Binding of aroma compounds with legumin. I. Binding of hexyl acetate with 11S globulin depending on the protein molecular state in aqueous medium

We report on the role of the protein molecular state in binding and release of an aroma compound in an aqueous medium. For this purpose, the quantitative binding parameters (these are, a total number of binding sites in the protein molecule, the intrinsic binding constant and Gibbs free energy of binding) of hexyl acetate (HxAc) (the major component of a wide variety of flavours) to 11S globulin of Vicia faba (the main storage protein of broad beans) were determined in an aqueous medium by a combination of ultrafiltration and gas–liquid chromatography under different experimental conditions, namely, at pH 7.2 (the native state of 11S globulin) as well as after both the acidic (pH 3.0) and heat (30 min at 90 °C, pH 7.2) denaturation of the protein. The native legumin possessed the most binding affinity for HxAc through its unique quaternary structure. The acid denaturation of the protein led to the complete loss of the protein capacity to bind HxAc. On the heat denaturation, the protein retained its capacity to bind the aroma compound but had significantly different binding parameters and binding mechanism from those of the native protein. A complete reversibility relative to the changes in concentration of the aroma compound has been observed for binding of HxAc to the native 11S globulin as distinct from the heat denatured protein.