Ultrasonication-Enabled Liposomal Encapsulation of Propolis Extract: Bioaccessibility, Bioavailability, and Food Application

Propolis is a natural bee product widely used for its antioxidant, antimicrobial, and antifungal properties. This study presents a simple ultrasonication-assisted liposome method to enhance the encapsulation of poorly water-soluble phenolic compounds in propolis extract. Propolis extract concentrations ranging from 0.05% to 0.5% were tested to evaluate the feasibility of the method. Primary and secondary liposomes were then characterized by encapsulation efficiency (EE), average particle size, and zeta potential to determine the optimum core material ratio. The retention of the bioactive compounds in the liposomes was then assessed by bioaccessibility, bioavailability, and food application studies. Encapsulation efficiency was between 52.76% and 76.12%, and secondary liposomes with 0.05% propolis extract showed the highest EE. The bioaccessibility study revealed that 0.5% propolis-loaded secondary liposomes had the highest total phenolic content (27.47 mg GAE/100 g) and antioxidant capacity (23.91 mg/100 g by DPPH and 38.92 mg TE/100 g by CUPRAC assay) after digestion. Bioavailability values of TPC, CUPRAC, and DPPH with 0.5% propolis-loaded secondary liposomes were found to be 64.63%, 83.31%, and 80.48%, respectively. Apigenin, caffeic acid, CAPE (caffeic acid phenyl esters), chrysin, cynarin, epicatechin, ferulic acid, gallic acid, naringenin, p-coumaric acid, pinocembrin, protocatechuic acid, quercetin, rutin, trans-cinnamic acid, and trihydroxy benzoic acid were determined by HPLC. Furthermore, apple juice enriched with these liposomes increased the stability and preservation of bioactive compounds during digestion. These findings highlight the potential of propolis-loaded liposomes as effective carriers in functional food systems.