Effects of ionic strength and sulfate upon thermal aggregation of grape chitinases and thaumatin-like proteins in a model system
Marangon, M.; Sauvage, F. X.; Waters, E. J.; Vernhet, A. ; Journal of Agricultural and Food Chemistry 2011; 59 (6) 2652–2662
Consumers expect white wines to be clear. During the storage of wines, grape proteins can aggregate to form haze. These proteins, particularly chitinases and thaumatin-like proteins (TL-proteins), need to be removed, and this is done through adsorption by bentonite, an effective but inefficient wine-processing step.
Alternative processes are sought, but, for them to be successful, an in-depth understanding of the causes of protein hazing is required. In this study, the roles played by ionic strength (I) and sulfate in the aggregation of TL-proteins and chitinases upon heating were investigated.
Purified proteins were dissolved in model wine and analysed by dynamic light scattering. The effect of I on protein aggregation was investigated within the range 2–500mM/l.
For chitinases, aggregation occurred during heating with I values of 100 and 500mM/l, depending on the isoform. This aggregation immediately led to the formation of large particles (3 µm, visible haze after cooling).
TL-protein aggregation was observed only with I of 500mM/l; it mainly developed during cooling and led to the formation of finite aggregates (400 nm) that remained invisible.
With sulfate in the medium, chitinases formed visible haze immediately when heat was applied, whereas TL-proteins aggregated during cooling but not into particles large enough to be visible to the naked eye.
Data show that the aggregation mechanisms of TL-proteins and chitinases are different and are influenced by the I and ionic content of the model wine. Under the conditions used in this study, chitinases were more prone to precipitate and form haze than TL-proteins.
(We recommend that you consult the full text of this article)
Published on 01/15/2013