The study of binding between~-Iactoglobulin and benzaldehyde was realized using two complementary techniques: static headspace and HPLC techniques. Static headspace analysis shows global retention of benzaldehyde whereas HPLC shows the presence of strong interactions. The interactions were studied in different media (water, NaCI (50 mmol-L'"), NaCI (50 mmol-L -1) + ethanol 13 v %), with or without heat treatment. © InralElsevier, Paris.-Iactoglobulin / benzaldehyde / interaction / static headspace / HPLC Résumé -Étude des liaisons entre le benzaldéhyde et la~-Iactoglobuline par headspace statique et chromatographie liquide haute pression dans des conditions physico-chimiques différentes. L'étude des interactions entre la~-lactoglobuline et le benzaldéhyde est réalisée à l'aide de deux techniques complémentaires: la technique de headspace statique et la technique de CLHP. La première met en évidence une rétention globale de l'arôme tandis que la seconde montre la présence d'interactions fortes. Les interactions sont étudiées dans des milieux différents (eau, NaCI (50 mmolL:"), NaCI (50 mrnol-L:") + éthanol 13 v %), avec ou sans traitement thermique.© InralElsevier, Paris.-Iactoglobuline / benzaldéhyde / interaction / headspace statique / CL HP * Correspondence and reprints. andriot@arome.dijon.inra.frThese results are part of european COST Action 96 "Interactions of food matrix with small ligands" and of DGAL program "Physico-chemical interactions between proteins and aroma in aqueous or emulsified media" partly financed by the French Ministry of Agriculture and Fisheries.

Foaming properties of solutions of ␤-lactoglobulin alone or in a mixture with isoamyl acetate were investigated through a conductimetric method. It was observed that addition of isoamyl acetate to ␤-lactoglobulin at molar ratios, R ϭ 1 and 2 led to enhanced foaming properties in comparison with ␤-lactoglobulin alone. In regards to the observed changes in tryptophan fluorescence properties, it is suggested that ␤-lactoglobulin ϩ isoamyl acetate might form a complex with a specific surface activity.

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β-Lactoglobulin (β-lg), which is found in the milk of several mammal species, is the most abundant protein in bovine whey (McKenzie, 1971). The interaction properties of β-lg with a large variety of small hydrophobic ligands have been extensively studied (Sawyer et al. 1998). β-Lg belongs to the super-family of hydrophobic molecule transporters called the lipocalins, which characteristically bind hydrophobic ligands inside a central calyx (Godovac-Zimmermann, 1988; Perez et al. 1989; Brownlow et al. 1997; Wu et al. 1997; Qin et al. 1998).At present, whey protein concentrates containing a high percentage of β-lg are commercially available in a very large quantity, but most of the processes used in milk technology involve heat-treatments that are known to affect the initial conformational state of β-lg. Such conformational changes have consequences for both the physicochemical and functional properties in food systems, including a decrease in the availability of lysine, due to Maillard reactions (Léonil et al. 1997) and a decrease in the affinity constant for binding to retinol (Laligant et al. 1991) and to flavour compounds (O'Neil & Kinsella, 1988). In the field of protein-volatile compound interactions, we have recently reported a significant enhancement of foaming properties of β-lg solutions (50 mM-NaCl, pH 6) in the presence of aroma compounds such as isoamyl acetate (Marin & Relkin, 1999), benzaldehyde (BZA; Marin & Relkin, 2000) and vanillin (Relkin & Vermersh, 2000). The observed increase in foaming properties of β-lg was postulated to be due to formation of surface active complexes between β-lg and aroma compounds.In the present work we have investigated the interaction between a β-lg concentrate (prepared by ultra-diafiltration on an industrial scale) and BZA; particularly, evidence was sought for the presence of covalently bound monomers, dimers and lactolated monomers.

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