Interactions of Vitamin D₃ with Bovine β-Lactoglobulin A and β-Casein

It is of nutritional significance to fortify processed dairy products (e.g., cheese, yogurt, and ice cream) with vitamin D₃; however, the inherent complexity of these foods may influence the stability and bioavailability of this nutrient. In the present study, the interactions of vitamin D₃ with β-lactoglobulin A and β-casein were investigated under various environmental conditions (i.e., pH and ionic strength) using fluorescence and circular dichroism spectroscopic techniques. The results indicated that vitamin D₃ was bound to both β-lactoglobulin A and β-casein depending on the solution conditions. The apparent dissociation constants ranged from 0.02 to 0.29 μM for β-lactoglobulin A, whereas the β-casein apparent dissociation constants ranged from 0.06 to 0.26 μM. The apparent mole ratios were also comparable, i.e., 0.51−2.04 and 1.16−2.05 mol of vitamin D₃ were bound per mole of β-lactoglobulin A and β-casein, respectively. It was concluded that these interactions may strongly influence vitamin D₃ stability and, hence, bioavailability in processed dairy products.

Keywords: Vitamin D₃ binding; β-lactoglobulin A; β-casein