Trace Urea Determination in Red Wine and Its Degradation Rate by Acid Urease

Abstract

An improved trace urea determination method in red wine, having the sensitivity of 50 µg/L, was developed by the modification of the pre-treatment procedure in the HPLC-fluorometric method previously reported for trace urea determination in white wine. Using this method, it was confirmed that the rate constant of the degradation of naturally occurring urea of 1 mg/L by an acid urease in a red wine was nearly the same as that of spiked urea of 30 mg/L in the same wine. Acid urease inhibitors in wines, fluoride ion, L-malic acid, and gallic acid were demonstrated to show no effect to urea determination in both the trace urea determination method and the conventional enzymatic method, both using the neutral urease derived from jack bean for the conversion of urea to ammonia which reacts with NADH or o-phthalaldehyde.