Background: Microemulsions are attractive delivery systems for therapeutic proteins and
peptides due to their ability to enhance bioavailability. Although different proteins and peptides have
been successfully delivered through such ternary systems, no information can be found about protein
loading and the formulation stability when such microemulsions are prepared with pharmaceuticallyapproved
oils and surfactants. The aim of this work was to optimise a ternary system consisting of water/
ethyl oleate/Span® 80-Tween® 80 and to determine its protein loading capacity and stability, using bovine
serum albumin (BSA) as a model of biomolecule.
Methods: The optimization was carried out using a Central Composite Design and all the prepared
formulations were characterised through dynamic light scattering, rheology, optical and polarized microscopy.
Subsequently, the maximum loading capacity was determined and the stability of the final
microemulsion with the highest content of protein was followed over six months. To investigate the
structural features of the protein, BSA was recovered from the microemulsion and analysed through
Results: After incorporation of the protein in the microemulsion, a decrease of its aqueous solubility
was observed. However, the formulation remained stable over six months and the native-like state of
the recovered protein was demonstrated by fluorescence spectroscopy
Conclusion: This study demonstrated the feasibility of preparing microemulsions with the highest content
of protein and their long-term stability.