- Email: [email protected]
Microwave-assisted hydrothermal extraction of natural malic acid for the synthesis of low transition temperature mixtures
Journal of Cleaner Production 113 (2016) 919e924
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Note from the field
Microwave-assisted hydrothermal extraction of natural malic acid for the synthesis of low transition temperature mixtures Chung Loong Yiin a, Suzana Yusup a, Armando T. Quitain b, *, Mitsuru Sasaki b, Yoshimitsu Uemura a, Tetsuya Kida b a
Biomass Processing Technology Cluster, Center of Biofuel and Biochemical Research, Mission Oriented Research (Green Technology), Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Tronoh, Perak, Malaysia Department of Applied Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 July 2015 Received in revised form 9 December 2015 Accepted 15 December 2015 Available online 23 December 2015
This work describes the utilization of microwave hydrothermal extracted malic acid from cactus, lophatherum herb, papaya and Luffa cylindrica as hydrogen bond donor for the synthesis of natural low transition temperature mixtures (LTTMs) with sucrose as hydrogen bond acceptor. The effects of parameters including reaction temperature, extraction time, mass of sample and oxidant, H2O2 were discussed. The saturation equation was used to fit with the experimental data, observing only a slight loss of the goodness of fit. The optimum conditions for microwave hydrothermal extraction were found to be at 1 g of sample, 200 C and 45 min in the presence of hydrogen peroxide (H2O2) as oxidant. Consequently, the proposed method was successfully applied to extract malic acid from plants and fruits for the synthesis of LTTMs. The LTTMs prepared from the extracted malic acid have identical physicochemical properties with the LTTMs derived from commercial malic acid due to the existence of hydrogen bond and the ability to dissolve lignin. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Microwave-assisted hydrothermal extraction Malic acid Kinetic modelling Synthesis Low transition temperature mixture Delignification
1. Introduction Conventional extraction techniques such as soaking, maceration, water percolation and solvent extraction for natural products normally require long extraction time and large volume of organic solvents. These also result into degradation of active compounds obtaining relatively lower extraction efficiency of the target com -Puigmartí et al., 2011; Chan et al., 2011; Wu et al., pounds (Molto 2012). Hydrothermal extraction using water is a natural and green alternative for natural product extraction at high temperature and pressure condition. This method has been used to extract polar organic compounds or to decompose lignocellulosic materials to produce valuable compounds such as saccharides and aromatic acids (Kitada et al., 2009; Matsunaga et al., 2013).
* Corresponding author. Tel.: þ81 96 342 3665; fax: þ81 96 342 3679. E-mail addresses: [email protected] (C.L. Yiin), drsuzana_yusuf@ petronas.com.my (S. Yusup), [email protected] (A.T. Quitain), msasaki@ kumamoto-u.ac.jp (M. Sasaki), [email protected] (Y. Uemura), [email protected] (T. Kida). http://dx.doi.org/10.1016/j.jclepro.2015.12.053 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
Microwave possesses many advantages for the extraction of bioactive compounds (Sanchez-Aldana et al., 2013) such as reduced processing time, higher extraction rates and more accurate control of reaction conditions (Tsubaki et al., 2012; Yemis and Mazza, 2012). Microwave-assisted extraction has been proven to be a promising technique for the extraction of phytochemicals from botanical plants and food samples (Xiao et al., 2012; Quitain et al., 2013). Direct interaction of microwaves helps to heat up the solvent and also lead to a tremendous increase in internal pressure, rupture of plant tissue and release of active compounds into the solvent (Dhobi et al., 2009; Mandal et al., 2007). Francisco et al., 2012 introduced 26 types of natural low transition temperature mixtures (LTTMs) from environmentally benign starting materials which show glass transition points instead of eutectic melting points. LTTMs can be prepared from cheap, readily available and toxicologically well characterized starting materials (Francisco et al., 2013). Preparation of LTTMs is in vicinity to the synthesis of deep eutectic solvents (Cvjetko Bubalo et al., 2014). The hydrogen bonding interactions of LTTMs lead to some of the promising characteristics of ionic liquids as solvents and shared by deep eutectic solvents (Francisco et al., 2012). The potentials of LTTMs to degrade the lignocellulosic biomass structure were
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evaluated and less biomass particles could be noticed after the pretreatment with the mixtures derived from malic acid (Francisco et al., 2012). Thus, natural abundant resources such as plants and fruits which contain high malic acid content have high potential to be used for the synthesis of LTTMs. The aim of the present work was to utilize the malic acid obtained from papaya, cactus, Luffa cylindrica and lophatherum herb via microwave-assisted hydrothermal extraction for the synthesis of natural LTTMs. The influencing parameters including extraction temperature, reaction time, mass of sample and oxidant, H2O2 were investigated. The extraction kinetics were modelled using saturation equation and compared with experimental results. The comparative study of the LTTMs prepared from commercial malic acid and microwave hydrothermal extracted malic acid in terms of hydrogen bonding and lignin solubility was also conducted. 2. Materials and methods 2.1. Raw materials and chemicals The plants and fruits with high content of malic acid such as papaya, cactus, L. cylindrica and lophatherum herb were used as the source of hydrogen bond donor for the synthesis of LTTMs. All these samples were ground using a blender with the power rating of 300 W for 20 min and dried completely in an oven at 50 C for 7 days. The sucrose (>97%) was obtained from Wako Pure Chemical Industries Ltd as the source of hydrogen bond acceptor. On the other hand, the lignin (96%, alkali lignin) was obtained from Tokyo Kasei Kogyo Co., Ltd. 2.2. Microwave-assisted hydrothermal extraction experiments The microwave used for the extraction of malic acid was CEM MARS 5 microwave digester. In each experimental run, a 50 mL of distilled water and dried sample were charged into the reactor. The microwave power of 600 W and pressure of 50 bar were chosen in this study (Zohourian et al., 2011). The solvent was centrifuged after the process of extraction. The supernatant was separated from the residue through filtration using an Advantec ashless quantitative filter paper (Grade 5C, <5 mm). The microwave-hydrothermal extraction was conducted at extraction temperatures of 140, 160, 180 or 200 C and reaction time at 15, 30, 45 or 60 min. The experiment was repeated with increasing mass of sample (0.1, 0.5, 0.75 and 1 g) and in the presence of oxidant, H2O2 solution (35 wt% H2O2) at equal proportion with the sample in a reactor (XP-1500 Plus). 2.3. High performance liquid chromatography (HPLC) analysis The percentages of malic acid extracted from the samples were analyzed by using JASCO high performance liquid chromatography (HPLC). HPLC analysis was conducted by using potassium dihydrogen phosphate buffer as a mobile phase with UV detection at l ¼ 210 nm. The pH value of mobile phase was adjusted to pH 2.8 by using 10 mM of phosphoric acid. The column used was Wakosil-II 5C18 HG Prep. The flow rate of the mobile phase was fixed at 0.5 mL/min and 20 mL as injection volume. 2.4. Mathematical model The overall kinetic data based on the yield of malic acid by microwave hydrothermal extraction were modelled using the saturation equation (Wong-Paz et al., 2014). The equation used was:
1 k 1 1 þ ¼ Ct Ceq t Ceq
(1)
where Ct, Ceq and k represents solute concentration in liquid phase at any time, the equilibrium solute concentration and the constant that describes the released fraction, respectively. The concordance between experimental data and calculated value is established by the correlation coefficient (R2). 2.5. Synthesis and analysis of LTTMs LTTMs were synthesized by adding sucrose into microwavehydrothermal extracted malic acid and heated up slowly in an oil bath with the molar ratio of malic acid-sucrose-water (MSW 1:3:10) until all the sucrose was dissolved. The excessive water content in the LTTMs was removed by freeze-drying (EYELA FDU1200) at 45 C, and stopped once the samples showed constant weight (Yiin et al., 2016). The hydrogen bonding of LTTMs was evidenced using Frontier FT-IR Spectrometer (PerkinElmer) equipped with attenuated total reflectance (ATR). The water content of freeze dried LTTMs was measured by using the Metrohm 870 Karl Fischer Titrino Plus. The solubility of lignin was determined using cloud point method (Francisco et al., 2012). 3. Results and discussion The malic acid is present in the plant materials being investigated such as papaya (Morais et al., 2015), cactus (Moßhammer et al., 2006), L. cylindrica (Chang et al., 2007) and lophatherum herb (Kozukue, 1986). Nevertheless, the extraction of malic acid under microwave-assisted hydrothermal conditions and specific quantifications of malic acid content of plant materials have not been reported. Thus, the spectra obtained from fruits and plants were compared with the standard in order to investigate the total area of peak for extracted malic acid at respective retention time. In this context, a calibration curve of L-malic acid's concentration (ppm) ^ against peak area (GEV.sec) was plotted for four working aqueous solutions ranging from 250 to 1000 ppm. The linear equation for the calibration curve is shown below:
y ¼ 106 x þ 60:674
R2 ¼ 0:9997
(2)
where x is frequency of output voltage/amplitude of spontaneous ^ signals (GEV.sec) and y is concentration of extracted malic acid (ppm). The results indicated that the malic acid in fruits and plants had been extracted by the proposed microwave-hydrothermal approach. 3.1. Influence of reaction temperature and extraction time on the malic acid yield It can be seen in Fig. 1 that the malic acid yield increased with increasing temperature and time up to 200 C and 45 min, respectively. Equilibrium was reached at temperature above 180e200 C. The results were comparable with the works of Zohourian et al. (2011) in which the extraction yield increased with increasing temperature and the yield decreased as a result of further degradation of target compounds above the optimum temperature. The solvent power increased at higher temperature due to the drop in viscosity and surface tension, facilitating the solvent to solubilize solutes and further improving matrix wetting
C.L. Yiin et al. / Journal of Cleaner Production 113 (2016) 919e924
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Fig. 1. Malic acid yield for microwave hydrothermal extraction at different extraction time durations (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
and penetration (Khajeh et al., 2009; Mandal et al., 2007). The high temperature may reach far above the boiling point of the solvent in closed vessels, leading to higher extraction efficiency (Veggi et al., 2013) Besides, hydrolysis of some organic compounds in the feedstocks into low molecular weight carboxylic acids might also occur at high temperature conditions. On top of that, the malic acid yield increased from 15 to 45 min but relatively lower values of malic acid yield were observed at treatment time longer than 45 min, due likely to degradation of the target compounds (Zohourian et al., 2011; Mandal et al., 2007). 3.2. Influence of sample's mass on the malic acid yield Fig. 2 shows the malic acid yield increased sharply with the mass of sample from 0.1 to 0.5 g. This phenomenon might be due to the increased microwave absorptivity with increasing amount of sample, which was responsible for the increase in yield of malic acid (Quitain et al., 2013). In this context, the solvent volume must be sufficient to ensure that the entire sample is immersed in the solvent throughout
3.3. Influence of oxidant, H2O2 on the malic acid yield Fig. 3 depicts the increment of malic acid yield for papaya, cactus, L. cylindrica and lophatherum herb in the presence of oxidant, H2O2 which are 11.4, 20.3, 30.0 and 47.5% respectively. This indicates that H2O2 significantly affects the malic acid yield from fruits and plants through microwave-assisted hydrothermal extraction. This is presumably due to the easy formation of OH radicals from H2O2 that could help in the production of lowmolecular-weight carboxylic acids (Quitain et al., 2002). 3.4. Model fitting for microwave-assisted hydrothermal extraction The kinetic data obtained in this study were modelled based on malic acid yield with respect to different reaction durations and temperatures. As shown in Fig. 4, the linearity of equation (1) was observed for all the temperatures with most of the correlation
3000 Yield (mg malic acid/g sample)
the whole irradiation process especially for the sample that will swell during the extraction (Tatke and Jaiswal, 2011). Nonetheless, the malic acid yield started to reduce when the mass of sample exceeds 0.5 g until 1.0 g of sample as the solvent-to-solute ratio decreased resulting in lower yield (Quitain et al., 2013).
2500 Papaya
2000
Luffa Cylindrica Cactus
1500
Lophatherum Herb
1000 500 0 0
0.2
0.4
0.6
0.8
1
1.2
Mass of sample (g) Fig. 2. Malic acid yield against mass of sample.
Fig. 3. Malic acid yield with or without oxidant, H2O2.
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coefficient values (R2) above 0.9000, indicating a good fit of the kinetic data with the linearized saturation equation. Model parameters, equilibrium concentration (Ceq) and extraction rate constant (k) were determined by fitting the experimental data presented in Table 1. The kinetic data of microwave-assisted hydrothermal extraction of malic acid from plants and fruits were illustrated in Fig. 5 with respect to the predictions given by the saturation equation model. Overall, a good fit between experimental data and theoretical extraction curves was observed. 3.5. Comparison of LTTMs derived from commercial and microwave-assisted hydrothermal extracted malic acid 3.5.1. Fourier transform infrared spectroscopy (FTIR) spectra analysis It can be seen in Fig. 6 that the representative peak of carboxylic acid group of malic acid with wavenumber 1710 cm1 for the C]O group broaden in the respective LTTMs due to hydrogen bonding. The hydroxyl group of malic acid had direct interaction with the carbonyl group by the formation of a stable dimetric hydrogenbonded structure in the liquid phase. Besides, the peaks involved in the H-bonding responsible for the formation of the LTTMs were shifted and broaden within the wavenumber range of 2500e3800 cm1 for the OH groups due to the stretching absorption of hydrogen bonding. Dotted red lines (in the web version) were used to delimit the main bands for the peak shifts and malic acid peaks. The results were comparable with the works of Francisco et al. (2012) based on the hydrogen bond existing between lactic acid and choline chloride as observed by FTIR analyses. 3.5.2. Screening of lignin solubility An overview of the results of screening of lignin solubility in LTTM is tabulated in Table 2, showing all mixtures to have the ability to dissolve lignin which was comparable with the lignin
Table 1 Predicted equilibrium concentrations and kinetic parameters obtained using the saturation equation. Sample
Temperature ( C)
Ceq (mg/g)
k (min1)
R2
Papaya
140 160 180 200 140 160 180 200 140 160 180 200 140 160 180 200
67.11 108.70 384.62 384.62 384.61 434.78 526.32 526.32 76.92 131.58 208.33 204.08 52.63 66.23 131.58 158.73
4.65 13.42 37.38 31.62 13.42 19.17 22.74 21.32 9.17 15.41 19.54 16.86 5.18 8.30 16.91 20.40
0.95 0.93 0.91 0.93 0.92 0.91 0.92 0.91 0.91 0.92 0.92 0.89 0.87 0.91 0.88 0.88
Cactus
Luffa cylindrica
Lophatherum herb
solubility capacity of the LTTM prepared from commercial malic acid (12.32 wt%). The LTTM derived from cactus had the highest lignin solubility capacity followed by lophatherum herb, papaya and L. cylindrica. Thus, the malic acid in plants and fruits had a great potential to be used for the synthesis of natural LTTMs for biomass delignification.
4. Conclusions The optimum conditions giving the maximum malic acid yield for papaya, cactus, L. cylindrica and lophatherum herb via microwave-assisted hydrothermal extraction were 1 g of sample, 200 C and 45 min in the presence of hydrogen peroxide (H2O2) as oxidant. A good fit between experimental data and theoretical extraction curves was observed using saturation equation. Besides, the hydrogen bonding of LTTMs was evidenced by the shifts in the
Fig. 4. Plot of 1/Ct values with respect to 1/t (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
C.L. Yiin et al. / Journal of Cleaner Production 113 (2016) 919e924
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Fig. 5. Kinetic modelling of malic acid yield from microwave-assisted hydrothermal extraction (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
Fig. 6. FT-IR spectra of extracted malic acid, sucrose and LTTM (MSW 1:3:10) (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
Table 2 Water content and lignin solubility in wt % for the LTTMs synthesized from commercial and natural malic acid. Name MSW MSW MSW MSW MSW
1:3:10 1:3:10 1:3:10 1:3:10 1:3:10
(commercial malic acid) (papaya) (cactus) (Luffa cylindrica) (lophatherum herb)
Water content (wt %)
Lignin (wt %)
7.89 7.58 7.61 7.36 7.54
12.32 9.38 10.12 9.16 9.58
representative peaks of the involved bonds in the FTIR spectra. The LTTMs derived from microwave hydrothermal extracted malic acid had comparable lignin solubility capacity with the LTTM prepared from commercial malic acid.
Acknowledgements The authors would like to acknowledge the funding supports from Fundamental Research Grant Scheme (FRGS) (0153AB-I89)
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and Japan Society for the Promotion of Science (JSPS) Bilateral Joint Research Program. References Chan, C.H., Yusoff, R., Ngoh, G., Kung, F.W., 2011. Microwave-assisted extraction of active ingredients from plants e a review. J. Chromatogr. A 1218, 6218e6225. Chang, K.W., Moon, C.S., Lee, H.D., Lee, C.J., Lee, U.C., 2007. Determination of the effective components in the various parts of Luffa cylindrica (L.) Roemer and development to remove the flesh from its fruit: (I) e determination of chemical components in the various parts of Luffa cylindrica (L.) Roemer by GC and GC/ MS. J. Korean Soc. Appl. Biol. Chem. (F) J. Korean Agric. Chem. Soc. 34, 366e372. Cvjetko Bubalo, M., Radosevi c, K., Radoj ci c Redovnikovi c, I., Halambek, J., Gaurina Sr cek, V., 2014. A brief overview of the potential environmental hazards of ionic liquids. Ecotoxicol. Environ. Saf. 99, 1e12. Dhobi, M., Mandal, V., Hemalatha, S., 2009. Optimization of microwave assisted extraction of bioactive flavonolignan-silybinin. J. Chem. Metrol. 3 (1), 13e23. Francisco, M., Bruinhorst, A., Kroon, M.C., 2012. New natural and renewable low transition temperature mixtures (LTTMs): screening as solvents for lignocellulosic biomass processing. Green Chem. 14, 2153e2157. Francisco, M., Bruinhost, A., Kroon, M.C., 2013. Low-transition-temperature mixtures (LTTMs): a new generation of designer solvents. Angew. Chem. Int. Ed. 52, 3074e3085. Khajeh, M., Akbari Moghaddam, A.R., Sanchooli, E., 2009. Application of Doehlert design in the optimization of microwave assisted extraction for determination of zinc and copper in cereal samples using FAAS. Food Anal. Methods 3, 133e137. Kitada, K., Machmudah, S., Sasaki, M., Goto, M., Nakashima, Y., Kumamoto, S., Hasegawa, T., 2009. Antioxidant and antibacterial activity of nutraceutical compounds from Chlorella vulgaris extracted in hydrothermal condition. Sep. Sci. Technol. 44, 1228e1239. Kozukue, E., 1986. Changes in chemical components of bamboo shoots during storage at 1 C or 20 C. J. Jpn. Soc. Nutr. Food Sci. 39, 49e53. Mandal, V., Mohan, Y., Hemalath, S., 2007. Microwave assisted extraction e an innovative and promising extraction tool for medicinal plant research. Pharmacogn. Rev. 1 (1), 7e18. Moßhammer, M.R., Stintzing, F.C., Carle, R., 2006. Evaluation of different methods for the production of juice concentrates and fruit powders from cactus pear. Innov. Food Sci. Emerg. 7, 275e287. Matsunaga, Y., Wahyudiono, Machmudah, S., Askin, R., Quitain, A.T., Sasaki, M., Goto, M., 2013. Hydrothermal extraction and micronization of polysaccharides from Ganoderma lucidum in a one-step process. BioResources 8 (1), 461e471.
-Puigmartí, C., Permanyer, M., Castellote, A.I., Lopez-Sabater, M.C., 2011. EfMolto fects of pasteurisation and high-pressure processing on vitamin C, tocopherols and fatty acids in mature human milk. Food Chem. 124, 697e902. Morais, D.R., Rotta, E.M., Sargi, S.C., Schmidt, E.M., Bonafe, E.G., Eberlin, M.N., Sawaya, A.C.H.F., Visentainer, J.V., 2015. Antioxidant activity, phenolics and UPLCeESI(-)eMS of extracts from different tropical fruits parts and processed peels. Food Res. Int. 77, 392e399. Quitain, A.T., Faisal, M., Kang, K., Daimon, H., Fujie, K., 2002. Low-molecular-weight carboxylic acids produced from hydrothermal treatment of organic wastes. J. Hazard. Mater. 93, 209e220. Quitain, A.T., Kai, T., Sasaki, M., Goto, M., 2013. Microwaveehydrothermal extraction and degradation of fucoidan from supercritical carbon dioxide deoiled Undaria pinnatifida. Ind. Eng. Chem. Res. 52, 7940e7946. Sanchez-Aldana, D., Aguilar, C.N., Nevarez-Moorillon, G.V., Contreras Esquivel, J.C., 2013. Comparative extraction of pectic and polyphenols from Mexican lime pomace and bagasse. Am. J. Agric. Biol. Sci. 8, 309e322. Tatke, P., Jaiswal, Y., 2011. An overview of microwave assisted extraction and its applications in herbal drug research. Res. J. Med. Plants 5, 21e31. Tsubaki, S., Oono, K., Onda, A., Yanagisawa, K., Azuma, J.i, 2012. Microwave assisted hydrothermal hydrolysis of cellobiose and effects of additions of halide salts. Bioresour. Technol. 123, 703e706. Veggi, P.C., Martinez, J., Meireles, M.A.A., 2013. Fundamentals of microwave extraction. In: Chemat, F., Cravotto, G. (Eds.), Microwave-Assisted Extraction for Bioactive Compounds. Springer, New York, US, pp. 15e52. Wong-Paz, J.E., Contreras-Esquivel, J.C., Muniz-Marquez, D., Belmares, R., Rodriguez, R., Flores, P., Aguilar, C.N., 2014. Microwave-assisted extraction of phenolic antioxidants from semiarid plants. J. Agric. Biol. Sci. 9, 299e310. Wu, T., Yan, J., Liu, R., Marcone, M.F., Aisa, H.A., Tsao, R., 2012. Optimization of microwave-assisted extraction of phenolics from potato and its downstream waste using orthogonal array design. Food Chem. 133, 1292e1298. Xiao, X., Song, W., Wang, J., Li, G., 2012. Microwave-assisted extraction performed in low temperature and in vacuo for the extraction of labile compounds in food samples. Anal. Chim. Acta 712, 85e93. Yemis, O., Mazza, G., 2012. Optimization of furfural and 5-hydroxymethylfurfural production from wheat straw by a microwave-assisted process. Bioresour. Technol. 109, 215e223. Yiin, C.L., Quitain, A.T., Yusup, S., Sasaki, M., Uemura, Y., Kida, T., 2016. Characterization of natural low transition temperature mixtures (LTTMs): green solvents for biomass delignification. Bioresour. Technol. 199, 258e264. Zohourian, T.H., Quitain, A.T., Sasaki, M., 2011. Phenolic content and antioxidant activities of Lawsonia inermis leaf extracts obtained by microwave-assisted hydrothermal method. J. Microw. Power Electromagn. Energy 45 (4), 193e204.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Note from the field
Microwave-assisted hydrothermal extraction of natural malic acid for the synthesis of low transition temperature mixtures Chung Loong Yiin a, Suzana Yusup a, Armando T. Quitain b, *, Mitsuru Sasaki b, Yoshimitsu Uemura a, Tetsuya Kida b a
Biomass Processing Technology Cluster, Center of Biofuel and Biochemical Research, Mission Oriented Research (Green Technology), Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Tronoh, Perak, Malaysia Department of Applied Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 July 2015 Received in revised form 9 December 2015 Accepted 15 December 2015 Available online 23 December 2015
This work describes the utilization of microwave hydrothermal extracted malic acid from cactus, lophatherum herb, papaya and Luffa cylindrica as hydrogen bond donor for the synthesis of natural low transition temperature mixtures (LTTMs) with sucrose as hydrogen bond acceptor. The effects of parameters including reaction temperature, extraction time, mass of sample and oxidant, H2O2 were discussed. The saturation equation was used to fit with the experimental data, observing only a slight loss of the goodness of fit. The optimum conditions for microwave hydrothermal extraction were found to be at 1 g of sample, 200 C and 45 min in the presence of hydrogen peroxide (H2O2) as oxidant. Consequently, the proposed method was successfully applied to extract malic acid from plants and fruits for the synthesis of LTTMs. The LTTMs prepared from the extracted malic acid have identical physicochemical properties with the LTTMs derived from commercial malic acid due to the existence of hydrogen bond and the ability to dissolve lignin. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Microwave-assisted hydrothermal extraction Malic acid Kinetic modelling Synthesis Low transition temperature mixture Delignification
1. Introduction Conventional extraction techniques such as soaking, maceration, water percolation and solvent extraction for natural products normally require long extraction time and large volume of organic solvents. These also result into degradation of active compounds obtaining relatively lower extraction efficiency of the target com -Puigmartí et al., 2011; Chan et al., 2011; Wu et al., pounds (Molto 2012). Hydrothermal extraction using water is a natural and green alternative for natural product extraction at high temperature and pressure condition. This method has been used to extract polar organic compounds or to decompose lignocellulosic materials to produce valuable compounds such as saccharides and aromatic acids (Kitada et al., 2009; Matsunaga et al., 2013).
* Corresponding author. Tel.: þ81 96 342 3665; fax: þ81 96 342 3679. E-mail addresses: [email protected] (C.L. Yiin), drsuzana_yusuf@ petronas.com.my (S. Yusup), [email protected] (A.T. Quitain), msasaki@ kumamoto-u.ac.jp (M. Sasaki), [email protected] (Y. Uemura), [email protected] (T. Kida). http://dx.doi.org/10.1016/j.jclepro.2015.12.053 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
Microwave possesses many advantages for the extraction of bioactive compounds (Sanchez-Aldana et al., 2013) such as reduced processing time, higher extraction rates and more accurate control of reaction conditions (Tsubaki et al., 2012; Yemis and Mazza, 2012). Microwave-assisted extraction has been proven to be a promising technique for the extraction of phytochemicals from botanical plants and food samples (Xiao et al., 2012; Quitain et al., 2013). Direct interaction of microwaves helps to heat up the solvent and also lead to a tremendous increase in internal pressure, rupture of plant tissue and release of active compounds into the solvent (Dhobi et al., 2009; Mandal et al., 2007). Francisco et al., 2012 introduced 26 types of natural low transition temperature mixtures (LTTMs) from environmentally benign starting materials which show glass transition points instead of eutectic melting points. LTTMs can be prepared from cheap, readily available and toxicologically well characterized starting materials (Francisco et al., 2013). Preparation of LTTMs is in vicinity to the synthesis of deep eutectic solvents (Cvjetko Bubalo et al., 2014). The hydrogen bonding interactions of LTTMs lead to some of the promising characteristics of ionic liquids as solvents and shared by deep eutectic solvents (Francisco et al., 2012). The potentials of LTTMs to degrade the lignocellulosic biomass structure were
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evaluated and less biomass particles could be noticed after the pretreatment with the mixtures derived from malic acid (Francisco et al., 2012). Thus, natural abundant resources such as plants and fruits which contain high malic acid content have high potential to be used for the synthesis of LTTMs. The aim of the present work was to utilize the malic acid obtained from papaya, cactus, Luffa cylindrica and lophatherum herb via microwave-assisted hydrothermal extraction for the synthesis of natural LTTMs. The influencing parameters including extraction temperature, reaction time, mass of sample and oxidant, H2O2 were investigated. The extraction kinetics were modelled using saturation equation and compared with experimental results. The comparative study of the LTTMs prepared from commercial malic acid and microwave hydrothermal extracted malic acid in terms of hydrogen bonding and lignin solubility was also conducted. 2. Materials and methods 2.1. Raw materials and chemicals The plants and fruits with high content of malic acid such as papaya, cactus, L. cylindrica and lophatherum herb were used as the source of hydrogen bond donor for the synthesis of LTTMs. All these samples were ground using a blender with the power rating of 300 W for 20 min and dried completely in an oven at 50 C for 7 days. The sucrose (>97%) was obtained from Wako Pure Chemical Industries Ltd as the source of hydrogen bond acceptor. On the other hand, the lignin (96%, alkali lignin) was obtained from Tokyo Kasei Kogyo Co., Ltd. 2.2. Microwave-assisted hydrothermal extraction experiments The microwave used for the extraction of malic acid was CEM MARS 5 microwave digester. In each experimental run, a 50 mL of distilled water and dried sample were charged into the reactor. The microwave power of 600 W and pressure of 50 bar were chosen in this study (Zohourian et al., 2011). The solvent was centrifuged after the process of extraction. The supernatant was separated from the residue through filtration using an Advantec ashless quantitative filter paper (Grade 5C, <5 mm). The microwave-hydrothermal extraction was conducted at extraction temperatures of 140, 160, 180 or 200 C and reaction time at 15, 30, 45 or 60 min. The experiment was repeated with increasing mass of sample (0.1, 0.5, 0.75 and 1 g) and in the presence of oxidant, H2O2 solution (35 wt% H2O2) at equal proportion with the sample in a reactor (XP-1500 Plus). 2.3. High performance liquid chromatography (HPLC) analysis The percentages of malic acid extracted from the samples were analyzed by using JASCO high performance liquid chromatography (HPLC). HPLC analysis was conducted by using potassium dihydrogen phosphate buffer as a mobile phase with UV detection at l ¼ 210 nm. The pH value of mobile phase was adjusted to pH 2.8 by using 10 mM of phosphoric acid. The column used was Wakosil-II 5C18 HG Prep. The flow rate of the mobile phase was fixed at 0.5 mL/min and 20 mL as injection volume. 2.4. Mathematical model The overall kinetic data based on the yield of malic acid by microwave hydrothermal extraction were modelled using the saturation equation (Wong-Paz et al., 2014). The equation used was:
1 k 1 1 þ ¼ Ct Ceq t Ceq
(1)
where Ct, Ceq and k represents solute concentration in liquid phase at any time, the equilibrium solute concentration and the constant that describes the released fraction, respectively. The concordance between experimental data and calculated value is established by the correlation coefficient (R2). 2.5. Synthesis and analysis of LTTMs LTTMs were synthesized by adding sucrose into microwavehydrothermal extracted malic acid and heated up slowly in an oil bath with the molar ratio of malic acid-sucrose-water (MSW 1:3:10) until all the sucrose was dissolved. The excessive water content in the LTTMs was removed by freeze-drying (EYELA FDU1200) at 45 C, and stopped once the samples showed constant weight (Yiin et al., 2016). The hydrogen bonding of LTTMs was evidenced using Frontier FT-IR Spectrometer (PerkinElmer) equipped with attenuated total reflectance (ATR). The water content of freeze dried LTTMs was measured by using the Metrohm 870 Karl Fischer Titrino Plus. The solubility of lignin was determined using cloud point method (Francisco et al., 2012). 3. Results and discussion The malic acid is present in the plant materials being investigated such as papaya (Morais et al., 2015), cactus (Moßhammer et al., 2006), L. cylindrica (Chang et al., 2007) and lophatherum herb (Kozukue, 1986). Nevertheless, the extraction of malic acid under microwave-assisted hydrothermal conditions and specific quantifications of malic acid content of plant materials have not been reported. Thus, the spectra obtained from fruits and plants were compared with the standard in order to investigate the total area of peak for extracted malic acid at respective retention time. In this context, a calibration curve of L-malic acid's concentration (ppm) ^ against peak area (GEV.sec) was plotted for four working aqueous solutions ranging from 250 to 1000 ppm. The linear equation for the calibration curve is shown below:
y ¼ 106 x þ 60:674
R2 ¼ 0:9997
(2)
where x is frequency of output voltage/amplitude of spontaneous ^ signals (GEV.sec) and y is concentration of extracted malic acid (ppm). The results indicated that the malic acid in fruits and plants had been extracted by the proposed microwave-hydrothermal approach. 3.1. Influence of reaction temperature and extraction time on the malic acid yield It can be seen in Fig. 1 that the malic acid yield increased with increasing temperature and time up to 200 C and 45 min, respectively. Equilibrium was reached at temperature above 180e200 C. The results were comparable with the works of Zohourian et al. (2011) in which the extraction yield increased with increasing temperature and the yield decreased as a result of further degradation of target compounds above the optimum temperature. The solvent power increased at higher temperature due to the drop in viscosity and surface tension, facilitating the solvent to solubilize solutes and further improving matrix wetting
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Fig. 1. Malic acid yield for microwave hydrothermal extraction at different extraction time durations (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
and penetration (Khajeh et al., 2009; Mandal et al., 2007). The high temperature may reach far above the boiling point of the solvent in closed vessels, leading to higher extraction efficiency (Veggi et al., 2013) Besides, hydrolysis of some organic compounds in the feedstocks into low molecular weight carboxylic acids might also occur at high temperature conditions. On top of that, the malic acid yield increased from 15 to 45 min but relatively lower values of malic acid yield were observed at treatment time longer than 45 min, due likely to degradation of the target compounds (Zohourian et al., 2011; Mandal et al., 2007). 3.2. Influence of sample's mass on the malic acid yield Fig. 2 shows the malic acid yield increased sharply with the mass of sample from 0.1 to 0.5 g. This phenomenon might be due to the increased microwave absorptivity with increasing amount of sample, which was responsible for the increase in yield of malic acid (Quitain et al., 2013). In this context, the solvent volume must be sufficient to ensure that the entire sample is immersed in the solvent throughout
3.3. Influence of oxidant, H2O2 on the malic acid yield Fig. 3 depicts the increment of malic acid yield for papaya, cactus, L. cylindrica and lophatherum herb in the presence of oxidant, H2O2 which are 11.4, 20.3, 30.0 and 47.5% respectively. This indicates that H2O2 significantly affects the malic acid yield from fruits and plants through microwave-assisted hydrothermal extraction. This is presumably due to the easy formation of OH radicals from H2O2 that could help in the production of lowmolecular-weight carboxylic acids (Quitain et al., 2002). 3.4. Model fitting for microwave-assisted hydrothermal extraction The kinetic data obtained in this study were modelled based on malic acid yield with respect to different reaction durations and temperatures. As shown in Fig. 4, the linearity of equation (1) was observed for all the temperatures with most of the correlation
3000 Yield (mg malic acid/g sample)
the whole irradiation process especially for the sample that will swell during the extraction (Tatke and Jaiswal, 2011). Nonetheless, the malic acid yield started to reduce when the mass of sample exceeds 0.5 g until 1.0 g of sample as the solvent-to-solute ratio decreased resulting in lower yield (Quitain et al., 2013).
2500 Papaya
2000
Luffa Cylindrica Cactus
1500
Lophatherum Herb
1000 500 0 0
0.2
0.4
0.6
0.8
1
1.2
Mass of sample (g) Fig. 2. Malic acid yield against mass of sample.
Fig. 3. Malic acid yield with or without oxidant, H2O2.
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coefficient values (R2) above 0.9000, indicating a good fit of the kinetic data with the linearized saturation equation. Model parameters, equilibrium concentration (Ceq) and extraction rate constant (k) were determined by fitting the experimental data presented in Table 1. The kinetic data of microwave-assisted hydrothermal extraction of malic acid from plants and fruits were illustrated in Fig. 5 with respect to the predictions given by the saturation equation model. Overall, a good fit between experimental data and theoretical extraction curves was observed. 3.5. Comparison of LTTMs derived from commercial and microwave-assisted hydrothermal extracted malic acid 3.5.1. Fourier transform infrared spectroscopy (FTIR) spectra analysis It can be seen in Fig. 6 that the representative peak of carboxylic acid group of malic acid with wavenumber 1710 cm1 for the C]O group broaden in the respective LTTMs due to hydrogen bonding. The hydroxyl group of malic acid had direct interaction with the carbonyl group by the formation of a stable dimetric hydrogenbonded structure in the liquid phase. Besides, the peaks involved in the H-bonding responsible for the formation of the LTTMs were shifted and broaden within the wavenumber range of 2500e3800 cm1 for the OH groups due to the stretching absorption of hydrogen bonding. Dotted red lines (in the web version) were used to delimit the main bands for the peak shifts and malic acid peaks. The results were comparable with the works of Francisco et al. (2012) based on the hydrogen bond existing between lactic acid and choline chloride as observed by FTIR analyses. 3.5.2. Screening of lignin solubility An overview of the results of screening of lignin solubility in LTTM is tabulated in Table 2, showing all mixtures to have the ability to dissolve lignin which was comparable with the lignin
Table 1 Predicted equilibrium concentrations and kinetic parameters obtained using the saturation equation. Sample
Temperature ( C)
Ceq (mg/g)
k (min1)
R2
Papaya
140 160 180 200 140 160 180 200 140 160 180 200 140 160 180 200
67.11 108.70 384.62 384.62 384.61 434.78 526.32 526.32 76.92 131.58 208.33 204.08 52.63 66.23 131.58 158.73
4.65 13.42 37.38 31.62 13.42 19.17 22.74 21.32 9.17 15.41 19.54 16.86 5.18 8.30 16.91 20.40
0.95 0.93 0.91 0.93 0.92 0.91 0.92 0.91 0.91 0.92 0.92 0.89 0.87 0.91 0.88 0.88
Cactus
Luffa cylindrica
Lophatherum herb
solubility capacity of the LTTM prepared from commercial malic acid (12.32 wt%). The LTTM derived from cactus had the highest lignin solubility capacity followed by lophatherum herb, papaya and L. cylindrica. Thus, the malic acid in plants and fruits had a great potential to be used for the synthesis of natural LTTMs for biomass delignification.
4. Conclusions The optimum conditions giving the maximum malic acid yield for papaya, cactus, L. cylindrica and lophatherum herb via microwave-assisted hydrothermal extraction were 1 g of sample, 200 C and 45 min in the presence of hydrogen peroxide (H2O2) as oxidant. A good fit between experimental data and theoretical extraction curves was observed using saturation equation. Besides, the hydrogen bonding of LTTMs was evidenced by the shifts in the
Fig. 4. Plot of 1/Ct values with respect to 1/t (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
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Fig. 5. Kinetic modelling of malic acid yield from microwave-assisted hydrothermal extraction (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
Fig. 6. FT-IR spectra of extracted malic acid, sucrose and LTTM (MSW 1:3:10) (a) papaya; (b) cactus; (c) Luffa cylindrica; (d) lophatherum herb.
Table 2 Water content and lignin solubility in wt % for the LTTMs synthesized from commercial and natural malic acid. Name MSW MSW MSW MSW MSW
1:3:10 1:3:10 1:3:10 1:3:10 1:3:10
(commercial malic acid) (papaya) (cactus) (Luffa cylindrica) (lophatherum herb)
Water content (wt %)
Lignin (wt %)
7.89 7.58 7.61 7.36 7.54
12.32 9.38 10.12 9.16 9.58
representative peaks of the involved bonds in the FTIR spectra. The LTTMs derived from microwave hydrothermal extracted malic acid had comparable lignin solubility capacity with the LTTM prepared from commercial malic acid.
Acknowledgements The authors would like to acknowledge the funding supports from Fundamental Research Grant Scheme (FRGS) (0153AB-I89)
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