8.1 Introduction

Many food colloids are stabilized, at least in part, by the presence of particulate material that accumulates at oil water or air water interfaces. As applied to emulsion droplets, this type of stabilization mechanism is commonly referred to as Pickering stabilization. ^[*] Some examples of particles involved in Pickering stabilization in food emulsions are casein micelles (in homogenized milk), egg-yolk lipoprotein granules (in mayonnaise) and fat crystals (in spreads and margarine).1 ^,2 In addition, dairy-type foams such as whipped creams and toppings are stabilized by a protective layer of partially aggregated emulsion droplets (or fat crystals) which adhere to the air bubbles during whipping.1 ^,2

This chapter reviews recent progress in the making and stabilization of food emulsions and foams using solid particles. To put the topic into context, we need to make direct comparison with the interfacial and stabilizing roles of the key molecular species emulsifiers, proteins and hydrocolloids. It will be assumed that the reader is familiar with the basic physico-chemical principles of surfactant and polymer adsorption, with the meaning of terms commonly used in colloid science like flocculation and coalescence , and with the essence of the established theories of stabilization (and destabilization) of food emulsions and foams, as described in existing texts.1 4

At their simplest, adsorbed particles at a liquid interface provide a mechanical barrier against instability. In keeping with this idea, an emulsion is better...