Application of differential pH technique to the determination of urea in Italian wines

Abstract

A method for the quantification of urea in wine, based on measuring the change in pH when urease is added to the sample, is presented and compared to the conventional dual enzyme (urease/glutamate dehydrogenase) approach. The method is linear in the range 0-30 mg·l^-1 in red, white and “raisin” wines, and the detection limit (0.3 mg·l^-1) is lower than for the usual enzymatic method. The differential pH technique presented here gives accurate quantification of urea in wine, being unaffected by the presence of ammonium. The amounts of urea in 195 still and sparkling commercially available wines with designation of geographic origin from the most renowned Italian grape growing areas were quantified. 17.4 % of samples were over the 3 mg·l^-1 level suggested by the International Organisation of Vine and Wine for urease treatment to limit the potential risk for ethyl carbamate formation during wine ageing. Yeast strains EC1118 and SP665 can minimise urea content in wine.