E. Simeonov, V. Koleva, Ch. Chilev

Transcription

1 Journal of the University of E. Chemical Simeonov, Technology V. Koleva, Ch. and Chilev Metallurgy, 46, 3, 0, SOLID LIQUID EXTRACTION OF FUROSTANAL SAPONINS FROM TRIBULUS TERRESTRIS E. Simeonov, V. Koleva, Ch. Chilev University of Chemical Technology and Metallurgy 8 Kliment Ohridsky, 756 Sofia, Bulgaria evgeni@uctm.edu Received 05 May 0 Accepted July 0 ABSTRACT Experimental kinetics was obtained by extraction from plants. The experiments were carried out with the solidliquid system Tribulus terrestris ethanol in a periodical stirred vessel. The impact of the temperature, liquid solid ratio and ethanol content in the extraction solvent on the furostanal saponins rate of extraction is investigated. The kinetic equation was used for the calculation of the standard function which is a way to investigate the solid-liquid extraction process. Using the standard function method, the effective diffusion coefficient D e was calculated for the solid-liquid system. Keywords: solid-liquid extraction, kinetics, effective diffusion coefficient, Tribulus terrestris, furostanol saponins. INTRODUCTION Tribulus terrestris is a flowering plant in the family Zygophyllaceae, native to warm temperate and tropical regions of the Old World in southern Europe, southern Asia, throughout Africa, and Australia. The entire aboveground part (Herba) of the plant is used for the preparation of extracts. They contain saponins (trilin, diostsin, gratsilin, protodioscin, metilprototribestsin, kikubasoponin), flavonoids (rutin, astragalin, quercetin, kempferol, isorhamnetin), sterols (sitosterol, kaempherol), fatty oils and potassium salts []. The plant s compounds have diuretic and tonic effect to human body and it is used by kidney stones. The main effect is to stimulate the reproductive system. The most valuable substances are the furostanol saponins and especially Protodioscin. The process of extraction of useful components from plant raw material is almost ever limited by the transfer inside the pores of the solid phase [-4]. Each experimental kinetic curve includes in a hidden way all factors influencing the diffusion process velocity, such as: polydispersion, anisotropy, solid particles form, characteristical change of concentration in the liquid phase. Quantitatively, these factors are estimated by the effective diffusion coefficient [5]. The exact calculation of D eff is important for the engineering design of the process. In the practice there are experimental methods [6] and methods combining experimental data and analytical solutions of the process. For the calculation of D eff the method of Standard function [,7,8] is used. METHOD OF SOLUTION The proposed method is based on the analysis of the kinetic behavior during periodical solid-liquid extraction by considering a diffusion model: C ( x, τ τ ) = D eff C X + t X C X () where: C - concentration in pores of the particles, kg.m -3 ; τ - time, s; t - shape factor, dimensionless. Method using Standard function Equation () combined with boundary conditions gives the following results for the three classical forms of the solid phase []: 309

2 Journal of the University of Chemical Technology and Metallurgy, 46, 3, 0 C C Deτ 0 C 4.( t + ) µ R =. e 0 Cm + β µ + 4( t + ). β ( + β ) where t=0 for plate, t= for cylinder and t= for sphere. If () is compared with the Standard function, which is: * C0 C Φ ( τ ) = = A B exp( Hτ ) (3) C0 Cm it is obvious that the coefficients A, B and H are respectively equal to [7]: A = (4) + β () 4.( t + ) B = (5) µ + 4( t + ). β ( + ) β µ De H = (6) R By A (â=0) D eff can be obtained like follows: HR B D eff = (7) ( t + ) EXPERIMENTAL The kinetic experiments were carried out in a stirred vessel with a control of the temperature and by mixing speed high enough to eliminate the external mass transfer resistance. During the experimental runs the concentration in the liquid phase C is changing with time (ô). The furostanol saponins concentration in the liquid phase was measured by spectro-photometric analysis according to Ph.Eur...5 (using Protodioscin as a standard) [9, 0] and using Spectrophotometer - BOECO Germany S- UV/Vis. The procedure follows the steps: exact volume of extract is evaporated to dry; methanol is added and the solution is filtered through a paper filter blue ribbon to ml; another 3 ml of methanol and 5 ml of reagent are added (the reagent is p-dimethylaminobenzaldehyde); the solution is heated in a water bath to 58 C for hours; after the solution cools down the absorption is measured at a wavelength of 55 nm against a blank (methanol + reagent); the comparative solution is % aqueous solution of cobalt dichloride hexahydrate (CoCl.6H O), whose absorption is measured at a wavelength of 55 nm against water. In calculating the content of furostanol saponins as an equivalent of protodioscin, correlation coefficient is used. Using the linearity of the function CoCl.6H O/ furostanol saponins, the calibration curve was obtained according to the equation: = 48.58c A (8) where A is the absorbability and c is the concentration of furostanol saponins. Three experimental parameters were changed to investigate their influence on the extraction process. They are temperature, liquid-solid ratio and composition of the extraction solvent mixture. Tests were carried out at 0 C, 5 C and 30 C by fixed liquid-solid ratio î = 0.0 m 3 kg - ; and at î = 0.0 m3.kg-, î = 0.0 m 3 kg - and î = 0.03 m 3 kg - by fixed temperature t = 30 C. The impact of ethanol concentration on the valuable compound concentration in the liquid phase after 700 s of extraction is determinate by experiments at 0 C and î = 0.0 m 3 kg - with 50 %, 70 % and 96 % ethanol as a solvent, respectively. RESULTS AND DISCUSSION The experimental data for the investigated system solid-liquid are shown in Figs. and. They can be described with acceptable accuracy by equation (9) C = A B exp( H ) (9) τ A, B and H are numerically determined on the basis of the experimental results. Their values are listed in Tables and for the different experimental conditions. Experiment were carried out at 0 o C, 5 o C and 30 o C and fixed liquid-solid ratio î = 0,0 m 3 kg -. Furostanol saponins concentration in the liquid phase is highest at 30 o C and analogically goes down with the temperature. This is shown on Fig.. Based on these 30

3 E. Simeonov, V. Koleva, Ch. Chilev Table. Values of A, B and H by different extraction temperatures. t = 0 C t = 5 C t = 30 C À Â Í Table. Values of A, B and H by different liquid-solid ratios. = î 0,0 = î 0,0 = î 0,03 m 3 kg - m 3 kg - m 3 kg - À Â Í Fig.. Experimental kinetics curves in a stirred batch apparatus by different extraction temperatures. Fig.. Experimental kinetics curves in a stirred batch apparatus by different liquid-solid ratios. 3

4 Journal of the University of Chemical Technology and Metallurgy, 46, 3, 0 Fig. 3. Concentration of furostanol saponins in the liquid phase depending on the solvent composition. Fig. 4. Standard functions calculated based on the experimental results by different temperatures of extraction. results it is considered that other experimental conditions impact on extraction rate should be investigated at 30 î Ñ. Higher temperature is not recommended due to the possibly of fibre extraction which will hinder extract purification. Solvent composition showed significant impact on the extraction of the value compounds. The results are presented on Fig. 3. It is visible that the best furostanol saponins extraction is achieved with 70 % ethanol. This corresponds to the data published in the literature before. Li, Zhang et al. carried out different experiments to determinate the impact of the solvent on the value compound extraction from Tribulus terrestris. They used 30 %, 50 % and 70 % ethanol, methanol and water as solvent and it was found out that the concentration of the extracted substances is highest by using 70 % ethanol and lowest by using water. The standard function is calculated for the three different process temperatures. The following equations are obtained from (9) for t = 0 o C * ( 0, τ ) Ô () τ = 0,967,008. e (0) for t = 5 o C * ( 0,0004. τ ) Ô () τ = 0,9773,005. e () for t = 30 o C * ( 0,0004. τ ) Ô () τ =,007,004. e () The Standard functions defined by equations (0 - ) for the three experimental temperatures are shown 3

5 E. Simeonov, V. Koleva, Ch. Chilev Acknowledgements The research leading to these results has received funding from the European Community s Seventh Frame- Table 3. Conditions for calculating Ô*(t). t = 0 o C t = 5 o C t = 30 o C Ñ 0, kg m -3 8,8 8,8 8,8 Ñ ð, kg m -3,55,7,3 β 0,0947 0,054 0,0695 Table 4. Values of D eff calculated by the method of standard function. t = 0 o C t = 5 o C t = 30 o C D eff, m s - 0, , , in Fig. 4. The conditions for calculating Ô*(t) are presented in Table 3. It is well known that the representations of the experimental data using the Standard function give the possibility to predict the kinetics when there is a change in the liquid-solid ratio (î) and on an internal diffusion regime. Using the Standard function method the effective diffusion coefficients for liquid-solid system at three different temperatures are calculated and presented in Table 4. CONCLUSIONS The experimental extraction kinetics of the system Tribulus terrestris/- ethanol in a batch stirred extractor was studied. The optimal extraction process conditions were determinate: temperature - 30 C, 70 % ethanol solution as an extraction solvent and liquidsolid ratio î = 0.0 m 3 kg -. Using the method of standard function the coefficient of effective diffusion was calculated for different experiment conditions. That gives the opportunity of calculating and managing the extraction process. work Program (FP/007-03) under grant agreement (No. PIAP-GA ). REFERENCES. J. Conrad et al., A novel furostanol saponins from Tribulus Terrestris of Bulgarian origin, Fitoterapia, 75, 004, 7-.. G.A. Axelrood, W. Lisjanski, Extraction (Solid-liquid systems), Chimia, St. Peterburg, USSR, 974, 5-8, (in Russian). 3. E. Simeonov, I. Tsibranska, A. Minchev, Soli-liquid extraction from plants - experimental kinetics and modelling, Chem. Eng. Journal, 73, 999, E. Simeonov, I. Seikova, I. Penchev, A. Minchev, Modelling of a screw Solid-liquid Extractor thought Concentration Evolution Experiments, Ind. Eng. Chem. Res., 4, 003, E. Simeonov, A. Minchev, th Romanian International Conference on Chemistry and Chemical Engineering, RICCCE, Bucharest, Romania, September 3-5, P.G. Romankov, V. Frolov, Mass transfer in chemical technologiy, Chimia, St. Peterburg, USSR,990, 6-34, (in Russian). 7. A. Minchev, S. Minkov, A model for determination of the effective diffusion coefficient by the standard function technique, J. App. Chem., 57, 984, E. Simeonov, I. Seikova, I. Penchev, A. Minchev, 33

6 Journal of the University of Chemical Technology and Metallurgy, 46, 3, 0 Scale-up of the Solid-Liquid Extraction Using Characteristic Function Technique, Industrial and Chemical Chemistry Research, 43, 004, E. Combarieu et al., Furostanol saponins from Tribulus Terrestris, Research and Development Laboratories, Indena, Italy, acc 5, D. Dinchev et al., Distribution of steroidal saponins in Tribulus Terrestris, Phytochemistry, 07, 007, 3. 34