3 Separation and ConcentrationTechnologies in Food Processing

Separation and concentration technologies are among the most important unit operations in food processing. From disk-bowl centrifugation for industrial-scale production of skim milk to crystallization for sucrose or ultrafiltration to recover soluble proteins from cheese whey, separation and concentration processes have improved food processing. These technologies have allowed the development of new food products and are being increasingly used for water recycling in food processing. Indeed, food processing consumes large volumes of water. For this reason, waste water treatments use membrane technologies as part of the solution to numerous environmental problems posed by the food industries. The first processes developed to separate food components selected physical or mechanical means that allowed simple separations involving solid–solid or solid–liquid systems. Screening processes separated solid-solid materials into different sizes, while filtration strictly involved the separation of solid–liquid systems. Among screening methods, the pneumatic separator used compressed gases to separate particles according to their masses; the vibration separator relied on vibration to move particles through different screens separating solids by their sizes or masses; and the magnetic separator applied magnetic fields to remove metallic particles. As for the filtration method, it included conventional filtration, mechanical expression (i.e. for juice extraction from fruits or vegetables), centrifugation, and membrane technologies. Another group of separation and concentration technologies relied on heat-induced phase changes as the driving force for the separation. From simple evaporation to distillation and solvent extraction, such approaches allowed for the concentration of many liquid foods (i.e. milk, fruit and vegetable juices, etc.) and for as the industrial production of ethanol, liquor, and vegetable oils. The most recent development involving phase change is the use of supercritical carbon dioxide (CO2), which has found many value-added applications for the food industry over the past decade. Conventional filtration relies on gravity, pressure or vacuum to create the driving force necessary for the liquid phase to pass throughout different kinds of filters (e.g. perforated plates, cellulose filter papers, glass fiber filters) or granularmaterial (e.g. sand or anthracite). Membrane technologies, including reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF), use pressure differences as the driving force of separation. Like conventional filtration, membrane filtration relies on filters but with much smaller pores. It thus covers a wide range of separations from the removal of particles >1 μm (MF) to water purification by the removal of solutes <10 nm (RO) (Cui et al., 2010). In addition, recent developments in electricallydriven separations (electrodialysis), low-pressure separation (pervaporation), and separations using functionalizedmembranes (ion exchangematerials) are opening new horizons in this fascinating field. Future trends in separation and concentration technologies will be characterized by an increased number of integrated combinations, or hybrid processes, combining single units of the before mentioned array of technologies