Egg white powder as gelling and stabilising agent for double emulsions

Water-in-oil-in-water double emulsions (W1/O/W2) consist of small droplets of an inner water phase (W1) entrapped in oil droplets (O) that are, in their turn, dispersed in another aqueous phase (W2). They have the typical structure of oil-in-water (O/W) emulsions but with a reduced fat content, thus resulting interesting for the development of reduced-fat foods. The main issue connected to real applications is the ability to mimic fat behaviour while showing a prolonged stability during storage. Gelling of the internal aqueous phase may be a useful strategy, together with the use of a strong lipophilic emulsifier as polyglycerol polyricinoleate (PGPR). Thus, the aim of this work was to study the effect of egg white powder (EW) as gelling and stabilising agent in double emulsions. In particular, the effects of EW concentration in W1 (0, 5, 10%) as well as volume fraction of W1 (20, 30, 40%) and W1/O (40, 50, 60%) on emulsion yield, rheological behavior, and creaming stability were evaluated. PGPR was used as emulsifier, and a fixed amount of EW (5%) was added in W2. All the samples showed high yields (>95%), meaning that almost all W1 remained entrapped in oil droplets. Creaming stability is of paramount importance for double emulsions intended as alternative fats in food formulation, since they have to be prepared beforehand and stored until use. The presence of EW in W1 significantly (p<0.001) increased double emulsion stability after 24 h at 4°C, while the samples with the lowest W1/O fraction (40%) resulted in the lowest stability (68%). Apparent viscosity and pseudoplastic behavior of double emulsions were significantly affected (p<0.001) by the amount of EW in W1. Increasing EW concentration, more viscous emulsions were obtained, with lower flow index (n) values and higher consistency coefficients (K). In conclusion, the work allowed to improve the knowledge about the effects of inner water phase gelling on double emulsions characteristics, demonstrating that EW can be considered a good stabilizing agent that also improved rheological behavior of these systems.