White wine proteins: how does the pH affect their conformation at room temperature?
Résumé
Our studies focused on the determination of aggregation mechanisms of proteins occurring in wine at room temperature. Even if wine pH range is narrow (2.8 to 3.7), some proteins are affected by this parameter. At low pH, the formation of aggregates and the development of a haze due to proteins sometimes occur. The objective of this work was to determine if the pH impacted on the conformational stability of wine proteins. Different techniques were used: circular dichroism and fluorescence spectroscopy to investigate the modification of their secondary and tertiary structure, but also the SAXS to determine their global shape. Four pure proteins were used, two considered as stable (invertase and thaumatin-like proteins) and two as unstable (two chitinase isoforms). Two pHs were tested to emphasize their behavior (pH 2.5 and 4.0). The present work highlighted that the conformational stability of some wine proteins (chitinases) was impacted by partial modifications, related to the exposure of some hydrophobic sites. These modifications were enough to destabilize the native state of the protein. These modifications were not observed on wine proteins determined as stable (invertase and thaumatin-like proteins).