Ionic Calcium in Milk and Whey

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Abstract
A calcium-sensitive electrode was used to measure the Ca++ in raw and processed milk. The standard deviation of measurement was [plus or minus]0.24 mmole per liter, and the coefficient of variation was 13%. The Ca++ of milk was in the range of 1.4 to 2.5 mmoles per liter and decreased as the milk was processed. After 24-hr, storage at 4C, the Ca++ returned to about the same concentration as before processing. Addition of nonfat dry milk solids to skimmilk in sufficient amount to increase the solids-not-fat to 9.8%, increased the Ca++ to 4.2 mmoles per liter. Rennet whey and milk had the same Ca++. Treatment of milk with anion exchange resin in the chloride form increased Ca++, presumably because of the removal of phosphates. The resin-treated milk reacted with rennet more rapidly than the untreated. Dilution of milk with water caused a logarithmic decrease in Ca++, with a correlation coefficient of -0.9.