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Calcium Ion Concentration in Milk

Division of Applied Biology, National Research Laboratories, Ottawa, Canada

ABSTRACT

The murexide method of Smeets (15), modified to give increased sensitivity and coupled with a pressure ultrafiltration technique that provides sufficient sample in approximately 1 hr., is a simple, convenient method for the determination of calcium ion in milk on a semiroutine basis. With suitable adjustment of the ionic strength and sodium content of the reference solutions, the method is applicable also to concentrated milk products.

Skimmilk was found to contain from 2.5 to 3.4 mM/liter Ca++. Addition of calcium to milk precipitated both phosphate and citrate but increased [Ca++]; addition of phosphate precipitated calcium and decreased [Ca++], and addition of citrate dissolved colloidal phosphate but decreased [Ca++]. The apparent solubility products of di- and tri-calcium phosphate in milk appear to be approximately 1.5 x 10^–5 and 1 x 10^–24, respectively.

Heating skimmilk caused precipitation of calcium phosphate and lowered [Ca++]. Concentration of milk also caused precipitation of calcium phosphate, but [Ca++] increased.

This article has been cited by other articles:

				R. R. Gangidi and L. E. Metzger Ionic calcium determination in skim milk with molecular probes and front-face fluorescence spectroscopy: simple linear regression. J Dairy Sci, November 1, 2006; 89(11): 4105 - 4113. [Abstract] [Full Text] [PDF]