Urea degradation in model wine solutions by free or immobilized acid urease in a stirred bioreactor.

In this work, a purified acid urease preparation was covalently immobilized on Eupergit C 250 L and stabilized with glycine. Its average activity was found to be 69 +/- 16% of the initial one after 34-day storage at 4 degrees C . The kinetics of urea degradation in a model wine solution by immobilized enzyme was confirmed to be of pseudo-first-order with respect to the urea concentration in the liquid bulk, its apparent pseudo-first-order kinetic rate constant (k(Ii)) being about one-fourth of that (k(If)) pertaining to the free enzyme. In the operating conditions tested, the reaction kinetics was estimated as unaffected by the contribution of the external film and intraparticle diffusion mass transfer resistances. Because in the presence of the high-inhibitory tannins extracted from grape seeds in the range of 3-620 g of GAE m(-3) the loss in k(Ii) was quite smaller than that in k(If), the biocatalyst tested here is likely to overcome the present limits to the application of free acid urease in wine treatment.