Casein micelles destabilization

Rombaut, R., Dejonckheere, V., and Dewettinck, K., Microfiltration of butter serum upon casein micelle destabilization, J. Dairy Sci., 89, 1915, 2006. 

These changes in the concentration of Ca2 + and pH lead to destabilization of the casein micelles. 

As discussed in Chapter 2 (p. 38), crystallization of lactose as x-monohyd-rate exacerbates the situation. The combination of increased concentrations of Ca2 + and reduced pH causes destabilization of the casein micelles. 

The major defect, which limits exploitation of frozen milk concentrates as consumer products, is the instability of the casein micelle system (Keeney and Kroger 1974 Morr 1975). The casein micelles gradually destabilize during storage of the frozen milk concentrate. 

The physical stability of the casein micelle system is closely related to the degree of lactose crystallization from the unfrozen phase of the frozen concentrate. Crystallization of lactose from the unfrozen solution temporarily raises its freezing point, causing additional water to freeze, thus increasing the concentration and promoting destabilization of casein micelles. 

Hydrolysis of the casein micelle-stabilizing K-casein by the action of selected acid proteinases (rennets), and the resultant slow quiescent aggregation of the destabilized micelles in the presence of calcium ions ( 3 mM) at 30-36°C (e.g., for most rennet-curd cheeses such as Cheddar, Mozzarella and Gouda)... 

The caseinate micelles of milk, which are quite stable to heat, may also be destabilized by freezing. On frozen storage of milk, the stability of caseinate progressively decreases and this may lead to complete coagulation (deMan, 1999). Enzymes have also been linked to protein denaturation, as it is known that low temperature decreases the activity of enzymes in tissue, but does not inactivate them (Lim et al., 2004 Zaritzky, 2006). 

The sequence of events following the enzymic action of clotting enzymes on /c-casein to destabilize the micelles is poorly understood. In part, this results from an incomplete understanding of the structure of the casein micelles. Studies of the structure of native micelles as they occur in milk are very few, indeed. Perhaps this stems from the difficul-... 

Specific attack of Phe-Met in -casein to destabilize casein micelle... 

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. 

Prodnction of yogurt and cheese involves destabilization of the milk emulsion with the assistance of microbial activity. In yogurt, the milk is coagulated and sonred by lactic acid produced by bacteria. Cheese making starts with an enzymatic modification of the casein micelles allowing them to co-precipitate with fat droplets, thus forming the cheese curd. 

Casein is very hydrophobic and, therefore, temperature sensitive. Low temperature or removal of calcium causes dissociation of /3-casein from the micelle and destabilizes the remaining micelle (Carpenter and Brown 1985 Dalgleish 1982). Soluble /3-casein can form aggregates of up to 40 monomers when heated. The C-terminal (hydrophobic) portions of /3-casein monomers clump together, and the N-terminal (hydrophilic) portions extend outward into the surrounding aqueous medium (Kinsella 1984). 

One of the applications of enzymes in the preparation of food gels is the production of cheese. During this process, chymosin hydrolyzes a specific bond of K-casein, resulting in the destabilization of the micelle structure followed by aggregation and formation of an insoluble coagulum. 

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