Comparisons between conventional, ultrasound-assisted and microwave-assisted methods for extraction of anthraquinones from Heterophyllaea pustulata Hook f. (Rubiaceae)

Abstract

This work reports a comparative study about extraction methods used to obtain anthraquinones (AQs) from stems and leaves of Heterophyllae pustulata Hook (Rubiáceae). One of the conventional procedures used to extract these metabolites from a vegetable matrix is by successive Soxhlet extractions with solvents of increasing polarity: starting with hexane to eliminate chlorophylls and fatty components, following by benzene and finally ethyl acetate. However, this technique shows a low extraction yield of total AQs, and consumes large quantities of solvent and time. Ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) have been investigated as alternative methods to extract these compounds, using the same sequence of solvents. It was found that UAE increases the extraction yield of total AQs and reduces the time and amount of solvent used. Nevertheless, the combination UAE with benzene, plus MAE with ethyl acetate at a constant power of 900 W showed the best results. A higher yield of total AQs was obtained in less time and using the same amount of solvent that UAE. The optimal conditions for this latter procedure were UAE with benzene at 50 °C during 60 min, followed by MAE at 900 W during 15 min using ethyl acetate as extraction solvent.

Pressurized hot water extraction of anthraquinones from Heterophyllaea pustulata Hook f. (Rubiaceae)

“…It is important to note that PHWE extractions showed an AQs recovery enhancement of up to 600% compared with traditional Soxhlet process with solvents of increasing polarity. As it was demonstrated in previous work [22], only a AQs yield of about 3-4 mg total AQs/g vegetable matrix was obtained using Soxhlet extraction for 16 h. On the other hand, using PHWE the extraction time is reduced from 16 h to 2 h. This high yield of AQ obtained by PHWE, is mainly due to the ability of the water to reduce the dielectric constant with increasing temperature, by modifying its polarity is possible to extract non-polar organic compounds. Furthermore, the temperature used in the high pressure process is higher than in Soxhlet extraction, favoring the extraction of solid compounds as AQs.…”

“…The plant material was air-dried at room temperature during seven days and separated into stems and leaves. Based on previous works [22] only stems were used for the study presented in this manuscript because of the AQs content in the stems is higher than the other plant parts.…”

Ultrasound Assisted Extraction for the Recovery of Phenolic Compounds from Vegetable Sources

“…Vázquez et al [56] reported that the UAE provided an extraction yield of 168 mg/g dry weight (DW) in the recovery of anthraquinones from stems of Rubiáceae, exceeding the extraction yield obtained by the Soxhlet method (34 Mg/g DW). In addition, there was a reduction on the extraction time of 16 to 2 h; a reduction in the amount of solvent used (from 36 mL/g to 20 mL/g) was also observed.…”

Ultrasonic-assisted extraction of anthraquinones from Heterophyllaea pustulata Hook f. (Rubiaceae) using ethanol–water mixtures

“…Also, it is important to note that the AQs yield extraction obtained is similar to yield obtained by traditional extraction methods for AQs, wich involve the use of a Soxhlet apparatus with organic solvents of increasing polarity, starting with hexane, followed by benzene, ethyl acetate, and ethanol (Barrera Vázquez et al, 2014). However, the UAE using ethanol presents Table 5 Comparison of extraction methods analyzed.…”

“…Ethanol is a non-toxic and economic solvent widely used in the extraction of active principles from plants (Barrera Vázquez et al, 2014). Being a polar organic solvent, ethanol is in principle an adequate solvent for the slightly polar AQs molecules.…”