154 DAIRY CHEMISTRY AND BIOCHEMISTRY and whey proteins while lactose and soluble salts are permeable; total milk protein may be produced by this method. The casein micelles permeate the membranes used in microfiltration(pore size 0.05-10 um)but bacteria are retained by membranes with pores of less than 0.5 um, thus providing a method for removing more than 99.9% of the bacteria in milk without heat treatment; microfiltration is being used increasingly in several sectors of the dairy industry. 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 4.3.6 Gel filtration ( gel permeation chromatography Filtration through cross- linked dextrans(e.g. Sephadex, Pharmacia, Upp sala, Sweden)makes it possible to fractionate molecules, including proteins on a commercial scale. It is possible to separate the casein and whey proteins by gel filtration but the process is uneconomical on an industrial 4.3.7 Precipitation with ethanol The caseins may be precipitated from milk by c. 40% ethanol while the whey proteins remain soluble; lower concentrations of ethanol may be used at lower pH values 4.3.8 Cryoprecipitation Casein, in a mainly micellar form, is destabilized and precipitated by freezing milk or, preferably, concentrated milk, at about-10'C; casein prepared by this method has some interesting properties but is not produced commer cially at present. 4.3.9 Rennet coagulation Casein may be coagulated and recovered as rennet casein by treatment of milk with selected proteinases(rennets ). However, one of the caseins, K-casein,is hydrolysed during renneting and therefore the properties of rennet casein differ fundamentally from those of acid casein. Rennet casein which contains the colloidal calcium phosphate of milk, is insoluble in water at pH 7 but can be dissolved by adding calcium sequestering agents, usually citrates or polyphosphates. It has desirable functional properties for certain food applications, e. g. in the production of cheese analogues154 DAIRY CHEMISTRY AND BIOCHEMISTRY and whey proteins while lactose and soluble salts are permeable; total milk protein may be produced by this method. The casein micelles permeate the membranes used in microfiltration (pore size - 0.05-10 pm) but bacteria are retained by membranes with pores of less than OSpm, thus providing a method for removing more than 99.9% of the bacteria in milk without heat treatment; microfiltration is being used increasingly in several sectors of the dairy industry. 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. 4.3.6 Geljltration (gel permeation chromatography) Filtration through cross-linked dextrans (e.g. Sephadex, Pharmacia, Upp￾sala, Sweden) makes it possible to fractionate molecules, including proteins, on a commercial scale. It is possible to separate the casein and whey proteins by gel filtration but the process is uneconomical on an industrial scale. 4.3.7 Precipitation with ethanol The caseins may be precipitated from milk by c. 40% ethanol while the whey proteins remain soluble; lower concentrations of ethanol may be used at lower pH values. 4.3.8 Cryoprecipitation Casein, in a mainly micellar form, is destabilized and precipitated by freezing milk or, preferably, concentrated milk, at about - 10°C; casein prepared by this method has some interesting properties but is not produced commer￾cially at present. 4.3.9 Rennet coagulation Casein may be coagulated and recovered as rennet casein by treatment of milk with selected proteinases (rennets). However, one of the caseins, K-casein, is hydrolysed during renneting and therefore the properties of rennet casein differ fundamentally from those of acid casein. Rennet casein, which contains the colloidal calcium phosphate of milk, is insoluble in water at pH 7 but can be dissolved by adding calcium sequestering agents, usually citrates or polyphosphates. It has desirable functional properties for certain food applications, e.g. in the production of cheese analogues