Ultrafiltration of milk

The ultrafiltration of milk using polysulphone or polyethersulphone type membranes has a number of applications. The ultrafiltration of milk on farms as a means of reducing refrigeration and transport costs, and the production of speciality milk-based beverages are attractive uses. Cheese manufacture using ultraliltration is another area where the use of membrane filtration is becoming more widespread in the dairy industry. 

J. L. Maubois, "AppHcation of Ultrafiltration to Milk Treatment for Cheese Making," in Ref. 27. 

Whey protein concentrates (WPC), which are relatively new forms of milk protein products available for emulsification uses, have also been studied (4,28,29). WPC products prepared by gel filtration, ultrafiltration, metaphosphate precipitation and carboxymethyl cellulose precipitation all exhibited inferior emulsification properties compared to caseinate, both in model systems and in a simulated whipped topping formulation (2. However, additional work is proceeding on this topic and it is expected that WPC will be found to be capable of providing reasonable functionality in the emulsification area, especially if proper processing conditions are followed to minimize protein denaturation during their production. Such adverse effects on the functionality of WPC are undoubtedly due to their Irreversible interaction during heating processes which impair their ability to dissociate and unfold at the emulsion interface in order to function as an emulsifier (22). 

Constituent Ultrafiltrate of skim milk Ultrafiltrate of liquid portion of frozen concentrated milk... 

Ultrafiltrates obtained using cellophane or polysulphone membranes at 20°C and a transmembrane pressure of c. 100 kPa are satisfactory, but the concentrations of citrate and calcium are slightly low due to sieving effects which are accentuated by high pressures. Dialysis of a small volume of water against at least 50 times its volume of milk (to which a little chloroform or azide has been added as preservative) at 20°C for 48 h is the most satisfactory separation procedure and agrees closely with results obtained... 

Davies, D.T. and White, J.C.D. (1960) The use of ultrafiltration and dialysis in isolating the aqueous phase of milk and in determining the partition of milk constituents between the aqueous and disperse phases. J. Dairy Res., 27, 171-90. 

Rose, D. and Tessier, H. (1959) Composition of ultrafiltrates from milk heated at 80 to 230°F in relation to heat stability. J. Dairy Sci., 42, 969-80. 

Smeets, W.J.G.M. (1955) The determination of the concentration of calcium ions in milk ultrafiltrate. Neth. Milk Dairy J., 9, 249-60. 

Concentration. Concentration by thermal evaporation markedly reduces the heat stability of milk, e.g. concentrated skim milk containing about 18% total solids coagulates in roughly 10 min at 130°C. The stability of the concentrate is strongly affected by pH, with a maximum at around pH 6.6, but stability remains low at all pH values above about 6.8 (Figure 9.20). Concentration by ultrafiltration has a much smaller effect on HCT than thermal evaporation, due to a lower concentration of soluble salts in the retentate. 

In addition to the general decrease in viscosity with increasing temperature, heating milk can also influence its rheology by heat-induced denatura-tion of cryoglobulins and/or other whey proteins. Concentration of milk, e.g. by ultrafiltration, prior to heating results in a greater increase in f/app than in milk heated before concentration. 

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. 

Jenness, R. and Koops, J. 1962. Preparation and properties of a salt solution which simulates milk ultrafiltrate. Neth. Milk Dairy J. 16, 153-164. 

Reuter, H. Hisserich, D. and Prokopek, D. 1981. Study on the formal kinetics of rennet coagulation of milk concentrated by ultrafiltration. Milchwissenschaft 36, 13-18. 

In a commercial response to the potential value of sphingolipids as functional food components, a patented process for preparing milk products enriched in both phospholipids and sphingolipids was developed (Dewet-tinck and Boone, 2002). These products are obtained by ultrafiltration of byproducts from the direct processing of milk or from the further processing of directly acquired byproducts. The ultrafiltration membrane used had a cut-off value ranging from 5,000 to 20,000 Da. 

Mahaut, M., Korolczuk, J. 2002. Effect of homogenisation of milk and shearing of milk gel on the viscosity of fresh cheeses obtained by ultrafiltration of coagulated milk. Industries Alim. 

Keogh, M.K., Murray, C.A., O Kennedy, B.T. 2003. Effects of ultrafiltration of whole milk on some properties of spray-dried milk powders. Int. Dairy J. 13, 995-1002. 

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. 

Milk protein standardization for continuous cheese making can also be done by ultrafiltration using ceramic membranes. Zirconia membranes with an average molecular weight cut-off (MWCO) of 70,000 daltons on carbon supports have been used for this purpose. The objective for this application is to concentrate either the whole volume of the milk to a volume concentration factor of 1.3 to 1.6 or just a fraction of the feed volume to a volume concentration factor of 3 to 4 followed by mixing the concentrate with raw milk to reduce the requirement of milk storage space [Merin and Daufin, 1989]. 

---