Abstract
Volatile essential oils (EOs), non-volatile rutin (RU), quercetin (QU), kaempferol (KA) and isorhamnetin (IS) were effectively extracted and isolated from seabuckthorn (Hippophae rhamnoides L.) leaves by ionic liquid-based ultrasound/microwave-assisted simultaneous distillation extraction (ILUMASDE). After optimization by response surface methodology, EOs, RU, QU, KA and IS were separated under the following optimum conditions: an ionic liquid of 1.0 M 1-butyl-3-methyl imidazole bromine salt ([C4mim]), liquid/solid ratio of 12 ml g−1, extraction time of 34 min, microwave power of 540 W and a fixed ultrasonic power of 50 W. Under the optimized conditions of ILUMASDE, the extraction yields of RU, QU, KA, IS and EOs were 9.18 ± 0.35, 5.52 ± 0.23, 3.03 ± 0.11, 5.64 ± 0.24 mg g−1 and 0.095 ± 0.004%, respectively. The yield of EOs obtained using ILUMASDE was 1.07-fold higher than that obtained by conventional hydrodistillation extraction (HDE). In addition, the components of the EOs obtained using ILUMASDE and HDE were similar. The extraction yields of RU, QU, KA, IS obtained by ILUMASDE were 1.03–1.35-fold higher than that obtained by the ethanol ultrasonic-assisted extraction (EUAE), ionic liquid-based ultrasonic-assisted extraction (ILUAE) and ionic liquid-based microwave-assisted extraction (ILMAE). And the extraction time used by ILUMASDE was 34 min, which is 14.17%, 56.67%, 56.67% and 85.00% less than those used by HDE, EUAE, ILUAE and ILMAE, respectively. Therefore, ILUMASDE can be considered a rapid and efficient method for extracting flavonoids and EO from seabuckthorn (Hippophae rhamnoids L.) leaves.
Highlights
Seabuckthorn (Hippophae rhamnoides L.), a deciduous shrub or dwarf tree of the Euphorbiaceae, is distributed in the temperate zone, cold temne and subtropical high mountain area of Eurasian continent [1,2], and is rich in a variety of bioactive substances, including flavonoids, triterpenoids, sterols, lipids and volatile oil, etc. [3,4,5]
The anion is considered to be the significant factor influencing the properties of Ionic liquids (ILs) [35]. 1-Alkyl-3methylimidazolium-based ILs are widely used in sample preparation and compounds extraction from plant materials, 1-Butyl-3-methylimidazolium-based ILs with the same concentrations but six different anions (Br−, Cl−, BF4−, ClO4−, HSO4− and NO3−) were used in UMASDE to identify the best IL anion [43]
The results show that the cation alkyl chain length significantly affects the yields of the target compounds and the highest yields of all the five target compounds were obtained using [C4mim]Br. This may be due to the difference of nano-structuring of alkyl domains within the IL, which affected the intermolecular forces between IL and the target compounds
Summary
Seabuckthorn (Hippophae rhamnoides L.), a deciduous shrub or dwarf tree of the Euphorbiaceae, is distributed in the temperate zone, cold temne and subtropical high mountain area of Eurasian continent [1,2], and is rich in a variety of bioactive substances, including flavonoids, triterpenoids, sterols, lipids and volatile oil, etc. [3,4,5]. The general application of traditional techniques above has been limited by several shortcomings, including time-consuming, poor recoveries, degradation of target compounds, atmospheric pollution [33,34] To overcome those shortcomings, an efficient extraction method is imperative to be considered in this study. Simultaneously ultrasonic/microwave-assisted extraction (UMAE), which combined the advantage of both ultrasonic and microwave, is a prevailing separation method and widely applied in food and pharmaceutical industry [37,38]. With respect to the advantages of ILs, UMAE and SDE, and on the basis of the previous work carried out by our research team, an ionic liquid-based ultrasonic/microwave-assisted simultaneous distillation and extraction (ILUMASDE) method for separating of the main flavonoids and EO from seabuckthorn leaves was proposed [40,41]. The yields of EOs, RU, QU, KA and IS obtained with the proposed technique were compared with conventional extraction methods
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