Quantitative determination of micellar calcium in milk and cheese using acid-base titration.

The distribution of calcium between the micellar and soluble phases in milk is altered during processing, which influences the characteristics of dairy products. A simple approach was used to quantitatively determine micellar calcium in milk and cheese from acid-base titration. The differential between titration and back titration curves at pH 5.5 was correlated with milk micellar calcium and a standard curve was obtained. The method was used to measure the effect of milk thermal history and protein fortification on milk micellar calcium concentration. Commercial cheeses were also analyzed for micellar calcium content. Milk storage at 4°C was responsible for low micellar calcium concentration (25.4 mg/g casein), but maturation at 34°C for 1 h increased micellar calcium concentration to 28.2 mg/g casein. Heat treatment further increased micellar calcium in milk, reaching 32.1 mg/g casein after 10 min at 90°C. Milk fortification up to 3.4% protein with milk protein concentrate had no effect on the concentration of calcium bound to casein, but the use of calcium and sodium caseinate significantly reduced micellar calcium concentration. Ten varieties of commercial cheeses were analyzed and the micellar calcium content ranged from 1.7 mg/g protein for Feta to 24.0 mg/g protein for Gouda.