Depositing alginate on the surface of bilayer emulsions

Depositing alginate on the surface of bilayer emulsions (with protein as the primary and polysaccharide as the secondary layer) is believed to improve its functionality, including: stability, storage-ability, retention, and release profile of encapsulated compounds. Recent literature has shown that polysaccharides with a higher charge density might displace polysaccharides with a lower charge density previously coated on the oil droplets and droplet aggregation is promoted. In order to investigate the competitive adsorption and possible displacement in the case that the two polysaccharides interact with each other, alginate is added to a bilayer emulsion, with whey protein isolate (WPI) as the primary and gum arabic as the secondary layer. Contrary to recent findings, alginate (highly charged polysaccharide) did not displace gum arabic (less charged polysaccharide) already deposited on the surface of droplets, which was unexpected. Alginate entrapped the whole bilayer emulsion in a network at pH 4, possibly via interaction between carboxylate groups of alginate and protein in gum arabic. This result is significant as it challenges previous hypotheses on competitive adsorption of biopolymers and has implications for the design of more effective delivery system of hydrophobic bioactive compounds.