Calcium Ion Concentration in Milk, Whey, and β-Lactoglobulin as Influenced by Ionic Strength, Added Calcium, Rennet Concentration, and Heat

Employing a calcium-sensitive electrode to estimate the calcium activity, additions of up to 2.5 mmoles of CaCle/liter of milk resulted in a linear response curve with about one-third of the added calcium remaining in the ionic state. The addition of rennet to milk resulted in a decrease in calcium ion concentration until coagulation occurred, at which time the calcium ion concentration in the curd-whey mixture gradually rose. fl-Lactoglobulin heated at 65 or 75 C for 30 rain did not bind more calcium than an unheated specimen. The 75 C treatment caused an increase in optical density which was greater at higher levels of added calcium. Samples heated at 65 C showed no such increase in optical density.