check out this website for everything we need to know about milk.
http://www.foodsci.uoguelph.ca/dairyedu/chem.html
This is the part that's relevant to the calcium and phosphorus discussion.
Minerals
All 22 minerals considered to be essential to the human diet are present in milk. These include three families of salts:
Sodium (Na), Potassium (K) and Chloride (Cl):These free ions are negatively correlated to lactose to maintain osmotic equilibrium of milk with blood.
Calcium (Ca), Magnesium (Mg), Inorganic Phosphorous (P(i)), and Citrate: This group consists of 2/3 of the Ca, 1/3 of the Mg, 1/2 of the P(i), and less than 1/10 of the citrate in colloidal (nondiffusible) form and present in the casein micelle.
Diffusible salts of Ca, Mg, citrate, and phosphate: These salts are very pH dependent and contribute to the overall acid-base equilibrium of milk.
The mineral content of fresh milk is given below:
Mineral Content per litre
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Sodium (mg) 350-900
Potassium (mg) 1100-1700
Chloride (mg) 900-1100
Calcium (mg) 1100-1300
Magnesium (mg) 90-140
Phosphorus (mg) 900-1000
Iron (ug) 300-600
Zinc (ug) 2000-6000
Copper (ug) 100-600
Manganese (ug) 20-50
Iodine (ug) 260
Fluoride (ug) 30-220
Selenium (ug) 5-67
Cobalt (ug) 0.5-1.3
Chromium (ug) 8-13
Molybdenum (ug) 18-120
Nickel (ug) 0-50
Silicon (ug) 750-7000
Vanadium (ug) tr-310
Tin (ug) 40-500
Arsenic (ug) 20-60
Structure: The Casein Micelle
Most, but not all, of the casein proteins exist in a colloidal particle known as the casein micelle. Its biological function is to carry large amounts of highly insoluble CaP to mammalian young in liquid form and to form a clot in the stomach for more efficient nutrition. Besides casein protein, calcium and phosphate, the micelle also contains citrate, minor ions, lipase and plasmin enzymes, and entrapped milk serum. These micelles are rather porous structures, occupying about 4 ml/g and 6-12% of the total volume fraction of milk.
The "casein sub-micelle" model has been prominent for the last several years, and is illustrated and described with the following link, but there is not universal acceptance of this model, and mounting research evidence to suggest that there is not a defined sub-micellar structure to the micelle at all. Another model of a more open structure is also defined with the following link.
In the submicelle model, it is thought that there are small aggregates of whole casein, containing 10 to 100 casein molecules, called submicelles. It is thought that there are two different kinds of submicelle; with and without kappa-casein. These submicelles contain a hydrophobic core and are covered by a hydrophilic coat which is at least partly comprised of the polar moieties of kappa-casein. The hydrophilic CMP of the kappa-casein exists as a flexible hair.
The open model also suggests there are more dense and less dense regions within the midelle, but there is less of a well-defined structure. In this model, calcium phosphate nanoclusters bind caseins and provide for the differences in density within the casein micelle.
Casein Micelle Structure 17 KB
Colloidal calcium phosphate (CCP) acts as a cement between the hundreds or even thousands of submicelles that form the casein micelle. Binding may be covalent or electrostatic. Submicelles rich in kappa-casein occupy a surface position, whereas those with less are buried in the interior. The resulting hairy layer, at least 7 nm thick, acts to prohibit further aggregation of submicelles by steric repulsion. The casein micelles are not static; there are three dynamic equilibria between the micelle and its surroundings:
the free casein molecules and submicelles
the free submicelles and micelles
the dissoved colloidal calcium and phosphate
The following factors must be considered when assessing the stability of the casein micelle:
Role of Ca++:
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