Aroma Compounds—Proteins Interaction Using Headspace Techniques

Abstract

Interactions between volatile compounds and proteins in aqueous solution, were studied using static and dynamic headspace techniques. The decrease of aroma compounds concentration in the headspace determined in static mode indicates a retention by 0-lactoglobulin, 2.4% (w/w), pH 3.4, 25 °C, varying from 8 to 60% for most of the compounds tested. However 2-hexanone and isoamyl acetate are not significantly retained by the protein and a salting-out effect is noticed for limonene. On the basis of these preliminary results the intensity of interactions of methyl ketones (C7 to C9), ethyl esters (C6 to C9), limonene and myrcene and ß-lactoglobulin for different pH values (2.0 to 11.0) were estimated by the determination of the infinite dilution activity coefficients (yi) by exponential dilution. For a constant pH value, the relative activity coefficient in the presence of 0-lactoglobulin (yr) of methyl ketones decreases significantly with the hydrophobicity of the volatiles whereas the relative activity coefficient value reaches a minimum for ethyl octanoate in the ester series. For limonene and myrcene an increase of yr is generally noticed whereas a decrease occurs in the presence of sodium casemate and bovine serum albumin. The variations of relative activity coefficient according to the pH of the medium can be related to structural modifications of the ß-lactoglobulin.