Modeling of urea degradation in white and rose wines by acid urease

The specific activity of a whole cell acid urease preparation was tested in five wines manufactured in the Apulia region of Italy in the 2003 vintage at both short and long treatment times, thus confirming the validity of the pseudo-first-order kinetic model to describe urea removal in real wines. The ratio between the experimental pseudo-first-order kinetic rate constant (k(Ie)) for any real wine tested and that (k(I)) referred to a model wine solution having the same composition and pH reduced from about 0.21 to 0.02 as the overall content of phenolic compounds (P) increased from 109 to 853 g m(-3) of gallic acid equivalent (GAE). The specific inhibitory effect of such compounds was explained by accounting for the equilibrium constant (K-P) of the reaction of polyphenols with acid urease, which was found to be about 21 g of GAE m(-3) for the real wines tested, whereas it ranged from about 16 to 45 g of GAE m(-3) when the model wine solution was enriched with tannins extracted from grape seeds or skins, respectively. A sequential experimental procedure consisting of accelerated acid urease tests at high doses of enzyme followed by accelerated ethyl carbamate tests on the resulting acid urease treated wine was recommended to assess preliminarily the technoeconomic feasibility of the acid urease hydrolytic process for the wine of concern.