Formation, stability and antioxidant activity of food-grade multilayer emulsions containing resveratrol

Interfacial deposition of biopolymer layers on oil droplets may be a suitable strategy for increasing the emulsion stability and protection of functional ingredients. Resveratrol is a naturally occurring phenolic compound with numerous health-promoting properties, but its usage is still restricted due to its poor water solubility and high chemical instability. The aim of this study was to formulate single-layer (lactoferrin) and multilayer (lactoferrin/alginate and lactoferrin/alginate/ε-poly-l-lysine) emulsions containing resveratrol and to study the emulsions stability and antioxidant activity during storage. All primary (single-layer) emulsions had average droplet diameters below 300 nm and ζ-potentials strongly positive, allowing the electrostatic deposition of another layer of anionic biopolymer, such as alginate. Secondary (multilayer) emulsions were highly unstable at low alginate concentrations, which was attributed to the bridging flocculation. At higher alginate concentrations, secondary emulsions were rather stable. Tertiary emulsions containing either low or high ε-poly-l-lysine concentrations presented flocculation, but formulations with 0.0036% (w/w) were fairly stable. The antioxidant activity of all resveratrol-loaded emulsions did not significantly change during storage, whereas it decreased in non-encapsulated resveratrol oil from the third week onwards. This study provides useful information for the design of delivery systems for resveratrol with relevance in food applications.