Aqueous foams and aerated oil-in-water emulsions partly stabilised by edible particles

The objectives of this thesis are to enhance the understanding of edible solid particle behaviour at oil-water and at air-water interfaces, and how their adsorption at these interfaces affects the emulsion and foam stability. Materials stabilised solely by solid particles are of great interest due to long-term stability, lower emulsifier content and also in order to replace surfactants and oils, which are often used in food and pharmaceutical products. The project is funded by Rich Products, a leading manufacturer of non-dairy icings and toppings. The interest of Rich Products in this research is in application of calcium carbonate nanoparticles in whipped cream formulations. Air bubbles in whipped cream are coated and stabilised by adsorption of fat droplets during aeration. Particular interest of the company was to see whether calcium carbonate particles could fulfil all or part of the role played by fat droplets in stabilising air bubbles in whipped cream. In addition, this may decrease the fat content of such whipped cream products, desirable for certain consumers.Aeration properties of aqueous dispersions of particles and an anionic food-grade surfactant, sodium stearoyl lactylate, are studied. It is shown that the hydrophilic nature of the particles prevented their adsorption at air-water interfaces. Oppositely charged surfactant molecules were used to modify the surface properties of the particles. The in situ surface modification of the particles upon adsorption of the surfactant molecules is shown to promote the adsorption of particles at air-water interfaces. The particles were observed to form a rigid barrier around air bubbles and provide long-term stability to aqueous foams. The effect of surfactant concentration, particle addition and aeration method are all presented. The progress in preparation of model whipping cream emulsions and aerated emulsions was then continued by preparation of palm kernel oil-in-water emulsions. It is shown how aeration of palm kernel oil-in-water emulsions in the presence of surface modified calcium carbonate particles provides long-term stability to aerated emulsions. The results from characterisation of the model whipped cream foams are presented and discussed in relation to foams stability. It is shown that adsorption of calcium carbonate particles together with palm kernel oil droplets around air bubbles prevents foam collapse and enhances the foam life-time. The effect of particle concentration, oil volume fraction and whipping duration on several properties of the model whipped creams are presented. Together with preparation and characterisation of model samples, aeration properties of Vanilla Bettercreme®, a commercial non-dairy ready-to-whip cream manufactured by the sponsor of the project are also presented. This product has been used as a reference in different stages of this project.Palm kernel oil-in-water emulsions stabilised by calcium carbonate particles or by sodium stearoyl lactylate are then compared in terms of their stability towards coalescence. It is observed that in the emulsions stabilised by surfactants, oil droplets joined together and resulted in emulsion destabilisation. On the other hand, in particle-stabilised emulsions adsorption of the particles around oil droplets creates a rigid barrier around them and prevents the droplets joining together. The effect of emulsifier concentration and oil volume fraction are studied in detail.Finally, preparation of oil-in-water emulsions and aerated oil-in-water emulsions containing non-crystallisable oils are investigated. The aim was to understand the interactions of fluid oil droplets with an air-water interface. Both the emulsions and aerated emulsions were stabilised by sodium stearoyl lactylate. It is shown that the oil type, surfactant concentration and the oil volume fraction affect the stability of the emulsions and aerated emulsions prepared. The size of oil droplets in aerated oil-in-water emulsions is shown to be the determining factor for their stability