Extraction of rosmarinic acid from Melissa officinalis L. by heat-, microwave- and ultrasound-assisted extraction techniques: A comparative study through response surface analysis

The goal of this study was to compare the extraction of rosmarinic acid from Melissa officinalis L. using three techniques (heat- -, microwave- and ultrasound- assisted extraction). In order to obtain the conditions that maximize the rosmarinic acid extraction, a response surface methodology was applied using the circumscribed central composite design of three variables with five levels. The relevant independent variables used for the process optimization were time, temperature and ethanol–water proportion for heat-assisted- and microwave-extration, whereas for the ultrasound method the ultrasonic power was variable. The responses used as criteria were the amount of rosmarinic acid was determined by HPLC-DADand the extraction yield of the obtained residue. Ultrasound extraction proved to be the most effective method, capable of yielding 86.3 ± 4.1 mg rosmarinic acid/g plant per dry weight (dw) at the optimal extraction conditions (33.0 ± 3.2 min, 371.7 ± 19.3 W and 39.9 ± 1.4% of ethanol). According to the content of rosmarinic acid, microwave- and heat-assisted extractions techniques were less effective, producing 49.4 ± 2.3 (at 26.5 ± 2.1 min, 108.6 ± 10.2 °C and 25.5 ± 0.9% of ethanol) and 59.4 ± 2.2 (at 106.2 ± 5.1 min, 88.0 ± 2.9 °C and 34.5 ± 1.6% of ethanol), respectively. Additionally, the solid/liquid ratio effect at the optimal values in a dose–response format was studied in view of its plausible transference at industrial level, showing a decreasing non-linear pattern from 5 to 120 g/L. In brief, the obtained results highlight the potential applications of using the leaves from M. officinalis as a source of rosmarinic acid.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013), REQUIMTE (UID/QUI/50006/2013 - POCI/01/0145/ FEDER/007265) and Caleja (SFRH/BD/93007/2013) and L. Barros (SFRH/BPD/107855/2015) grants. This work was also financially supported by: Project POCI-01-0145-FEDER-006984 – Associate Laboratory LSRE-LCM funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) – and by national funds through FCT - Fundação para a Ciência e a Tecnologia. To Xunta de Galicia for financial support for the post-doctoral researcher of M.A. Prieto. The authors also thank to company Mais Ervas, Lda (Alfandega da Fé, Portugal), for providing the M. officinalis samples.