Membranes for Enhanced Emulsification Processes

The use of membrane technology for the production of single and double emulsions has been proven feasible for a wide range of systems. The low energy requirements and mild process conditions (shear stress and temperature) of membrane emulsification (ME) compared to conventional processes makes it of interest for the production of emulsion-based foods. However, membrane fouling and low productivity are the main concerns preventing widespread application. Premix ME, in which a pre-emulsion is passed through a microporous system to reduce the size of the droplets, has much higher productivity than cross-flow ME (in which the droplets are formed in situ from the membrane/continuous phase interface); however, premix emulsification is more susceptible to fouling.<br/><br/>This chapter reviews the different membranes and microporous systems used in premix ME to produce single and double food emulsions, and the effect of fouling on process performance and productivity is discussed. The influence of operational variables and emulsion formulation are related to the performance of premix ME, and scaling relations are presented. The use of premix ME to produce oil-in-water (O/W) emulsions has been mainly for vegetable oil/water emulsions stabilized with different surface-active agents. It has been shown that protein-stabilized O/W emulsions have lower fluxes than emulsions stabilized with small anionic or nonionic emulsifiers; the use of proteins, however, has been helpful to protect carotene-loaded emulsions against oxidation. Premix ME has also been used to produce water-in-oil-in-water (W1/O/W2) emulsions, through homogenization of a W1/O emulsion in water. Although operation parameters, mainly related to the type of microstructured system (from inorganic membranes to microporous packed beds), can be set to produce stable W1/O/W2 emulsions, encapsulation of a particular bioactive compound follows a case-study approach.