IAN R. McKINNON

MARY-ANN AUGUSTIN

PUNSANDANI UDABAGE

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 CaCl2 or mixtures of NaH2PO% and Na2HPO% to reconstituted skim 
milk (90 g milk 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 milk, 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 milk 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 [ges     ] 20 mmol EDTA or [ges     ] 30 mmol 
citrate/kg milk 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 irreversible.</jats:p

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

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