Analytical Sciences

Abstract − Analytical Sciences, 37(2), 377 (2021).

Electrochemical Analysis of Coffee Extractions at Different Roasting Levels Using a Carbon Nanotube Electrode
Ryotaro WADA,* Shota TAKAHASHI,* Hitoshi MUGURUMA,* and Naomi OSAKABE**
*Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto, Tokyo 135-8548, Japan
**Department of Bioscience and Engineering, College of Systems Engineering and Science, Shibaura Institute of Technology, 307 Fukasaku, Minuma, Saitama 337-8570, Japan
This study reports on the electrochemical analysis of coffee extractions at different roasting levels by using a carbon nanotube (CNT) electrode. The roasting levels, ranging from 1 (low) to 6 (high), were determined according to the roasting time after fixing the roasting temperature. Level 1 roasting resulted in light roasted beans and level 6 in dark roasted ones. Based on the roasting level, the concentration of chlorogenic acids, including 3-caffeoylquinic (3CQ), 4-caffeoylquinic (4CQ), and 5-caffeoylquinic (5CQ) acid, can be determined. Cyclic voltammetry (CV) experiments revealed that the reduction current at +0.27 V was proportional to the concentration of chlorogenic acids. High-performance liquid chromatography (HPLC) revealed an inverse correlation between the roasting level and chlorogenic acid amount. The total amounts of chlorogenic acids in coffee extractions determined by HPLC were in agreement with those obtained by CV using the CNT electrode at roasting levels 1 – 5. At level 6, the amount of chlorogenic acids determined by the current peak was larger than that detected by HPLC. As a result, the chlorogenic acid amount was overestimated in the CV experiment at +0.27 V, indicating that electrochemically active materials were generated at level 6. The CV profile showed that the reduction peak at +0.10 V increased with an increase in roasting level. Thus, the peak intensity at +0.10 V can be used to evaluate the roasting level even if the concentration or dilution conditions are provided.