Effect of barrier properties of zein colloidal particles and oil-in-water emulsions on oxidative stability of encapsulated bioactive compounds

Background: Oxidation of encapsulated bioactive compounds is a key challenge that limits shelf-life of bioactive containing products. The objectives of this study were to compare differences between the oxidative barrier properties of biopolymer particle based encapsulation system (zein colloidal particles) and oil-in-water emulsions and evaluate the impact of these differences on oxidative stability of encapsulated bioactives. Methods: Both zein colloidal particles and oil-in-water emulsions were stabilized by casein protein. The oxidative barrier properties of the selected encapsulation systems were determined by measuring the permeation rate of peroxyl radicals and oxygen across the interface. Peroxyl radical permeation rates were correlated with stability of a model bioactive, curcumin and oxygen permeation rates were correlated with stability of another model bioactive, retinol. Results: Radical permeation rate was significantly higher in oil-in-water emulsions compared to zein colloidal particles, indicating enhanced barrier property of zein colloidal particles against peroxyl radical induced oxidation. Consistent with these results, stability of curcumin encapsulated in zein colloidal particles was significantly higher compared to that in oil-in-water emulsions. Oxygen permeation measurements showed no significant differences in the barrier properties of both encapsulation systems against oxygen permeation. Consistent with these results, the oxidative stability of retinol was similar in both encapsulation systems. Conclusions: The results of this study demonstrate the advantages of biopolymer particle based encapsulation system in limiting free radical induced oxidation of encapsulated bioactives and also demonstrate the ineffectiveness of both encapsulation systems in limiting oxygen permeation.