Complexes between fatty acids and native or aggregated β-lactoglobulin: binding properties and biological function
Résumé
Food structure can have a profound influence on delivering health benefits. Bioaccessibility of nutrients can be affected by their interaction with food components. The dairy protein β-lactoglobulin (βlg) is known to bind hydrophobic ligands such as fatty acids (FA). However, this protein is highly sensitive to the process conditions used in the dairy industry. Therefore βlg is often present in non-native or aggregated forms in processed food. This structural change may modify the protein affinity for FA and the biological properties of the FA/protein complexes. In this study we investigated the interaction of bovine βlg isolated under different structural forms (native, covalent dimer and nanoparticles) with linoleate (C18:2, cis,cis-9,12-octadecadienoic acid) and conjugated linoleic acids (CLA, C18:2), and the impact of those complexes on their biological activity in vitro. Two different sets of binding sites were determined for the interaction between linoleate and βlg, regardless of its state of aggregation, using intrinsic fluorescence spectroscopy and isothermal titration calorimetry. By increasing the level of βlg aggregation (from oligomers to nanoparticles), the linoleate/βlg stoichiometry increased but the association constants remained similar for both sets of binding sites. Native βlg was more sensitive to gastric in vitro digestion in the presence of linoleate than in the absence of linoleate, due to the increased level of denaturation/aggregation of βlg. Uptake of linoleate in Caco-2 cells was decreased in presence of the native βlg as observed by confocal microscopy and a monolayer that mimics the intestinal barrier. In contrast, the cell uptake of CLA, which is less water soluble than linoleate, is higher when complexed by βlg than in its free form. Therefore, it is proposed that βlg can act as a molecular carrier and alter the bioaccessibility of FA depending on their solubility.