Shelf life, multiple emulsions

Slow release rates and remarkable long shelf-life (months) were obtained compared to typical multiple emulsions stabilized by two short surfactants (SMO and polyoxyethylene (20) sorbitan monolaurate). Finally, the long lifetime of the emulsions allowed study via diffusing wave spectroscopy (DWS) of the interactions between the droplets and the globule surface [37],... 

Double emulsions are also very useful for food application. Sensitive food materials and flavors can be encapsulated in w/o/w emulsions. Sensory tests have indicated that there is a significant taste difference between w/o/w emulsions and o/w emulsions containing the same ingredients, and that there is a delayed release of flavor in double emulsions [61]. W/o/w or o/w/o multiple emulsions having a concentrated aqueous-soluble flavor or a concentrated oil-soluble flavor encapsulated in the internal phase can be prepared. Food products obtained with these particulates exhibit enhanced flavor perception and extended shelf-life [62]. 

To achieve the above criteria complex multipheise systems are formulated (i) Oil-in-Water (0/W) emulsions (ii) Water-in-Oil (W/0) emulsions (iii) solid/liquid dispersions (suspensions) (iv) emulsions-suspension mixtures (suspoemulsions) (v) nanoemulsions (vi) nanosuspensions (vii) multiple emulsions. All these disperse systems require fundamental understanding of the interfacial phenomena involved, such as the adsorption and conformation of the various surfactants and polymers used for their preparation. This will determine the physical stability/instability of these systems, their application and shelf-life. 

Mechanical Stabilization by Microcrystalline Cellulose Some attempts have been made to improve the shelf-life of multiple emulsions by incorporating small solid particles in the surfactant formulations. The idea was to allow the particles to adsorb onto the oil droplets so that they can provide a mechanical barrier against coalescence (Aveyard et al., 2003). Oza and Frank (1989) were the first to develop the concept by using colloidal microcrystaUine cellulose (MCC) instead of water-soluble surfactant in W/OAV emulsions containing oil-soluble hydrophobic surfactants (Spans). Emulsions, stable for up to 1 month, contained a network of MCC particles adsorbed at the outer oil-water interface. 

The authors of this review envisaged (Benichou et al., 2007a, b) WPI/poly-saccharide conjugates to stabilize the outer interface of W/O/W and the inner interface of O/W/O multiple emulsions and found significant improvement both in the stability and in the release of markers (glucose, vitamin Bi, lipohilic veterinary drug) compared to the use of the protein only. These new amphiphilic adducts serve as good steric stabilizers, improve stability and shelf-life, and slow the release of the markers. They therefore play a double role in the emulsions film formation and barrier to the release of small molecules at the internal interface, and steric stabilizers of the inner oil-water interface. 

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