Isabelle Andriot

Interactions between β-Lactoglobulin and Aroma Compounds : Different Binding Behaviors as a Function of Ligand Structure

Interactions between beta-lactoglobulin (BLG) in its monomeric form and a wide range of aroma compounds were investigated by Fourier transform infrared (FT-IR) and 2D nuclear magnetic resonance (NMR) spectroscopies. A screening of the ligands was carried out by FT-IR through the amide I region changes of BLG upon binding. The location of two binding sites was determined by 2D NMR from the study of 10 selected ligands with different structures. All of the data suggest at least two binding behaviors as a function of the chemical class, the hydrophobicity, or the structure of the ligands. The binding of the elongated aroma compounds, such as 2-nonanone or ethyl pentanoate, within the central cavity involves residues located at the entrance of the calyx and Trp19. The binding onto the protein surface of aroma compounds that have or adopt a compact structure occurs in a site located between strand beta-G, alpha helix, and strand beta-I.

Retention effect of human saliva on aroma release and respective contribution of salivary mucin and α-amylase

As great differences were observed in the amount of α-amylase in human saliva, there is a need to better understand the effect of this protein alone or in mixture with mucin on aroma compound partitioning. We report the respective role of mucin and α-amylase on the air/liquid partition coefficients of two series of 5 methyl-ketones and 5 ethyl-esters. We confirm that mucin affects the release of aroma compounds and, for the first time, we demonstrate the ability of α-amylase to decrease the release of aroma compounds. For both proteins, we report the involvement of hydrophobic effects. Interestingly, no cumulative effect was observed when both proteins were mixed together in solution. We hypothesize that protein-protein interactions occur between the two proteins and decrease the total number of available binding sites for aroma compounds. The effect of human saliva is also investigated and compared to that of artificial salivas. In the presence of human saliva the release of ketones is lower than in water and slightly higher than in the presence of artificial saliva composed of α-amylase and/or mucin. Esters are more affected by the presence of human saliva than ketones. This observation is due to the presence of an esterase activity in saliva, which activity increases with the hydrophobicity of esters. The difference observed in aroma release between artificial and human salivas could be explained by the presence of other salivary proteins in human saliva.

Protein-flavour interactions

* Introduction * Protein structure in relation to flavour binding * Nature and strength of the interactions * Effect of medium on protein-flavour interactions * Perspective consequences in food systems: some examples * Conclusion and future trends * Sources of further information * References