α-Tocopherol-loaded freeze-dried liposomes and proliposomes: powder properties and thermal performance

Dry lipid-based formulations can enhance the handling and preservation of lipophilic bioactives, though their efficacy depends heavily on formulation composition and processing conditions. This study compared α-tocopherol-loaded freeze-dried liposomes (FD_LPs) and proliposomes (PLPs) formulated with either mannitol (PLPs_MAN) or trehalose (PLPs_TRE) as carriers. All three formulations were evaluated for reconstitution characteristics, powder properties, and thermal performance after rehydration. Additionally, a four-week storage stability test was conducted at 4, 25, and 40 °C, restricted to FD_LPs and PLPs_MAN. Upon reconstitution, all formulations exhibited mean vesicle diameters ranging from 561.5 to 669.3 nm and polydispersity index (PDI) values of approximately 0.57-0.60, indicating relatively broad particle size distributions. Initial entrapment efficiencies (EE) were high, exceeding 93% for all samples. Among the formulations, PLPs_MAN exhibited the lowest moisture content. Both PLP formulations demonstrated lower hygroscopicity and superior flow indices compared to FD_LPs. Under thermal stress (90 °C, 12 h), PLPs_TRE showed the lowest TBARS response, whereas PLPs_MAN maintained the highest DPPH radical-scavenging activity. After four weeks at 40 °C, mean EE values were lower than their initial values for both tested formulations, reaching 73.7% for FD_LPs and 79.0% for PLPs_MAN. Overall, both proliposome formulations exhibited more favorable powder flow indices and lower hygroscopicity than FD_LPs, whereas their thermal responses depended on the endpoint examined. The four-week storage findings apply only to FD_LPs and PLPs_MAN and do not establish the storage performance of PLPs_TRE. Differences in carrier loading and processing limit attribution of the observed effects to carrier identity alone.