Electrochemical quantification of condensed tannins in extracts and herbal medicines using 3D-printed electrodes

Abstract

Many herbal medicines contain bioactive polyphenolic compounds, such as flavonoids, tannins, phenolic acids, and lignans. Assessing the quality of these medicines requires sensitive and selective analytical methods for this class of compounds. However, traditional colorimetric assays like Folin–Ciocalteu and vanillin sulfuric lack specificity since they respond to several classes of phenolics, which may lead to overestimated results. Furthermore, these assays demand extensive sample preparation and specialized infrastructure, limiting their application in rapid or on-site analyses. In this study, an electroanalytical method based on square-wave voltammetry (SWV) was developed and validated using a 3D-printed polylactic acid/carbon black (PLA/CB) electrode. Catechin was employed as an electrochemical probe for the indirect quantification of condensed tannins, expressed as catechin equivalents (CE), in extracts of Syzygium malaccense and in herbal medicines of Syzygium cumini. The calibration curve for catechin showed excellent linearity (R² = 0.9995) and was successfully applied to extracts of S. malaccense leaves and stems, as well as to S. cumini tincture and capsule formulations. The condensed tannin contents were 0.134 ± 0.003 mg CE g⁻¹ for S. malaccense leaves, 0.071 ± 0.047 mg CE g⁻¹ for branches, 0.030 ± 0.001 mg CE g⁻¹ for S. cumini capsules, and 0.005 ± 0.001 mg CE g⁻¹ for S. cumini tincture. Using traditional colorimetric techniques such as Folin–Ciocalteu and vanillin sulfuric acid, a similar trend in results was observed. These findings demonstrate the applicability of the electroanalytical method in complex matrices and highlight the potential of 3D-printed electrodes as a low-cost and portable alternative for quality control of herbal medicines.