Fabrication and characterization of filled hydrogel particles based on sequential segregative and aggregative biopolymer phase separation

In this study, filled hydrogel particles were created based on the ability of proteins and ionic polysaccharides to phase separate through both aggregative (complexation) and segregative (incompatibility) mechanisms. At pH 7, a mixture of 3% (w/w) high-methoxy pectin and 3% (w/w) sodium caseinate phase separated through a segregative mechanism. Following centrifugation, the phase separated system consisted of an upper pectin-rich phase and a lower casein-rich phase. Casein-coated lipid droplets added to the phase separated pectin/caseinate system partitioning into the lower casein-rich phase. This was attributed to a reduction in the unfavorable osmotic stress in this phase associated with biopolymer depletion. When shear was applied this system formed an oil-in-water-in-water (O/W₁/W₂) emulsion consisting of oil droplets (O) contained within a casein-rich watery dispersed phase (W₁) suspended in a pectin-rich watery continuous phase (W₂). Acidification of the O/W₁/W₂ system from pH 7–5 promoted adsorption of pectin around the casein-rich W₁ droplets, resulting in the formation of filled hydrogel particles (d = 3–4 μm) that remained stable to aggregation or dissociation when stored for 24 h at ambient temperature. These particles may be useful as encapsulation and delivery systems for lipophilic components in the food, cosmetics and pharmaceutical industries.