The effect of pH on calcium and phosphorus distribution between micellar and serum phase after enrichment of skim milk with calcium d-lactobionate

Abstract

Speciation is important for good bioavailability of calcium from food and beverages. Effective calcium enrichment of dairy products for prevention of osteoporosis accordingly depends on the calcium compound added. Calcium d-lactobionate (50, 30 or 3 mM) was added to reconstituted skim milk with pH adjusted to 6.6, 6.0, 5.7 and 5.4 at 25 °C in order to investigate the distribution of calcium and phosphorus between micellar and serum phase and the speciation of calcium in the serum phase for enriched milk. The calcium from added calcium d-lactobionate was found to distribute between the micellar and serum phase at pH 6.6–6.0, while at pH 5.7–5.4, the added calcium remained in the serum phase. The concentration of phosphorus after enrichment was increased in the micellar phase and decreased in the serum phase at pH 6.6–6.0, while at pH 5.7–5.4, phosphorus remained constant in both phases. A decrease of total protein content and caseins in milk serum phase was observed after milk enrichment at all pH values as documented by protein determination and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Moreover, concentration of α-lactalbumin remained unchanged, while concentration of β-lactoglobulin decreased after addition of calcium d-lactobionate at all investigated pH values. Bioavailability of calcium from enriched dairy products depends on transfer to the micelles, and pH control is accordingly concluded to be critical for the use of calcium d-lactobionate for enrichment. The pH value needs to be taken into account when new calcium-enriched dairy products are designed to fulfil the primary role of having a product with high nutritional value and good calcium bioavailability.