Alpha-lactalbumin: A new carrier for vitamin D3 food enrichment

Vitamin D is a fat-soluble regulatory vitamin maintaining blood calcium and phosphorus concentrations within a narrow physiological range. Binding to an appropriate delivery system can enhance vitamin D-3 solubility, simplify its transport, protect it from degradation and increase its bioavailability. Alpha-lactalbumin as a milk protein is a good candidate for a vitamin encapsulation. Binding properties and conformational change of bovine apo alpha-lactalbumin upon interaction with vitamin D-3 were investigated by calorimetry, spectroscopy and by molecular docking. Tryptophan fluorescence quenching indicates that the protein conformation changes in the presence of vitamin D-3. However, according to far UV CD results, the secondary structure of the protein was altered in the presence of vitamin D-3. The molecular modeling showed that Van der Waals interactions, hydrogen bond and hydrophobic interactions play a major role in the binding of vitamin D-3 to the alpha-lactalbumin hydrophobic pocket. The particle size of alpha-lactalbumin and vitamin D-3 complex is much larger than the native protein. Surprisingly, in the presence of vitamin D-3, the thermal stability of the protein decreases. The binding constant and standard Gibbs free energy change (Delta G degrees) of binding vitamin D-3 to the protein obtained from ITC are 3.66 x 105 M-1 and -7.6 kcal mol(-1), respectively, what agrees with results obtained by measurement of fluorescence and by molecular docking. The formed complex is a suitable candidate in order to enrich the low-fat food and non-alcohol drinks. According to the results, alpha-lactalbumin can be introduced suitable carrier for vitamin D-3. (C) 2014 Elsevier Ltd. All rights reserved.