Adsorption kinetics of beta-lactoglobulin at the air/solution interface: impact of pre-heating and addition of isoamyl acetate

We compared the kinetics of adsorption at the air/solution interface of bet a-lactoglobulin alone or in mixture with isoamyl acetate at a concentration where it remains water-soluble. Addition of isoamyl acetate to beta-lactog lobulin, at molar ratios equal to 1 or 2, led to a decrease in the surface tension in the short-time region, but the steady-state value of surface ten sion was close to that of pre-heated solution of beta-lactoglobulin alone, only for molar ratio equal to 2. Pre-heating mixtures at this molar ratio i ncreased the adsorption kinetics more significantly in comparison with non- heated mixtures and pre-heated pure solutions of beta-lactoglobuline. In pa rallel, tryptophan spectrofluorimetric spectra obtained from non-heated or pie-heated solutions indicated in both cases that addition of isoamyl aceta te: to beta-lactoglobulin were accompanied by a quenching of fluorescence i ntensity, while a slight red-shift in wavelength of maximum fluorescence in tensity occured only for pre-heated mixtures. The results were discussed in terms of formation of beta-1g/IAA complexes with a specific activity at th e air/solution interface. (C) Inra/Elsevier, Paris.