Effect of Heat-Treat Methods on the Soluble Calcium Levels in the Commercial Milk Products

Milk is well known to be rich in some nutrients such as protein, calcium, phosphorus, and vitamins. In particular, absorption and bioavailability of calcium receive lots of attention because calcium is very little absorbed until it is changed to the ionized form in the intestine. In this study, concentration of the soluble calcium was determined in the commercial bovine milk products, which were processed by different heat-treatment methods for pasteurization. As for general constituents, lactose, fat, protein, and mineral were almost same in the liquid milk products by different processors. Ultrafiltration of the skimmed milk caused little change in the permeate as for lactose content but both fat and protein decreased. pH values ranges from 6.57-6.62 at room temperature and slightly increase after centrifugation, 10,000 g, 10 min. Rennet-coagulation activity was the lowest in the ultra high temperature (UHT-)milk compared to the low temperature long time (LTLT-) and high temperature short time (HTST-)milk products. Each bovine milk products contains 1056.5-1111.3 mg/kg of Ca. The content of sulfhydryl group was the lowest in raw milk compared to the commercial products tested. For the skimmed milks after ultrafiltration with a membrane (Mw cut-off, 3 Kd), soluble Ca in the raw milk was highest at 450.2 mg/kg, followed by LTLT-milk 336.4-345.1 mg/kg, HTST-milk 305.5-313.3 mg/kg, UHT-milk 370.3-380.2 mg/kg in the decreasing order. After secondary ultrafiltration with a membrane (Mw cut-off, 1 kD), total calcium in raw milk had a highest of 444.2 mg/kg, and those in the market milk products. As follow: UHT-milk, 371.3 to 378.2 mg/kg; LTLT-milk, 333.3 to 342.2 mg/kg; HTST-milk 301.9 to 311.2 mg/kg in a decreasing order.