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The Scientific World Journal
Volume 2014, Article ID 437081, 8 pages
http://dx.doi.org/10.1155/2014/437081
Research Article

In Vitro Study on the Antioxidant Potentials of the Leaves and Fruits of Nauclea latifolia

1Oxidative Stress Research Centre, Department of Biomedical Sciences, Faculty of Health & Wellness Sciences, Cape Peninsula University of Technology, Bellville 7535, South Africa
2Department of Wellness Sciences, Faculty of Health & Wellness Sciences, Cape Peninsula University of Technology, Cape Town 8000, South Africa

Received 3 April 2014; Revised 13 May 2014; Accepted 19 May 2014; Published 11 June 2014

Academic Editor: Okezie I. Aruoma

Copyright © 2014 Ademola O. Ayeleso et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study was carried out to investigate the in vitro antioxidant potentials of the leaves and fruits of Nauclea latifolia, a straggling shrub or small tree, native to tropical Africa and Asia. Hot water extracts of the leaves and fruits of Nauclea latifolia were assessed for their total polyphenolic, flavanol, and flavonol contents as well as 1-diphenyl-2-picrylhydrazyl (DPPH) scavenging ability, ferric reducing antioxidant power (FRAP), Trolox equivalence antioxidant capacity (TEAC), and oxygen radical absorbance capacity (ORAC) assays. The aqueous extract of the leaves was found to contain higher level of total polyphenols ( mg GAE/g), flavanol ( mg CE/g), and flavonol ( mg QE/g) than the extract of the fruits with values of  mg GAE/g (total polyphenol),  mg CE/g (flavanol), and  mg QE/g (flavonol). Similarly, the aqueous extract of the leaves also exhibited higher DPPH (IC50 20.64 mg/mL), FRAP (μmol AAE/g), TEAC (μmol TE/g), and ORAC (μmol TE/g) than the extract of the fruits with DPPH (IC50 120.33 mg/mL), FRAP (μmol AAE/g), TEAC (μmol TE/g), and ORAC (μmol TE/g). The present study showed that Nauclea latifolia has strong antioxidant potentials with the leaves demonstrating higher in vitro antioxidant activities than the fruits.

1. Introduction

Free radicals, which belong to a group of reactive oxygen species (ROS), are produced through endogenous source, that is, the human body itself, and exogenous sources such as tobacco smoke, burning of fossil fuels, and ozone [1]. The imbalance between the production of ROS and the activity of the antioxidant defences is referred to as oxidative stress [1]. The inhibiting or preventive effects of herbs or spices against the deleterious consequences of oxidative stress are due to the presence of natural antioxidants in them [2]. Drug formulations that are antioxidant based are used in the prevention and treatment of complex diseases which include atherosclerosis, stroke, diabetes, Alzheimer’s disease, and cancer [2, 3].

Nauclea latifolia Smith (family: Rubiaceae) is a straggling, evergreen, multistemmed shrub or small tree native to tropical Africa and Asia. It normally produces interesting flowers, edible, but not appealing, large red ball fruits with long projecting stamens [4]. Commonly used parts of Nauclea latifolia include the leaves, roots, stem, and fruits. The fruits serve as key source of food for the baboons, livestock, reptiles, birds, and man [4]. Phytochemicals majorly found in Nauclea latifolia include indole-quinolizidine, alkaloids (glycoalkaloids), and saponins [5]. Nkafamiya et al. [6] also reported that the fruits of Nauclea latifolia contain copper, iron, cobalt, calcium, magnesium, zinc, phosphorus, and vitamins (A, B1, B2, C, and E).

Throughout recorded history, Nauclea latifolia herbal remedies have been frequently seen in various places and are being used as major means of therapeutic medical treatment [7]. Traditionally, the infusions and decoctions from the stem bark and leaves of the plant are used for the treatment of malaria, stomach ache, fever, diarrhea, and nematodes infections [810]. Several studies have confirmed the health potentials of Nauclea latifolia. Some of its medicinal effects include antimalarial [11], antidiabetic [8], antihypertensive [1214], antipyretic and antinociceptive [15], and anti-inflammatory and analgesic activities [7]. It is also known to have a strong antibacterial property [16, 17]. This study was conducted to investigate the antioxidant potentials in the aqueous extracts of the leaves and fruits of Nauclea latifolia as these could be the contributing factors to their health beneficial effects.

2. Materials and Methods

2.1. Preparation of Plant Extracts

The plant was identified and authenticated by a plant scientist (Mr Omotayo) and deposited at the herbarium (E-herbarium UHAE 261) in the Department of Plant Science, Ekiti State University, Ado Ekiti, Nigeria. The dried and powdered leaves and fruits (150 g) were extracted with 750 mL of hot (100°C) distilled water. After 30 min, the extracts were filtered out and used for the assays.

2.2. Liquid Chromatography-Mass Spectrometry (LC-MS) Technique

LC-MS was performed on a Dionex HPLC system (Dionex Softron, Germering, Germany) equipped with a binary solvent manager and autosampler coupled to a Brucker ESI Q-TOF mass spectrometer (Bruker Daltonik GmbH, Germany). Constituents of the aqueous plant extracts were separated by reversed phase chromatography on a Thermo Fisher Scientific C18 column 5 μm, 4.6 × 150 mm (Bellefonte, USA), using a linear gradient of 0.1% formic acid in water (solvent A) and acetonitrile (solvent B) as solvent at a flow rate of 0.8 mL min−1, an injection volume of 10 μL, and an oven temperature of 30°C. MS spectra were acquired in negative mode. Electrospray voltage was set to +3500 V. Dry gas flow was set to 9 L min−1 with a temperature of 300°C and nebulizer gas pressure was set to 35 psi.

2.3. Determination of Total Polyphenol, Flavanol, and Flavonol Contents

The total polyphenol content in the aqueous plant extracts was determined using the Folin-Ciocalteu’s phenol reagent according to the method described by Singleton et al. [18] and was determined spectrophotometrically using a microplate reader and expressed as mg gallic acid standard equivalents (GAE) per gram sample. The flavanol content of the aqueous plant extracts was determined colorimetrically at 640 nm using the aldehyde DMACA and expressed as mg catechin standard equivalents (CE) per gram sample [19, 20]. The flavonol content of the aqueous plant extracts was determined spectrophotometrically at 360 nm and expressed as mg quercetin standard equivalents (QE) per gram sample [21]. All determinations were done in triplicates.

2.4. DPPH Free Radical Scavenging Activity

DPPH free radical scavenging activity of the aqueous plant extracts was carried out according to a method described by Zheleva-Dimitrova [22] with slight modifications. Briefly, 10 μL of the different concentrations of the aqueous plant extracts was reacted with 190 μL of DPPH solution (0.00625 g DPPH in 50 mL methanol) and the absorbance of the samples was determined after 30 min using a Multiskan Spectrum plate reader (Thermo Fisher Scientific, USA) at 517 nm. Free radical scavenging activity of the samples was expressed according to the equation below: where is the absorbance of DPPH• in solution without an antioxidant and is the absorbance of DPPH• in the presence of an antioxidant. IC50 value (concentration of sample where absorbance of DPPH decreases 50% with respect to absorbance of blank) of the sample was determined. All determinations were done in triplicates.

2.5. Ferric Reducing Antioxidant Power Assay

The FRAP assay was done using the method described by Benzie and Strain [23]. Briefly, 10 μL of the diluted aqueous plant extracts was mixed with 300 μL FRAP reagent in a 96-well clear plate. The FRAP reagent was a mixture (10 : 1 : 1, v/v/v) of acetate buffer (300 mM, pH 3.6), tripyridyl triazine (TPTZ) (10 mM in 40 mM HCl), and FeCl3·6H2O (20 mM). After incubation at room temperature for 30 min, the plate was read at a wavelength of 593 nm in a Multiskan Spectrum plate reader (Thermo Fisher Scientific, USA). Ascorbic acid (AA) was used as the standard and the results were expressed as μmol AAE/g sample. All determinations were done in triplicates.

2.6. Trolox Equivalence Antioxidant Capacity Assay

The TEAC assay was carried out using the principle of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activity according to a method described by Ou et al. [24]. ABTS+ solution was prepared a day before use by mixing ABTS salt (8 mM) with potassium persulfate (3 mM) and then storing the solution in the dark until the assay could be performed. The ABTS+ solution was further diluted with distilled water. Twenty five microlitres (25 μL) of the diluted aqueous plant extracts was mixed with 300 μL ABTS+ solution in a 96-well clear microplate. The plate was read after 30 min incubation at room temperature in a Multiskan Spectrum plate reader (Thermo Fisher Scientific, USA) at 734 nm. Trolox was used as the standard and results were expressed as μmol TE/g sample. All determinations were done in triplicates.

2.7. Oxygen Radical Absorbance Capacity (ORAC) Assay

The ORAC assay was conducted according to the method of Re et al. [25] on a 96-well microplate using a Fluorescence plate reader (Thermo Fisher Scientific, Waltham, Mass., USA). The reaction consisted of 12 μL of diluted aqueous plant extracts and 138 μL of fluorescein (14 μM), which was used as a target for free radical attack. The reaction was initiated by the addition of 50 μL AAPH (768 μM) and the fluorescence was (emission 538 nm, excitation 485 nm) recorded every 1 min for 2 hours. Trolox was used as the standard and results were expressed as μmol/g sample. All determinations were done in triplicates.

2.8. Statistical Analysis

Results are expressed as the means ± standard deviations. The significance of difference between mean values of different plant extracts was determined by t-test using Graph Pad PRISM 5.

3. Results and Discussion

Essential source of new chemical substances with potential therapeutic effects is thought to be obtained from medicinal plants [7, 26, 27]. The antioxidant contents of medicinal plants may contribute to protection against diseases [28]. Natural antioxidants have attracted a great deal of public and scientific attention because of their health-promoting effects [29]. An imbalance between the production of reactive oxygen species (ROS) and the activity of the antioxidant defences leads to oxidative stress [1]. In the pathology of several human diseases such as atherosclerosis, inflammation, cancer, rheumatoid arthritis, and neurodegenerative diseases like Alzheimer’s disease and multiple sclerosis, ROS have been implicated [1]. Attention is on antioxidant agents of natural origin due to their abilities to scavenge free radicals [28, 30]. Antioxidant capacity is associated with compounds that can protect a biological system against the damaging effect of ROS and reactive nitrogen species (RNS) [31].

3.1. Polyphenolic Contents in the Aqueous Extracts of the Leaves and Fruits of Nauclea latifolia

Phenolic compounds are found usually in both edible and nonedible plants with several biological effects which include antioxidant activity [32]. Figure 1 shows that the aqueous extract of the leaves of Nauclea latifolia contains chlorogenic acid, catechin, cynaroside, tangeritin, rutin/hesperidin, and hyperoside. Figure 2 shows that the aqueous extract of the fruits of Nauclea latifolia contains syringic acid, nobiletin, tangeritin, catechin, chrysoeriol, and isorhamnetin. In this study, the total polyphenolic contents of the aqueous plant extracts of the leaves and fruits were determined using the diluted Folin-Ciocalteu reagent. The total polyphenolic content was higher in the aqueous extract of the leaves than in the extract of the fruits with mean values of  mg GAE/g and  GAE/g sample, respectively (Figure 3). The flavanol content was also higher in the aqueous extract of the leaves ( mg CE/g) than in the extract of the fruits (0.15 ± 0.01 mg CE/g). In a similar vein, flavonol content was significantly higher in aqueous extract of the leaves (2.22 ± 0.37 mg QE/g) than in the extract of fruits ( QE/g) (Figure 3). Overall, the results showed that aqueous extracts of both the leaves and the fruits are rich in polyphenols with the leaves having higher polyphenols than the fruits.

fig1
Figure 1: LCMS chromatogram of phenolic acid and flavonoids in the aqueous extract of Nauclea latifolia leaves. (A) Chlorogenic acid, (B) catechin, (C) cynaroside, (D) tangeritin, (E) rutin/hesperidin, and (F) hyperoside.
fig2
Figure 2: LCMS chromatogram of phenolic acid and flavonoids in the aqueous extract of Nauclea latifolia fruits. (A) Syringic acid, (B) nobiletin, (C) tangeritin, (D) catechin, (E) chrysoeriol, and (F) isorhamnetin.
437081.fig.003
Figure 3: Total polyphenol, flavanol, and flavonol contents in the aqueous extracts of the leaves and fruits of Nauclea latifolia. All significant differences are at . a-a, b-b, c-cBars having the same alphabets are significantly different from each other.
3.2. DPPH Radical Scavenging Activity in the Aqueous Extracts of the Leaves and Fruits of Nauclea latifolia

DPPH radical is used as a stable free radical to determine the antioxidant activity of natural compounds and the scavenging of stable radical (DPPH) is considered a valid and easy assay to evaluate scavenging activity of antioxidants [3335]. In this assay, purple color of DPPH is reduced to α,α-diphenyl-β-picrylhydrazine (yellow colored) when neutralised. The extent of the change in color is proportional to the concentration and strength of the antioxidants [28]. In this study, the aqueous extracts of both the leaves and the fruits were able to show free radical scavenging abilities (Figure 4). It was observed that the aqueous extract of the leaves had higher DPPH activity than the extract of the fruits with the concentration of sample where absorbance of DPPH decreases 50% with respect to absorbance of blank (IC50) to be 20.64 mg/mL and 120.33 mg/mL, respectively. The effect of antioxidants on DPPH could be due to their hydrogen donating ability [36].

437081.fig.004
Figure 4: DPPH radical scavenging activity in the aqueous extracts of the leaves and fruits of Nauclea latifolia. All significant differences are at . a-aBars having the same alphabets are significantly different from each other.
3.3. Ferric Reducing Antioxidant Power in the Aqueous Extracts of the Leaves and Fruits of Nauclea latifolia

The extent at which the aqueous extract of the leaves and fruits of Nauclea latifolia could reduce ferric ions was done with FRAP assay. This assay is made possible by low molecular weight antioxidants of hydrophilic and/or hydrophobic nature [37]. FRAP assay has been used to compare antioxidant activity in plants and mammals [3840]. The action of electron donating antioxidants causes a change in the absorbance at 593 nm due to the formation of blue colored Fe+2 tripyridyl triazine (TPTZ) compound from the colorless oxidized Fe+3 form [41, 42]. The aqueous extract of the leaves showed higher FRAP (μmol AAE/g sample) than the extract of the fruits (μmol AAE/g sample). It was clearly shown that even though the aqueous extracts of both the leaves and the fruits have the abilities to reduce ferric ions, the activity of the leaves was higher (Figure 5).

437081.fig.005
Figure 5: Antioxidant activities (FRAP, TEAC, and ORAC) in the aqueous extracts of the leaves and fruits of Nauclea latifolia. All significant differences are at . a-a, b-b, c-cBars having the same alphabets are significantly different from each other.
3.4. Trolox Equivalence Antioxidant Capacity in the Aqueous Extracts of the Leaves and Fruits of Nauclea latifolia

The TEAC assay is based on the suppression of the absorbance of radical cations of 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by antioxidants in the sample when ABTS incubates with a peroxidase (metmyoglobin) and H2O2 [43, 44]. It entails a technique that produces a blue/green ABTS+ chromophore through the reaction of ABTS and potassium persulfate [30]. The assay is particularly interesting in plant extracts because the wavelength absorption at 734 nm eliminates color interference [45]. The results also showed a higher TEAC in the aqueous extract of the leaves than in the extract of the fruits with values of 94.83 ± 3.57 μmol TE/g sample and μmol TE/g sample, respectively (Figure 5). In this study, the antioxidant content of the aqueous plant extracts captured the free radical (ABTS) and resulted in a color loss and consequent reduction in absorbance which corresponds to the antioxidant concentration.

3.5. Oxygen Radical Absorbance Capacity in the Aqueous Extracts of the Leaves and Fruits of Nauclea latifolia

The ORAC assay is used to assess the antioxidant activity of biological substrates which ranges from pure compounds, that is, melatonin and flavonoids, to complex matrices such as vegetables and animal tissues [46]. It measures antioxidant inhibition of peroxyl-radical-induced oxidations and shows the radical chain breaking antioxidant activity by H-atom transfer [24, 31]. The ORAC assay uses 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) for free radical generation. AAPH which is water soluble has been widely used as a free radical initiator for biological studies and the haemolysis caused by AAPH allows studies involving membrane damage induced by free radicals [4750]. The results showed the mean value of ORAC for aqueous extract of the leaves to be 196.55 ± 0.073 μmol TE/g sample while that of the fruits was 55.88 ± 0.073 μmol TE/g sample (Figure 5). The ORAC results also showed the potency of the aqueous plant extracts to protect against oxidative damage.

In conclusion, the results from this study revealed that the aqueous extracts of both the leaves and the fruits of Nauclea latifolia have antioxidant potentials with the leaves demonstrating stronger activities. The medicinal properties of this plant could be due to its antioxidant potentials as evident from this present work. More studies are however needed for investigating its usefulness in the management and treatment of various diseases.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgment

This work was supported through funding from Cape Peninsula University of Technology, Bellville, South Africa.

References

  1. S. krovánková, L. Mišurcová, and L. Machů, “Antioxidant activity and protecting health effects of common medicinal plants,” Advances in Food and Nutrition Research, vol. 67, pp. 75–139, 2012. View at Google Scholar
  2. N. A. Khalaf, A. K. Shakya, A. Al-Othman, Z. El-Agbar, and H. Farah, “Antioxidant activity of some common plants,” Turkish Journal of Biology, vol. 32, no. 1, pp. 51–55, 2008. View at Google Scholar · View at Scopus
  3. T. P. A. Devasagayam, J. C. Tilak, K. K. Boloor, K. S. Sane, S. S. Ghaskadbi, and R. D. Lele, “Free radicals and antioxidants in human health: current status and future prospects,” Journal of Association of Physicians of India, vol. 52, pp. 794–804, 2004. View at Google Scholar · View at Scopus
  4. O. James and H. H. Ugbede, “Hypocholesterolemic effects of Nauclea latifolia (Smith) fruit studied in albino rats,” American Journal of Tropical Medicine and Public Health, vol. 1, no. 1, pp. 11–21, 2011. View at Google Scholar
  5. S. D. Karou, T. Tchacondo, D. P. Ilboudo, and J. Simpore, “Sub-saharan rubiaceae: a review of their traditional uses, phytochemistry and biological activities,” Pakistan Journal of Biological Sciences, vol. 14, no. 3, pp. 149–169, 2011. View at Publisher · View at Google Scholar · View at Scopus
  6. I. I. Nkafamiya, A. J. Manji, U. U. Modibbo, and H. A. Umaru, “Biochemical evaluation of Cassipourea congoensis (Tunti) and Nuclea latifolia (Luzzi) fruits,” African Journal of Biotechnology, vol. 5, no. 24, pp. 2461–2463, 2006. View at Google Scholar · View at Scopus
  7. A. D. T. Goji, A. Mohammed, Y. Tanko, I. Ezekiel, A. O. Okpanchi, and A. U. U. Dikko, “A study of the anti-inflammatory and analgesic activities of aqueous extract of Nauclea latifolia leaves in Rodent,” Asian Journal of Medical Sciences, vol. 2, no. 6, pp. 244–247, 2010. View at Google Scholar
  8. A. Gidado, D. A. Ameh, and S. E. Atawodi, “Effect of Nauclea latifolia leaves aqueous extracts on blood glucose levels of normal and alloxan-induced diabetic rats,” African Journal of Biotechnology, vol. 4, no. 1, pp. 91–93, 2005. View at Google Scholar · View at Scopus
  9. A. Gidado, D. A. Ameh, S. E. Atawodi, and S. Ibrahim, “Hypoglycaemic activity of Nauclea latifolia sm. (Rubiaceae) in experimental animals,” African Journal of Traditional, Complementary and Alternative Medicines, vol. 5, no. 2, pp. 201–208, 2008. View at Google Scholar · View at Scopus
  10. O. N. Maitera, M. E. Khan, and T. F. James, “Phytochemical analysis and the chemotherapeutics of leaves and stem-bark of Nauclea latifolia grown in Hong, Adamawa State Nigeria,” Asian Journal of Plant Sciences, vol. 1, no. 3, pp. 16–22, 2011. View at Google Scholar
  11. F. Benoit-Vical, A. Valentin, V. Cournac, Y. Pélissier, M. Mallié, and J.-M. Bastide, “In vitro antiplasmodial activity of stem and root extracts of Nauclea latifolia S.M. (Rubiaceae),” Journal of Ethnopharmacology, vol. 61, no. 3, pp. 173–178, 1998. View at Publisher · View at Google Scholar · View at Scopus
  12. P. I. Akubue and G. C. Mittal, “Clinical evaluation of a traditional herbal practice in Nigeria: a preliminary report,” Journal of Ethnopharmacology, vol. 6, no. 3, pp. 355–359, 1982. View at Google Scholar · View at Scopus
  13. Z. A. M. Nworgu, D. N. Onwukaeme, A. J. Afolayan, F. C. Amaechina, and B. A. Ayinde, “Preliminary Studies of blood lowering effects of Nauclea latifolia in rats,” African Journal of Pharmacology, vol. 2, no. 2, pp. 37–41, 2008. View at Google Scholar
  14. F. V. Udoh and T. Y. Lot, “Effects of leaf and root extracts of Nauclea latifolia on the cardiovascular system,” Fitoterapia, vol. 69, no. 2, pp. 141–146, 1998. View at Google Scholar · View at Scopus
  15. G. S. Taïwe, E. N. Bum, E. Talla et al., “Antipyretic and antinociceptive effects of Nauclea latifolia root decoction and possible mechanisms of action,” Pharmaceutical Biology, vol. 49, no. 1, pp. 15–25, 2011. View at Publisher · View at Google Scholar · View at Scopus
  16. A. M. El-Mahmood, J. H. Doughari, and F. J. Chanji, “In vitro antibacterial activities of crude extracts of Nauclea latifolia and Daniella oliveri,” Scientific Research and Essays, vol. 3, no. 3, pp. 102–105, 2008. View at Google Scholar · View at Scopus
  17. W. Okiei, M. Ogunlesi, E. A. Osibote, M. K. Binutu, and M. A. Ademoye, “Comparative studies of the antimicrobial activity of components of different polarities from the leaves of Nauclea latifolia,” Research Journal of Medicinal Plant, vol. 5, no. 3, pp. 321–329, 2011. View at Google Scholar
  18. V. L. Singleton, R. Orthofer, and R. M. Lamuela-Raventós, “Analysis of total phenols and other oxidation substrates and antioxidants by means of folin-ciocalteu reagent,” Methods in Enzymology, vol. 299, pp. 152–178, 1998. View at Publisher · View at Google Scholar · View at Scopus
  19. J. A. Delcour and J. D. de Varebeke, “A new colorimetric assay for flavonoids in pilsner beers,” Journal of the Institute of Brewing, vol. 91, no. 1, pp. 37–40, 1985. View at Google Scholar
  20. D. Treutter, “Chemical reaction detection of catechins and proanthocyanidins with 4-dimethylaminocinnamaldehyde,” Journal of Chromatography A, vol. 467, pp. 185–193, 1989. View at Google Scholar · View at Scopus
  21. G. Mazza, L. Fukumoto, P. Delaquis, B. Girard, and B. Ewert, “Anthocyanins, phenolics, and color of Cabernet Franc, Merlot, and Pinot Noir wines from British Columbia,” Journal of Agricultural and Food Chemistry, vol. 47, no. 10, pp. 4009–4017, 1999. View at Publisher · View at Google Scholar · View at Scopus
  22. D. Z. Zheleva-Dimitrova, “Antioxidant and acetylcholinesterase inhibition properties of Amorpha fruticosa L. and Phytolacca americana L,” Pharmacognosy Magazine, vol. 9, no. 34, pp. 109–113, 2013. View at Publisher · View at Google Scholar · View at Scopus
  23. I. F. F. Benzie and J. J. Strain, “The ferric reducing ability of plasma (FRAP) as a measure of “antioxidant power”: the FRAP assay,” Analytical Biochemistry, vol. 239, no. 1, pp. 70–76, 1996. View at Publisher · View at Google Scholar · View at Scopus
  24. B. Ou, M. Hampsch-Woodill, and R. L. Prior, “Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe,” Journal of Agricultural and Food Chemistry, vol. 49, no. 10, pp. 4619–4626, 2001. View at Publisher · View at Google Scholar · View at Scopus
  25. R. Re, N. Pellegrini, A. Proteggente, A. Pannala, M. Yang, and C. Rice-Evans, “Antioxidant activity applying an improved ABTS radical cation decolorization assay,” Free Radical Biology and Medicine, vol. 26, no. 9-10, pp. 1231–1237, 1999. View at Publisher · View at Google Scholar · View at Scopus
  26. N. R. Farnsworth, “Screening plants for new medicine,” in Biodiversity, E. O. Wilson, Ed., Part II, pp. 88–97, National Academy Press, Washington, DC, USA, 1989. View at Google Scholar
  27. T. Eisner, “Chemical prospecting: a call for action,” in Ecology, Economic and Ethics: The Broken Circles, F. E. Borman and S. R. Kellert, Eds., Yale University Press, 1990. View at Google Scholar
  28. N. Saeed, M. R. Khan, and M. Shabbir, “Antioxidant activity, total phenolic and total flavonoid contents of whole plant extracts Torilis leptophylla L,” BMC Complementary and Alternative Medicine, vol. 12, article 221, 2012. View at Publisher · View at Google Scholar · View at Scopus
  29. F. Anwar, A. Jamil, S. Iqbal, and M. A. Sheikh, “Antioxidant activity of various plant extracts under ambient and accelerated storage of sunflower oil,” Grasas y Aceites, vol. 57, no. 2, pp. 189–197, 2006. View at Google Scholar · View at Scopus
  30. T. Osawa, S. Kavakishi, M. Namiki, Y. Kuroda, D. M. Shankal, and M. D. Waters, Antimutagenesis and Anticarcinogenesis Mechanisms II, Plenum, New York, NY, USA, 1990.
  31. A. Karadag, B. Ozcelik, and S. Saner, “Review of methods to determine antioxidant capacities,” Food Analytical Methods, vol. 2, no. 1, pp. 41–60, 2009. View at Publisher · View at Google Scholar · View at Scopus
  32. M. P. Kähkönen, A. I. Hopia, H. J. Vuorela et al., “Antioxidant activity of plant extracts containing phenolic compounds,” Journal of Agricultural and Food Chemistry, vol. 47, no. 10, pp. 3954–3962, 1999. View at Publisher · View at Google Scholar · View at Scopus
  33. M. Suhaj, “Spice antioxidants isolation and their antiradical activity: a review,” Journal of Food Composition and Analysis, vol. 19, no. 6-7, pp. 531–537, 2006. View at Publisher · View at Google Scholar · View at Scopus
  34. M. Öztürk, F. Aydoǧmuş-Öztürk, M. E. Duru, and G. Topçu, “Antioxidant activity of stem and root extracts of Rhubarb (Rheum ribes): an edible medicinal plant,” Food Chemistry, vol. 103, no. 2, pp. 623–630, 2007. View at Publisher · View at Google Scholar · View at Scopus
  35. M. Maizura, A. Aminah, and W. M. Wan Aida, “Total phenolic content and antioxidant activity of kesum, ginger (Zingiber officinale) and turmeric (Curcuma longa) extract,” International Food Research Journal, vol. 18, pp. 529–534, 2011. View at Google Scholar
  36. N. Gherraf, S. Ladjel, B. Labed, and S. Hameurlaine, “Evaluation of antioxidant potential of various extracts of Traganum nudatumdel,” Plant Sciences Feed, vol. 1, no. 9, pp. 155–159, 2011. View at Google Scholar
  37. K. Shukla, P. Dikshit, M. K. Tyagi, R. Shukla, and J. K. Gambhir, “Ameliorative effect of Withania coagulans on dyslipidemia and oxidative stress in nicotinamide-streptozotocin induced diabetes mellitus,” Food and Chemical Toxicology, vol. 50, no. 10, pp. 3595–3599, 2012. View at Publisher · View at Google Scholar · View at Scopus
  38. H. B. Niemeyer and M. Metzler, “Differences in the antioxidant activity of plant and mammalian lignans,” Journal of Food Engineering, vol. 56, no. 2-3, pp. 255–256, 2003. View at Publisher · View at Google Scholar · View at Scopus
  39. P.-J. Tsai, J. McIntosh, P. Pearce, B. Camden, and B. R. Jordan, “Anthocyanin and antioxidant capacity in Roselle (Hibiscus sabdariffa L.) extract,” Food Research International, vol. 35, no. 4, pp. 351–356, 2002. View at Publisher · View at Google Scholar · View at Scopus
  40. C. Priyanka, D. A. Kadam, A. S. Kadam, Y. A. Ghule, and V. T. Aparadh, “Free radical scavenging (DPPH) and ferric reducing ability (FRAP) of some gymnosperm species,” International Research Journal of Botany, vol. 3, no. 2, pp. 34–36, 2013. View at Google Scholar
  41. Y. Li, C. Guo, J. Yang, J. Wei, J. Xu, and S. Cheng, “Evaluation of antioxidant properties of pomegranate peel extract in comparison with pomegranate pulp extract,” Food Chemistry, vol. 96, no. 2, pp. 254–260, 2006. View at Publisher · View at Google Scholar · View at Scopus
  42. A. D. Gupta, V. Pundeer, G. Bande, S. Dhar, I. R. Ranganath, and G. S. Kumari, “Evaluation of antioxidant activity of four folk antidiabetic medicinal plants of India,” Pharmacologyonline, vol. 1, pp. 200–208, 2009. View at Google Scholar · View at Scopus
  43. A. L. Rice and J. B. Burns, “Moving from efficacy to effectiveness: red palm oil's role in preventing vitamin A deficiency,” Journal of the American College of Nutrition, vol. 29, no. 1, supplement, pp. 302S–313S, 2010. View at Google Scholar · View at Scopus
  44. L. Wang, S. Liu, A. D. Pradhan et al., “Plasma lycopene, other carotenoids, and the risk of type 2 diabetes in women,” American Journal of Epidemiology, vol. 164, no. 6, pp. 576–585, 2006. View at Publisher · View at Google Scholar · View at Scopus
  45. H.-B. Li, C.-C. Wong, K.-W. Cheng, and F. Chen, “Antioxidant properties in vitro and total phenolic contents in methanol extracts from medicinal plants,” LWT—Food Science and Technology, vol. 41, no. 3, pp. 385–390, 2008. View at Publisher · View at Google Scholar · View at Scopus
  46. C.-T. Yeh and G.-C. Yen, “Induction of hepatic antioxidant enzymes by phenolic acids in rats is accompanied by increased levels of multidrug resistance-associated protein 3 mRNA expression,” Journal of Nutrition, vol. 136, no. 1, pp. 11–15, 2006. View at Google Scholar · View at Scopus
  47. Y.-J. Cai, Q.-Y. Wei, J.-G. Fang et al., “The 3,4-dihydroxyl groups are important for trans-resveratrol analogs to exhibit enhanced antioxidant and apoptotic activities,” Anticancer Research, vol. 24, no. 2, pp. 999–1002, 2004. View at Google Scholar · View at Scopus
  48. L. Hou, B. Zhou, L. Yang, and Z.-L. Liu, “Inhibition of human low density lipoprotein oxidation by flavonols and their glycosides,” Chemistry and Physics of Lipids, vol. 129, no. 2, pp. 209–219, 2004. View at Publisher · View at Google Scholar · View at Scopus
  49. L. Hou, B. Zhou, L. Yang, and Z.-L. Liu, “Inhibition of free radical initiated peroxidation of human erythrocyte ghosts by flavonols and their glycosides,” Organic and Biomolecular Chemistry, vol. 2, no. 9, pp. 1419–1423, 2004. View at Publisher · View at Google Scholar · View at Scopus
  50. A. A. Fadda, R. E. El-Mekawy, A. El-Shafei, H. S. Freeman, D. Hinks, and M. El-Fedawy, “Design, synthesis, and pharmacological screening of novel porphyrin derivatives,” Journal of Chemistry, vol. 2013, Article ID 340230, 11 pages, 2013. View at Publisher · View at Google Scholar · View at Scopus