Phytochemical , nutritional and antioxidant capacity of five Ivorian edible leaves aqueous extracts

Article history: Received on: 02/05/2016 Revised on: 17/07/2016 Accepted on: 04/08/2016 Available online: 26/09/2016 Boiled aqueous extract from five Ivorian edible leaves (Solanum scabrum, Ipomea batatas, Corchorus olitorius, Basella alba, Hibiscus sabdariffa) have been analyzed for their antioxidant contents, phytochemical and nutritional compositions. I. batata extract showed the highest amount of antioxidant (167.52 μg/100gTE), total polyphenol (34.18 mg/100 g TE) and total flavonoid (12.67 mg/100g TE). The higher energy value (225.5 kcal) was obtained in S. scrabrum extract. The highest amount of zinc and potassium were found in S. scrabrum extract (0.28 and 362.1 mg/100 g DW; respectively). Maximum amount of copper (1.16 mg/100 g DW) and calcium (777.9 mg/100 g DW) were obtained in H. sabdariffa extract. The highest content of iron (49.81 mg/100 g DW) and magnesium (201 mg/100 g DW) were observed in B. alba extract. The highest content of sodium (2.39 mg/100 g DW) was obtained in C. olitorius extract. All extracts contained secondary metabolites such as polyphenols (tannins, flavonoids), sterols and terpenes, which have medicinal potent.


INTRODUCTION
Different parts of plants were used in human diet since prehistoric times.In fact, traces of edible leaves have been found in ancient Egyptian archaeological sites.Some edible leaves were historically documented in ancient Greece, in ancient Rome (Thurstan et al., 1994).In sub-Saharan Africa, there are more than 45,000 plant species; a thousand can be consumed as such (Maundu et al., 1993).Ivorian flora includes several edible wild species known by populations (Ambe, 2005).They play an important role in agriculture and in food thereby generating significant income both in rural and urban areas.They are important sources of vitamins, minerals, proteins, fibers and carbohydrates and thus contribute to improve the nutritional status of populations.Some edibles plants have medicinal properties and are used to treat various diseases (malaria, .intestinal parasites, infection etc.) (Stevels, 1990;Mnzava, 1997;Chweya and Eyzaguirre, 1999;Schippers, 2004).Free radicals are atoms or group of atoms that have one or more unpaired electrons.When their production becomes excessive in the body, we are talking about oxidative stress.A role of oxidative stress has been postulated in many diseases, including diabetes mellitus, agerelated eye disease, and neurodegenerative diseases such as Parkinson's disease and many others (Stefanis et al., 1997;Rao et al., 2006).Unfortunately, the antioxidants produced naturally are not enough to neutralize all of the free radicals in the body.Therefore, a constant supply of external sources of antioxidants should be a part of one's daily diet, in order to reduce oxidative stress and related damage.The oxidative effects of free radicals could be annihilating by consumption of edible plants rich in trace elements and polyphenols.The present study, therefore investigated the in vitro antioxidant activity and chemical compositions of boiled aqueous extract from five Ivorian edible leaves (Solanum scabrum, Ipomea batatas, Corchoruus olitorius, Spinacia oleracea, Hibiscus sabdariffa) used as soop.
After collecting, leaves were dried at 18°C in laboratory during two weeks.The dried leaves were reduced in fine powders and packed in sealed bags until analysis.Aqueous extracts were obtained after boiling at 100°C in 250 mL distilled water and filtering 5g of crushed leaves for 30 min.

Phytochemical study
The phytochemical study, based on color and / or precipitation tests was carried out on aqueous extracts from leaves of five edible plants (Bagre et al., 2007).Target molecules families of this screening were polyphenols (tannins, flavonoids, anthocyanins), saponins, steroids, terpenoids and alkaloids.

Total polyphenol content
Total polyphenol content was determined by colorimetry, using the Folin-Ciocalteu's (F-C) method (Singleton and Rossi, 1965;Wood et al., 2002).Diluted F-C reagent (1/10, v/v, 2.5 mL) was added to 30 µL of sample in a capped glass tube.After 2 min of incubation in the dark at room temperature, 2 mL of aqueous sodium carbonate (75 g.L -1 ) was added.After gentle stirring, the mixture was placed in a water bath at 50 •C for 15 min and rapidly cooled down to stop the reaction.Absorbance was measured at λmax = 760 nm using a UV-visible spectrophotometer (Jasco V530, Japan).Total polyphenol content was expressed as gallic acid equivalent (mg/100 g dry weight).Samples were analyzed in triplicate.

Total flavonoid content
The total flavonoid content was determined by the aluminum chloride colorimetric method described by Marinova et al., (2005).In a 25 mL volumetric flask, 0.75 mL of NaNO 2 distilled water solution (5%, w/v) was added to 2.5 mL aliquot of the sample.The color reaction was left to develop for 5 min in the dark and at room temperature.Then, 0.75 mL of AlCl 3 distilled water solution (10%, w/v) and 5 mL NaOH solution (1 M) were successively added to the flask.The mixture was diluted to the mark with distilled water.After gentle mixing, the solution absorbance was measured at λmax = 510 nm.The total flavonoid content was expressed as quercetin equivalent (mg/100 g dry weight).Samples were analyzed in triplicate.

Trolox equivalent antioxidant capacity (TEAC) using ABTS •+ radical-scavenging assay
Antioxidant capacity was determined using the procedure reported by Koffi et al. (2013).The ABTS•+ solution was prepared by mixing equal volumes of ABTS •+ salt solution (87.7 mg salt in 20 mL distilled water, 8 mmol.L -1 ) and potassium persulphate (K 2 S 2 O 8 ) solution (1.62 10 -3 g salt in 20 mL distilled water, 3 mmol.L -1 ).The final 40 mL stock solution obtained was kept at room temperature in the dark for 16 hours before use.The volume of stock solution needed for TEAC assay was first diluted with methanol in order to obtain an absorbance of 0.7 at λmax = 734 nm.A sample volume of 0.1 mL was mixed with 3.9 mL of diluted ABTS •+ stock solution and the mixture was incubated for 6 min exactly, in the dark at 30 o C. Absorbance was measured at λmax = 734 nm, and had to be higher than 20 % of the absorbance of the diluted ABTS •+ stock solution itself, otherwise the sample solution had to be diluted accordingly.Pure Methanol was used as a blank solution.TEAC was expressed as trolox equivalent (mg/100 g dry weight).Samples were analyzed in triplicate.

Mineral analysis
Aqueous extracts were analyzed for Zn, Ca, Cu, Fe, Mg, Na and K contents using a flame atomic absorption photometer (Varian AA 20 Spectrometer, Australia).The concentration or level of each element was determined by reference to a calibration curve.

Proximate analysis
The proximate analyses were carried out in triplicates and the results obtained were average value.The estimation of protein, lipid and fiber contents from aqueous leaves was performed using AOAC method (Cunniff, 1999).Carbohydrate content was carried out using Phenol-Sulfuric Acid method (Dubois et al., 1956;Agbo et al., 1996).

Determination of energy or calorific value
The total energy value (kcal/100g) of dry leaves was estimated using the method described by FAO (2002) as shown below: Energy value = (% protein x 4) + (% lipid x 9) + (% carbohydrate x 4)

Statistical analysis
Results were expressed as mean ± standard deviation of three replicate.Data were evaluated by one way analysis of variance (ANOVA) using statistica 7.1 (StatSoft, Inc, USA) solfware.Newman-keuls test performed to determine significant.

Phytochemical screening
The phytochemical screening of aqueous extracts from five Ivorian edibles leaves revealed presence of polyphenols (tannins, flavonoids), steroids and terpenoids (Table 1).Consumption of polyphenols has been linked to lowered risks of many chronic diseases including cancer, cardiovascular diseases, chronic inflammation and many degeneration diseases (Tsao, 2010).Increasing numbers of terpenoids are being found to have antibacterial, anti-malarial, anti-inflammatory and anti-cancer activities (Mahato and Sen, 1997).In this study, aqueous extracts did not show a presence of alkaloids.Saponins were detected in all aqueous extracts excepted H. sabadariffa extract.Saponins are also important in human nutrition.Several biological effects have been ascribed to saponins, such as membrane-permeabilising, immunostimulant, hypocholesterolaemic and anticarcinogenic properties (Francis et al., 2002).The presence of bioactive compounds in these extract indicate their medicinal value.

Phytochemical composition and antioxidant capacity
Figure 1 presents antioxidant capacity of aqueous extract from five Ivorian edible leaves.The extract of Ipomea batatas presented the highest antioxidant capacity (16.75 mg/ 100 g DW) followed by that of Corchoruus olitorius (8.79 mg/ 100 g DW), Hibiscus sabdariffa (6.31 mg/ 100 g DW), Solanum scabrum (6.21 mg/ 100 g DW) and Basella alba (1.71 mg/ 100 g DW).antioxidant capacity from aqueous extract.This result confirmed antioxidant properties of polyphenols (Balasundram et al., 2006;Dai and Mumper, 2010).Polyphenolic antioxidants from dietary sources are frequently a topic of interest due to widespread scientific agreement that they may help lower the incidence of certain cancers, cardiovascular and neurodegenerative diseases, and DNA damage and even may have antiaging properties (Obrenovich et al., 2010).They played a role in prevention of degenerative diseases, particularly cardiovascular diseases and cancers (Scalbert et al., 2005).

Nutritional composition of aqueous leaves
Figure 3 presents the result for macro-nutrients of aqueous extracts from five Ivorian edible leaves.
The higher value of protein was 31.58 g/100 g DW in Solanum scabrum extract and the lowest was 19.07 g/100 g DW in Hibiscus sabdariffa with the following decreasing order: Solanum scabrum > Basella alba > Corchoruus olitorius > Ipomea batatas > Hibiscus sabdariffa.So, S. scabrum could be used as food protein supplement.
C. olitorius contained the highest lipid contents (1.4 g/100 g DW) followed by S. scabrum, H. sabdariffa, B. alba and I. batatas (1.36, 1.15, 1.14, 0.74 g/100 g DW; respectively).High contents of lipid in human diet are principal sources of obesity and other relative diseases.Dietary fat composition can interfere in the development of obesity due to the specific roles of some fatty acids that have different metabolic activities, which can alter both fat oxidation and deposition rates, resulting in changes in body weight and/or composition (Coelho et al., 2011).H. sabdariffa, S. scabrum and B. alba have the higher fiber contents; the lower fiber contents were observed in C. olitorius extract.Carbohydrate of aqueous extract from selected Ivorian edible leaves range between 19.75 and 29.87 g/100 g DW.The decreasing order has below: Hibiscus sabdariffa > Corchoruus olitorius > Ipomea batatas > Solanum scabrum > Basella alba.The result showed that S. scabrum extract has higher energy value when compared to others.The aqueous extract of B. alba, despite presented the lowest energy value.So, S. scrabrum extract could be food supplement.
The present study also investigated micro-nutrients such as zinc (Zn), calcium (Ca), copper (Cu), iron (Fe), magnesium (Mn), sodium (Na) and potassium (K).Table 2 shows their mean concentration.These micro-nutrients are very important in the body.Zinc is necessary for the growth and multiplication of cells, skin integrity, bone metabolism, and functioning of taste and eyesight (Varsha et al., 2012).Zn is also an anti-inflammatory and antioxidant agent (Prasad, 2009).Calcium is important for construction and maintenance of bone and normal function of nerves and muscles (Soetan et al., 2010).Copper is essential for maintaining the strength of the skin, blood vessels, epithelial and connective tissue throughout the body.Iron plays a role in the production of hemoglobin, myelin, melanin and it also keeps thyroid gland functioning normally (Osredkar and Sustar, 2011).Iron is essential for haemoglobin formation, normal functioning of central nervous system and in the oxidation of carbohydrates, protein and fats (Adeyeye and Otokili, 1999).The deficiencies of magnesium are unusual but may lead to bone deformities, rashes, reduced hair growth (Varsha et al., 2012).Sodium and potassium are important in the maintenance of osmotic balance between cells and the interstitial fluid (Soetan, Olaiya et al., 2010).The highest amount of zinc was found in S. scrabrum extract (0.28 mg/100 g DW) followed in decreasing order by H. sabdariffa > C. olitorius > I. batatas > B. alba.Important content of Ca (777.9 mg/100 g DW) was obtained in H. sabdariffa extract followed by that of B. alba, C. olitorius, I. batatas and S. scrabrum.The highest copper content (1.16 mg/100 g DW) was determined in H. sabdariffa extract and the lower value (0.61 g/100 g DW) was obtained from B. alba.The highest and lowest iron content (49.81 and 12.67 g/100 g DW) were obtained from B. alba and C. olitorius, respectively.B. alba (201 mg/100 g DW) have high magnesium content; I. batatas with 8.5 mg/100 g DW has minimum Mg content.The maximum (2.39 mg/100 g DW) and minimum (1.39 mg/100 g DW) sodium contents were for C. olitorius and H. sabdariffa, respectively.Medium sodium contents were 1.76, 1.63 and 1.43 mg/100 g for B. alba, S. scrabrum and I. batatas, respectively.

CONCLUSION
This study revealed that boiled aqueous extract from Ipomea batatas represents a promising sources of phenolic antioxidants.The five edibles leaves contain phytochemicals such as tannins, flavonoids, sterols and terpenes.These leaves extracts contain again saponins and leuco-anthocyanins in all the plant extracts excepted Hibiscus sabdariffa and Basella alba extracts.Phytochemicals found in aqueous extract could be benefits for human health.The results indicate also that studied leaves contained macronutrients and micronutrients.It could therefore be concluded that studied edibles leaves can contribute to supplement other major nutrients source using by human.
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Conflicts of interest:
There are no conflicts of interest.

Table 1 :
Phytochemical screening of aqueous extract from five Ivorian edible leaves.

Table 2 :
Micro-nutrients of aqueous extract from five Ivorian edible leaves. 0.01 a For each column, letters equals indicate that the means difference is not significant at p ˂ 0.05.