Milk Salts: Technological Significance - Advanced Dairy Chemistry - page 364

(in vivo), it is likely that these polymers would have greater attachment/linkage
to the rest of the micelle structure, making them more difficult to remove.
Also, the attractive balance in -casein is not very sensitive to changes in
phosphoserine involvement in CCP nanoclusters (so the loss of some CCP
crosslinks at low temperatures does not have a major impact on its dissocia-
tion from the micelle) as they do not interact through CCP crosslinks. In
contrast, for -casein, if some of the CCP crosslinks are dissolved at low
temperatures then the exposed negative charge on the phosphoserine residues
would make the binding of -casein to other casein molecules unfavourable.
This type of process could allow some of the -casein to dissociate as the
temperature is lowered. It is likely that the -casein that dissociates is closer to
the micelle surface or if not, then the -casein freed by this process would have
some potential chances to re-attach/associate with other caseins as it diffuses
through the inner micelle network out to the bulk solution.
-Casein-deficient mice, produced by genetic modification, were unable
to lactate because of destabilization of the micelles in the lumina of the
mammary gland (Shekar et al., 2006). The milk of various species appears
to have a -casein or Ca-stabilizing casein (i.e. a casein that does not have a
phosphate cluster), whereas some milks contain little or no s -caseins (human
milk) and various ratios of s -to -caseins.

9.6.3. Nature of Colloidal Calcium Phosphate

The nature of CCP or micellar Ca phosphate (as it is sometimes called)
has been the subject of intense study and debate over the years. There have
been several reviews of the nature of CCP (Pyne, 1934; McGann and Pyne,
1960; Schmidt, 1980; van Dijk, 1990; Holt, 1992, 1995; De Kruif and Holt,
2003). Schmidt (1980, 1982) considered the CCP to be a ubiquitous coating
or ''cement'' that bonded many casein molecules together. McGann et al.
(1983a,b) reported that the CCP depositions in milk systems consist of
spherical granules (other later names for these granules include nanoclus-
ters) 2-3 nm in diameter. Such a large entity is incompatible with the small
type of CCP structures proposed by van Dijk (1990) or Schmidt (1980).
For many years, CCP was believed to be a basic Ca phosphate salt (e.g.
Pyne and McGann, 1960). Pyne and McGann (1960) and McGann et al.
(1983a) reported that in CCP, the Ca/P i ratio is > 1.5, which would make it
some type of basic salt, like apatite or tricalcium phosphate (e.g. Ca 3 (PO 4 ) 2 ).
Citrate and magnesium are also associated with the CCP phase. Various other
studies have suggested that CCP is a more acidic phase, such as some brushite-
type structure (CaHPO 4 ) (e.g. Holt et al., 1982). Various groups have consid-
ered CCP to be amorphous, i.e. lacking a crystalline structure (Pyne and