Response Surface Methodology as a Predictive Tool and UPLC-HRMS Analysis of Phenolic Rich Extract from Verbena officinalis L. Using Microwave-Assisted Extraction: Part I

Phytochemicals, such as phenolic compounds, are of great interest due to their health-benefitting antioxidant properties and possible protection against inflammation, cardiovascular diseases and certain type of cancers. Maximum retention of these phyto-chemicals during extraction requires optimized process parameter conditions. Verbena officinalis was treated using "green" technic and "green" solvent by elaboration of an efficient alternative protocol in order to obtain a phenolic rich extract. A microwave-assisted extraction (MAE) method was investigated to obtain high phenolic compounds content from this plant with high antioxidant activities. The main studied extraction parameters were: time (t: 5 to 25 min), irradiation power (P: 150 to 750 W), liquid-to-solid ratio (R: 10 to 50 mL g(-1)) and pH (pH: 3 to 7). A microwave-assisted extraction showed that the best performance, resulting in an extract with phenolic and flavonoid contents (94.48 mg GAE/g DW and 64.07 mg QE/g DW, respectively), a DPPH and FRAP says (23.99 mu g/ml and 997.46 mu M of BHT/g DW, respectively). The optimal conditions were: extraction time = 15 min, microwave power = 550 W, solvent pH equal to 5.5 and liquid-to-solid ratio = 39 ml/g. To our knowledge, the polyphenolic rich extract has been analyzed using UPLC-HRMS apparatus which allowed us to identify seven phenolic compounds: verbascoside, isoverbascoside, hydroxytyrosol glucoside and four flavonoid compounds including: Cirsilineol, Catechine (+),Naringenin and quercetin-3-O-rutinoside. Results showed that this innovative and green extraction method (microwave extraction) can be used successfully to obtain bioactive compounds in higher amounts from Verbena officinalis.