Structural and chemical modifications of β-lactoglobulin induced by aldehydes (abstract only)

Abstract

Aldehydes are odour-active compounds issued from reactions such as lipid oxidation. They react with other food constituents such as proteins, that decreases their availability as aroma compounds, but also induces alterations of the proteins. This study was aimed to evidence the structural and chemical modifications of β-lactoglobulin in the presence of aldehydes varying in their unsaturation. β-Lactoglobulin solutions (1 g/l; 20mM phosphate buffer, pH 6.8; 80mM NaCl) were stored at 40°C in the presence of hexanal, 2-hexenal or 2,4-hexadienal (aldehyde/protein molar ration = 25) for 3 days. Whatever the aldehyde, formation of more hydrophobic, modified protein was evidenced by reverse phase HPLC. The fixation of the aldehydes by the protein was evaluated by headspace-gas chromatography. UV-Vis, circular dichroism and fluorescence spectra evidenced, only in the presence of the unsaturated aldehydes, changes in the protein structure, in the environment of its tryptophanyl residues and formation of new fluorescent compounds. Covalent protein dimmers, not due to disulfure bonds, were also produced. Analysis of amino acid composition and mass spectrometry of tryptic hydrolysate of the reaction mixtures gave information on the nature of the chemical modifications.