Procedimento di valutazione dell’instabilità delle proteine contenute in una bevanda a pH acido (2004). Brevetto Italiano UD2004A000162, depositato il 3 Agosto 2004, Università degli Studi di Udine.PCT New analytical approach to unstable protein evaluation in musts and wines International patent pending agosto 2005

The risk of protein instability is present in wines and must be correctly estimated in order to intervene appropriately to prevent the problem, in respect of the overall quality of the wine. In consideration of the risk of instability of wine proteins, various methods have been proposed and utilised to foresee the phenomenon. Nevertheless, evaluations with methods currently in use provide contradictory results and make it difficult to interpret the final data. Considering the disparate responses to current methods and their intrinsic problems, a new test was realised that takes advantage of the electropositivity of proteins at wine pH, proteins being practically the only substances with a positive electric charge. The method realises the electro neutralisation of the proteins, which become insoluble when they reach the isoelectric point, determining a measurable degree of turbidity. The reactant used is a stabilised, titled mixture of anionic organic polyelectrolytes, which can be standardised. Addition of the reactant produces rapid neutralisation of only the proteins, without interacting with the other components of the wine, such as tannins and polysaccharides, whether they are in solution or colloidal form. Additionally, the sample must not be filtered, because the difference in turbidity between the original sample and the sample after addition of the reactant is evaluated. The response of the proteins on the model solution is perfectly linear, even if the intensity of the reaction may vary from protein to protein; this aspect does not influence the result, inasmuch as it is precisely what we are effectively interested in: namely, to evaluate potential instability, which may therefore be different according to the type of protein. On the basis of the results obtained with the proteins analysed, an analytical sensitiveness of about 10 mg/L was obtained, which is a more than acceptable value to meet oenological requirements. From the experiments conducted a wine may be considered potentially unstable when it shows a test value of even just a few turbidity units (NTU). The rapidity and simplicity of execution (1 min) of the test make it applicable even directly in the wine cellar, which may enable oenologists to perform on-line controls on protein stabilisation, without having to send samples to the laboratory; the information is therefore immediately usable and manageable in the wine cellar. The analytical approach through electro neutralisation of the positive charge of proteins in wine is a more specific method with respect to some systems in use, and thus allows exclusive evaluation of potential protein instability, without overestimating the problem and running the risk of performing stabilising treatments that do not respect the quality of the wine.