Water-in-oil emulsions stabilized by surfactants, biopolymers and/or particles: a review

Background: Considering the global rise of obesity and food-linked cardiovascular diseases, food industries are often challenged to produce low fat or fat-free products. Incorporation of water in the form of water-in-oil (W/O) emulsions to replace fat offers a promising strategy to address this research challenge. Scope and approach: This review aims to provide succinct insights into the stabilization of W/O emulsions, focusing on interfacial design using surfactants, biopolymers, particles and/or combinations thereof that have been researched in the last decade. Particular emphasis has been given to particle (Pickering) stabilization of water droplets with bio-derived as well as non-bio-derived particles. In addition, the stabilization of W/O emulsions via viscosity modification is also briefly examined. Key findings and conclusions: Although polyglycerol polyricinoleate (PGPR, E476) is considered as the 'classic' surfactant when it comes to stabilization of W/O emulsions, the focal point of current research has recently shifted towards the use of particle stabilizers that allow longer term stabilization against coalescence and Ostwald ripening. In particular, Pickering stabilizers that are derived from natural, biodegradable sources, such as zein, cellulose, lignin, starch and polyphenol crystals (curcumin and quercetin), with or without further modification, have attracted burgeoning attention due to the rising popularity of 'clean-label' products amongst consumers. Using such particles, or intelligently combining particles with biopolymers to stabilize high water volume fractions in oil continuous matrices, plus the use of biopolymers to gel the water phase, offer promising new applications in food and allied soft matter manufacturing areas in the future.