抄録
Determination of urea in rice wines was performed by using a spectrophotometric flow-injection analysis (FIA) system introducing an acid urease column as a recognition element. An acid urease, having specific properties of showing catalytic activity in low pH range and tolerance to ethanol in comparison to those of a urease from jack-beans, was covalently immobilized onto porous glass beads and then, packed into a small polymer column. This flow-type of the biosensing system was assembled with a sample injection valve, the immobilized enzyme column, a gas-diffusion unit, and a flow-through quartz cell attached to a UV/VIS detector. Standard urea solutions were measured through monitoring variations in absorbance resulting from pH shift due to ammonia molecules enzymatically generated. A wide, linear relationship was obtained between the concentration of urea (7.8 µM - 1.0 mM) and the change in absorbance. Followed by several investigations for application of this FIA system for measurement of urea in commercially available rice wines, the real samples were injected into the FIA system and urea in the samples were determined. These results were compared with those obtained with use of an F-kit method which was widely used for determination of urea. Comparative studies exhibited that this FIA system might be a powerful tool for urea determination in alcoholic beverages.
