The objective of this study was the optimization of the extraction process of several medicinal plants of the Mediterranean flora, and their extracts’ further evaluation regarding their potential biological activity. This work aimed to design and optimize the extraction method for recovering the targeted compounds from rosemary (Rosmarinus officinalis), St. John’s wort (Hypericum perforatum) and chamomile (Matricaria recutita) towards the extraction yield and quality of the extracts.
Raw materials were collected, dried, and ground in desired particle sizes (200, 500, 1000 µm). Ethanol was used as solvent; and extraction was performed using conventional extraction methods (Soxhlet), as well as novel extraction techniques (Ultrasound Assisted Extraction (UAE), Microwave Assisted Extraction (MAE) and their combination (UAE-MAE)). The optimized parameters were Ultrasound and Microwave intensity, and extraction time. All extracts were evaluated towards their total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity. TPC was determined by Folin–Ciocalteu method, while the antioxidant activity was estimated with the DPPH assay.
Optimum particle size was 500 µm for rosemary, and 1000 µm for both St. John’s wort and chamomile. In general, the increase of extraction time leads to increase of efficiency. However, the extraction time is not an independent variable, since the ultrasound and microwave intensities affect the yield. In specific, the increment of intensity in both techniques, as well as their combination, increases the efficiency of the extraction and reduces the time. Moreover, it was observed that after a certain intensity value the yield remains constant or slightly decreases, due to degradation phenomena. Thus, the optimum ultrasound intensity for rosemary and chamomile was 450 W, while for St. John’s wort was 700 W. Regarding microwave extraction parameters, for all tested plants the value of 200 W was selected as optimum, except for St. John’s wort (200 W). The optimum set of values were also selected for UAE-MAE. Results also indicate that the extracts were rich in phenolic compounds, possessing also a remarkable antioxidant activity in all the organic solvent systems tested.