Solute distribution and stability in emulsion-based delivery systems: an EPR study

Area of Science:

• Food science and technology
• Materials science
• Physical chemistry

Background:

• Oil-in-water emulsions are crucial for delivering hydrophobic compounds in various industries.
• Solid lipid nanoparticles (SLN) show promise for controlled solute release, but solute localization within them is not well understood.

Purpose of the Study:

• To investigate the localization and behavior of small hydrophobic molecules within liquid and crystalline lipid droplets in emulsions.
• To understand how droplet phase (liquid vs. crystalline) affects solute distribution and mobility.

Main Methods:

• Emulsification of alkanes (tetradecane, eicosane) with a spin probe (PTMIO) in sodium caseinate solution.
• Electron Paramagnetic Resonance (EPR) spectroscopy to analyze probe localization and mobility.
• Chemical reduction of the probe to quantify its aqueous phase concentration.

Main Results:

• The spin probe (PTMIO) was found in both aqueous and lipid phases.
• Hydrophobic probe predominantly localized in liquid tetradecane droplets (70-77%).
• Probe was completely excluded from crystalline eicosane droplets into the aqueous phase.

Conclusions:

• Droplet crystallization, as seen with eicosane, effectively excludes hydrophobic solutes from the lipid core.
• Solute molecules are driven to the aqueous phase and interact with the droplet interface.
• This phenomenon offers a mechanism for controlling solute availability in emulsion-based delivery systems.