity was evaluated using Caco-2 cells, and phenolic release was assessed under simulated gastrointestinal conditions. MHPE-loaded liposomes exhibited nano-sized particles (77-78 nm), low PDI (0.21), and high negative ζ-potential (-43.11 to -47.01 mV) during two months of storage at 4 °C. Transmission electron microscopy confirmed predominantly spherical vesicles with sizes consistent with dynamic light scattering measurements. Encapsulation efficiency remained high (81.50% initially; 73.60% after 28 days). Both free and extract-loaded liposomes were non-cytotoxic to Caco-2 cells. Encapsulated MHPE showed slower phenolic release compared with the free extract. Overall, liposomal encapsulation effectively enhanced the stability and controlled release of macadamia husk phenolics, supporting their potential use as functional food and nutraceutical ingredients.