Novel methods for casein production

Cryoprecipitation. When milk is frozen and stored at about — 10°C, the ionic strength of the liquid phase increases with a concomitant increase in [Ca ] and a decrease in pH (to approximately 5.8) due to precipitation of calcium phosphates with the release of hydrogen ions (H ) (Chapter 5). These changes destabilize the casein micelles which precipitate when the milk is thawed. 

Cryodestabilization of casein limits the commercial feasibility of frozen milk, which may be attractive in certain circumstances. However, cryode-stabilized casein might be commercially viable, especially if applied to milks concentrated by ultrafiltration, which are less stable than normal milk. Cryodestabilized casein may be processed in the usual way. The product is dispersible in water and can be reconstituted as micelles in water at 40°C, The heat stability and rennet coagulability of these micelles are generally similar to those of normal micelles and casein produced by cryodestabilization may be suitable for the production of fast-ripening cheeses, e.g. Mozzarella or Camembert, when the supply of fresh milk is inadequate. As far as we are aware, casein is not produced commercially by cryodestabilization. 

Precipitation with ethanol. The casein in milk coagulates at pH 6.6 on addition of ethanol to about 40% stability decreases sharply as the pH is reduced, and only 10-15% ethanol is required at pH 6. Ethanol-precipitated casein may be dispersed in a micellar form and has very good emulsifying properties. The commercial production of ethanol-precipitated casein is probably economically viable but the process is not being used commercially. 

Membrane processing. The use of ultrafiltration (UF) for the production of whey protein concentrates (WPCs) is now well established (p. 223). Obviously, UF or diafiltration (DF) can be used to prepare products enriched in total milk protein. Products with protein concentrations up to 85% have been produced and assessed for a range of functionalities and applications (Fox and Mulvihill, 1992). 

The development of large-pore membranes facilitates the separation of whey proteins from casein micelles by microfiltration (MF). Membranes used in MF have cut-offs in the range 0.01-10/im, and therefore casein micelles may be in the permeate or retentate streams, depending on the pore size of the MF membranes chosen. MF with large-pore membranes very effectively removes bacteria and somatic cells from milk and may also be used to remove lipoprotein complexes from whey prior to the production of WPCs with improved functionality. The preparation of micellar casein by MF is still at the exploratory stage. 

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