A Fluorescence-based Method for Estimation of Oxygen Barrier Properties of Microspheres

In this study, we developed a fluorescence method to quantify oxygen barrier properties for wall materials used in microencapsulation of oxygen-sensitive compounds. We used a reversible, oxygen quenching dye, tris (4,7-diphenyl-1, 10-phenanthroline) ruthenium(II) dichloride complex, as a marker to monitor oxygen transport across spray-dried and freeze-dried Hi-cap100 and maltodextrin microspheres. We fit the rate of oxygen transport to Fick's second law and extrapolated an effective oxygen diffusion coefficient Deff. Results show that the Deff for spray-dried maltodextrin and Hi-cap100 formulations were in the range of 6.46 × 10^-15 to 7.45 × 10^-15  m² /s and 16.0 × 10^-15 to 22.4 × 10^-15 m² /s, respectively. Results also show an increasing trend in thiobarbituric acid reactive substances reaction rate constants, with an increasing D_eff for each formulation. Additionally, freeze-dried maltodextrin formulations had significantly higher D_eff (31.1 × 10^-15 to 36.0 × 10^-15 m² /s) compared to spray-dried matrices due to a more porous morphology. This new method provides a framework for the in situ estimation of D_eff for wall materials in microspheres. Potential applications include the design and selection of wall materials for maximum oxidative stability of encapsulated ingredients. PRACTICAL APPLICATION: Currently, the selection of wall materials used in microencapsulation of lipids takes a trial-and-error approach, which can be time consuming and prone to error. In this study, we developed a new methodology to directly assess the oxygen barrier properties of wall materials in microspheres. This method can be used by food scientists to screen wall materials in order to optimize the oxidative stability of encapsulated lipids.