Ultrafiltration concentration process

A newer juice concentration process, requiring minimal heat treatment, has been appHed commercially in Japan to citms juice concentration. The pulp is separated from the juice by ultrafiltration and pasteurized. The clarified juice containing the volatile flavorings is concentrated at 10°C by reverse osmosis (qv) and the concentrate and pulp are recombined to produce a 42—51 °Brix citms juice concentrate. The flavor of this concentrate has been judged superior to that of commercially available concentrate, and close to that of fresh juice (11). 

Ultrafiltration — This process has been successful with mixtures difficult to separate, such as oily machining wastes and oily wastewater. A pressure-driven filtration membrane separates multicomponent solutes from solvents, according to molecular size, shape and chemical bonding. Substances below a preselected molecular size are driven through the membrane by hydraulic pressure, while larger molecules, such as oil droplets, are held back. Effluent oil concentration depends on influent concentration, but properly operated ultrafiltration units can produce oilfree water (less than 0.1 ppm for all practical purposes). 

A concentration process involves removal of a solvent, typically water from a macromolecular solution. Ultrafiltration is the method of choice for large-scale concentration. The selectivity issue involving removal of water from a macromolecular solution using ultrafiltration is trivial. The main challenge in a concentration process is maintaining a high productivity on account of the increased macromolecular concentration in the feed solution. Some of the main applications of macromolecular concentration using ultrafiltration are listed below [2] ... 

Many authors have evaluated the performances of membrane processes as separation units. Gonzalez et al (2007) studied an integrated process for food-grade lactic acid production from whey ultrafiltrate the process consisted in a sequence of steps, such as fermentation, ultraflltration, ion exchange, RO and final concentration by vacuum evaporation. The highest contribution to the total investment cost was the concentration step, whereas the fermentation step required the highest operating cost. The proposed process was demonstrated to be economically viable as summarized in Table 23.2. 

In practice it is used to separate species that differ appreciably in size, which have a reasonably large difference in diffusion rates. Solute fluxes depend on the concentration gradient in the membrane. Hence, dialysis is characterized by low flux rates, in comparison to other membrane processes, such as reverse osmosis and ultrafiltration, membrane processes that depend on applied pressure. 

Potential widespread use of steviosides requires an easy and effective extraction method. Enzymatic extraction of stevioside from Stevia rebaudiana leaves with cellulase, pectinase, and hemicellulase, using various parameters, such as concentration of enzyme, incubation time, and temperature, has been reported [33]. Purification is achieved through adsorption, colunm chromatography, and ion-exchange electrolytic technique for rebaudioside A, rebaudioside C, and dulcoside A [34]. An ultrafiltration (UF) process was reported for recovery of 45 % steviosides from an extract of leaves. Final purification was achieved by two consecutive mixed bed ion-exchange processes. The ion exchangers improved purity of the final product to 90 % [35]. 

Consider Figure 6.4.9(a), where, at time t = 0, a batch solution of volume, Vp, is introduced as feed to the vessel on top of the membrane this well-mixed solution has a molar concentration, C,o, of macrosolute species i. If after some time the well-mbced batch feed solution volume is reduced to Vjr, the volume of the retentate, by means of ultrafiltration, what is the macrosolute concentration Qr in the retentate It may be assumed that the observed macrosolute rejection for the species i remains constant during this concentration process (assuming that the macrosolute is substantially rejected). The extent of volume reduction in the well-mbced feed solution is often identified as the... 

Fruit juice processing is a major use for membrane filters, particularly for clarification (using microfiltration or ultrafiltration), concentration (using reverse osmosis) and deacidification (using electrodialysis). The clarification of apple juice by ultrafiltration is now an important process, whether making clear juice or natural (i.e. cloudy) ones. 

Reverse osmosis and ultrafiltration are processes for separating liquid solutions. The driving force for these separations comes from a pressure difference. This pressure difference does increase the chemical potentials on the feed side, but it does not dramatically alter the concentrations on this side. As a result, these separations are different than the gas separations described in the previous section, where the feed concentrations are directly proportional to the feed pressure. 

Ultrafiltration is currently dominated by two large apphcations, the recovery of electropaint waste water and the recovery of proteins from dairy wastes. The former application results from the use of solvent-free paints, especially for automobiles. These paints are electrostatically apphed. Any wash water is then processed to recover suspended pigments and other colloidal material. In the dairy industry, cheese whey can be concentrated and purified. In some cases, ultrafiltration concentrates valuable albumins that are lost in conventional processes. 

K. marxianus var. fragilis which utilizes lactose, produces a food-giade yeast product from cheese whey or cheese whey permeates collected from ultrafiltration processes at cheese plants. Again, the process is similar to that used with C. utilis (2,63). The Provesteen process can produce fragiUs yeast from cheese whey or cheese whey permeate at cell concentrations ia the range of 110—120 g/L, dry wt basis (70,73). 

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Membrane-retained components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. It is the objective of ultrafiltration to recover or concentrate particular species in the retentate (eg, latex concentration, pigment recovery, protein recovery from cheese and casein wheys, and concentration of proteins for biopharmaceuticals) or to produce a purified permeate (eg, sewage treatment, production of sterile water or antibiotics, etc). Diafiltration is a specific ultrafiltration process in which the retentate is further purified or the permeable sohds are extracted further by the addition of water or, in the case of proteins, buffer to the retentate. 

Diafiltration is an ultrafiltration process where water or an aqueous buffer is added to the concentrate and permeate is removed (50). The two steps may be sequential or simultaneous. Diafiltration improves the degree of separation between retained and permeable species. 

P. Dejmek, "PermeabiHty of the Concentration Polarization Layer in Ultrafiltration of Macro Molecules," Proceedings of the International Symposium, Separation Processes by Membranes, Paris, Mar. 13—14,1975. 

The egg products are finally processed and spray-dried. Sometimes Hquid egg whites are concentrated before spray-drying by ultrafiltration (qv) or reverse osmosis procedures. Table 5 presents the effect of egg quaUty on the different egg product manufacturing processes. 

Membrane Processes Membrane processes are also used diafiltration is convenient for the removal of small contaminating species such as salts and smaller proteins, and can be combined with subsequent steps to concentrate the protein. Provided that proper membrane materials have been selected to avoid protein-membrane interactions, diafiltration using ultrafiltration membranes is typically straightforward, high-yielding and capital-sparing. These operations can often tolerate the concentration or the desired protein to its solu-bihty limit, maximizing process efficiency. 

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