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

The purpose of the present study was to compare the polyphenolic compounds extracted from five <i>Sideritis</i> species grown in Greece; <i>S. scardica</i>, <i>S. clandestina</i>, <i>S. raeseri</i>, <i>S. euboea</i>, and <i>S. syriaca,</i> 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 <i>S. scardica</i>. 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% (<i>v</i>/<i>v</i>) 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 <i>Sideritis</i> extracts. Phenolic compounds were then extracted under these conditions, from the five <i>Sideritis</i> 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 <i>Sideritis</i> extracts, evaluated via HPLC-DAD-MS, were compared. A similar phenolic profile was observed among the five <i>Sideritis</i> species, with HYP and ISC derivatives showing variations in their contents as a function of <i>Sideritis</i> species. MAE <i>Sideritis</i> extracts could be considered green and natural antioxidants for medicinal, cosmetic, and food purposes, accompanied by sustainable approaches.