Interactions between methyl ketones and beta-lactoglobulin: Sensory analysis, headspace analysis, and mathematical modeling

Interaction of flavor compounds with proteins is known to have an influence on the release of flavor from food. Hydrophobic interactions were found be tween beta-lactoglobulin and methyl ketones; the affinity constant increase s by increasing the hydrophobic chain. Addition of beta-lactoglobulin (0.5 and 1%) to aroma solutions (12.5, 50, and 100 mu L L-1) of three methyl ket ones induces a significant decrease in odor intensity. The chosen methyl ke tones were 2-heptanone (K-b = 330), 2-octanone (K-b = 950), and 2-nonanone (K-b = 2440). The release of these flavor compounds (50 mu L L-1) was studi ed by static headspace in water solution (50 mM NaCl, pH 3) with different concentrations of beta-lactoglobulin (0, 0.5, 1, 2, 3, and 4%). Increasing the concentration of protein increases the retention of volatiles, and this effect is greatest for 2-nonanone, the compound with the highest affinity constant, and lowest for 2-heptanone. A mathematical model previously devel oped to describe flavor release from aqueous solutions containing flavor-bi nding polymers (Harrison, M.; Hills, B.P. J. Agric. Food Chem. 1997, 45, 18 83-1890) was used to interpret the data. The model assumes that the polymer -flavor interaction is reversible and the rate-limiting step for release is the transfer of volatiles across the macroscopic gas-liquid interface. Thi s model was used to predict the equilibrium partitioning properties and the rate of release of the three methyl ketones. Increasing the affinity const ant leads to decreased release rates and a lower final headspace aroma conc entration.