Ionic strength of milk

Gupta et ai, 1984). The dissociation constants (p,K a s) of citric acid at the ionic strength of milk are 3.0, 4.5, and 4.9 (Walstra and Jenness, 1984). Owing to their acidic properties, mono- and disodium citrates may be used to correct the pH of a cheese blend, e.g., when a high proportion of very mature cheese is used. 

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. 

Boulet M, Marier JR (1960) Solubility of tricalcium citrate in solutions of variable ionic strength and milk ultrafiltrates. J Diary Sci 43 155-164... 

Differential Solubility Methods. Numerous methods have been developed to obtain one or more of the various caseins from whole casein or directly from skim milk based on their differential solubility (Thompson 1971 Mackinlay and Wake 1971 Whitney 1977). While some early procedures indicated the possibility of fractionating whole casein into different components, it was not until the 1950s that systematic procedures were proposed for the fractionation of casein into Warner s a-, 0-, and y-caseins. Hipp et al. (1952) developed two procedures which have been used extensively or partially incorporated into other methods. The first is based upon the differential solubilities of the caseins in 50% alcohol in the presence of ammonium acetate by varying the pH, temperature, and ionic strength. The second procedure involves the dispersion of whole casein in 6.6 M urea and the separa-... 

To study the clotting of micellar casein skim milk prepared from low-heat skim milk powder was diluted 16 times with 0.01 M CaCl2, to which NaCl was added to adjust the ionic strength. 

The influence of the ionic strength on the clotting time of -casein at 35°C is shown in Figure 4. The pronounced minimum is strongly reminiscent of the minimum found with milk (11,12), though it occurs at a considerably lower ionic strength. 

Figure 2. Clotting of micellar casein by rennet at different ionic strengths. Absorbance measurements in the Cary 14 spectrophotometer at 500 nm in 0.5-cf cuvettes 35°C skim milk diluted 16 times clotting strength in reaction mixture 1.43 SU. Time flows to the left. (A) I = 0.04 (B) I = 0.06 (C) I = 0.12.

Although less frequently discussed, heat processes often influence the textures and chemistries of the intermediate and end products, and thermal treatments are not without consequences on milk proteins that are denatured. Denaturation of proteins occurs under precise conditions of pH, temperature and ionic strength leading to their unfolding. Denaturation is significantly slower when proteins are near their isoelectric point. Only (3-lactoglobulin is irreversibly denatured at pH 7 and 70°C a-lactalbumin is denatured at pH 6.7 and 65°C. Aggregation of these proteins, besides hydrophobic... 

Figure 2. Effect of pH and ionic strength on the solubility of an acid-precipitated protein fraction from soy milk. ( — ) Unheated 60-sec microwave (Ar-A) hot water.

Zhang, Z., Dalgleish, D.G., and Goff, H.D. (2004). Effect of pH and ionic strength on competitive protein adsorption to air/water interfaces in aqueous foams made with mixed milk proteins. Coll. Surf. B. Biointerfaces 34, 113-121. 

Bazinet L, Ippersiel D, Gendron C, Mahdavi B, Amiot J, and Lamarche F. Effect of added salt and increase in ionic strength on skim milk electroacidification performances. J. Dairy Res. 2001 68(2) 237-250. 

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