Design of ionic liquid-based microwave-assisted extraction of flavonoids from Cyclea barbata Miers. and its lipoxygenase inhibitory activity

Green grass jelly ( Cyclea barbata Miers .) is a plant from Indonesia that is believed to have anti-inflammatory activity. This study aims to find the optimum condition in grass jelly extraction using the ionic liquid-microwave assisted extraction toward total flavonoid content (TFC) and lipoxygenase activity (LIA). The experimental design was performed using the parameters variable including extraction time, liquid–solid ratio, and ionic liquids concentration to obtain the optimum condition. The optimization analysis used response surface methodology (RSM) with Box– Behnken design (17 trials) to obtain a predictive model with TFC and LIA as a response surface value. In the present study, the optimum condition was suggested by RSM analysis with parameter variables, including extraction time of 17 minutes, 1-butyl-3-methylimidazolium bromide ([BMIM]Br) concentration of 1.76 mol/l, and the liquid–solid ratio of 38.21 ml/g. The equation of regression quadratic model was obtained to predict TFC and LIA as follows: TFC = 2.43A + 2.43B + 1.42C + 0.33AB − 3.20AC − 0.46BC − 4.90A2 − 3.10B 2 − 3.10C 2 + 28.32 with R 2 = 0.8336 and LIA = 0.066A + 8.22B + 0.97C + 2.47AB − 5.86AC + 1.96BC − 9.99A 2 − 13.75B 2 − 13.11C 2 + 63.53 with R 2 = 0.9207, respectively.


INTRODUCTION
Green grass jelly (Cyclea barbata Miers.) is a species of Menispermaceae family which is widespread and utilized by people in many parts of Asia such as Indonesia, Thailand, India, and Burma. In Java and Sumatra island of Indonesia, the local community traditionally uses this plant as an anti-inflammatory (Siregar and Miladiyah, 2011). Some research has stated that the green grass jelly leaves contain phenolic compounds (Arkarapanthu et al., 2005;Sahasakul et al., 2015) , flavonoids (flavonol), saponins (Kusmardiyani et al., 2014), rich in pectin (Hertanto et al., 2017;Yuliarti et al., 2017) and nutrients (Sahasakul et al., 2015). In general, flavonoids have anti-inflammatory activities as described by Kumar and Pandey (2013).
Inflammation is the body's response to dangerous conditions such as infections and tissue injuries to maintain homeostasis (Medzhitov, 2008). Arachidonic acid metabolism influences inflammatory mechanisms through two pathways: lipoxygenase (LOX) and cyclooxygenase (COX). Both these pathways produce the biological mediators of inflammation including leukotriene, prostaglandin, and thromboxane (Akula and Odhav, 2008).
Conventional extraction methods take a long time and have low efficiency, and also uses excessive organic solvents (Azmir et al., 2013;Bubalo et al., 2014;Carda-broch et al., 2008). As the process of extraction develops, many new extraction methods use fewer solvents and consider the efficiency of the extraction time (Azmir et al., 2013;Tang et al., 2012;Wang et al., 2011). Recently, alternative solvents have been found that can replace organic solvents that are low-volatile ionic liquids, capable of dissolving specific compounds, heat-stable, and non-flammable (Chemat et al., 2012). An ionic liquid as a green solvent can be combined with non-conventional extraction methods, mainly using microwave-assisted extraction methods (IL-MAE) (Chemat and Vian, 2014). Some studies have reported that the IL-MAE method successfully extracts secondary metabolite compounds optimally including flavonoid group (Ahmad et al., 2017b;Tang et al., 2013;Wei et al., 2012;Zhang et al., 2014;.
However, the studies related to optimization and application of green extraction using the IL-MAE method and research on inhibition of the lipoxygenase activity from green grass jelly leaves have not been reported. Therefore, this study contributes to the knowledge of the extraction engineering of secondary metabolite and biological properties of this plant. This study aimed to obtain an optimal IL-MAE method to the extraction of flavonoids from green grass jelly leaves and investigate its lipoxygenase inhibitory activity.

Plant materials
Green grass jelly leaves were obtained from Bogor, West Java, Indonesia and was identified at Laboratory of Biosystematics, Indonesian Institute of Science (Lembaga Ilmu Pengetahuan Indonesia) Cibinong, West Java, Indonesia. The sample specimen (DC-001984-F) was collected at the Laboratory of Pharmacognosy-Phytochemistry, Faculty of Pharmacy, Universitas Indonesia, Depok, West Java, Indonesia.

Ionic liquid-based microwave-assisted extraction procedure
The IL-MAE method was performed based on literature (Ahmad et al., 2017a;2017b), with a slight modification. Briefly, a 0.5 g of the dried sample of Green grass jelly leaves were extracted using [BMIM]Br solvent in the microwave (Modena 900 W) with some conditions as can be seen in Table 1. The separation of the residue and the extract solution was conducted by filtration. The filtrate (extract) was cooled and left for 10-12 hours at the room temperature. Then, the filtrate was partitioned with liquid-liquid extraction using ethyl acetate. The ethyl acetate layers were separated and evaporated to obtain the dried extracts.

Determination of total flavonoid content
The total flavonoid content (TFC) of each extract was analyzed by aluminum chloride colorimetry method based on literature (Baba and Malik, 2015;Chang et al., 2002;Do et al., 2014) with a slight modification. In brief, 0.5 ml of sample solution or the standard solution were mixed in 1.5 ml methanol, 0.1 ml 10% aluminum chloride, 0.1 ml of 1 M sodium acetate, and 2.8 ml aqua DM (double-distilled water). The mixture was incubated for 30 minutes at the room temperature, and absorbance was measured at 434 nm optimum wavelength. Quercetin solution (3, 4, 5, 6, 7, and 8 µg/ml, respectively) was used as standards.
The yield of TFC in extract sample was examined using equation formula of standards (Y = 0.0568X + 0.0576 and R 2 = 0.9992, where Y is the yield of TFC and X is the absorbance), and the result was expressed as milligram quercetin equivalent per gram extract (mg QE/g extract).

Lipoxygenase inhibitory activity assay
The lipoxygenase inhibitory activity (LIA) assay was performed according to the study reported by Dzoyem et al. (2015). Briefly, a 10-µl extract and baicalein solution were added 1,690 µl of 0.2-M borate buffer solution, 1,000 µl of 300 µM linoleic acid substrate solution, and the mixture was incubated for 10 minutes at 25°C. After the incubation, the mixture was added to 300 µl of 1,000 unit/ml lipoxygenase solution and was incubated again for 15 minutes at 25°C. Then, the sample solution was added to 1,000 µl methanol, and the absorbance was measured at 234 nm using a spectrophotometer UV. Percentage of LIA was examined using equation formula as follows: where A is the absorbance of the blank solution with an enzyme; B is the absorbance of blank solution without enzyme; C is the absorbance of the sample solution with an enzyme; and D is the absorbance of sample solution without enzyme.

Optimization of the IL-MAE method by response surface methodology
IL-MAE method optimization was conducted using response surface methodology (RSM) to estimate the interaction of process and factors parameters (independent parameters) against the TFC and LIA (dependent parameters). Box-Behnken design (tree-factor-three level) was used in this study, with 17 trials (in triplicate) for the extraction parameters optimization (Table 1). A regression model was examined with a multilinear quadratic model using Design-Expert v10 software.

Extraction process and pre-optimization
The extraction process was performed using the IL-MAE method to obtain the optimum extraction on total flavonoid content (TFC) and LIA from green grass jelly leaves. Pre-optimization was conducted with some parameters variable condition including extraction time, liquid-solid ratio, and [BMIM]Br concentration to know the best condition. In this study, each parameter's variable was selected (Table 1) based on literature (Fan et al., 2012;.

Total flavonoid content determination
Based on the result of total flavonoid content (TFC) determination (as can be seen in Fig. 1) demonstrated that the maximum of TFC (30.32 mg QE/g) was obtained from fifth trials. On the other hand, the lowest of TFC (13.20 mg QE/g) showed in second trials. Based on different combination of parameter variable at the experimental design, showed extraction time effect of TFC on the range from 5 to 25 minutes performed to obtain the optimal of extraction condition and the optimum of extraction time obtained for 15 minutes extraction time. Regarding liquidsolid ratio, the maximum of TFC was obtained at 40 ml/g with the range from 30 to 50 ml/g the increase of rate (after 40 ml/g) led to a decrease on the TFC. Meanwhile, [BMIM]Br concentration effect of TFC extraction on the range from 1 to 3 mol/l conducted to give the optimal concentration and the optimum concentration obtained at 2 mol/l.

Determination of lipoxygenase inhibitory activity
The preliminary test was performed to obtain the optimum conditions in the LIA assay using some parameters including the pH buffer of the boric acid solution, the linoleic acid substrate, and the lipoxygenase enzyme according to literature (Kumari et al., 2011;Xu et al., 2012). In this study, the optimization of pH performed on 8.0, 8.5, 9.0, and 9.5 and the optimum condition was obtained at pH 8.5 ( Fig. 2A). Optimization of the linoleic acid substrate solution was conducted to determine the optimum substrate concentration, when binding correctly with the enzyme. Based on the previous study, Xu et al. (2012)    was done on the concentration of 100, 200, 300, 400, and 500 µM. The optimum condition was 300 µM (Fig. 2B), whereas, the optimization of enzyme solution was performed using several concentrations of 400, 800, and 1,000 unit/ml, and the optimum solution was 1,000 unit/ml (Fig. 2C).
The LIA assay was conducted using baicalein as a standard (Putri et al., 2017). Baicalein is a flavonoid from flavonols groups (Kusmardiyani et al., 2014) that has the capability to inhibit the lipoxygenase activity due to hydroperoxy-octadecadienoate (HPOD) was not formed (Putri et al., 2017). The higher the baicalein content, the less HPOD was formed so that, higher the inhibition percentage (Putri et al., 2017). Table 2 demonstrates that the baicalein concentration from 0.1 to 0.25 µg/ml can inhibit from 33.36% to 80.05% with the linear regression equation of y = 0.7864x + 1.8526 (R 2 = 0.9975). In this study, the IC 50 value of baicalein was 0.2 µg/ml which indicates that the enzyme works well. Figure 3 showes the highest of the LIA in 12th trials with an inhibitory percentage of 69.29%. Although the highest levels of LIA were not at fifth trials (where the most top of the TFC) and 12th trials also used the optimum condition variable include 40 ml/g liquid-solid ratio, 15 minutes extraction time, and 2 mol/l [BMIM]Br concentration.

Optimization of the IL-MAE method
Three factors with three levels (−1, 0, +1), including liquid-solid ratio (30, 40, and 50 ml/g), extraction time (5, 15, and 25 minutes), and [BMIM]Br concentration (1, 2, and 3 mol/l) were optimized using RSM with Box-Behnken design. Data analysis was performed to obtain the optimum condition for extraction of flavonoid using the IL-MAE method and LIA, the specific protocols of experimental design of parameters conditions are shown in Table 1. Based on the obtained results using RSM analysis with Design Expert v10 software, in Figure 4, demonstrated the threedimension contour of the response surface for interaction between the factor and process parameters.
To further study the response surface plot for the TFC and LIA of the obtained extracts as a function were analyzed and developed based on the equation formula from RSM analysis results to determine the optimum condition, including liquid-solid ratio to extraction time ([BMIM]Br concentration = 2 mol/l), liquid-solid ratio to [BMIM]Br concentration (extraction time = 15 minutes), and extraction time to [BMIM]Br concentration (liquid-solid ratio = 40 ml/g). The different experimental designs  of the extraction process with response (TFC and LIA) are demonstrated in Table 3. The obtained data were calculated by multilinear regression analysis based on the response surface.
The final model of TFC and LIA from green grass jelly leaf (C. barbata) was given by: TFC = 2.43A + 2.43B + 1.42C + 0.33AB − 3.20AC − 0.46BC − 4.90A 2 − 3.10B 2 − 0.98C 2 +27.13 and LIA = 0.066A + 8.22B + 0.97C + 2.47B − 5.86AC + 1.96BC − 9.99A 2 − 13.75B 2 − 13.11C 2 + 63.53, respectively. Table 4 demonstrates the significant model with a F-value of 3.90. There is only a 4.33% chance that a "Model F-value" this large could occur due to noise. The value of "Prob > F" less than 0.0500 indicated model terms were significant.    The "Lack of Fit F-value" of 4.08 implies the "Lack of Fit" is not significant relative to the pure error. There is a 10.41% chance that a "Lack of Fit F-value" this large could occur due to noise and non-significant "Lack of Fit" is good.
In Table 5, the model F-value of 9.03 implies the model is significant. There is only a 0.42% chance that a "Model F-values" this large could occur due to noise. The value of "Prob > F" less than 0.05 indicate model terms are significant. The significance of the value of 1.77 "Lack of Fit" with F value > 0.05 is not significant relative to the pure error. There is a 29.11% chance that a "Lack of Fit F-value" this large could occur due to noise. Table 6 shows the credibility of regression equations, the correlation coefficient "R-Squared" of 0.8416 (TFC) and 0.9207 (LIA) were obtained implies this model can express correlation of model more than 80% and 90%, respectively. A negative "Pred R-Squared" of TFC implied that the overall mean might be a better predictor of response than the current model, whereas the "Pred R-Squared" of LIA (0.2226) is not as close to the "Adj R-Squared" of 0.8188 as one might normally expect. "Adequacy Precision" measures the signal-to-noise ratio. The ratio of 5.671 (TFC) and 7.891 (LIA) indicates an adequate signal, where both ratios greater than four was desirable.
Based on the results of RSM analysis, the optimum condition was suggested with the parameter variable as follows: liquid-solid ratio of 38.21 ml/g, extraction time of 17 minutes, and [BMIM]Br concentration of 1.76 mol/l with TFC and LIA prediction of 26.38 ± 1.30 mg QE/g sample and 62.8558% ± 2.62%, respectively.

CONCLUSION
Based on the results, the design of the IL-MAE method to TFC extraction and LIA from Green grass jelly leaf (C. barbata) has attempted. The optimum condition of the IL-MAE method was obtained the parameter variables include 17 minutes extraction time, 1.76 mol/l [BMIM]Br concentration, and 38.21 ml/g liquid-solid ratio with the TFC prediction value of 29.07 mg QE/g sample.
This research was an early stage to develop the extraction method to obtain the target compound from natural products plant in an efficient, rapid, and environmental friendly. Future research should be performed for the optimization of extraction procedure in other parameter variables, pilot scale, isolation, and identification of flavonoid content (mainly the active target compound) from this plant by using green chemistry approaches. The results were obtained using Design Expert v10.03 software.