Double emulsions stabilized by new molecular recognition hybrids of natural polymers

Water-in-oil-in-water (W/O/W) double emulsions with improved stability and less polydispersity in droplet size distribution were prepared using polyglycerol polyricinoleate (PGPR) as emulsifier in the inner aqueous phase and replacing the common nonionic hydrophilic monomeric emulsifiers by a "protein-polysaccharide hybrid" in the outer interface. Amphiphilic macromolecular hybrids with specific interfacial recognition capabilities to be termed "biomacro-molecular-recognition hybrids" have been prepared in aqueous solution by interacting whey protein isolate (WPI) with hydrocolloids (xanthan gum, galactomannans) at selected pH and weight ratios. The binary aqueous mixtures do not coacervate or precipitate but form stable molecular adducts. At pH lower than the isoelectric point of the protein (pH 4.6), the yield of encapsulation of glucose (a model marker) in the inner phase of the double emulsion is close to 95%. The emulsion droplets are stabilized by both steric and electrostatic contributions (zeta potential is close to +30 mV). Rheological measurements indicate that, at low pH, such systems behave as viscous ones with G" (loss modulus) greater than G' (storage modulus). Men the pH is close or greater than the isoelectric point of the protein, the system exhibits a more pronounced elastic behavior (G' < G") that can explain the reduction in emulsification capabilities of such mixtures. In this case the yield of encapsulation is less than 10% and the double emulsion droplets are larger than 10 mum. At pH < 2, the adducts can efficiently stabilize double emulsions and serve as an efficient and thick barrier against the release of vitamin B(1) entrapped in the core of the W/O/W double emulsions. The release of the vitamin was less than 18% after three weeks of storage at room temperature (against 100% of release at neutral pH). Copyright (C) 2003 John Wiley Sons, Ltd.