Mineral and casein equilibria in milk: effects of added salts and calcium-chelating agents

We have investigated the Effects of adding a range of mineral salts and calcium-chelating agents on the distribution of casein and minerals between the non pelleted and pelleted phases of milk obtained upon centrifugation at 78000 g for 90 min. Adding CuCl2 or mixtures of NaH2PO4 and Na2HPO4 to reconstituted skim milk (90 g milli solids/kg) at, pH 6.65 increased both pelleted casein and pelleted calcium phosphate. Opposite effects were obtained by adding citrate or EDTA. The change in pelleted calcium phosphate was not simply related to casein release from the micelle. Upon adding 5 mmol EDTA/kg milli, 20 % of the pelleted Ca, 22 % of the pelleted phosphate and 5 % of the micellar casein were removed. Increasing the concentration of EDTA to 10 mmol/kg milli decreased the pelleted Ca by 44 % and the pelleted phosphate by 46 %, and caused 30 % of the micellar casein to be released. The effects of adding phosphate, citrate or EDTA at pH 6.65, followed by the addition of CaCl2, demonstrated the reversibility of the dissolution and formation of the micellar calcium phosphate. There were limits to this reversibility that were related to the amount of colloidal calcium phosphate removed from the casein micelles, Adding CaCl2 to milk containing greater than or equal to 20 mmol EDTA or greater than or equal to 30 mmol citrate/kg milli did not. result in complete reformation of casein micelles. Light scattering experiments confirmed that the dissolution of moderate amounts of colloidal calcium phosphate had little effect.. on micellar size and were reversible, while the dissolution of larger amounts of colloidal calcium phosphate resulted in large reductions in micellar size and was ir reversible.