MILK PROTEINS 153 lactose will interact with casein on heating via the maillard browning reaction, with undesirable consequences The procedure used for the industrial production of acid (isoelecti asein is essentially the same as that used on a laboratory scale, except for many technological differences(section 4. 15.1).The whey proteins may be recovered from the whey by salting out, dialysis or ultrafiltration 4.3.2 Centrifugation Because they occur as large aggregates, micelles, most (90-95%)of the casein in milk is sedimented by centrifugation at 100 000 g for 1 h. Sedimen tation is more complete at higher (30-37'C)than at low(2C)temperature, at which some of the casein components dissociate from the micelles and are non-sedimentable. Casein prepared by centrifugation contains its original level of colloidal calcium phosphate and can be redispersed as micelles with properties essentially similar to the original micelles demented milk Addition of CaCl 2 to about 0. 2 M causes aggregation of the casein such that it can be readily removed by low-speed centrifugation. If calcium is added at 90C, the casein forms coarse aggregates which precipitate readily. this principle is used in the commercial production of some 'casein co-precipi- tates'in which the whey proteins, denatured on heating milk at 90 C for 10 min, co-precipitate with the casein. Such products have a very high ash 4.3.4 Salting-out methods Casein can be precipitated from solution by any of several salts. Addition of NH4)2SO4 to milk to a concentration of 260 g l- causes complete precipi tation of the casein together with some whey proteins(immunoglobulins, Ig). MgSO4 may also be used. Saturation of milk with Nacl at 37C precipitates the casein and Igs while the major whey proteins re emain soluble, provided they are undenatured. This characteristic is the basis of a commercial test used for the heat classification of milk powders which contain variable levels of denatured whey proteins 4.3.5 Ultrafiltration The casein micelles are retained by fine-pore filters. Filtration through large-pore ceramic membranes is used to purify and concentrate casein on a laboratory scale. Ultrafiltration(UF)membranes retain both the caseinsMILK PROTEINS 153 lactose will interact with casein on heating via the Maillard browning reaction, with undesirable consequences. The procedure used for the industrial production of acid (isoelectric) casein is essentially the same as that used on a laboratory scale, except for many technological differences (section 4.15.1).The whey proteins may be recovered from the whey by salting out, dialysis or ultrafiltration. 4.3.2 Because they occur as large aggregates, micelles, most (90-95%) of the casein in milk is sedimented by centrifugation at 100 000 g for 1 h. Sedimen￾tation is more complete at higher (30-37°C) than at low (2°C) temperature, at which some of the casein components dissociate from the micelles and are non-sedimentable. Casein prepared by centrifugation contains its original level of colloidal calcium phosphate and can be redispersed as micelles with properties essentially similar to the original micelles. Cen tr ifuga t ion 4.3.3 Centrifugation of calcium-supplemented milk Addition of CaCI, to about 0.2 M causes aggregation of the casein such that it can be readily removed by low-speed centrifugation. If calcium is added at 90"C, the casein forms coarse aggregates which precipitate readily. This principle is used in the commercial production of some 'casein co-precipi￾tates' in which the whey proteins, denatured on heating milk at 90°C for lOmin, co-precipitate with the casein. Such products have a very high ash content. 4.3.4 Salting-out methods Casein can be precipitated from solution by any of several salts. Addition of (NH,),SO, to milk to a concentration of 260 g 1- causes complete precipi￾tation of the casein together with some whey proteins (immunoglobulins, Ig). MgSO, may also be used. Saturation of milk with NaCl at 37°C precipitates the casein and Igs while the major whey proteins remain soluble, provided they are undenatured. This characteristic is the basis of a commercial test used for the heat classification of milk powders which contain variable levels of denatured whey proteins. 4.3.5 Ultrajiltration The casein micelles are retained by fine-pore filters. Filtration through large-pore ceramic membranes is used to purify and concentrate casein on a laboratory scale. Ultrafiltration (UF) membranes retain both the caseins