Characterisation of the β-lactoglobulin/α-tocopherol complex and its impact on α-tocopherol stability

beta-Lactoglobulin (beta-LG), the major whey protein in the milk of ruminants, has a high affinity for small hydrophobic molecules. In the present study, its interaction with lipophilic alpha-tocopherol, the most abundant and biologically active form of vitamin E, was investigated using circular dichroism, fluorescence, high performance liquid chromatography and turbidity analysis. The interaction did not disrupt the secondary or tertiary structures of beta-LG. It was dependent on the aggregation of alpha-tocopherol and on beta-LG/alpha-tocopherol ratios, with one binding site appearing to be the protein internal cavity and the other in the hydrophobic surface pocket at protein concentrations 1/10 that of the vitamin. Formation of complexes with beta-LG increased the solubility of alpha-tocopherol. The protein also protected alpha-tocopherol somewhat against decomposition, which depended on the protein concentration and was most effective at a beta-LG concentration of one-tenth the alpha-tocopherol concentration. Protein-nutrient complexes might therefore be useful in the development of functional foods. (C) 2010 Elsevier Ltd. All rights reserved.