Estimation of Tea Polyphenols by Differential Pulse Voltammetry with Electrodes Modified by Tyrosinase Extracted from Crude Sources

Abstract

Tea contains various polyphenols exhibiting antioxidant activities. To measure total polyphenol content quantitatively, we purified tyrosinase extracted from crude source such as potato, banana and modified platinum working electrode with this enzyme. Recovery of tyrosinase from potato and banana was achieved by extraction of crude enzyme with phosphate buffer solution (PBS) at pH = 7.4 followed by ammonium sulfate precipitation (20–60%), dialysis against 10 mM PBS at pH = 7.4 and ion exchange chromatography in DEAE-cellulose -52 colunm. The activity of the enzyme was assayed at an optimum pH of 6.8 and a Km of 3.46–11.68 mM was obtained. Differential pulse voltammetry (DPV) was then performed on the enzyme-modified electrode to exploit the oxidation of polyphenols by tyrosinase. Various grades of tea were tested for total polyphenols (TP) and the results were compared with those obtained using commercial enzyme and by HPLC. A very good correlation index is 0.98 was obtained between the TP content by HPLC and that determined by DPV with purified tyrosinase from potato. The methods exhibited very low limits of detection (0.579–0.635 mg/l). The results ensured that DPV could be a useful technique for determination of TP in tea for its quality evaluation.