Chemistry Reference
In-Depth Information
Figure 9.4.
Dual-binding model for the casein micelle. CN is casein and CCP is colloidal
calcium phosphate (Horne, 1998).
large, so that their effects on interparticle interactions may be rather strong
(Piazza, 2004).
Each casein molecule effectively functions as a block copolymer, with
the hydrophobic region(s) offering the opportunity for a multitude of indivi-
dual, weak, hydrophobic interactions (driven by the thermodynamically
favourable exclusion of water by this type of association). The hydrophilic
regions of the casein molecules contain the phosphoserine cluster (or clus-
ters), with the exception of
-casein which has no such cluster, each offering
multiple functionality for crosslinking.
s1
-Casein can polymerize (self-
associate) through the hydrophobic blocks, forming a worm-like chain.
Further growth is limited by the strong electrostatic repulsion of the hydro-
philic regions, but in the casein micelle the negative charges of the phospho-
serine clusters are neutralized by intercalating their phosphate groups into a
facet of the Ca phosphate nanoclusters. This has two very important implica-
tions for the micelle. First, by removal of a major electrostatic repulsion
component, it increases the propensity for hydrophobic bonding upstream
