Real-time measurement of oxygen transport across an oil–water emulsion interface Original Research Article

A method for real-time, in situ measurement of oxygen transport across oil-in-water emulsion interface was developed. This method is based on reversible fluorescence quenching of tris ruthenium (II) bis (hexafluorophosphate) complex dye encapsulated in the oil phase of an emulsion upon interaction with oxygen. Oxygen transport across the oil–water interface for four different emulsions (whey protein isolate (WPI), sodium-dodecyl sulphate (SDS), cross-linked WPI and SDS–chitosan emulsions) was measured and effective diffusion coefficients were calculated. Results show that cross-linking of WPI did not alter the oxygen transport rate (p > 0.01), while addition of a chitosan layer to the SDS emulsion significantly reduced the oxygen transport rate (p < 0.01). An increase in temperature from 25 to 40 °C reduced the oxygen transport rate in WPI and cross-linked WPI emulsions (p < 0.01). Effective diffusion coefficient values for transport of oxygen based on fluorescence data were 0.14–1.15 × 10−12 cm2/s for the tested emulsions. Regardless of relatively low effective diffusion coefficients, the selected emulsions exhibited poor barrier properties in limiting oxygen transport across an emulsion interface. In summary, this rapid method is sensitive to detect changes in rate of oxygen transport due to changes in temperature and chemical composition of emulsion interface. This method can be used to screen and evaluate the barrier properties of encapsulation matrices leading to rational design of encapsulated structures.