Ultrasonic-Assisted Extraction of the Botanical Dietary Supplement

Oct 17, 2012 - The roots of Polygonum cuspidatum produce several phenolic compounds, including trans-resveratrol (1), trans-piceid (2), and emodin (3)...
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Ultrasonic-Assisted Extraction of the Botanical Dietary Supplement Resveratrol and Other Constituents of Polygonum cuspidatum Bao-Yuan Chen,†,‡ Chia-Hung Kuo,§,‡ Yung-Chuan Liu,⊥ Li-Yi Ye,∥ Jiann-Hwa Chen,*,† and Chwen-Jen Shieh*,§ †

Graduate Institute of Molecular Biology, National Chung Hsing University, Taichung, 402, Taiwan Biotechnology Center, National Chung Hsing University, Taichung, 402, Taiwan ⊥ Department of Chemical Engineering, National Chung Hsing University, Taichung, 402, Taiwan ∥ Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Fujian, 361005, People’s Republic of China §

S Supporting Information *

ABSTRACT: The roots of Polygonum cuspidatum produce several phenolic compounds, including trans-resveratrol (1), trans-piceid (2), and emodin (3), and are a commercial source of the botanical dietary supplement 1. Ultrasonic-assisted extraction technology and conventional shaking extraction procedures were compared for the extraction of 1−3 from P. cuspidatum roots, using 50% ethanol as a food grade solvent. These compounds were extracted successfully, and their mass transfer coefficients were calculated by fitting the experimental results to a model derived from Fick’s second law. The results indicated that ultrasonic-assisted extraction had higher mass transfer efficacies and extraction yields for 1−3 as compared with conventional shaking extraction. Under the extraction conditions used (extraction temperature 50 °C; ultrasonic power 150 W), yields of 3.5, 9.2, and 7.8 mg/g were obtained for 1−3, respectively.

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present time, P. cuspidatum roots are used as a commercial source of resveratrol.14 Polygonum cuspidatum Siebold & Zucc., also called Japanese knotweed, is a perennial herb belonging to the Polygonaceae family and grows widely in Asia and North America. In mainland China and Japan, the roots of P. cuspidatum have been used as an herbal medicine to treat arthralgia, chronic bronchitis, jaundice, amenorrhea, hypertension, and hypercholesterolemia.15 In addition to trans-resveratrol (1), transpiceid (2) and emodin (3) have been also isolated from the roots of P. cuspidatum.16,17 Piceid (2) has been shown to be a good antioxidant and shows potential anti-inflammatory and cardioprotective activities.5,18 Emodin (3) possesses antiinflammatory, antibacterial, and antineoplastic activities.19−21

esveratrol (trans-3,5,4′-trihydroxystilbene) is a polyphenolic compound present in several plants. It is a phytoalexin that protects plants from attack by fungi and other pathogens and can also act as a remedial agent against injury, stress, and UV radiation.1 In recent years, resveratrol has become widely available as a botanical dietary supplement in the United States. Resveratrol is recognized as a bioactive agent and has shown antioxidative, anticarcinogenic, and antitumor properties in laboratory studies.2−5 In addition, resveratrol inhibits platelet aggregation and prevents low-density lipoprotein (LDL) oxidation, which provide cardioprotective effects.6 Studies have found that resveratrol can induce the expression of the Saccharomyces cerevisiae SIRT1 gene, whose gene product (an NAD-dependent enzyme, sirt1) has been shown to directly correlate with cellular longevity.7 Resveratrol can extend the life span of one-year-old male mice with highcaloric diets and may modulate known longevity pathways favorably to improve overall health.8 Resveratrol is a common constituent of the human diet, which has been found in grapes, red wine, berries, and peanuts.4,9 However, resveratrol in these dietary items occurs only in small amounts, ranging from 0.02 to 3.8 mg/L.3,5 Reports have shown that resveratrol can be extracted successfully from grape canes,10 peanut skins,11 and peanut roots.12 Burns et al. pointed out that Polygonum cuspidatum contains high concentrations of stilbenes.13 At the © 2012 American Chemical Society and American Society of Pharmacognosy

Received: June 5, 2012 Published: October 17, 2012 1810

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Extraction of resveratrol (1) by a conventional method including heating under reflux with alcoholic solvent has been reported.10,12 Recently, the ultrasonic-assisted extraction technique has attracted attention increasingly due to its inherent advantages, such as a reduction in extraction time, an increase in extraction yield, and a decrease in the thermal degradation of bioactive compounds.22−24 In the present investigation, extraction of compounds 1−3 from the roots of P. cuspidatum was investigated using an ultrasonic-assisted extraction technique. A mass transfer model was employed to determine the effect of ultrasound on the extraction efficacy. The roots of P. cuspidatum were ground into a powder and extracted in an ultrasonic bath or a traditional shaking water bath for various times up to 1 h. These extracts were analyzed by HPLC. Three dominant peaks that had the same retention times as the peaks from HPLC analysis of authentic resveratrol, piceid, and emodin were observed in each analysis. A representative result is shown in Figure 1. The three

Figure 2. Effects of extraction time and method on the yields of compounds 1 (●), 2 (⧫), and 3 (▲). The extraction conditions were set as follows: solvent, 50% ethanol; solvent to solid ratio, 20 mL/g; extraction temperature, 50 °C. The extraction was performed under ultrasonic power at 150 W (filled symbols) or shaking at 100 rpm (empty symbols).

material surface causes an increase in pressure and temperature, which destroy the cell walls of the plant matrix and release compounds into the solution.27 Therefore, ultrasound can increase extraction yields and decrease extraction times. Karacabey and Mazza reported that the optimal conditions for the conventional extraction of resveratrol (1) from milled grape canes was 50−70% ethanol concentration and 83.6 °C.10,28 Mantegna et al. reported yields of 2.15 and 11.84 mg/g for 1 and 2, respectively, from ultrasound-assisted extraction of P. cuspidatum using methanol as extraction solvent.29 However, methanol has a high toxicity in humans. Whether the extraction products are used directly as a dietary supplement or as an ingredient of functional foods, ethanol can be a better solvent than methanol for the extraction of 1 and 2, as presented in Figure 1. Mass transfer is the result of a concentration gradient during the extraction process. The concentration gradient is timedependent, and diffusion may be represented by Fick’s second law.30 The diffusion model based on the mass transfer can be used to explain the effect of ultrasound on the enhancement of the extraction rate. Estimation of diffusion coefficients is important for the determination of mass transfer rates, which can be calculated by fitting the experimental data.31−33 Plots of ln[Cs/(Cs − Ct)] versus extraction time for compounds 1−3 are shown in Figure 3, where Cs is the equilibrium concentration in mg/L and Ct is the concentration at time t (s) in mg/L. The linear regression with the correlation coefficient (R2 = 0.95−0.99) was obtained for the extraction of the three compounds. Since the slope equals kLA/V (V (m3) is the volume of solution and A (m2) is the surface area of particles), the mass transfer coefficients (kL) could therefore be determined. The kL values calculated from Figure 3a were 1.1218 × 10−4, 1.1298 × 10−4, and 4.5214 × 10−5 m/s for ultrasonic-assisted extraction of compounds 1−3, respectively. On the other hand, the kL values calculated from Figure 3b were 1.6925 × 10−5, 1.8712 × 10−5, and 2.6017 × 10−6 m/s for shaking extraction of compounds 1−3, respectively. From these results, it was found that ultrasonic-assisted extraction increased the mass transfer coefficient by 6- to 17-fold compared to conventional shaking extraction. The improvement of the extraction efficiency was due to acceleration of the solid−liquid

Figure 1. Representative HPLC analysis of P. cuspidatum root extract. The retention times for peaks 1−3 were the same as those for peaks from HPLC analysis of authentic trans-resveratrol, trans-piceid, and emodin, respectively.

compounds recovered from the three dominant peaks were subjected to 1H NMR and ESIMS analysis for structural identification, and the results are shown in the Supporting Information. Figure 2 shows the yields of 1−3 from either ultrasonic-assisted extraction or traditional shaking extraction. With the ultrasonic-assisted extraction, the yields of compounds 1−3 reached a maximum at 3.5, 9.2, and 7.8 mg/g after extraction for 4, 4, and 20 min, respectively. However, only 3.1, 8.8, and 4.1 mg/g of compounds 1−3 were obtained by conventional shaking extraction for 30 min. Ultrasonic-assisted extraction increases yields 12.9%, 4.5%, and 90.2% for 1−3, respectively, as compared to traditional solvent extraction. Thus, ultrasonic-assisted extraction increases both extraction yield and rate, leading to reduction in the extraction time and a higher productivity. Dong et al. demonstrated that the extraction yield of salvianolic acid B from the roots of S. miltiorrhiza under ultrasound-assisted extraction was higher than under the conventional refluxing method.25 Xia et al. showed that ultrasonic-assisted extraction increases the extraction yields of aromatic components and glycosidic aromatic precursors.26 The present results are in good agreement with their earlier work. Ultrasound creates cavitations in the liquid solution, and subsequent collapse of the cavity bubbles close to the plant 1811

dx.doi.org/10.1021/np300392n | J. Nat. Prod. 2012, 75, 1810−1813

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min, and the UV detector was set at a wavelength of 303 nm. transResveratrol (98%), trans-piceid (≥95%), and emodin (≥95%) were purchased from Changsha Nutramax Biotechnology (Changsha, People’s Republic of China), Sigma-Aldrich (St. Louis, MO, USA), and MP Biomedicals (Irvine, CA, USA), respectively, and used as standards for HPLC and for the generation of calibration curves. Compounds 1−3 for the three major elution peaks from HPLC analysis of the P. cuspidatum extract (Figure 1) were identified as transresveratrol, trans-piceid, and emodin, respectively. The concentrations of compounds 1−3 were determined using their peak areas referenced to the calibration curves constructed in each case. All reagents and chemicals used were of analytical grade. Plant Material. The roots of P. cuspidatum were provided by Jing Jiue Co., Ltd. (Taichung, Taiwan). The plant material was identified by Prof. Y. H. Tseng, Department of Forestry, National Chung-Hsing University. A voucher specimen (No. 13550 TCF) was deposited in the Herbarium of the Department of Forestry, National Chung Hsing University. Conventional Shaking Extraction. Dried P. cuspidatum roots were ground into a powder, which was passed through a sieve of 30 to 45 mesh and used for this study. The powder obtained was about 0.62 mm in size. Powdered P. cuspidatum roots (0.1 g) were extracted with 2 mL of 50% ethanol in a cap-sealed glass tube. The glass tubes were placed in an orbital shaking bath (100 rpm) at 50 °C for various extraction times. The glass tube was then taken out from the ultrasonic bath followed by centrifugation at 13 000 rpm for 10 min. The supernatant was used for HPLC analysis. Ultrasonic-Assisted Extraction. Powdered P. cuspidatum roots (0.1 g) were extracted with 2 mL of 50% ethanol in a cap-sealed glass tube. The glass tubes were placed in a temperature-controlled ultrasonic bath (40 kHz, Delta DC150H, Taiwan) set at 50 °C and 150 W of ultrasonic power for various extraction times. The glass tube was then taken out from the ultrasonic bath followed by centrifugation at 13 000 rpm for 10 min. The supernatant was used for HPLC analysis. Determination of Mass Transfer Coefficients. For the extraction of P. cuspidatum root powder with 50% ethanol in the ultrasonic bath, the rate of mass transfer of the solute, i.e., 1−3, from the solid surface to the liquid is the controlling factor for extraction efficacy. It is assumed that diffusion of the solute in the solid (powder) is very rapid compared to diffusion in the liquid. The rate of mass transfer of the solute being dissolved in the solution is given by eq 1:30

Figure 3. Determination of mass transfer coefficients for compounds 1−3 during (a) ultrasonic-assisted extraction and (b) conventional shaking extraction.

mass transfer by ultrasound. The enhancement of mass transfer was caused by ultrasonic cavitation because it was the only variable added in this experiment. In this study, high concentration levels of resveratrol (1) were extracted from P. cuspidatum roots by either ultrasoundassisted or conventional solvent extraction using 50% ethanol as the solvent. Two other compounds, 2 (piceid) and 3 (emodin), were extracted simultaneously. The present data have demonstrated that ultrasound-assisted extraction of 1−3 can be easily carried out within a short time period and possesses advantages such as the use of a lower temperature and obtaining a higher extraction yield. The observed content of 1 extracted from P. cuspidatum roots was higher than the content of 1 extracted from other food sources reported in the literature.5

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NA = kL(CAS − CA ) A

(1)

where NA is the amount (mg) of solid solute A that dissolves into a solution per second, A is the surface area of particles (in m2), kL is a mass transfer coefficient (in m/s), CAS is the saturation solubility of solid solute A in the solution (in mg/L), and CA is the concentration of A (in mg/L) in the solution at time t (in s) . By material balance in a batch system, the rate of accumulation of A in the solution is equal to eq 1, shown as eq 2:

V

dCA = NA = AkL(CAS − CA ) dt

(2)

Integrating t = 0 and CA = CA0 with t = t and CA = CA gives eq 3: ⎛ CAS ⎞ kLA ln⎜ t ⎟= V ⎝ CAS − CA ⎠

EXPERIMENTAL SECTION

General Experimental Procedures. 1H NMR spectra were recorded on a Varian INOVA 600 NMR spectrometer in DMSO-d6. ESIMS data were recorded on a Finnigan LCQ ion trap mass spectrometer (Thermo Finnigan, San Jose, CA, USA). Analysis of the P. cuspidatum root extract was carried out by HPLC (Hitachi L-7400; Tokyo, Japan) using a Zorbax Eclipse XDB C8 column (250 mm × 4.6 mm). A mixture of water and methanol containing 0.1% acetic acid was used for gradient elution, i.e., methanol from 10% to 50% for the first 20 min, methanol from 50% to 100% between 20 and 24 min, and 100% for the last 6 min of elution. The flow rate was set at 1.0 mL/

(3)

It is then possible to determine the transfer coefficient kL by plotting the ln[CAS/(CAS − CA)] versus time from eq 3. With V as the volume of solution (m3), the surface area of particles A (m2) can be calculated by eq 4 according to the method of Rakotondramasy-Rabesiaka et al.33

A= 1812

3mplant ρrp

(4) dx.doi.org/10.1021/np300392n | J. Nat. Prod. 2012, 75, 1810−1813

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where mplant is the weight of P. cuspidatum dry root powder in the vessel (g), ρ is the wet powder density (kg/m3), and rp is the powder particle size (m).

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR and ESIMS spectroscopic data of trans-resveratrol (1), trans-piceid (2), and emodin (3) are available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +886-4-2284-0485, ext. 231. Fax: +886-4-2287-4879. Email: [email protected] (J.H.C.). Tel: +886-4-22840450, ext. 5121. Fax: +886-4-2286-1905. E-mail: cjshieh@nchu. edu.tw (C.J.S.). Author Contributions ‡

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by research funding grants provided by the National Science Council of Taiwan (101-2313-B-005040-MY3).

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