Viola odorata: Influence of supercritical fluid extraction on the efficiency of ultrasound- and microwave-assisted extraction of bioactive compounds

This study aimed at examining the effect of supercritical carbon dioxide (ScCO2) extraction on the subsequent extraction of the Viola odorata polar bioactive components. The raw material was firs submitted to ScCO2 extraction for the extraction of the lipophilic fraction. Then the exhausted raw material was subjected to ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) in order to extract the polar components. ScCO2 extraction was performed under the pressure of 300 bar and at a temperature of 40 °C for 4 hours. In order to see the effect of ScCO2, the UAE and MAE (50% aqueous ethanol solution as solvent) were conducted on both exhausted (residue-after the ScCO2) and unexploited raw materials. Also, the impact of the various UAE and MAE conditions was tested. The UAE was conducted on two different temperatures (40 and 50 °C) at the constant extraction time (40 and 20 min). MAE was conducted on two different extraction powers (470 and 800 W) and at the constant extraction time (10 min). The results were focused on the content of total phenols, total flavonoids and antioxidant activity of the obtained extracts. The yield during the ScCO2 process was 1.43% (w/w). It was noted that the extracts obtained by applying UAE and MAE after the ScCO2 were noticeably richer in the content of total phenols. UAE conditions of 40 °C and 20 min showed the highest yield of total phenols, recording 70.38 mg GAE/g DE, while the MAE at the power of 470 W achieved 11.89% higher yield of polyphenols in residue extracts. The antioxidant activity has also been in correlation with the concentration of polyphenols