ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

NADES design, characterization and optimization for selective extraction of polyphenols from Stachys species

Marinela Cvetanoska, Marina Stefova, Jane Bogdanov, Vladimir Ivanovski, and Jasmina Petreska Stanoeva

Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University in Skopje, Skopje, Macedonia

E-mail: jasmina.petreska@pmf.ukim.mk

Received: 24 July 2025  Accepted: 17 November 2025

Abstract:

Sustainable and green extraction methods are vital for isolating bioactive phytochemicals from pharmacologically significant plants, including Stachys species. This study investigated the application of natural deep eutectic solvents (NADES) for green extraction of polyphenols from Stachys iva Griseb., focusing on phenolic acids, phenylethanoids, and 5,7- and 5,7,8-hydroxyflavones. Fourteen NADES were synthesized and characterized by density, pH, conductivity, surface tension, refractive index, viscosity, and. FT-IR spectroscopy. Extraction efficiency was strongly influenced by pH, viscosity, and polarity of the solvents, with optimal results obtained at low pH (~ 2) and viscosity (< 50 mPa s), and intermediate surface tension (50–60 mN/m). A Box–Behnken design was used to optimize extraction parameters: time, temperature, water content, and solvent volume. Organic acid-based NADES, such as choline chloride–acetic (ChA), lactic (ChL), and citric acid (ChC), showed low pH (1.13–3.32), enhancing extraction efficiency, especially for phenolic acids and phenylethanoids. ChA achieved the highest yields: phenolic acids (10.63 mg/g), phenylethanoids (71.43 mg/g), and 5,7-hydroxyflavones (4.78 mg/g). ChC was most effective for 5,7,8-hydroxyflavones, including isoscutellarein (14.19 mg/g) and hypolaetin (4.81 mg/g). Sugar-based NADES showed low efficiency due to high viscosity and surface tension, while moderately viscous NADES achieved superior results. The optimal extraction conditions were 40 min, 40% water, 15 mL solvent volume, and 50 °C. NADES demonstrated high efficiency and selectivity for polyphenol extraction from Stachys iva, performing comparably or better than 70% methanol. These results support NADES as sustainable alternatives for use in phytotherapy and green analytical chemistry.

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Keywords: Natural deep eutectic solvents; Polyphenols; Selective extraction; Stachys

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04526-2

Chemical Papers 80 (3) 2479–2493 (2026)