Extraction of phenolic compounds from Satureja macrostema using microwave-ultrasound assisted and reflux methods and evaluation of their antioxidant activity and cytotoxicity

Satureja macrostema (SM) is commonly used as a spice and medicinal plant in Mexico. Ethanolic extracts at different concentrations (E0, E50, E75, E100) were obtained by reflux (RE) and microwave-ultrasound assisted (MUAE) techniques at three extraction times (30, 60, and 120 min). The total phenolics content (TPC), total flavonoids content (TFC), and total soluble solids (TSS), as well as the antioxidant activity by DPPH and ABTS assays were determined. Results showed that active compound concentrations were dependent on the extraction conditions. The solvent and time of extraction affected TPC, TFC, and TSS values rather than the extraction technique. For the antioxidant activity, MUAE extracts displayed lower median inhibition concentration (IC50) values than RE, resulting in a higher radical scavenging ability, which can be attributed to the lower temperatures used in MUAE and the higher stability of the extracted compounds. A Pearson correlation was aimed to establish the significant effects between the variables. It was found that ABTS was highly correlated to TPC for both extraction techniques. The extracts E50-120 min for RE and E100-30 min for MUAE, with significant higher TPC (114.08 ± 0.25 and 133.91 ± 0.39 mgGAE/gTSS respectively) and lower IC50 (12.31 ± 0.02 and 10.85 ± 0.13 μgTSS/mL respectively) were chosen for HPLC and cytotoxicity assays. Rosmarinic acid was found as the main component in both SM extracts. Cytotoxicity was performed exposing lymphocytes to both extracts at two concentrations (0.1 and 1.0 mgTSS/mL), using Neutral Red (NR) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Cell viability data did not show statistically significant difference compared with untreated cells (p < 0.05), therefore, a cytotoxic effect of SM extracts was not found even at 1.0 mgTSS/mL.