Complexes between linoleate and native or aggregated β-lactoglobulin: interaction parameters and in vitro cytotoxic effect

Abstract

The dairy protein β-lactoglobulin (βlg) is known to form a complex with fatty acids (FA). Due to industrial processing, βlg is often in its non-native form in food products, which can modify the FA/βlg complex properties. We investigated the interaction of bovine βlg, in selected structural forms (native βlg, a covalent dimer and as nanoparticles), with linoleate (C18:2). Using fluorescence and Isothermal Titration Calorimetry, linoleate was found to bind βlg at two different binding sites. Regardless of the structural state of βlg, association constants remained in the same order of magnitude. However, the stoichiometry increased up to 6-fold for nanoparticles, compared to that of native βlg. The impact of these structural changes on linoleate uptake in vitro was measured by cytotoxicity assays on Caco-2 cells. The order of cytotoxicity of linoleate was as follows: free>complexed to dimers>complexed to nanoparticles>complexed to native βlg. Therefore, the in vitro cytotoxicity of linoleate could be modulated by altering the state of βlg aggregation, which in turn affects its binding capacity to the FA.

Keywords: Aggregation; CLA; CMC; Cytotoxicity; DMEM; Dulbecco’s modified Eagle medium; FA; FAME; FBS; GC; GP-HPLC; ITC; Interaction; K(a); LA; LCFA; Linoleate; N-acetyl-tryptophanamide; NATA; PBS; association constant; conjugated linoleic acid; critical micelle concentration; fatty acid; fatty acid methyl ester; foetal bovine serum; gas chromatography; gel permeation high performance liquid chromatography; isothermal titration calorimetry; linoleic acid; long chain fatty acid; n; phosphate buffered saline; reaction stoichiometry; α-lactalbumin; αla; β-Lactoglobulin; β-lactoglobulin; βlg.