Polyphenol Analysis in Black Tea with a Carbon Nanotube Electrode

• Published in: Analytical Sciences Vol. 35; no. 5; pp. 529 - 534
• Main Authors: MURAKAMI, Satoshi, TAKAHASHI, Shota, MUGURUMA, Hitoshi, OSAKABE, Naomi, INOUE, Hitoshi, OHSAWA, Tatsuya
• Format: Journal Article
• Language: English
• Published: Singapore The Japan Society for Analytical Chemistry 10-05-2019; Springer Nature Singapore; Japan Science and Technology Agency
• Subjects: Analytical Chemistry; Black tea; Carbon nanotube; Carbon nanotubes; Catechin; Catechol; Chemistry; cyclic voltammetry; Electrochemical analysis; Electrochemistry; Electrodes; Epigallocatechin gallate; High performance liquid chromatography; Liquid chromatography; Oxidation; Polyphenols; Pyrogallol; redox reaction; Tea; theaflavin; Theaflavins; Carbon nanotube; cyclic voltammetry; epigallocatechin gallate; theaflavin; redox reaction
• ISSN: 0910-6340; 1348-2246
• DOI: 10.2116/analsci.18P516

An electrochemical analysis of polyphenols (theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3′-gallate (TF2B), theaflavin-3,3′-digallate (TF3), and epigallocatechingallate (EGCG)) in a black tea infusion is demonstrated. The characterization of each polyphenol in a solution containing only a single type of polyphenol for a redox reaction at the CNT electrode with cyclic voltammetry (CV) was conducted. The oxidation peak at around +0.30 V for TF1 is assigned to catechol group in a benzotropolone ring. The oxidation peak at around +0.35 V for TF2A, TF2B, and TF3 is assigned to both of the catechol groups in the benzotropolone ring and the pyrogallol group in the gallate ring. The oxidation peak at around +0.35 V for EGCG is assigned to a pyrogallol group in the gallate ring. Current changes of those individual polyphenols at the peak potential are proportional to their concentrations (linear range 0.28 – 94 μM; detection limit 0.11 μM). The CV curve for real black tea, which is mainly composed of a mixture of the mentioned five compounds, is produced by the sum of those. The current change of the mixture solution of polyphenols is also proportional to the mass concentration of the total polyphenols and the sensitivity defined as the slope of current vs. concentration plot is independent of the ratio of the individual polyphenols. This indicates that the peak current at around +0.35 V can quantify the total amount of polyphenols in a black tea. Additionally, the shape of the CV curve can roughly estimate the ratio of [catechins]/[theaflavins]. The values for real samples determined from CVs show good agreement with that obtained by high-performance liquid chromatography.