Bioactive Compounds of Green Phenolic Extracts Obtained via Microwave-Assisted Extraction of <i>Sideritis</i> Species Grown in Greece

Abstract

The purpose of the present study was to compare the polyphenolic compounds extracted from five Sideritis species grown in Greece; S. scardica, S. clandestina, S. raeseri, S. euboea, and S. syriaca, using the Microwave-Assisted Extraction (MAE) process. To maximize the extraction yield (EY), total phenolic compounds (TPC), hypolaetin (HYP) and isoscutellarein (ISC), derivative contents (target phenolics), the response surface methodology was used for S. scardica. A Box–Behnken design was undertaken to study the effect of ethanol concentration (30–100%), extraction temperature (40–100 °C), and extraction time (5–25 min) on the responses. The optimal MAE parameters were 87.9% (v/v) ethanol, 25 min, and 100 °C. Under these conditions, there was a good agreement between experimental and predicted values, indicating the reliability of the predictions for Sideritis extracts. Phenolic compounds were then extracted under these conditions, from the five Sideritis species under investigation. The TPC, total flavonoid content (TFC), antioxidant activity based on DPPH, ABTS, and FRAP assays as well as the phenolic profile of different Sideritis extracts, evaluated via HPLC-DAD-MS, were compared. A similar phenolic profile was observed among the five Sideritis species, with HYP and ISC derivatives showing variations in their contents as a function of Sideritis species. MAE Sideritis extracts could be considered green and natural antioxidants for medicinal, cosmetic, and food purposes, accompanied by sustainable approaches.

Keywords

• mountain tea
• microwave-assisted extraction
• phenolic profile
• antioxidant activity
• <i>Sideritis</i> species
• isoscutellarein