Ruolo delle PR-proteins nell'instabilità dei vini bianchi.

The aim of this thesis is to present the recent advances in the study of protein haze in white wines. Protein haze causes economical loss because consumers don't accept turbid wines, hence many studies are focused on discover its mechanism, which still remains partly unsolved. The actual knowledge is that two main classes of proteins are involved: Chtinases and Thaumatin-Like Proteins (TLP), since they are present in the haze. Moreover it has been demonstrated that protein haze could develope in two different ways, depending on the wine pH. The first occurs at pH close to proteins' isoelectric point (higher values) and is an isoelctric precipitation, while the second at lower values and involves especially TLP. In this case the process takes place in three phases: protein denaturation promoted by a so-called x-factor (a low molecular mass substance), aggregation and finally precipitation. Many variables can influence protein haze, included temperature, ionic strenght, organic acids, ethanol content, metal ions and phenolic substances, but the highest influence is exerted by electric conductivity and protein concentration. Currently protein haze is prevented with the use of bentonite, a clay which removes proteins by binding them, but it has several drawbacks, for example loss of product, hazards for the workers and the environment and decrease in wine quality. Many alternatives to bentonite are examined, for example different adsorbents, physical removal of proteins, proteolytic enzymes combined with flash pastorization, but none of them reached a big spread, so more efforts are required.