Hydrogenated plant-based lecithins as excipients for cosmetic and pharmaceutical applications : a physical-chemical study

Lecithin is a generic term that is often used to indicate a product mainly constituted of phospholipids. Lecithins can be used in pharmaceutical and cosmetic field as wetting agents, emulsifiers and building blocks for the production of liposomes and micelles. One of its main sources are plants. From their extraction a final product mainly constituted of phosphatidylcholines and phosphatidylethanolamines can be obtained. Common issue connected to freshly extracted lecithins is the presence of a product rich in double bonds subject to photo and air oxidation. By adding in the purification process a further catalytic step, it is possible to form stable hydrogenated lecithin products. Despite their widespread use, little is known about the physicochemical properties of such hydrogenated lecithins, detailed studies mainly based on X-ray scattering methods on mono- and multi-layers have been performed. Additionally, the emulsifying properties of these lecithins such as Hydrophilic-Lipophilic Deviation (HLD parameter) and solubility have also been studied. General findings are that mixtures with higher amounts of phosphatidylcholines (90–100 %) formed a well-defined lamellar phase showing in monolayers complete absence of charge, while lecithins with lower phosphatidylcholine contents (75–80 %) formed charged monolayers and positionally uncorrelated bilayers due to the presence of charged species. The hydrogenated phospholipids (PLs) studied were highly soluble in several co-solvents which are suitable for the incorporation of these phospholipids into relevant dermal formulations. The studied PLs are able to stabilize innovative dermal colloidal formulations such as cerosomes and to improve the incorporation of them into Stratum corneum models. In conclusion, the following studies will allow a more rational selection of hydrogenated lecithins for the formulation of cosmetic and pharmaceutical products.