Cold agglutination

IgM, an immunoglobulin in milk, forms a complex with lipoproteins. This complex, known as cryoglobulin, precipitates onto the fat globules and causes flocculation. The process is known as cold agglutination. As fat globules cluster, the speed of rising increases and sweeps up the smaller globules with them. The cream layer forms very rapidly, within 20 to 30 min, in cold milk. 

The viscosity of milk and milk products is reported to be important in the rate of creaming. The viscosity of milk increases with decrease in temperature because the increased voluminosity of casein micelles temperatures above 65°C increases viscosity due to the denaturation of whey proteins pH an increase or decrease in the pH of milk also causes an increase in casein micelle voluminosity. Fat globules that have undergone cold agglutination may be dispersed due to agitation, causing a decrease in viscosity. 

Under certain conditions (e.g. moderate shear rates, at fat contents below 40% and at temperatures above 40°C, at which the fat is liquid and no cold agglutination occurs) milk, skim milk and cream are, in effect, fluids with Newtonian rheological properties. Newtonian behaviour can be described by the equation ... 

The coefficient of viscosity for whole milk at 20°C, but not affected by cold agglutination of fat globules, is about 2.127 mPa s. Values for water and milk plasma at 20°C are 1.002 and 1.68 mPas, respectively. Casein, and to a lesser extent fat, are the principal contributors to the viscosity of milk whey proteins and low molecular mass species have less influence. 

At a temperature <40°C, milk does not behave as a Newtonion fluid the deviation from Newtonian flow becomes larger as the temperature decreases (Randhahn, 1973 Wayne and Shoemaker, 1988 Kristensen et ah, 1997). Viscosity of milk decreases with increasing shear rate at a temperature below 40°C (Randhahn, 1973), which Mulder and Walstra (1974) suggested may be due to disruption of clusters of milk fat globules, which were formed as a result of cold agglutination. 

Colloidal interactions between emulsion droplets play a primary role in determining emulsion rheology. If attractions predominate over repulsive forces, flocculation can occur, which leads to an increase in the effective volume fraction of the dispersed phase and thus increases viscosity (McCle-ments, 1999). Clustering of milk fat globules due to cold agglutination increases the effective volume fraction of the milk fat globules, thereby increasing viscosity (Prentice, 1992). 

Payens, T.A.J., Both, P. 1970. Cryoglobulins from milk and a mechanism for cold agglutination of milk fat globules. Immunochemistry. 7, 869. 

Moeschlin S, Wagner K (1952) Agranulocytosis due to the occurrence of leukocyte-agglutinins (pyramidon and cold agglutins). Acta Haematol (Basel) 8 29-41 Moult PJA, Sherlock S (1975) Halothane-related hepatitis. A clinical study of twenty-six cases. Q J Med 44 99-114... 

Weber RJ, Qem LW 1981. The molecular mechanism of cryoprecipitation and cold agglutination of an IgM Waldenstrom macroglobulinemia with anti-Gd specificity sedimentation analysis and localization of interacting sites. J Immunol 127 300-305. 

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