Comparative assessment of PLE and SFE for the selective extraction of compounds of interest from Ruta graveolens

Abstract

[Introduction]: Ruta graveolens, commonly known as rue, is an herbaceous perennial plant with bluish-green leaves that emits a powerful odor and has a bitter taste. This plant has shown different pharmacological activities and is employed in folk medicine for treatment of rheumatism, dermatitis, pain and many inflammatory diseases. The main components reported in Ruta graveolens are quinoline, furoquinoline, acridone alkaloids, flavonoids, and coumarins, mainly furanocoumarins. Although traditional extraction of these compounds is mainly done by maceration, nowadays the use of green extraction techniques provides an efficient, fast, selective and environmentally friendly alternative. In this regard, technologies based on compressed fluids play an important role, being supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE) the most widely employed. The aim of this work was to evaluate the ability of PLE and SFE to selectively extract families of compounds of interest from the aerial part and root of Ruta graveolens. PLE was carried out at 100 bar for 20 min. Three different temperatures were studied (40 °, 105 ° and 170 ° C) and two green solvents (d-limonene and ethyl acetate) and its mixture (50:50 v/v) were used. In SFE, extraction with supercritical CO2 (scCO2) was carried out, increasing the pressure every 60 min (up to 100, 200 and 350 bars) at a temperature of 40 °C. Two conditions were tested: dry sample or moistened sample before reaching the pressure of 350 bar. SFE extracts were collected in ethanol and ethyl acetate. Rue extracts obtained by SFE and PLE were chemically characterized by GC–q-TOF-MS.

[Results and discussion]: The extraction yield and the relative abundance of the different groups of metabolites (alkaloids, furanocoumarins, terpenes, amines, fatty acids and other compounds) identified by GC-q-TOF-MS were evaluated. Alkaloids, terpenes and furanocoumarins were identified in all extracts, and differences in abundance and selectivity according to the compressed fluid used and the conditions tested were found. Furthermore, arborinine is an alkaloid that was only identified in the aerial part of the plant, while furanocoumarins -isopimpinelina and xantotoxina- along with some other coumarins and amides were only identified in the root. Concerning PLE, the extraction of alkaloids from the root was favored with any of the solvents used. However, in the aerial part, alkaloids’ extraction was promoted by ethyl acetate while the extraction of terpenes improved with d-limonene and mixture d-limonene – ethyl acetate (50:50 v/v). Regarding SFE, when the extracts were collected in ethanol, terpenes abundance increase, while collecting them in ethyl acetate, increased the alkaloids content while, at the same time, terpenes decreased, with a difference of 20%. Moistening the sample at 350 bar pressure and collecting the extract in ethyl acetate facilitates the extraction and recovery of alkaloids.

[Conclusions]: In this study, two different compressed fluid technologies, PLE and SFE, were described for the first time to extract phytochemicals from the aerial part and the roots of Ruta graveolens using GRAS – generally recognized as safe – solvents. Specific compounds were identified for each part of the plant and selectivity of different families could be reached in different conditions.