Desenvolvimento de métodos eletroanalíticos de quantificação de taninos condensados em espécies vegetais

Abstract

The quality assessment of herbal medicines requires sensitive and selective analytical methodologies for the identification and quantification of bioactive phenolic compounds. Classical methods, such as Folin–Ciocalteu and sulfuric vanillin, although widely employed, present limitations regarding selectivity, as they react with different classes of phenolics, potentially leading to overestimation of the results. Moreover, these methods demand laborious sample preparation steps and dedicated laboratory infrastructure, which hinders rapid and in loco analyses. In this context, an electroanalytical method based on square-wave voltammetry (SWV) was developed and validated, employing a 3D-printed electrode composed of polylactic acid (PLA) and carbon black (CB), for the indirect quantification of catechin as a marker of condensed tannins in plant samples of Syzygium malaccense and in herbal medicines of Syzygium cumini. Samples, prepared at 5 mg mL⁻¹, were subjected to a clean-up procedure and analyzed electrochemically in 0.5 mol L⁻¹ H₂SO₄ containing 30% ethanol. The analytical curve for catechin showed excellent linearity (R² = 0.9995) and was applied to the quantification of ethanolic extracts of S. malaccense leaves and stems, as well as S. cumini tincture and capsule formulations. The contents of proanthocyanidins, expressed as mg catechin equivalent per g of sample, were: S. malaccense leaves (1.43 mg CE/g), branches (3.96 mg CE/g), S. cumini capsules (2.12 mg CE/g), and tincture (1.44 mg CE/g). Additionally, total phenolic content determined by the Folin–Ciocalteu method ranged from 128.2 ± 8.3 to 303.7 ± 9.1 mg GAE/g extract, while proanthocyanidin content ranged from 66.1 ± 7.6 to 156.4 ± 7.2 mg CE/g extract, with higher values observed in ethanolic extracts and tincture. The results demonstrate that the proposed methodology is effective even in the presence of complex plant and pharmaceutical matrices. The use of 3D-printed electrochemical sensors represents an innovative, low-cost alternative with potential for in loco application in the quality control of herbal medicines.