Encapsulation of Iron within W1/O/W2 Emulsions Formulated Using a Natural Hydrophilic Surfactant (Saponin): Impact of Surfactant Level and Oil Phase Crystallization

Abstract

The influence of quillaja saponin on the formation and stability of water-in-oil-in-water (W1/O/W2) emulsions was investigated. In particular, the ability of these emulsions to encapsulate iron (ferrous sulfate) in a form that would not promote lipid oxidation was examined. The emulsions were formed using a two-step process. First, iron sulfate was dissolved in the aqueous phase used to form 20 wt% water-in-oil (W1/O) emulsions stabilized by polyglycerol polyricinoleate (PGPR). Second, W1/O/W2 emulsions were fabricated by homogenizing the W1/O emulsions (20 wt%) with another aqueous phase (80 wt%) containing quillaja saponin (0.5, 1, 2, 3, and 4 wt%). The diameter of the oil droplets in the W1/O/W2 emulsions decreased with increasing saponin concentration. Confocal microscopy confirmed that the W1/O/W2 emulsions consisted of tiny water droplets entrapped inside oil droplets that were dispersed in an external water phase. Rheological analysis showed the W1/O/W2 emulsions were shear-thinning fluids. The iron encapsulation efficiency of the emulsions remained high (> 82%) throughout storage for 28 days at ambient temperature. Lipid oxidation of the iron-loaded W1/O/W2 emulsions could be retarded by incorporation of rice bran stearin in the oil phase. The double emulsions developed in this work have potential for encapsulation and delivery of iron in functional foods containing oxidizable lipids.