Synergistic effects of polyglycerol ester of polyricinoleic acid and sodium caseinate on the stabilisation of water–oil–water emulsions Jiahong Su a , John Flanagan a , Yacine Hemar b,1 , Harjinder Singh a, * a Riddet Centre, Massey University, Private Bag 11, Palmerston North 222, New Zealand b Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand Abstract The inherent thermodynamic instability of water–oil–water (W/O/W) emulsions has restrictions for their application in food systems. The objective of this study was to develop a food grade W/O/W emulsions with high yield and stability using minimal concentrations of surfactants. Emulsions were prepared using soybean oil, polyglycerol ester of polyricinoleic acid (PGPR) alone or in combination with sodium caseinate (NaCN) as emulsifier(s) for primary water-in-oil (W/O) emulsions and NaCN as the sole emulsifier for secondary W/O/W emulsions. Increasing the concentration of PGPR (0.5–8%w/v) had no effect on the droplet sizes of the resulting W/O/W emulsions. However, significant increases in droplet sizes of W/O/W emulsions were observed when the concentration of NaCN in external phase was reduced from 0.5 to 0.03% (w/v) (p!0.05). Percentage yields of emulsions (using a water-soluble dye) improved when PGPR concentration in the inner phase was increased from 0.5 to 8% (w/v). A stable W/O/W emulsion with a yield O90% could be prepared with 4% (w/v) PGPR alone as primary hydrophobic emulsifier and 0.5% (w/v) NaCN as external hydrophilic emulsifier. The concentration of PGPR in the inner phase could be reduced to 2% (w/v) without affecting the yield and stability of the W/O/W emulsion by partially replacing PGPR with 0.5% (w/v) NaCN, which was added to the aqueous phase of the primary W/O emulsion. The results indicate that a possible synergistic effect may exist between PGPR and NaCN, thus allowing formulation of double emulsions with reduced surfactant concentration. q 2005 Elsevier Ltd. All rights reserved. Keywords: Multiple emulsions; PGPR; Stability; Milk proteins 1. Introduction Multiple emulsions are systems in which the dispersed phase is itself an emulsion, and they can be classified into two major types: water–oil–water emulsion (W/O/W) and oil–water–oil emulsion (O/W/O). Multiple emulsions have found industrial applications in various fields such as pharmaceuticals and cosmetics as a mean of micro- encapsulation (Couvreur, Blanco-Prieto, Puisieux, Roques, & Fattal, 1997; Okochi & Nakano, 2000). However, despite their immense potential, the application of multiple emulsions in food systems has been limited by their inherent thermodynamic instability, which causes leakage of the encapsulant from the inner aqueous phase, flocculation of the droplets or phase separation during processing and storage (Hino, Shimabayashi, Tanaka, Nakano, & Okochi, 2001; Benichou, Aserin, & Garti, 2004). A stable primary emulsion is essential for the overall stability of multiple emulsions. For food grade W/O/W emulsions, the stability of the primary W/O emulsion is determined by the nature of oil phase, type of emulsifiers and the nature of entrapped materials or encapsulant, particularly if the encapsulant contains electrolytes (Dick- inson, Evison, Owusu & Williams, 1994). Measures such as reducing the droplet size, increasing the viscosity of the inner aqueous phase, modifying the nature of the oil phase by increasing its viscosity or by adding carriers, adding complexing agents to the oil, or modifying the vegetable oil to be less water soluble might improve the stability of W/O primary emulsion (Garti, 1997a). Food Hydrocolloids 20 (2006) 261–268 www.elsevier.com/locate/foodhyd 0268-005X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2004.03.010 * Corresponding author. Tel.: C64 6 3564401; fax: C64 6 3505655. E-mail address: h.singh@massey.ac.nz (H. Singh). 1 Present address: Fonterra Research Centre, Palmerston North, New Zealand