P1: SFK/UKS BLBS102-c40 P2: SFK BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come 40 Separation Technology in Food Processing technologies in the food processing area have undergone an explosive growth The competitive nature of the biotechnologies applied to the pharmaceutical and food industries for costeffective manufacturing have provided much impetus for the development and use of new separation techniques on a large scale, but at a lower cost Aside from the conventional separation techniques such as solvent and water extraction (solid–liquid contacting extraction or leaching), crystallization, precipitation, distillation, and liquid–liquid extraction, etc., have already been incorporated in basic food processing and well established and commercialized A number of newer separation techniques as promising alternative methods for improved application in food engineering have been implemented on the commercial scale, including supercritical CO2 fluid extraction, membrane-based separation, molecular distillation, and pressured low-polarity water extraction procedures These newer techniques have made impressive advances in obtaining adequate segregations of components of interest with maximum speed, minimum effort, and minimum cost at as large a capacity as possible in productionscale processes These techniques have been implemented for the purification of proteins, characterization of aromas, whey protein removal from dairy products, extraction of health-benefiting fish oil, and clarification of beverages including beer, fruit juices, and wine The separation processes and technologies for high value-added products are based on their polarity and molecular size Many potential high-value products can be developed from natural resources by different separation technologies and processes Carotenoids, including lycopene, β-carotene, astaxanthins, and lutein, make up a world market nearing $1 billion with a growth rate of about 3% Therefore, efforts to utilize natural agricultural materials for the production of high value-added products, especially health-promoting foods and ingredients, are of great interest to the food and biotechnology industries MAIN SEPARATION PROCESSES IN FOOD INDUSTRIAL APPLICATIONS Separation processes such as extraction, concentration, purification, and fractionation of nutrients or bioactive components from agricultural materials are the main processes used to obtain highvalue end products All separations rely on exploiting differences in physical or chemical properties of mixture of components Some of the more common properties involved in separation processes are particles or molecular size and shape, density, solubility, and electrostatic charge In some operations, more than one of these physical and chemical properties is involved As a unit operation, the separation process plays a key function in the whole procedure for value-added food processing The science of separation consists of a wide variety of processes, including mechanical, equilibrium, and chromatographic methods Mechanical Separation Processes Centrifugation The centrifugation process works to separate immiscible liquids or solids from liquids by the application of centrifugal force A 765 centrifuge is a spinning settling tank The rapid rotation of the entire unit replaces gravity by a controllable centrifugal or radial force Centrifugal separation is used primarily in solid–liquid or liquid–liquid separation processes, where the process is based on density difference between the solid or liquids Centrifugation is typically the first step in which the suspended solids or liquids are separated from the fluid phase Various designs of centrifuge are used in the food industry such as removal of solids from juice, beverage, fermentation broths, or dewatering of food materials Most centrifugal processes are carried out on a batch basis However, some automatic and continuous centrifuge equipment and process are applied in the food and biotechnology industry Filtration Filtration is the separation of two phases, solid particles or liquid droplets, and a continuous phase such as liquid or gas, from a fluid stream by passing the mixture through a porous medium Filtration finds applications through the food and biotechnology industries Filtration is employed at various stages in food manufacture, such as the refining of edible oils, clarification of sugar syrups, fruit juice, vinegar, wine, and beer, as well as yeast recovery after fermentation Filtration is also carried out to clarify and recover cells from fermentation broths in the biotechnology area Filtration can be classified into conventional and nonconventional filtrations The conventional filtration process uses filtration media with coarse selectivity and cannot separate similar size particles It usually refers to the separation of solid, immiscible particles from liquid streams Conventional filtration is typically the first step in which the suspended solids are separated from the fluid phase Membrane Separation Nonconventional filtration processes use membrane separation technology This nonconventional filtration has evolved into a quite sophisticated technique with the advent of membranes whose pore size and configuration can be controlled to such a degree that the filtration area is maximized while keeping the total volume of the unit small A membrane separation process is based on differences in the ability to flow through a selective barrier (membrane) that separate two fluids It should permit passage of certain components and retain certain other components of the mixture Membrane separation processes are classified as microfiltration, ultrafiltration, and reverse osmosis according to the pore size of the membranes Ion-Exchange and Electrodialysis Ion-exchange and electrodialysis are distinct separation processes, but both processes are based on the molecular electrostatic charge P1: SFK/UKS BLBS102-c40 P2: SFK BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm 766 Printer Name: Yet to Come Part 7: Food Processing Electrodialysis Equilibration Separation Processes The electrodialysis process is based on the use of ion-selective membranes, which are sheets of ion-exchange resin The process permits the separation of electrolytes from nonelectrolytes in solution and the exchange of ions between solutions The electrodialysis process is used to separate ionic species in the food and biotechnology industries In the electrochemical separation process, a gradient in electrical potential is used to separate ions with charged, ionically selective membranes The electrodialysis process is used widely to desalinate brackish water to produce potable water The process is also used in the food industry to deionize cheese whey and in a number of pollution-control applications The following processes are the unit operations commonly observed in the food industry that involve equilibrium between solid and liquid phases Ion-Exchange Evaporation The ion-exchange process is defined as the selective removal of charged molecules from one liquid phase by transfer to a second liquid phase by a solid ion-exchange material The mechanism of absorption is electrostatic opposite charges on the solutes and ion-exchanger The feed solution is washed off, followed by desorption, in which the separated species are recovered back into solution in a purified form The main areas using it are sugar, dairy (separation of protein, amino acids), and water purification Ion-exchange processes are also widely used in the recovery, separation, and purification of biochemicals, monoclonal antibodies, and enzymes Evaporation is the concentration of a solution by evaporating water or other solvents The process is largely dependent on the heat sensitivity of the material Boiling temperatures can be lowered under vacuum Most commercial evaporators work in the range 40–90◦ C and minimize the residence time in the heating zone, for the concentration of heat-sensitive liquid foods and volatile flavor and aroma solutions The final product after an evaporation process is usually in the liquid form Solid/Solid Separation Solid/solid separation is a mechanical separation such as in a milling separation facility Solid/solid separation can be achieved on the basis of particle size from the sorting of large food units down to the molecular level Shape, moisture content, electrostatic charge, and specific gravity may affect the separation process Screening of materials through perforated beds (wire mesh, cloth screen) produces materials of more uniform particle size For example, screening is usually used to sort and grade many food materials such as fruits, vegetables, and grains A wide range of geometric designs of flat bed and rotary fixed aperture screens are used in the food industry Sedimentation (Precipitation or Settling) Adsorption Absorption is a process whereby a substance (absorbate or sorbate) is accumulated on the surface of a solid Absorption process is used to recover and purify the desired products from a mixture of liquids Adsorption is used for decolorization and enzyme and antibiotic recovery Liquid-phase adsorption is usually used for the removal of contaminants present at low concentrations in process streams Crystallization Crystallization processes can be used to separate a liquid material from a solid Crystallization separates materials and forms solid particles of defined shape and size from a supersaturated solution by creating crystal nuclei and growing these nuclei to the desired size Crystallization is often used in a high-resolution, polishing, or confectioning step during the separation of biological macromolecules Crystallization can be affected by either cooling or evaporation to form a supersaturated solution in which crystal nuclei formation may occur Sometimes, it is necessary to seed the solution by addition of solute crystals Batch and continuous operations of crystallization processes are used in commercial food production Dewatering (Dehydration or Drying) Dewatering is the process applied to separate water (or volatile liquids) from solids, slurries, and solutions to yield solid products The sedimentation process is based on gravitational settling of solids in liquids Sedimentation processes are slow and are widely used in water and effluent treatment processes Extraction Magnetic Separation Solid–Liquid Extraction, e.g., Organic–Aqueous Extraction Magnetic separation relies on the behavior of individual particles under the influence of magnetic forces When exposed to a magnetic field, ferromagnetic materials are attracted along lines of magnetic force from points of lower magnetic field intensity to points of higher magnetic field intensity Solvent extraction is a method for a solvent–solvent or solvent–solid contacting operation The solid is contacted with a liquid phase in the process called solid–liquid extraction or leaching in order to separate the desired solute constituent or to remove an unwanted component from the solid phase Solid–liquid extraction or leaching is a P1: SFK/UKS BLBS102-c40 P2: SFK BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come 40 Separation Technology in Food Processing separation process affected by a fluid involving the transfer of solutes from a solid matrix to a solvent It is an operation extensively used to recover many important high-value food components such as oil from oilseeds, protein from soybean meal, phytochemicals from plants, etc Solid–liquid extraction is also used to remove undesirable contaminants or toxins from food materials Liquid–Liquid Extraction, e.g., Two-Phase Aqueous Extraction Liquid–liquid extraction separates a dissolved component from its solvent by transfer to a second solvent, mutually nonmiscible with the carrier solvent The liquid–liquid extraction as a technology has been used in the antibiotics industry for several decades and now is recognized as a potentially usefully separation step in protein recovery on a commercial production Supercritical Fluid Extraction Supercritical CO2 fluid extraction is mostly for high value-added products that are sensitive to heat, light, and oxygen The extraction process is implemented in a supercritical region where the extraction fluid (e.g., CO2 ) has liquid-like densities and solvating strengths but retains the penetrating properties of a gas Distillation Distillation is a physical separation process used to separate the components of a solution (mixture) that contains more components in the liquid mixture, by the distribution of gas and liquid in each phase The principle of separation is based on the differences in composition between a liquid mixture and the vapor formed from it, because each substance in the mixture has its own unique boiling point 767 Affinity Chromatography Affinity chromatography exploits the natural, biospecific interactions that occur between biological molecules These interactions are very specific and because of this affinity separation process are very high resolution methods for the purification of food products such as proteins Affinity chromatography has a gel surface that is covered with molecules (ligand) binding a particular molecule or a family of molecules in the sample Size-Exclusion Chromatography Size-exclusion chromatography, also known as gel permeation chromatography when organic solvents are used, is used to control the pore size of the stationary phase so as to separate molecules according to their hydrodynamic volume and molecular size Ion-Exchange Chromatography Ion-exchange chromatography and a related technique called ion-exclusion chromatography are based on differences in the electric charge density of their molecules during charge–charge interaction of molecules It is a variation of absorption chromatography in which the solid adsorbent has charged groups chemically linked to an inert support Ion-exchange chromatography is usually used for recovery and purification of amino acids, antibiotics, proteins, and living cells Hydrophobic Interaction Chromatography Hydrophobic interaction chromatography is based on a mild adsorption process, and separates solutes by exploiting differences in their hydrophobicity Reverse Phase Chromatography Chromatographic Methods Chromatography is a separation technique based on the uneven distribution of analytes between a stationary (usually a solid) and a mobile phase (either a liquid or a gas) Chromatography can be conducted in two or three dimensions Two-dimensional chromatography, for example paper chromatography, is almost solely used for analytical purposes Column chromatography separation is the most common form of chromatography used in the food processing field for further purification of high value-added components Many variations exist on the basic chromatography methods Some well-established methods are listed below Liquid–Solid Absorption Chromatography (e.g., Hydroxyapatite) In absorption, molecules in a fluid phase concentrate on a solid surface without any chemical change Physical surface forces from the solid phase attract and hold certain molecules (substrate) from the fluid surrounding the surface Reverse phase chromatography is based on the similar principles of hydrophobic interaction chromatography The difference is that the solid support is highly hydrophobic in reverse phase chromatography, which allows the mobile phase to be aqueous ENGINEERING ASPECTS OF SEPARATION PROCESSES Much of the recent process development for the separation of valuable components from natural materials has been directed toward high value-added products For the recovery of valuable components from raw materials, applications of separation technologies to recover major or minor components from agricultural commodities is usually a solid–liquid contacting operation As research moves into commercial production, there is a great need to develop scalable and cost-effective methods of separation technologies The successful and effective development of separation technologies is a critical issue in the chain of valueadded processing of agricultural materials such as developments in functional food ingredients, nutrients, and nutraceuticals P1: SFK/UKS BLBS102-c40 P2: SFK BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm 768 Printer Name: Yet to Come Part 7: Food Processing Separation operations are interphase mass transfer processes because they involve certain heat, mass, and phase transfers, as well as chemical reactions among food components The engineering properties of the targeted food components via separation systems include separation modeling, simulations, optimization control studies, and thermodynamic analyses The principles of mass conservation and component transfer amounts are used to analyze and design industrial processes Molecular intuition and a thermodynamic approach constitute powerful tools for the design of a successful separation process The following issues of engineering properties are important for process optimization and simulation Chemical equilibration—binary, ternary, and multicomponent systems in solid–liquid contacting operation, Diffusivity (pressure diffusion, thermal diffusion, gaseous diffusion) and convection, Solubility of targeted components under different separation operating conditions, Iso-electric points and charge dependence on pH, Chemical interaction kinetics (colloid formation and affinity), Physical properties of particles of the food material, Flux and fouling properties in membrane separation processes, Solvent selection, recycling, and management, Nature of solvents, optimum composition of mixed solvents for certain nutrient separations, and solvent residues in food products are factors to be optimized 10 Some solvent treatments such as evaporation, concentration, de-watering, de-coloring, toxicological analyses, waste minimization, recycling, and disposal are necessary SEPARATION SYSTEM DESIGN Technical Request for a Separation System An important consideration in determining the appropriateness of a separation technique and system is the actual purity requirement for the end products In design of organic solvent (toxic chemical)-free separation technologies and systems, there are several essential technical approach requirements for technology advances, such as combination of new techniques available for system optimization, product design and reasonable separation and purification steps, environmentally friendly process, less air pollution and industrial waste (e.g., energy, greenhouse gases emission, reduction of waste water production), and economic feasibility and raw material selection Food Quality and Separation System The major issues related to product quality after separations are the impacts of processing on bioactive compounds and the nutritional aspects of foods, as well as the quality characteristics To meet the food safety regulations, no toxic chemical solvent residues are permitted in the end food products, e.g., “green” food products Nutrition and health regulations must be met Also important are a high stability of nutrients and bioactive components, processes operating at low temperatures to reduce thermal effects, processes that exclude light to reduce light induced (UV) irradiation effects, and processes that exclude oxygen to reduce oxygen effects And the final product must maintain uniformity and quality consistency, and purity can meet food grade or pharmaceutical grade requirements Scaling Up Technology for Industrial Production Scaling up of a natural product separation process is by no means a simple affair The enormous variations from process to process necessitate careful attention to details at all stages of product development When the technology in a food process is designed for industrial-scale production, an important area for consideration is the balance of capital and operating costs as the scale of the separation operation increases Scale up of separation technology also involves optimization with respect to increasing the efficiency of each stage, giving rise to increasing demands on the accuracy of the assay system NEW TECHNOLOGY DEVELOPMENT Extraction of health-promoting components from plant materials has usually been accomplished by conventional extraction processes such as solid–liquid extractions employing methanol, ethanol, acetone, or hexane and also through steam distillation or evaporation processes to remove solvents from extracts Currently, the demand for natural bioactive compounds is increasing due to their use by the functional food and pharmaceutical industry Thus, there has been increasing interest in the use of environmentally friendly “green” separation technologies able to provide high quality–high bioactivity extracts while precluding any toxicity associated with the solvent Some of the motivations to employ “green” separation technologies as a viable separation technique are (a) tightening government regulations on toxicchemical solvent residues and pollution control, (b) consumers’ concern over the use of toxic chemical solvents in the processing, and (c) increased demand for higher quality products that traditional processing techniques cannot meet One of the most important considerations in developing new extraction processes is the safety aspect In this sense, a variety of processes involving extractions with supercritical CO2 fluid extraction, membrane-based separation, molecular distillation, and pressured low-polarity water extraction, etc., are generally recognized as “green” separation technology and are considered clean and safe processes to meet the requirements (Ib´an˜ ez et al 1999, Fernandez Perez et al 2000, Herrero et al 2006, Chang et al 2008) They have been developed and are regarded as innovative emerging separation technologies that meet food quality and safety requirements These processes can be used to solve some of the problems associated with conventional organic solvent-oriented separation processes Operation parameters and other factors related to the quality of the original plant, its geographic origin, the harvesting date, its storage, and its pretreatment process prior to extraction also influence the P2: SFK BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come 40 Separation Technology in Food Processing separation operations and the final composition of the extracts obtained Supercritical CO2 Fluid Technology Changes in food processing practices and new opportunities for innovative food products have spurred interest in supercritical CO2 fluid extraction Supercritical CO2 fluid technology has been widely used to extract essential oils, functional fatty acids, and bioactive compounds, and also been applied in recently developed extraction and fractionation for carbohydrates (Glisic et al 2007, Shi et al 2007a, Monta˜ne´ s et al 2008, Mitra et al 2009, Monta˜ne´ s et al 2009, Sanchez-Vicente et al 2009, Shi et al 2010a, 2010b) Supercritical CO2 fluid extraction is a novel separation technique that utilizes the solvent properties of fluids near their thermodynamic critical point Supercritical CO2 is being given a great deal more attention as an alternative to organic chemical industrial solvents, and increased governmental scrutiny and new regulations restricting the use of common industrial solvents such as chlorinated hydrocarbons It is one of the “green” separation processes that provides nontoxic and environmentally friendly attributes and leaves no traces of any toxic chemical solvent residue in foods When CO2 fluid is forced into a pressure and temperature above its critical point (Fig 40.1), CO2 becomes a supercritical fluid Under these conditions, various properties of the fluid are placed between those of a gas and those of a liquid Although the density of a supercritical CO2 fluid is similar to a liquid and its viscosity is similar to a gas, its diffusivity is intermediate between the two states Thus, the supercritical state of a fluid has been defined as a state in which liquid and gas are indistinguishable from each other or as a state in which the fluid is compressible (i.e., similar behavior to a gas), even though possessing a density similar to that of a liquid and with similar Pressure (MPa) P1: SFK/UKS BLBS102-c40 Liquid phase PC Supercritical region Tc=31.1°C Pc=7.38MPa Solid phase Triple point Gas phase TC Temperature (°C) Figure 40.1 Supercritical pressure–temperature diagram for carbon dioxide 769 solvating power Because of its different physicochemical properties, supercritical CO2 provides several operational advantages over traditional extraction methods Because of their low viscosity and relatively high diffusivity, supercritical CO2 fluids have better transport properties than liquids They can diffuse easily through solid materials and therefore give faster extraction yields One of the main characteristics of a supercritical fluid is the possibility of modifying the density of the fluid by changing its pressure and/or its temperature Since density is directly related to solubility (Ravent´os et al 2002, Shi and Zhou 2007, Shi et al 2009a), by altering the extraction pressure, the solvent strength of the fluid can be modified The characteristic traits of CO2 are inertness, nonflammability, noncorrosiveness, inexpensive, easily available, odorless, tasteless, and environmentally friendly Its near-ambient critical temperature makes it ideal for thermolabile natural products (Mendiola et al 2007) CO2 has its favorable properties and the ease of changing selectivity by the addition of a relatively low amount of modifier (co-solvent) such as ethanol and other polar solvents (e.g., water) CO2 may be considered the most desirable supercritical fluid for extracting natural products for food and medicinal uses (Shi et al 2007b, Kasamma et al 2008, Shi et al 2009b, Yi et al 2009) Other supercritical fluids, such as ethane, propane, butane, pentane, ethylene, ammonia, sulphur dioxide, water, chlorodifluoromethane, etc., are also used in supercritical fluid extraction processes In a supercritical CO2 fluid extraction process, supercritical CO2 fluid has a solvating power similar to organic liquid solvents and a higher diffusivity, with lower surface tension and viscosity The physicochemical properties of supercritical fluids, such as the density, diffusivity, viscosity, and dielectric constant, can be controlled by varying the operating conditions of pressure and temperature or both in combination (Tena et al 1997, Shi et al 2007a, 2007b, 2007e, Kasamma et al 2008, Shi et al 2009b) The separation process can be affected by simply changing the operating pressure and temperature to alter the solvating power of the solvent After modifying CO2 with a co-solvent, the extraction process can significantly augment the selective and separation power and in some cases extend its solvating powers to polar components (Shi et al 2009a) Supercritical CO2 fluid extraction is particularly relevant to food and pharmaceutical applications involving the processing and handling of complex, thermo-sensitive bioactive components, and an increased application in the areas of nutraceuticals, flavors, and other high-value items such as in the extraction and fractionation of fats and oils (Reverchon et al 1992, Rizvi and Bhaskar 1995), the purification of a solid matrix, separation of tocopherols and antioxidants, removal of pesticide residues from herbs, medicines, and food products, the detoxification of shellfish, the concentration of fermented broth, fruit juices, essential oils, spices, coffee, and the separation of caffeine, etc (Perrut 2000, Gonz´alez et al 2002, Miyawaki et al 2008, Martinez et al 2008, Liu et al 2009a, 2009b) This technology has been successfully applied in the extraction of bioactive components (antioxidants, flavonoids, lycopene, essential oils, lectins, carotenoids, etc.) from a variety of biological materials such as hops, spices, tomato skins, and ... usually used to sort and grade many food materials such as fruits, vegetables, and grains A wide range of geometric designs of flat bed and rotary fixed aperture screens are used in the food industry... irradiation effects, and processes that exclude oxygen to reduce oxygen effects And the final product must maintain uniformity and quality consistency, and purity can meet food grade or pharmaceutical... 1999, Fernandez Perez et al 2000, Herrero et al 2006, Chang et al 20 08) They have been developed and are regarded as innovative emerging separation technologies that meet food quality and safety