Stability and release properties of double-emulsions stabilised by caseinate–dextran conjugates

The subject of the present paper was to investigate the possibility of stabilising water-in-oil-in-water emulsions (W/O/W) by using sodium caseinate (SC)–dextran (Dex) conjugates in order to influence the release of vitamin B12 from the inner water phase (W1) to the outer aqueous phase (W2). To prepare the conjugate the SC was combined with Dex (Mr 250,000 or 500,000 g/mol) and incubated at 60 °C and a humidity of 79% for 8 h. The double emulsions, with encapsulated vitamin B12, were prepared using a two-step emulsification technique. Whereas different amounts of polyglycerin polyricinoleate (PGPR, E476) were the hydrophobic emulsifier, the conjugate and the SC alone were used as the hydrophilic emulsifiers. The investigations comprised the determination of the particle size distribution of the W/O/W emulsion and measurement of the amount of vitamin B12 migration from W1- to the W2-phase during the second stage of emulsion preparation and after heating or pH changing of emulsion. The water-containing oil droplets of the W/O/W emulsions were smaller and distributed more narrowly using SC–Dex conjugate as emulsifier instead of pure protein. Under acidic conditions, the conjugate-containing emulsions were more coalescence stable than the emulsions with SC, and the vitamin B12 release from the inner W1-phase was significantly decreased.