Ultrafiltration of whey

Following ultrafiltration of whey, the permeate passes over a reverse osmosis (qv) membrane to separate the lactose from other components of the permeate. Reverse osmosis can be used to remove water and concentrate soHds in a dairy plant, giving a product with 18% soHds and thus decreasing the difficulty of waste disposal. Concentration of rinse water gives a product with 4—5% total soHds. Proper maintenance of the membrane allows for use up to two years. Membranes are available for use up to 100°C with pH ranges from 1 to 14 the usual temperature range is 0—50°C. 

Regular cleaning is required to maintain the performance of all ultrafiltration membranes. The period of the cleaning cycle can vary from daily for food applications, such as ultrafiltration of whey, to once a month or more for ultrafiltration membranes used as polishing units in ultrapure water systems. A typical cleaning cycle is as follows ... 

Ultrafiltration of whey is a major membrane-based process in the dairy industry however, the commercial availability of this application has been limited by membrane fouling, which has a concomitant influence on the permeation rate. Ultrasound cleaning of these fouled membranes has revealed that the effect of US energy is more significant in the absence of a surfactant, but is less markedly influenced by temperature and transmembrane pressure. The results suggest that US acts primarily by Increasing turbulence within the cleaning solution [91]. 

Concentration of whev proteins. As mentioned earlier, microfiltration can be used to remove bacterias. In addition, they are capable of separating phospholipids, fats and casein fines of sweet whey or sour (acidified) whey. Ultrafiltration of whey has been well proven to provide an array of protein products of diverse compositions and properties. Inorganic membrane filtration can be used at different stages of the process to make whey protein concentrates (WPC) in powder form with a protein content reaching 50%. 

Cheryan, M. and Kuo, K.P., Hollow fibers and spiral wound modules for ultrafiltration of whey Energy consumption and performance, J. Dairy Sci., 67, 1406, 1984. 

In the ultrafiltration of whey, protein concentrates depleted of lactose to various extents are obtained, depending on the number of stages and amount of wash water. Another, less gentle method involves the heating of whey (95 °C, 3 min) by direct steam injection, followed by precipitation of the denatured proteins at pH 4.5, separation in a sedimentation centrifuge (2000-4000 min ), and drying. 

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. 

Ultrafiltration. Membranes are used that are capable of selectively passing large molecules (>500 daltons). Pressures of 0.1—1.4 MPa (<200 psi) are exerted over the solution to overcome the osmotic pressure, while providing an adequate dow through the membrane for use. Ultrafiltration (qv) has been particulady successhil for the separation of whey from cheese. It separates protein from lactose and mineral salts, protein being the concentrate. Ultrafiltration is also used to obtain a protein-rich concentrate of skimmed milk from which cheese is made. The whey protein obtained by ultrafiltration is 50—80% protein which can be spray dried. 

Whey concentration, both of whole whey and ultrafiltration permeate, is practiced successfully, but the solubility of lactose hmits the practical concentration of whey to about 20 percent total sohds, about a 4x concentration fac tor. (Membranes do not tolerate sohds forming on their surface.) Nanofiltration is used to soften water and clean up streams where complete removal of monovalent ions is either unnecessary or undesirable. Because of the ionic character of most NF membranes, they reject polyvalent ions much more readily than monovalent ions. NF is used to treat salt whey, the whey expressed after NaCl is added to curd. Nanofiltration permits the NaCl to permeate while retaining the other whey components, which may then be blended with ordinaiy whey. NF is also used to deacidify whey produced by the addition of HCl to milk in the production of casein. 

Industrially, whey proteins are prepared by ultrafiltration or diafiltration of whey (to remove lactose and salts), followed by spray drying these products, referred to as whey protein concentrates, contain 30-80% protein. 

Manufacture of crystalline lactose from permeate derived by ultrafiltration of lactic casein whey presents special problems because of the low pH, high lactate concentration, and high calcium and phosphate concentrations (Hobman 1984). Research at the New Zealand Dairy Research Institute has led to a pilot-scale process whereby calcium phosphate complexes are partially removed before evaporation by an alkali and heat treatment to precipitate them, followed by centrifugation to clarify the treated permeate. Removal of about 50% of the calcium is sufficient to avoid problems during evaporation. 

The fat globules of milk reduce the conductivity by occupying volume and by impeding the mobility of ions. Thus the conductivity of whole milk is less than that of skim milk by about 10%, and that of cream varies with the fat content (Gerber 1927 Muller 1931 Prentice 1962). Homogenization of milk does not measurably influence conductivity (Prentice 1962). The conductivity of whey and ultrafiltrate is slightly greater than that of skim milk (Schulz 1956 Schulz and Sydow 1957). A possible relationship between the electrical conductivity and physical stability of evaporated milk and concentrated infant milk products has been reported (Hansson 1957). Samples of poor physical stability tended to have relatively low conductivity values compared to those of the more stable products. 

Ruegg, M., Moor, U. and Blanc, B. 1977. A calorimetric study of the thermal denatura-tion of whey proteins in simulated milk ultrafiltrate. J. Dairy Res. 44, 509-520. 

Mucchetti, G. and Taglietti, P. 1993. Demineralization of whey and ultrafiltration permeate by electrodialysis. Scienza e Tecnica Lattiero-Casearia 44, 51-62. 

Perez, A., Andres, L.J., Alvarez, R., Coca, J., and Hill, C.G. 1994. Electrodialysis of whey permeates and retentates obtained by ultrafiltration. J. Food Process Eng. 17, 177-190. 

Ultrafiltration Liquid Microporous membrane with pressure gradient Separation of whey from cheese... 

Whey protein concentrate. The whey protein used was prepared by ultrafiltration and spray drying. Protein content (N x 6.55) was 68% (dry weight). Lipid content was 7.1% (dry weight). In order to study heat induced aggregation by spectrophotometric methods the turbidity of the dilute protein dispersions was too high. The turbidity of whey protein dispersions is caused by lipids associated with proteins probably in the form of emulsified oil droplets. This fraction was removed by precipitation at pH 4.5 from dispersions made in dist. water and separated by centrifugation at 40 000 xg. 

Vasiljevic, T., and Jelen, P. (1999). Temperature effect on behaviour of minerals during ultrafiltration of skim milk and acid whey. Milchwissenschaft 54(5), 243-246. 

It has been proven over the years that the effect of fouling can be lessened to some extent for the application of whey concentration by pretreating the feed streams for the ultrafilters. Whey contains many insoluble solids such as casein fines, lipoprotein complex, mineral precipitates, free fats and microorganisms. Clarification of these debris helps reduce fouling potential during ultrafiltration. In addition, it is quite evident that calcium phosphate minerals in whey are not stable and their precipitation in the membrane pores often results in flux decline. Demineralization of whey before ultrafiltration helps maintain high permeate flux considerably [Muir and Banks, 1985]. 

Lau et al. [188] have shown that calcium ions are linked to phospholipids. The binding of calcium with hpids inhibits the formation of lipid/protein complexes. The decrease in mineral salts, particularly in magnesium and calcium ions, during processes 2 and 3 promotes the lipid/protein complexes formation. This phenomenon was confirmed by higher precipitation levels for lipids and proteins in process 3 in comparison with process 1 (Table 21.11). Equation 21.1 also means that an increase of components should improve the lipid/protein complexes formation. This increase of may be obtained by a concentration step of whey solutions by ultrafiltration. 

Ultrafiltration may be integrated into the cheesemaking process either for partial milk concentration or full milk concentration (Table 22.1), in which cutting and whey drainage are entirely eliminated and 100% of the whey proteins of milk are retained in the cheese matrix [28,75,76], The reduced volume of the liquid pre-cheese and the absence of whey drainage from the curd when UF pre-cheese is used lead to the reduction of rennet requirement by -80% compared to what is usually needed in conventional manufacture of cheese [25,77],... 

Aimar, P., Taddei, C., Lafaille, J.P., and Sanchez, V., Mass transfer limitations during ultrafiltration of cheese whey with inorganic membranes, J. Membr. Sci., 38, 203, 1988. 

Rao, H.G., Mechanisms of flux decline during ultrafiltration of dairy products and influence of pH on flux rates of whey and buttermilk. Desalination, 144, 319, 2002. 

Kuo, K.P. and Cheryan, M., Ultrafiltration of acid whey in spiral-wound unit Effect of operating parameters on membrane fouling, J. 

---