Tyrosinase immobilized reactor as a fast tool for polyphenolic index of tea

A new approach for the determination of polyphenolic index of black and green teas has been developed employing a bioreactor with mushroom tyrosinase immobilized on aminopropyl-controlled pore glass (AMP-CPG). Initially a linear correlation (r2 = 0.997) of catechin content between the Folin-Ciocalteu (FC) and the enzymatic assays is obtained. Our method appears to be more specific and rapid. Successively the inhibition of the enzymatic oxidation of catechin by some tea components like gallic acid (GA), epigallocatechin (EGC), epigallocatechingallate (EGCG) and epicatechin (EC) is investigated. Finally when tea samples are analyzed by using the new method it appears that green tea is the strongest inhibitor followed by black tea and flavored tea. The level of polyphenols, which is correlated to the extent of inhibition, is reported as epigallocatechin equivalents and the results are compared with those obtained using the FC assay and the vanillin index. The differences in phenol content found by applying the three methods are discussed in terms of the different specificities of the analytical basis. © 2009 Elsevier Inc. All rights reserved.