Extraction, chemical composition and antioxidant activity of flavonoids from Cyclocarya paliurus (Batal.) Iljinskaja leaves
Introduction
Cyclocarya paliurus (Batal.) Iljinskaja (C. paliurus) which belongs to the genus Cyclocarya Iljinskaja (Juglangdaceae), is the sole species in its genus, and mainly found in the mountainous regions in the tropics and subtropics (Xie, Li, Nie, Wang, & Lee, 2006). It grows mainly in the south of China, and is called “sweet tea tree” in Chinese (Xie, Shen et al., 2013). The leaves of C. paliurus are used in folk medicine for the treatment of diabetes mellitus, hypertension, hyperliposis, etc. (Li et al., 2000, Kurihara et al., 2003, Xie et al., 2010a, Xie et al., 2013b). The leaves of this plant have been widely used in China, which may be related to abundant organic compounds, especially flavonoids. Flavonoids are found to be the main active compounds in C. paliurus (Xie, Wang, Yi, & Wang, 2004), which have many biological activities, such as preventing hyperglycemia, diabetes mellitus, hypertension and coronary heart disease. Many flavonoids were isolated from C. paliurus, such as cyclocarioside, cyclocaric acid, kaempferol, quercetin and isoquercitrin. (Shu et al., 1996, Xie et al., 2004; Zhang et al., 2010).
Conventional techniques to obtain flavonoids, such as heating, boiling, or refluxing, usually require several hours or even days for the extraction process and a large volume of solvent, and may result in a loss of flavonoids due to hydrolysis, ionisation and oxidation during extraction (Li, Chen, & Yao, 2005). Microwave irradiation, which has proved to be a clean, efficient and convenient energy source, has been widely utilised in natural products extraction (Jiao et al., 2014, Xie et al., 2012, Zhang et al., 2013). Microwave-assisted extraction (MAE) is known to be a fast and efficient method for the extraction of flavonoids from plants. Compared with the traditional methods, MAE has many advantages, such as higher extraction rate, shorter extraction time, use of less solvent, better productivity and higher quality products (Chen et al., 2007, Zhang et al., 2011). Recently, MAE has been applied to extract various bioactive compounds from plants, such as terpenes from caraway seeds (Chemat, Aït-Amar, Lagha, & Esveld, 2005), quercetin from Flos Sophorae (Li et al., 2004) and flavonoids from cultivated Epimedium sagittatum (Zhang et al., 2013). A dynamic MAE system designed by Chen et al. (2008) markedly enhanced extraction yield of flavonoids from Herba Epimedii. To our knowledge, the optimised conditions of MAE used in extraction of flavonoids from C. paliurus have not been reported yet.
Response surface methodology (RSM), an important tool in process and product improvement, is a collection of experimental design and optimisation techniques that enables the researcher to determine the relationship between the response and the independent variables (Eren & Kaymak-Ertekin, 2007). To the best of our knowledge, there has been no report about the application of RSM in the optimisation of MAE conditions for the extraction of flavonoids from the leaves of C. paliurus.
The objective of this study was to optimise the MAE conditions for the extraction of flavonoids from C. paliurus. RSM was employed to study the optimal temperature, extraction time, solid–liquid ratio and concentration of alcohol, which could maximise the yield of flavonoids from C. paliurus. Then, the colorimetric method with AlCl3/methanol system was used to quantify total flavonoids, which has been reported to be a simple, quick and accurate method (Zhao, Xu, & Liu, 2004). In addition, the antioxidant activity of flavonoids from C. paliurus, obtained under optimised MAE extraction conditions was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay. The chemical composition of the MAE extract was also evaluated by liquid chromatography–mass spectrometry (LC–MS) analysis.
Section snippets
Plant materials
The leaves of C. paliurus were collected in Xiushui County, Jiangxi Province, China. A voucher specimen was deposited at the State Key Laboratory of Food Science and Technology, Nanchang University, China. The leaves were air dried and ground into a fine powder (40–60 mesh) in a mill.
Chemicals and reagents
Methanol and formic acid (HPLC grade) were obtained from Merck (Darmstadt, Germany). Ethanol was purchased from Shanghai Chemicals and Reagents Co. (Shanghai, China). Quercetin was supplied by China Institute for
Effect of temperature
Experiments were conducted to study the effect of temperature on the yield of flavonoids from C. paliurus. The extraction was performed at 40, 50, 60, 70, 80 and 90 °C, respectively, the extraction time was fixed to 5 min, the ratio of solvent to material was fixed to 20:1, 90% ethanol was selected as solvent, and the other conditions were kept the same. Generally, when MAE is conducted in closed vessels, the temperature could be increased above the boiling point of the solvent. These elevated
Conclusions
Microwave irradiation, which has proved to be a clean, efficient and convenient energy source, has been utilised in the extraction of flavonoids from C. paliurus. RSM was successfully applied for optimisation of MAE of flavonoids from C. paliurus leaves. It was effective for estimating the effect of five independent variables. Both the temperature and concentration of ethanol had highly significant effects on the response value. The optimal flavonoids yield of 14.97 mg/g from 1 g dried C. paliurus
Conflict of interest
Authors declare no conflicts of interest.
Acknowledgements
This work was supported by the research projects of Chinese National Natural Science Fund (No. 31201297), the Research Foundation for Objective-Oriented Project of State Key Laboratory of Food Science and Technology, Nanchang University, China (No. SKLF-ZZA-201301), and the Science Funds of Educational Commission of Jiangxi Province, China (No. GJJ14144).
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These authors contributed equally to this work.