Caseins without calcium

The following factors must be considered when assessing the stability of the casein micelle The role of Ca++ is very significant in milk. More than 90% of the calcium content of skim milk is associated in some way or another with the casein micelle. The removal of Ca++ leads to reversible dissociation of P-casein without micellular disintegration. The addition of Ca++ leads to aggregation. The same reaction occurs between the individual caseins in the micelle, but not as much because there is no secondary structure in casein proteins. 

We have seen earlier in this chapter how the self-assembly of casein systems is sensitively affected by temperature. Another thermodynamic variable that can affect protein-protein interactions in aqueous media is the hydrostatic pressure. Static high-pressure treatment causes the disintegration of casein micelles due to the dismption of internal hydro-phobic interactions and the dissociation of colloidal calcium phosphate. This phenomenon has been used to modify the gelation ability of casein without acidification as a consequence of exposure of hydrophobic parts of the casein molecules into the aqueous medium from the interior of the native casein micelles (Dickinson, 2006). High-pressure treatment leads to a reduction in the casein concentration required for gelation under neutral conditions, especially in the presence of cosolutes such as sucrose (Abbasi and Dickinson, 2001, 2002, 2004 Keenan et al., 2001). 

Although CCP represents only about 6% of the dry weight of the casein micelle, it plays an essential role in its structure and properties and hence has major effects on the properties of milk it is the integrating factor in the casein micelle without it, milk is not coagulable by rennet and its heat and calcium stability properties are significantly altered. In fact, milk would be a totally different fluid without colloidal calcium phosphate. 

As discussed in Chapter 4 (p. 186), Holt (1994) has proposed that casein has evolved with the ability to bind high concentrations of calcium and phosphate so that milk can contain high levels of these ions, which are essential for neonatal growth, without precipitation in the ducts of the mammary glands. 

The experiments with urea, in particular, demonstrate most clearly that casein micelles can be broken down into much smaller particles without rupturing the casein-calcium phosphate linkages. Hydro-phobic and hydrogen bonding are therefore important in maintaining the integrity of micelles. Nevertheless, the importance of the colloidal calcium phosphate is clear, as was demonstrated by McGann... 

Ostrom, K.M., Borschel, M.W., Westcott, J.E., Richardson, K.S., Kerbs, N.F. 2002. Lower calcium absorption in infants fed casein hydrolysate- and soy protein-based infant formulas containing palm olein versus formulas without palm olein. J. Am. College Nutr. 21, 654-659. 

The calcium content of the meals was increased by adding milk or lowfat cheese. In the studies on the effect of protein, the animal protein sources were milk, cheese, boiled beef and boiled egg. To further increase, the protein content without at the same time increasing the calcium or zinc content, sodium caseinate was used in one meal. 

Transglutaminase treatment of milk offers a novel way to improve the heat stability of milks without the use of chemical additives. Transglutaminase-treated milk had markedly improved heat stability at pH > 6.5 compared to untreated milk. This may be related to the effect of intramolecular cross-links formed in transglutaminase-treated milk, which prevents the dissociation of caseins from the micelles imder conditions where it would have otherwise occurred (e.g., when colloidal calcium phosphate is removed). This was considered to be the mechanism by which the enzyme-treated milk was stabilized to heat treatment (O Sullivan et al., 2002a,b). 

White, amorphous powder or granules without odor or taste. Very sparingly sol in water and in nonpolar organic solvents sol in aqueous so]ns of alkalies, levorotatory. The isoelectric zone is around pH 4.7 sol in coned HCI with light violet color. Amphoteric forms salts with both acids and bases. Present in bovine milk as neutral calcium caseinate and in human milk as potassium caseinate. Precipitated from solns satd with metallic salts. Forms a hard, inso] plastic with formaldehyde. 

Hydration. The ability of proteins to bind and hold water without syner-esis is critical in many foods, e.g. comminuted meat products. Although the caseins are relatively hydrophobic, they bind c. 2g H20g protein, which is typical of proteins. Hydration increases with increasing pH and is relatively independent of NaCl concentration, which is especially important in the efficacy of casein in meat-based products. The water-holding capacity of sodium caseinate is higher than that of calcium caseinate or micellar casein. 

Casein is soluble in alkali hydroxides and in this way the soluble Na, K and NH4 salts are obtained commercially. Calcium caseinate will form stable colloidal dispersions while sodium and potassium caseinates dissolve to form viscous solutions and eventually aqueous gels above about 17% concentrations. The alkali metal salts are very stable to heat over a wide range of conditions. They can be heated to 140°C for several hours at pH 7, without decomposition. 

Dozens of different peptides have been identified in cheeses. Most of them arise from and -caseins and a few are from aj2-and K-caseins. The proteinases involved in hydrolysis of aj -casein are mainly cathepsin D originating from milk and cell-envelope proteinase from thermophilic starters, while P- and aj2-caseins are mainly hydrolysed by plasmin. Moreover, peptidases from starters are also active throughout the ripening process, presumably similar to those from non-starter lactic acid bacteria. For example, the bitterness of mature Gouda cheese is caused by calcium and magnesium chlorides, some bitter-tasting free amino acids and is modified by peptides, which arise from the hydrolysis of fS-casein (such as decapeptide Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn-Ser and derived nonanpeptide without the terminal serine) and casein (tetrapeptide Leu-Pro-Gln-Glu). 

Whole milk is composed of both whey and casein proteins and has been shown to be better at supporting muscle PS acutely compared to hydrolyzed soy protein. Milk ingestion has also been associated with lower blood pressure and a reduced risk of hypertension. Recently, increased intake of dairy products such as milk and yogurt has been shown to enhance weight loss. However, the proposed mechanism that was shown to exist in animal models does not seem to transfer to humans. Thus, the mechanism for the associated weight loss appears to be calcium independent, " at least when calcium intake is adequate. In a multicenter trial, milk intake without weight loss did not ehdt favorable changes in metabolic outcomes. 

Figure 2.24 Hydration heat flow of three different self-levelling compounds based on ternary binders portland cement-calcium aluminate cement-calcium sulfate (portland cement dominated) which differ only in the amount of the flow agent casein. A formulation without casein is compared to two formulations with half the usual and the usual dosage of casein. (Adapted from Kighelman, J., Hydration and structure development of ternary binder system as used in self-levelling compounds , PhD Thesis no. 37777, cole Polytechnique Federale de Lausanne, Switzerland, 2007.)...

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