DETERMINATION OF L-ASCORBIC-ACID IN GREEN TEA WITH AN ENZYME REACTOR ELECTRODE SYSTEM

A continuous system for the determination of ascorbic acid with an enz yme reactor electrode was developed and applied to the measurement of ascorbic acid in green tea produced by a microwave heating (2 450 MHz) and a conventional method. The system consisted of an enzyme reactor, an oxygen electrode, an A/D converter, a microcomputer and a peristal tic pump. The reactor (phi 2 x 50 mm) was packed with ascorbate oxidas e immobilized on chitosan porous beads. One assay could be completed w ithin 3 min. The limit of detection was 1 mg/100 ml, the relative erro r was within 2% (n =40) and the response was linear up to 1 000 mg/100 ml. The immobilized enzyme was sufficiently stable for at least 3 mon ths at room temperature. The results for tea extracts correlated satis factorily well with those obtained by the enzyme method (F-kit) and 2, 6-dichlorophenolindophenol method. These results suggest that the sys tem proposed is a simple, rapid and economical method for the determin ation of ascorbic acid in foods. Furthermore, it was proved a larger a mount of ascorbic remained in the green tea produced by microwave heat ing compared with that produced by a conventional method.