The Open Chemical Engineering Journal




ISSN: 1874-1231 ― Volume 13, 2019

Useful Bioactive Substances from Wastes: Recovery of Trans-Resveratrol from Grapevine Stems



George Angelov*, Lubomir Boyadzhiev, Silviya Georgieva
Institute of Chemical Engineering, Bulgarian Academy of Sciences, Sofia, 1113, Bulgaria

Abstract

The methods for producing natural resveratrol are of big interest because of the many health benefits of this substance and its increasing use in functional foods, food supplements and para-pharmaceutical preparations. Generally, resveratrol is extracted from different natural sources, most of them usually produced for consumption purposes (grapes, nuts). This paper presents a method for recovery of resveratrol from a widely available raw material - grapevine stems, a by-product of vine pruning. An efficient extraction-fractionation scheme is developed, based on shifting the phase equilibrium, by which more concentrated extracts of resveratrol are obtained. After a simple extraction, the initial extract is further separated into two fractions, containing either water or ethanol-soluble compounds. Using this approach, the resveratrol’s low water solubility helps isolate it from other water-soluble substances. The resulting product is almost ten times more concentrated in trans-resveratrol than the initial total extract. Additionally, a fraction containing water-soluble polyphenols is obtained, which could be used for water-based pharmaceutical and cosmetic preparations.

Keywords: Extraction, grapevine stems, polyphenols, resveratrol.


Article Information


Identifiers and Pagination:

Year: 2016
Volume: 10
Issue: Suppl-1, M2
First Page: 4
Last Page: 9
Publisher Id: TOCENGJ-10-4
DOI: 10.2174/1874123101610010004

Article History:

Received Date: 17/9/2015
Revision Received Date: 17/12/2015
Acceptance Date: 23/12/2015
Electronic publication date: 08/04/2016
Collection year: 2016

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© Angelov et al. Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution-Non-Commercial 4.0 International Public License (CC BY-NC 4.0) (https://creativecommons.org/licenses/by-nc/4.0/legalcode), which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.


* Address correspondence to this author at the Institute of Chemical Engineering, Bulgarian Academy of Sciences, Acad. Bonchev St., Block 103, 1113 Sofia, Bulgaria; Tel: +35929793286; E-mail: gang@bas.bg




1. INTRODUCTION

Resveratrol (3,5,4’-trihydroxystilbene) is a natural phenol compound which belongs to the stilbene family. It was first isolated from a poisonous plant, Veratrum album [1M. Takaoka, "Resveratrol, a new phenolic compound from Veratrum grandiflorum", J. Chem. Soc. Japan, vol. 60, pp. 1090-1100, 1939.]. Due to its many health benefits, this substance is the subject of intensive research. Resveratrol exists as two structural isomers-cis and trans. Resveratrol’s trans-isomer is stable, has better biological activity, and is naturally produced by some plants as a self-defense agent in response to fungal infection, injury, or exposure to ultraviolet light [2P. Langcake, and R.J. Price, "Production of resveratrol by Vitus vinifera as response to infection or injury", Physiol. Plant Pathol., vol. 9, pp. 77-86, 1976.
[http://dx.doi.org/10.1016/0048-4059(76)90077-1]
, 3Q.H. Pan, L. Wang, and J.M. Li, "Amounts and subcellular localization of stilbene synthase in response of grape berries to UV irradiation", Plant Sci., vol. 176, pp. 360-366, 2009.
[http://dx.doi.org/10.1016/j.plantsci.2008.12.004]
].

Resveratrol is found in more significant quantity in the roots of Japanese knotweed (Itadori plant, Polygonum cuspidatum), in grapes and in many other fruits and vegetables commonly used for human consumption, e.g. peanuts, blueberries, cranberries, mulberries etc. [4L.M. Chung, M.R. Park, J.C. Chun, and S.J. Yun, "Resveratrol accumulation and resveratrol synthase gene expression in response to abiotic stresses and hormones in peanut plants", Plant Sci., vol. 164, pp. 103-109, 2003.
[http://dx.doi.org/10.1016/S0168-9452(02)00341-2]
-6A. Amri, J.C. Chaumeil, S. Sfar, and C. Charrueau, "Administration of resveratrol: What formulation solutions to bioavailability limitations?", J. Control. Rel., vol. 158, no. 2, pp. 182-193, 2012.
[http://dx.doi.org/10.1016/j.jconrel.2011.09.083] [PMID: 21978644]
].

Numerous studies on resveratrol have demonstrated positive health effects such as reduced coronary heart disease and atherosclerosis [7J. Constant, "Alcohol, ischemic heart disease, and the French paradox", Clin. Cardiol., vol. 20, no. 5, pp. 420-424, 1997.
[http://dx.doi.org/10.1002/clc.4960200504] [PMID: 9134271]
, 8J.M. Wu, Z.R. Wang, T.C. Hsieh, J.L. Bruder, J.G. Zou, and Y.Z. Huang, "Mechanism of cardioprotection by resveratrol, a phenolic antioxidant present in red wine (Review)", Int. J. Mol. Med., vol. 8, no. 1, pp. 3-17, 2001.
[PMID: 11408943]
], reduced effects of some neurological diseases (Alzheimer, Parkinson) [9S. Bastianetto, W.H. Zheng, and R. Quirion, "Neuroprotective abilities of resveratrol and other red wine constituents against nitric oxide-related toxicity in cultured hippocampal neurons", Br. J. Pharmacol., vol. 131, no. 4, pp. 711-720, 2000.
[http://dx.doi.org/10.1038/sj.bjp.0703626] [PMID: 11030720]
] and carcinogenesis [10P. Signorelli, and R. Ghidoni, "Resveratrol as an anticancer nutrient: molecular basis, open questions and promises", J. Nutr. Biochem., vol. 16, no. 8, pp. 449-466, 2005.
[http://dx.doi.org/10.1016/j.jnutbio.2005.01.017] [PMID: 16043028]
]. Resveratrol helps counteract the detrimental effects of a high-fat diet [11J. Ferrières, "The French paradox: lessons for other countries", Heart, vol. 90, no. 1, pp. 107-111, 2004.
[http://dx.doi.org/10.1136/heart.90.1.107] [PMID: 14676260]
,12J.A. Baur, K.J. Pearson, N.L. Price, H.A. Jamieson, C. Lerin, A. Kalra, V.V. Prabhu, J.S. Allard, G. Lopez-Lluch, K. Lewis, P.J. Pistell, S. Poosala, K.G. Becker, O. Boss, D. Gwinn, M. Wang, S. Ramaswamy, K.W. Fishbein, R.G. Spencer, E.G. Lakatta, D. Le Couteur, R.J. Shaw, P. Navas, P. Puigserver, D.K. Ingram, R. de Cabo, and D.A. Sinclair, "Resveratrol improves health and survival of mice on a high-calorie diet", Nature, vol. 444, no. 7117, pp. 337-342, 2006.
[http://dx.doi.org/10.1038/nature05354] [PMID: 17086191]
] and shows ability to increase stress resistance and lifespans [13D.R. Valenzano, E. Terzibasi, T. Genade, A. Cattaneo, L. Domenici, and A. Cellerino, "Resveratrol prolongs lifespan and retards the onset of age-related markers in a short-lived vertebrate", Curr. Biol., vol. 16, no. 3, pp. 296-300, 2006.
[http://dx.doi.org/10.1016/j.cub.2005.12.038] [PMID: 16461283]
].

Due to its significance in both plant protection and human health, there is growing interest in the extraction of resveratrol from different natural sources, most of them usually produced for consumption purposes (grapes, nuts). While there is already evidence of high resveratrol concentration in grape berries and red wine, there is recent information for its presence in the grapevine itself. Resveratrol concentration varies by plant part and is highest in the stems and minimal in the leaves [14W. Wang, K. Tang, H.R. Yang, P.F. Wen, P. Zhang, H.L. Wang, and W.D. Huang, "Distribution of resveratrol and stilbene synthase in young grape plants (Vitis vinifera L. cv. Cabernet Sauvignon) and the effect of UV-C on its accumulation", Plant Physiol. Biochem., vol. 48, no. 2-3, pp. 142-152, 2010.
[http://dx.doi.org/10.1016/j.plaphy.2009.12.002] [PMID: 20060310]
]. This is why grapevine stems, which are by-products of vine pruning usually destroyed by burning, can be regarded as a widely available potential source of natural resveratrol.

Almost insoluble in water, resveratrol has been extracted by numerous organic solvents or their mixtures with water [15X. Sun, B. Peng, and W. Yan, "Measurement and correlation of solubility of trans-resveratrol in 11 solvents", J. Chem. Thermodyn., vol. 40, pp. 735-738, 2008.
[http://dx.doi.org/10.1016/j.jct.2007.10.006]
]. Previous studies on extraction of resveratrol from grapevine stems have revealed the importance of the dielectric constant of organic or organic-water solvents on the extraction yield [16S. Rayne, E. Karacabey, and G. Mazza, "Grape cane waste as a source of trans-resveratrol and trans-viniferin: High-value phytochemicals with medicinal and anti-phytopatogenic applications", Ind. Crops Prod., vol. 27, pp. 335-340, 2008.
[http://dx.doi.org/10.1016/j.indcrop.2007.11.009]
]. The most commonly used solvent is an ethanol-water mixture [16S. Rayne, E. Karacabey, and G. Mazza, "Grape cane waste as a source of trans-resveratrol and trans-viniferin: High-value phytochemicals with medicinal and anti-phytopatogenic applications", Ind. Crops Prod., vol. 27, pp. 335-340, 2008.
[http://dx.doi.org/10.1016/j.indcrop.2007.11.009]
-20E. Karacabey, and G. Mazza, "Optimization of antioxidant activity of grape cane extracts using response surface methodology", Food Chem., vol. 119, pp. 343-348, 2010.
[http://dx.doi.org/10.1016/j.foodchem.2009.06.029]
]. A multi-step extract-enrichment process using a rather specific and low-capacity laboratory technique has been previously proposed for the separation of resveratrol from the crude ethanolic extract: preparative column chromatography on polyamide carrier [21 Aaviksaar, M. Haga, T. Pussa, M. Roasto, and G. Tsoupras, "Purification of resveratrol from vine stems", Proc. Estonian Acad. Sci., vol. 52, pp. 155-164, 2003.]. In general, the reported studies aim to obtain better yields and more concentrated extracts of resveratrol. The purpose of the present work is to treat the extraction of grapevine stems in a more complex manner, combining better yield of total extract and separation of organic-soluble polyphenols, including resveratrol, from water-soluble polyphenols. On one hand, such separation is a way to obtain more concentrated resveratrol fraction, and on the other hand, it allows the recovery and further use of the water-soluble polyphenols present in the total extract.

2. EXPERIMENTAL

2.1. Plant Material

The solid matter to be extracted consists of dry vine stems of Cabernet Sauvignon cultivar from Plovdiv region of Bulgaria, year 2012. They are disintegrated into 1-2 mm particles.

2.2. Chemicals and Analyses

Trans-resveratrol, acetonitrile, Folin-Ciocalteu reagent (2N solution) and Gallic acid (GA) were provided by Sigma-Aldrich (Germany). Ethanol 96% and dehydrated Na2CO3 were purchased from Valerus (Bulgaria). The solvent was a mixture of 77% ethanol and 23% water.

Analyses were made for trans-resveratrol (TR) and total polyphenolic content (TPC) of the products obtained.

2.3. Trans-Resveratrol

HPLC reverse-phase methods are typically more convenient than other forms of liquid chromatography [22J.L. Rudolf, A.V. Resurreccion, F.K. Saalia, and R.D. Phillips, "Development of a reverse-phase high-performance liquid chromatography method for analyzing trans-resveratrol in peanut kernels", Food Chem., vol. 89, pp. 623-638, 2005.
[http://dx.doi.org/10.1016/j.foodchem.2004.05.033]
]. Analyses were performed using a Knauer HPLC system comprised of a sample injector, Knauer Smartline Menager 5000, Knauer Smartline Pump 1000, and variable wavelength detector. Trans-resveratrol peak areas were determined at 306 nm. Analyses were performed by using C-18 Supelco column (250 mm, 4.6 mm). The mobile-phase flux was 0.6 mL min-1. The eluent was a mixture of 40% acetonitrile and 60% water. The injection volume was 10 μl. Calibration was done using trans-Resveratrol solutions 0.1-0.5 g L-1. Trans-resveratrol standard was stored at low temperature (4oC) in a flask wrapped with aluminum foil to minimize light-induced isomerization.

2.4. Total Polyphenolic Content (TPCGA)

TPC was determined by the standard method using Folin-Ciocalteu reagent [23V.L. Singleton, and J.A. Rossi, "Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents", Am. J. Enol. Vitic., vol. 16, pp. 144-158, 1965.]. The treated extract samples obtain a color proportional to their TPC. Their light absorbance was analyzed with double-beam UV-VIS-spectrophotometer (UNICAM®-Helios β) at 765 nm and the TPC was evaluated comparatively to a calibration line obtained with Gallic Acid as a standard (TPCGA).

2.5. Yield of Dry Extract

It was obtained by evaporation of the liquid extracts at mild temperature (80oC) and weighting of the dried solid residue.

2.6. Experimental Procedure

The solvent used is 77v%/23v% ethanol/water mixture, which is in the 70-80% ethanol content range found to have high extraction affinity to resveratrol [16S. Rayne, E. Karacabey, and G. Mazza, "Grape cane waste as a source of trans-resveratrol and trans-viniferin: High-value phytochemicals with medicinal and anti-phytopatogenic applications", Ind. Crops Prod., vol. 27, pp. 335-340, 2008.
[http://dx.doi.org/10.1016/j.indcrop.2007.11.009]
].

As reported, the extraction yield is improved when raising the temperature [17E. Karacabey, and G. Mazza, "Optimization of solid-liquid extraction of resveratrol and other phenolic compounds from milled grape canes (Vitis vinifera)", J. Agric. Food Chem., vol. 56, no. 15, pp. 6318-6325, 2008.
[http://dx.doi.org/10.1021/jf800687b] [PMID: 18636680]
], undoubtedly due to increased solubility at higher temperatures. Consequently, the extraction is conducted at solvent’s boiling point under reflux. Additional agitation is not applied because the convective agitation at boiling is rather intensive.

Our preliminary study has shown that solvent-to-solid ratio (hydromodule) of at least 5:1 is necessary for good wetting of raw material and for providing efficient interphase contact. At this or higher hydromodule, solubility constraints due to insufficient quantity of solvent are avoided. Also, our kinetic studies have shown that processing time of about 1 hour is enough for completing the extraction (see Fig. 1). Longer phase contact does not result in higher yield of extracted matter.

Fig. (1)

Kinetics of polyphenols’ extraction from vine stems.



Based on our previous experience [18G. Angelov, S.S. Boyadzhieva, and S.S. Georgieva, "Rosehip extraction: Process optimization and antioxidant capacity of extracts", Cent. Eur. J. Chem., vol. 12, pp. 502-508, 2014.
[http://dx.doi.org/10.2478/s11532-013-0395-0]
,19G. Angelov, S. Georgieva, S. Boyadzhieva, and L. Boyadzhiev, "Optimizing the extraction of globe artichoke wastes", C. R. Acad. Bulg. Sci., vol. 68, no. 10, pp. 1235-1240, 2015.], extraction at high temperature, high enough solvent-to-solid ratio, and contact time of about 1 hour creates the necessary conditions for reaching a quasi-equilibrium state, i.e. only insignificant quantity of solid matter is further extracted at longer phase contact. So, the solid-solvent mixture was extracted twice by boiling in a flask under reflux for an hour (temperature about 80°C for ethanol-water mixture used, at hydromodule 1/10 - 10 g plant material and 100 mL solvent). Both extracts were collected together and sampled for analyses (TR, TPC, and dry matter). The crude liquid extract was then distilled to remove the ethanol. This shifted the phase equilibrium in the residue towards low solubility of resveratrol (which is soluble in ethanol). So, in the absence of ethanol, the target component should precipitate. The separation was aided by cooling the liquid extract in refrigerator (4oC) for 12 hours, which resulted in sediment formation. The precipitated material was removed by filtration, dried, weighed and then analyzed for TR and TPC. The remaining filtrate was an aqueous solution of the water-soluble components dissolved initially in the crude extract. This filtrate was also dried and analyzed for TR and TPC. As resveratrol was our only target, other polyphenolic compounds were quantified as a group (TPC) and not as single components.

The ethanol-water solvent co-extracts a number of substances soluble in either ethanol or water. The purpose of the above procedure is to separate the total initial extract into two fractions an ethanol-soluble fraction and a water-soluble fraction. The precipitate produced after ethanol removal contains predominantly ethanol-soluble substances, i.e. resveratrol should be retained in the precipitate, while the remaining liquid phase contains predominantly water soluble-components. Consequently, their separation from the total extract helps to obtain a fraction with higher concentration of the target component.

3. RESULTS AND DISCUSSION

Generally, the experiments were carried out in triplicate runs in order to ensure higher accuracy and to check reproducibility. The results reported represent mean values of repeated runs. The experimental results for dried matter yields of total extract, solid residue after ethanol removal (“Ethanol” fraction) and filtrate (“Aqueous” fraction) are given in Table 1 (column C1) as mg of solid matter per g of raw material.

According to Table 1, which shows quasi-equilibrium state extraction results, the yield of total extracted matter at the above-mentioned extraction conditions is 43.7 mg g-1 raw material (column C1, row R2), or 4.37%. Polyphenols are 14.4% of this crude product (C3, R2), and the amount of trans-resveratrol is 3.5% (C2, R2).

Table 1

Amounts of extracted matter at quasi-equilibrium state.




After filtration and drying, the precipitate (“Ethanol” fraction) contains 28.5% trans-resveratrol (C2, R3), which in practice is the full trans-resveratrol content of the total extract since the filtrate (“Aqueous” fraction) is essentially free of resveratrol (C2, R4). As a result of this proposed separation scheme, the concentration of trans-resveratrol in the “Ethanol” fraction is 8 times higher than in the total extract (R3/R2 of column C2) or 190 times higher compared to its concentration in the raw material (R3/R1 of column C2).

Since resveratrol is a phenolic compound, preferably soluble in ethanol, the “Ethanol” fraction contains mostly trans-resveratrol (row R3, C2/C3=0.964) and a small amount of other ethanol-soluble polyphenols (row R3, (C3-C2)/C3=0.035). The dry “Aqueous” fraction contains about 10% of water-soluble polyphenols (C3, R4). The part of resveratrol in all extracted polyphenols is about 24% (row R2, C2/C3).

The distribution of TR in the course of the proposed extraction and fractionation method is illustrated in Fig. (2).

Fig. (2)

Process scheme.



According to [21 Aaviksaar, M. Haga, T. Pussa, M. Roasto, and G. Tsoupras, "Purification of resveratrol from vine stems", Proc. Estonian Acad. Sci., vol. 52, pp. 155-164, 2003.], the content of trans-resveratrol in vine stems varies significantly with cultivar and period of pruning. Autumn-harvested stems contain more resveratrol, from 1 to 4.7 mg g-1 stems depending on cultivar. Our results show 1.53 mg g-1, which falls in the above range and quantifies the content of TR in the dry stems of the studied cultivar Cabernet Sauvignon from a local region from a particular year.

CONCLUSION

An efficient process is developed for recovery of resveratrol from vine stems. Based on shifting of phase equilibrium, this method allows for obtaining significantly more concentrated extracts of resveratrol compared to conventional solid-liquid extraction. To achieve this, the initial extract obtained via classical extraction is further separated into two fractions, containing either water or ethanol soluble compounds, respectively. Using this approach, resveratrol is separated from water-soluble substances and the resulting fraction is about 8 times more concentrated in resveratrol than the initial extract. Additionally, a fraction containing water-soluble polyphenols is obtained, which could be useful for application in water-based pharmaceutical and cosmetic preparations.

Generally, the proposed method is appropriate for efficient recovery of resveratrol from a widely available renewable natural raw material (grapevine stems) usually treated and discarded as waste otherwise.

CONFLICT OF INTEREST

The authors confirm that this article content has no conflict of interest.

ACKNOWLEDGEMENTS

Declared none.

REFERENCES

[1] M. Takaoka, "Resveratrol, a new phenolic compound from Veratrum grandiflorum", J. Chem. Soc. Japan, vol. 60, pp. 1090-1100, 1939.
[2] P. Langcake, and R.J. Price, "Production of resveratrol by Vitus vinifera as response to infection or injury", Physiol. Plant Pathol., vol. 9, pp. 77-86, 1976.
[http://dx.doi.org/10.1016/0048-4059(76)90077-1]
[3] Q.H. Pan, L. Wang, and J.M. Li, "Amounts and subcellular localization of stilbene synthase in response of grape berries to UV irradiation", Plant Sci., vol. 176, pp. 360-366, 2009.
[http://dx.doi.org/10.1016/j.plantsci.2008.12.004]
[4] L.M. Chung, M.R. Park, J.C. Chun, and S.J. Yun, "Resveratrol accumulation and resveratrol synthase gene expression in response to abiotic stresses and hormones in peanut plants", Plant Sci., vol. 164, pp. 103-109, 2003.
[http://dx.doi.org/10.1016/S0168-9452(02)00341-2]
[5] J.B. Jiménez, J.M. Orea, A.G. Urena, P. Escribano, P. López de la Osa, and A. Guadarrama, "Short anoxic treatments to enhance trans-resveratrol content in grapes and wine", Eur. Food Res. Technol. A, vol. 224, pp. 373-378, 2007.
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[http://dx.doi.org/10.1016/j.jconrel.2011.09.083] [PMID: 21978644]
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[PMID: 11408943]
[9] S. Bastianetto, W.H. Zheng, and R. Quirion, "Neuroprotective abilities of resveratrol and other red wine constituents against nitric oxide-related toxicity in cultured hippocampal neurons", Br. J. Pharmacol., vol. 131, no. 4, pp. 711-720, 2000.
[http://dx.doi.org/10.1038/sj.bjp.0703626] [PMID: 11030720]
[10] P. Signorelli, and R. Ghidoni, "Resveratrol as an anticancer nutrient: molecular basis, open questions and promises", J. Nutr. Biochem., vol. 16, no. 8, pp. 449-466, 2005.
[http://dx.doi.org/10.1016/j.jnutbio.2005.01.017] [PMID: 16043028]
[11] J. Ferrières, "The French paradox: lessons for other countries", Heart, vol. 90, no. 1, pp. 107-111, 2004.
[http://dx.doi.org/10.1136/heart.90.1.107] [PMID: 14676260]
[12] J.A. Baur, K.J. Pearson, N.L. Price, H.A. Jamieson, C. Lerin, A. Kalra, V.V. Prabhu, J.S. Allard, G. Lopez-Lluch, K. Lewis, P.J. Pistell, S. Poosala, K.G. Becker, O. Boss, D. Gwinn, M. Wang, S. Ramaswamy, K.W. Fishbein, R.G. Spencer, E.G. Lakatta, D. Le Couteur, R.J. Shaw, P. Navas, P. Puigserver, D.K. Ingram, R. de Cabo, and D.A. Sinclair, "Resveratrol improves health and survival of mice on a high-calorie diet", Nature, vol. 444, no. 7117, pp. 337-342, 2006.
[http://dx.doi.org/10.1038/nature05354] [PMID: 17086191]
[13] D.R. Valenzano, E. Terzibasi, T. Genade, A. Cattaneo, L. Domenici, and A. Cellerino, "Resveratrol prolongs lifespan and retards the onset of age-related markers in a short-lived vertebrate", Curr. Biol., vol. 16, no. 3, pp. 296-300, 2006.
[http://dx.doi.org/10.1016/j.cub.2005.12.038] [PMID: 16461283]
[14] W. Wang, K. Tang, H.R. Yang, P.F. Wen, P. Zhang, H.L. Wang, and W.D. Huang, "Distribution of resveratrol and stilbene synthase in young grape plants (Vitis vinifera L. cv. Cabernet Sauvignon) and the effect of UV-C on its accumulation", Plant Physiol. Biochem., vol. 48, no. 2-3, pp. 142-152, 2010.
[http://dx.doi.org/10.1016/j.plaphy.2009.12.002] [PMID: 20060310]
[15] X. Sun, B. Peng, and W. Yan, "Measurement and correlation of solubility of trans-resveratrol in 11 solvents", J. Chem. Thermodyn., vol. 40, pp. 735-738, 2008.
[http://dx.doi.org/10.1016/j.jct.2007.10.006]
[16] S. Rayne, E. Karacabey, and G. Mazza, "Grape cane waste as a source of trans-resveratrol and trans-viniferin: High-value phytochemicals with medicinal and anti-phytopatogenic applications", Ind. Crops Prod., vol. 27, pp. 335-340, 2008.
[http://dx.doi.org/10.1016/j.indcrop.2007.11.009]
[17] E. Karacabey, and G. Mazza, "Optimization of solid-liquid extraction of resveratrol and other phenolic compounds from milled grape canes (Vitis vinifera)", J. Agric. Food Chem., vol. 56, no. 15, pp. 6318-6325, 2008.
[http://dx.doi.org/10.1021/jf800687b] [PMID: 18636680]
[18] G. Angelov, S.S. Boyadzhieva, and S.S. Georgieva, "Rosehip extraction: Process optimization and antioxidant capacity of extracts", Cent. Eur. J. Chem., vol. 12, pp. 502-508, 2014.
[http://dx.doi.org/10.2478/s11532-013-0395-0]
[19] G. Angelov, S. Georgieva, S. Boyadzhieva, and L. Boyadzhiev, "Optimizing the extraction of globe artichoke wastes", C. R. Acad. Bulg. Sci., vol. 68, no. 10, pp. 1235-1240, 2015.
[20] E. Karacabey, and G. Mazza, "Optimization of antioxidant activity of grape cane extracts using response surface methodology", Food Chem., vol. 119, pp. 343-348, 2010.
[http://dx.doi.org/10.1016/j.foodchem.2009.06.029]
[21] Aaviksaar, M. Haga, T. Pussa, M. Roasto, and G. Tsoupras, "Purification of resveratrol from vine stems", Proc. Estonian Acad. Sci., vol. 52, pp. 155-164, 2003.
[22] J.L. Rudolf, A.V. Resurreccion, F.K. Saalia, and R.D. Phillips, "Development of a reverse-phase high-performance liquid chromatography method for analyzing trans-resveratrol in peanut kernels", Food Chem., vol. 89, pp. 623-638, 2005.
[http://dx.doi.org/10.1016/j.foodchem.2004.05.033]
[23] V.L. Singleton, and J.A. Rossi, "Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents", Am. J. Enol. Vitic., vol. 16, pp. 144-158, 1965.

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"It is important that students and researchers from all over the world can have easy access to relevant, high-standard and timely scientific information. This is exactly what Open Access Journals provide and this is the reason why I support this endeavor."


Jacques Descotes
(Centre Antipoison-Centre de Pharmacovigilance, France)

"Publishing research articles is the key for future scientific progress. Open Access publishing is therefore of utmost importance for wider dissemination of information, and will help serving the best interest of the scientific community."


Patrice Talaga
(UCB S.A., Belgium)

"Open access journals are a novel concept in the medical literature. They offer accessible information to a wide variety of individuals, including physicians, medical students, clinical investigators, and the general public. They are an outstanding source of medical and scientific information."


Jeffrey M. Weinberg
(St. Luke's-Roosevelt Hospital Center, USA)

"Open access journals are extremely useful for graduate students, investigators and all other interested persons to read important scientific articles and subscribe scientific journals. Indeed, the research articles span a wide range of area and of high quality. This is specially a must for researchers belonging to institutions with limited library facility and funding to subscribe scientific journals."


Debomoy K. Lahiri
(Indiana University School of Medicine, USA)

"Open access journals represent a major break-through in publishing. They provide easy access to the latest research on a wide variety of issues. Relevant and timely articles are made available in a fraction of the time taken by more conventional publishers. Articles are of uniformly high quality and written by the world's leading authorities."


Robert Looney
(Naval Postgraduate School, USA)

"Open access journals have transformed the way scientific data is published and disseminated: particularly, whilst ensuring a high quality standard and transparency in the editorial process, they have increased the access to the scientific literature by those researchers that have limited library support or that are working on small budgets."


Richard Reithinger
(Westat, USA)

"Not only do open access journals greatly improve the access to high quality information for scientists in the developing world, it also provides extra exposure for our papers."


J. Ferwerda
(University of Oxford, UK)

"Open Access 'Chemistry' Journals allow the dissemination of knowledge at your finger tips without paying for the scientific content."


Sean L. Kitson
(Almac Sciences, Northern Ireland)

"In principle, all scientific journals should have open access, as should be science itself. Open access journals are very helpful for students, researchers and the general public including people from institutions which do not have library or cannot afford to subscribe scientific journals. The articles are high standard and cover a wide area."


Hubert Wolterbeek
(Delft University of Technology, The Netherlands)

"The widest possible diffusion of information is critical for the advancement of science. In this perspective, open access journals are instrumental in fostering researches and achievements."


Alessandro Laviano
(Sapienza - University of Rome, Italy)

"Open access journals are very useful for all scientists as they can have quick information in the different fields of science."


Philippe Hernigou
(Paris University, France)

"There are many scientists who can not afford the rather expensive subscriptions to scientific journals. Open access journals offer a good alternative for free access to good quality scientific information."


Fidel Toldrá
(Instituto de Agroquimica y Tecnologia de Alimentos, Spain)

"Open access journals have become a fundamental tool for students, researchers, patients and the general public. Many people from institutions which do not have library or cannot afford to subscribe scientific journals benefit of them on a daily basis. The articles are among the best and cover most scientific areas."


M. Bendandi
(University Clinic of Navarre, Spain)

"These journals provide researchers with a platform for rapid, open access scientific communication. The articles are of high quality and broad scope."


Peter Chiba
(University of Vienna, Austria)

"Open access journals are probably one of the most important contributions to promote and diffuse science worldwide."


Jaime Sampaio
(University of Trás-os-Montes e Alto Douro, Portugal)

"Open access journals make up a new and rather revolutionary way to scientific publication. This option opens several quite interesting possibilities to disseminate openly and freely new knowledge and even to facilitate interpersonal communication among scientists."


Eduardo A. Castro
(INIFTA, Argentina)

"Open access journals are freely available online throughout the world, for you to read, download, copy, distribute, and use. The articles published in the open access journals are high quality and cover a wide range of fields."


Kenji Hashimoto
(Chiba University, Japan)

"Open Access journals offer an innovative and efficient way of publication for academics and professionals in a wide range of disciplines. The papers published are of high quality after rigorous peer review and they are Indexed in: major international databases. I read Open Access journals to keep abreast of the recent development in my field of study."


Daniel Shek
(Chinese University of Hong Kong, Hong Kong)

"It is a modern trend for publishers to establish open access journals. Researchers, faculty members, and students will be greatly benefited by the new journals of Bentham Science Publishers Ltd. in this category."


Jih Ru Hwu
(National Central University, Taiwan)


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