Determination of phenolic compounds and evaluation of the antioxidant properties of four plants from Burkina Faso

95 Kagambega et al. Int. J. Biosci. 2020 RESEARCH PAPER OPEN ACCESS Determination of phenolic compounds and evaluation of the antioxidant properties of four plants from Burkina Faso Windmi Kagambega, Lassina Ouattara, Crépin I. Dibala*, Judith N. Semporé, Mamoudou H. Dicko Laboratory of Biochemistry, Biotechnology, Food Technology and Nutrition (LABIOTAN), University of Joseph Ki-ZERBO, 09 P.O.Box : 848, Ouagadougou 03, Burkina Faso Key words: Phenolic compounds, Antioxidant activities, Daniella oliveri, Sclerocarya birrea, Maranthes polyandra, Ptelopsis suberosa. http://dx.doi.org/10.12692/ijb/17.1.95-105 Article published on July 17, 2020 Abstract Daniella oliveri (Caesalpiniaceae), Sclerocarya birrea (Anacardiaceae), Maranthes polyandra (Chrysobalanaceae), Ptelopsis suberosa (Combretaceae) have long been regarded as the medicinal plants. This research work was designed to evaluate the polyphenolic content, and antioxidant activity of extracts and fractions of these four plants of Burkina Faso. The extraction of the bioactive compounds was carried out by hydroethanolic maceration followed by a liquid-liquid fractionation with solvents of increasing polarities. Total phenols and flavonoids were determined by the Folin-Ciocalteu reagent and aluminum trichloride spectrophotometer, respectively. The antioxidant activities of the samples were evaluated by various in vitro assays like total reducing power, DPPH scavenging and ABTS radical cation decolorization assays. The highest extraction yields were obtained with ethyl acetate and butanol fractions. Of these four plants, only the species Ptelopsis suberosa had the highest levels of phenolic compounds. The total phenol and total flavonoid contents were respectively 22.37 ± 0.21 mg EAG / 100 mg and 16.05 ± 0.13 mg EQ / 100 mg hydroethanolic extract, 21.31 ± 0.21 mg EAG / 100 mg and 11.82 ± 1.98 mg EQ / 100 mg ethyl acetate fraction and 18.07 ± 0.41 mg EAG / 100 mg and 11, 22 ± 1.31 mg EQ / 100 mg butanolic fraction. The low levels of phenolic compounds were obtained with the species Maranthes polyandra. The results of the antioxidant activities showed that the hydroethanolic extract of Ptelopsis suberosa and the fraction of ethyl acetate of Maranthes polyandra present the best antioxidant activities with respectively an IC50 of 0.36 ± 0.19 and 0.47 ± 0.12 μg/mL and an inhibitory power of the radical ABTS of 32.28 ± 0.68 and 34.81 mg /g. The present study demonstrated that these four plants are an important source of phenolic compounds and have interesting antioxidant properties. * Corresponding Author: Dr Crépin I. Dibala  [email protected] International Journal of Biosciences | IJB | ISSN: 2220-6655 (Print), 2222-5234 (Online) http://www.innspub.net Vol. 17, No. 1, p. 95-105, 2020 96 Kagambega et al. Int. J. Biosci. 2020 Introduction The use of plants by man merges with the very history of humanity for multiple purposes: cosmetic, food and pharmacological (Agbangnan, 2011). Thousands of scientific works have shown the presence of bioactive compounds of medicinal plants. These bioactive compounds have many therapeutic possibilities compared to chemotherapy which becomes more complicated and does not always bring the expected results. These works make it possible to offer more safety in the use of plants and they open new perspectives in the prevention and treatment of many pathologies. Unlike synthetic drugs, the medicinal plant not only provides an active ingredient but a multitude of compounds with complementary therapeutic effects, forming a balanced biochemical complex, the totum. Its softer and deeper action balances the body by stimulating natural defenses (Autran, 2010). Polyphenols are quantitatively the most important secondary metabolites of plants. They have a wide variety of structures ranging from compounds containing a single phenolic nucleus (phenolic acid) to complex polymeric compounds such as tannins (catechin polymers and epicatechin having several tens of units). Polyphenols have the ability to modulate the activity of a large number of enzymes and some cell receptors. In addition, "in vitro", a large number of polyphenols are recognized for their antioxidant, anti-inflammatory, antifungal, antiviral and anticancer properties (Hamza et al., 2006). Polyphenols are the most common antioxidants in our diet. Several studies have been conducted on the impact of plant consumption on health. Most of these studies have shown a decline in the risk factor for many conditions such as myocardial infarction, lung cancer, colon cancer, stomach cancer, kidney cancer, prostate cancer, and breast cancer. Indeed, oxidation is a widespread phenomenon both in the food field (lipid oxidation) and physiological (oxidative stress). The ingestion of polyphenols through fruits and vegetables could allow our body to strengthen its defense against the oxidative processes that threaten our cells daily (Khan, 2010). Polyphenols, because of their antioxidant properties, have the capacity to trap free radicals, which are constantly generated by our body or formed in response to attacks from our environment (tobacco, pollutants, infections ...). In Burkina Faso, according to the Ministry of Health, two thousand species of medicinal plants were already identified in 2004. Among these plants are: Daniella oliveri (Caesalpiniaceae), Sclerocarya birrea (Anacardiaceae), Ptelopsis suberosa (Chrysobalanaceae) and Maranthes polyandra (Combretaceae) that are widespread in many areas. These are planting whose leaves and barks are traditionally used in the treatment of several diseases such as malaria, cough, chronic ulcers, sexual infections, diarrhea, dysentery and many other purposes (Ouôba et al., 2006).Previous phytochemical analyzes performed on Daniella oliveri, Sclerocarya birrea, Ptelopsis suberosa and Maranthes polyandra have shown the presence of a number of secondary metabolites, namely: saponosides, tannins, triterpene and flavonoids (Nacoulma, 1996 ; Iwueke et al., 2008 ; Mundi et al., 2012). Apart from the identification of these secondary metabolites, only few information exists on the polyphenolic composition and the ability to trap free radicals by the extracts of these plants. Therefore, this study aimed at evaluating the polyphenolic content and antioxidant activity of these four plants. Materials and methods Chemicals and reagents The Folin-ciocalteu reagent, sodium carbonate, aluminium trichloride, gallic acid and quercetin were purchased from Sigma-aldrich chemie, Steinheim, Germany. 2, 2-diphenylpicrylhydrazyl (DPPH), trichloroacetic acid, and solvents used were from Fluka Chemie, Switzerland. Ascorbic acid was from Labosi, Paris, France. Plant materials The different barks of the Daniella oliveri, 97 Kagambega et al. Int. J. Biosci. 2020 Sclerocarya birrea, Maranthes polyandra and Ptelopsis suberosa plants were harvested in the region of the upper basins (village of Nasso) in the month of February 2016. The plants were identified by the laboratory of Biology and Vegetal Ecology (UFR / ST, University of Nazi BONI). The different parts of the bark were dried at room temperature, away from the sun. They are then reduced to powder, kept in freezer bags for different extractions. Maceration The previously dried bark of the trunk was then reduced to fine particles by grinding with an electric grinder (tecator cyclotec 1093 sample mill). The powders thus obtained were used to carry out a cold ethanol maceration according to the method described by Zirihi et al. (2003). For each plant, 50 g of bark powder was introduced into a 500 ml flask containing a mixture of ethanol and distilled water (70:30). The whole was subjected to magnetic stirring for 48 hours. At the end of these 48 hours, the mixture was filtered (filter paper schleicher and schuell 240 MM) and the filtrate obtained concentrated by rotary evaporation (Buchi Rotavapor R-200, Switzerland). Part of the aqueous solution was oven dried at 50°C until complete evaporation of the water and the other fractionated with immiscible organic solvents of increasing polarity. Separations of extracts by liquid-liquid separation For fractionation, the aqueous phases of the four plants are subjected to a series of liquid-liquid partitioning with immiscible organic solvents of increasing polarity: 50 ml of the hydroethanol macerates are extracted with 2 x 50 ml of n-hexane (n-H). The n-H solutions are combined and then concentrated under reduced pressure. The concentrates obtained are dried and the residues thus obtained constitute the hexanic fractions (FH). The aqueous phases which have been exhausted with hexane are again extracted as above but with 2 × 50 ml of ethyl acetate as the solvent. The solutions are pooled, concentrated and dried to give the ethyl acetate fractions (FAE). The aqueous phases resulting from the two previous treatments are extracted with n-butanol (2 x 50 ml). The n-butanol solutions are combined and allowed to evaporate at room temperature to give the butanol fractions (FB). At the end of all these operations, three fractions were obtained for each plant: hexane fraction (FH), ethyl acetate fraction (AcOEt) and butanolic fraction (Bu). The fraction residues were packed in waterproof plastic flasks and stored at 4°C until use. The yields of different crude extract and fraction were calculated and expressed as grams of extract residues/100 g of dried plant materials. Total phenols The estimation of the total extractable phenolic compounds content was carried out by the FolinCiocalteu method of Singleton (1999). It is based on the high oxidability of phenolic compounds. The reagent (Folin-Ciocalteu) used is a mixture of phosphomolybdate and sodium tungstate, which is reduced during the oxidation of phenols in an alkaline medium to a mixture of tungsten blue and molybdenum (Ribereau, 1968). The color produced (with a maximum absorption at 760 nm) is proportional to the amount of polyphenols present in the plant extracts to be assayed. The extracts or fractions are dissolved in pure methanol to have a concentration of 10 mg / ml and then diluted to 1/100 in distilled water. A volume of 0.5 ml of the diluted solution was then mixed with 2.5 mL of 0.2 N Folin-Ciocalteu reagent and incubated for 5 min. 2 mL of a solution of sodium carbonate at 75 g / L in distilled water is then added and the mixture incubated for 2 hours. At the end of the incubation, the optical densities are read at 760 nm using a CECIL 2041 Series spectrophotometer. Total phenol levels are determined using a standard curve with gallic acid (0-200 mg /L) as a standard. In total, 3 readings are made for each extract and fraction and the result given is an average from these analyzes. The results are expressed in mg Equivalent Gallic Acid per 100 mg of extract or fraction (mg EAG/100 mg extract or fraction). 98 Kagambega et al. Int. J. Biosci. 2020 Total flavonoïds The method used for the estimation of flavonoid levels in extracts and fractions of plants was described by Dowd adapted by Arvouet-Grand et al. (1994). The yellowish coloration given in this method is due to the formation of a complex between the aluminum chloride and the oxygen atoms present on the carbons 4 and 5 of the flavonoids (Lagnika, 2005). A volume of 5 ml of 2% AlCl3 in pure methanol is mixed with an equal volume of 1 mg / ml extract or fraction in methanol. The optical densities are read after 10 min at 415 nm using a CECIL 2041 Series spectrophotometer. Quercetin (0-100 mg / l) was used as a standard for the development of the calibration curve. A mixture of 5 mL of extract or fraction and 5 mL of methanol without AlCl3 served as a blank. Three readings are performed per sample of extract and fraction and the results are expressed in mg Equivalent Quercetin (EQ) per 100 mg of extract or fraction (mg EQ /100 mg). Antioxidant activity Two tests were used to evaluate the in vitro antioxidant capacity of the crude hydroethanol extracts and fractions of the four species studied in this work, it is the scavenging power of the cation radical ABTS ● + and the scavenging power of the radical DPPH ● +. This step is intended to detect hydroethanol extracts and plant fractions with high antioxidant activity. DPPH It is the measure of antioxidant activity that evaluates the ability to reduce a stable free radical. The spectrophotometric method for 2,2-diphenyl-1picrylhydrazyl (DPPH) described by Velazquez et al. (2003) is used. The 1,1-diphenyl-2-picrylhydrazyl molecule (DPPH) is a stable free radical, the solution of which has a violet coloration and a characteristic absorption at 517 nm. When a DPPH solution is mixed with an antioxidant hydrogen donor substance, there is formation of the reduced form. This causes the loss of purple coloration in yellow color characterized by a band of absorption in the visible at 517 nm (Brand-Williams, 1995). We can summarize the reaction in the form of the equation: Where: (AH) represents a compound capable of yielding a hydrogen to the DPPH (violet) radical for conversion to diphenyl picryl hydrazine (yellow) (Brand-William et al., 1995). A methanolic solution of DPPH at 20 mg /L is prepared. After a series of dilutions of the stock solution, a triplate is prepared for each concentration of the extract or fraction under consideration. 0.75 mL of each extract or fraction and 1.5 mL of DPPH were added to each tube. After an incubation of 15 minutes, the absorbances are read at 517 nm and the methanol is used as a blank sample. The antioxidant activity is expressed as a percentage inhibition according to the following formula: % inhibition = (White Absorbance - Sample Absorbance) / White Absorbance × 100% Three readings are carried out by extract or fraction and the average of the IC50 (concentration causing 50% inhibition of the DPPH radical) determined graphically, is calculated. ABTS The method described by Re et al. (1999) was used. It is based on the decolorization of a stable radical cation, ABTS ● + (2, 2’-azinobis- [3ethylenzothiazoline-6-sulfonic acid]) in ABTS in the presence of antioxidant compounds at 734 nm. The radical cation ABTS ● + was regenerated by mixing an aqueous solution of ABTS (7 mM) with 2.5 mM potassium persulfate (final concentration) and the mixture is kept in the dark at room temperature for 12 hours before use. The mixture was then diluted with ethanol to give an absorbance of 0.70 ± 0.02 at 734 nm using the spectrophotometer. For each extract or fraction, a methanolic solution (10 mg / mL) is diluted 100th in ethanol. Thus 10 μL of sample (diluted solution), of the reference substance 99 Kagambega et al. Int. J. Biosci. 2020 (quercetin) were mixed with 990 μL of the fresh solution of ABTS ● +. The whole is protected from light for 15 minutes and the absorbances were read at 734 nm spectrophotometer against a standard curve of trolox. The concentration of compounds having a reducing effect on the radical cation ABTS ● + is expressed in mg Trolox equivalent (mgET/g). Statistical analysis For statistical analysis, Microsoft Excel was used to obtain standard curves and graphs. ANOVA, were used to perform multiple comparison tests at p<0.05 significance level. Results and discussion Extractions yields The hydroethanol extraction and fractionation by liquid-liquid separation of the phenolic compounds of the different plants allowed us to determine the yields of the crude extracts as well as the different fractions. The results are expressed as a percentage of dry matter. Table 1. Yields of extractions and splits. Plants Extractions yields (%) Danielle oliveri Hydroéthanolicextract 28,62 ± 0,94 Ethyl acetate fraction 14,84 ± 0,54 butanolic Fraction 5,8 ± 0,4 Sclérocarya birrea Hydroéthanolicextract 21,02 ± 0,21 Ethyl acetate fraction 7,48 ± 0,41 butanolic Fraction 8,64 ± 0,5 Maranthes polyandra Hydroéthanolicextract 14,4 ± 0,41 Ethyl acetate fraction 0,44 ± 0,1 butanolic Fraction 2,24 ± 0,16 Pteléopsis suberosa Hydroéthanolicextract 14,28 ± 1,05 Ethyl acetate fraction 0,88 ± 0,24 butanolic Fraction 9,84 ± 0,64 Results indicated by different letters are statistically distinct (p <0.0001). The results obtained for the crude hydroethanol extracts, show that the highest yield is that of the hydroethanolic extract of the species Daniella oliveri (28.62 ± 0.94%) followed by the species Sclerocarya birrea (21.02 ± 0.94%) followed by Maranthes polyandra (14.4 ± 0.41%) and the lowest value in the species Ptelopsis suberosa (14.28 ± 1.05%) (Table 1). For the liquid-liquid partition made from the hydroethanol extract, the highest yields are observed at the level of the fractions by the medium polar solvents (fraction of ethyl acetate) to polar (butanolic fraction). Determination of polyphenolic compounds The hydroethanol extracts and the fractions (ethyl acetate and butanol) were used to determine the phenolic compounds. Total phenol The total phenol levels of the extracts and fractions of the species were determined from a regression curve obtained from a gallic acid solution which gave the following equation: y = 9.5876x + 0.0067; R² = 0.9956. These results show that the total phenol contents vary from 13.27 ± 0.2 (Daniella oliveri ethyl acetate fraction) to 22.37 ± 0.21 mg EAG / 100 mg (hydroethanolic extract of Ptelopsis suberosa) (Table 2). The high levels of total phenols were obtained with the hydroethanolic extract of Ptelopsis suberosa, followed by the ethyl acetate and butanol fraction of the same plant. The species Ptelopsis suberosa thus contains interesting total phenol levels compared to other species. Of the two solvents used for the liquidliquid fractionation of the hydroethanol extracts of the four species, the ethyl acetate fractions showed 100 Kagambega et al. Int. J. Biosci. 2020 high levels compared to the butanol fractions. Ethyl acetate is therefore the organic solvent favorable to the extraction of total phenols. The fractionation of the crude extracts made it possible to group the compounds contained in our plants according to their polarity. This made it possible to present quantitative differences in flavonoids between the fractions of the same plant on the one hand and on the other hand between the fractions of the same nature of our four plants. Table 2. Total phenol content of extracts and fractions. Plants Extractions Total polyphenol contents (mg EAG / 100 mg extract or fraction) Danielle oliveri Hydroéthanolicextract 13,46±0,28hi Ethyl acetate fraction 13,27±0,2d butanolic Fraction 13,83±0,08ghi Sclérocarya birrea Hydroéthanolicextract 15,16±0,42f Ethyl acetate fraction 16,07±0,71e butanolic Fraction 14,11±0,27gh Maranthes polyandra Hydroéthanolicextract 14,18±0,3g Ethyl acetate fraction 17,83±0,34d butanolic Fraction 13,81±0,39ghi Pteléopsis suberosa Hydroéthanolicextract 22,37±0,21a Ethyl acetate fraction 21,31±0,89b butanolic Fraction 18,07±0,41c Results indicated by different letters are statistically distinct (p <0.0001). Total flavonoids The total flavonoid contents of the plants were determined against a standard curve (y = 0.0249x, R2 = 0.9943) of quercetin. These results indicate that the flavonoid contents of the extracts and fractions of these four species vary from 0.83 ± 0.50 mg EQ / 100 mg (hydroethanol extract of Maranthes Polyandra) to 16.05 ± 0.13 mg EQ / 100 mg (extract hydroethanolic acid of Ptelopsis Suberosa) (Table 3). The highest levels were obtained with the species Ptelopsis suberosa. From these results, we can say that the total phenol content of Daniella olivera (hydroethanolic extract) is much higher than that obtained by Koudoro et al. (2015) in Benin, unlike flavonoids, which were respectively 0.39 ± 0.24 mg EAG / 100 mg and 7.9 ± 1.28 mg EQ / 100 mg extract. Cyanidine was used as a reference substance for the determination of flavonoids instead of quercetin; which could explain this difference. These disparities in the content of phenolic Compounds can also be explained by various factors such as the nature of the soil, the microclimate and also the period of harvest because these factors are of paramount importance in plant biosynthesis (Millogo, 2008). The phenolic content of a plant depends on a number of intrinsic and extrinsic factors (Falleh et al., 2008). In addition, the hydroethanol extracts record the levels of high total polyphenols (22.37 ± 0.21 mg EAG / 100mg hydroethanolic extract of Pteléopsis suberosa). The work conducted by Mahmoudi et al. (2013) and by Koffi et al. (2010) confirm our results by indicating that ethanol in combination with water allows for better extraction of total polyphenols. Indeed, the addition of water to organic solvents increases the solubility of polyphenols (Sripad et al., 1982, Mohammedi, 2011) by modulating the polarity of the organic solvent. This increase may be due to the weakening of the hydrogen bonds in the aqueous solutions. It could also be due to the increase in the basicity and ionization of polyphenols in such solutions (Sripad et al., 1982). The solubility of polyphenols depends mainly on the number of hydroxyl groups, molecular weight and the length of the basic backbone carbonic chain (Mohammedi, 2011). 101 Kagambega et al. Int. J. Biosci. 2020 Table 3. Flavonoid contents, extracts and fractions. Plants Extractions Flavonoids content totals (mgEQ / 100 mg extract or fraction) Danielle oliveri Hydroéthanolicextract 2,32 ±0,38de Ethyl acetate fraction 3,57±0,26cd butanolic Fraction 4,19±0,96c Sclérocarya birrea Hydroethanolicextract 3,12±0,52cd Ethyl acetate fraction 2,33±0,31d butanolic Fraction 4,16±0,71c Maranthes polyandra Hydroethanolicextract 0,83 ± 0,50e Ethyl acetate fraction 3,50±0,11cd butanolic Fraction 2,88±0,34cd Pteléopsis suberosa Hydroéthanolicextract 16,05±0,13a Ethyl acetate fraction 11,82±1,98b butanolic Fraction 11,22±1,31b Results indicated by different letters are statistically distinct (p <0.0001). Activity anti-radical In the body, various types of oxidation take place and lead to the accumulation of free radicals. Also, the diversity and specificity of antioxidants (radical scavengers, electron donors or hydrogen atoms) make it necessary to evaluate the antioxidant activity by various methods. Thus, two (02) methods (DPPH and ABTS) were used to evaluate the anti-radical activity of hydroethanol extracts and fractions of Daniella oliveri, Sclerocarya birrea, Maranthes polyandra, Ptelopsis suberosa. Anti-radical activity DPPH The anti-radical activity (AAR) of plant extracts reflects their ability to reduce free radicals. The evaluations of the anti-radical properties of the extracts and fractions of the four species made it possible to calculate the DPPH reduction percentages by increasing concentrations of extracts. Concentrations trapping 50% of free radicals (IC50) were determined by the curves of the percentages of inhibitions as a function of the concentrations of extracts. We obtain curves having an exponential appearance with the presence of a stationary phase which signifies the almost total reduction of the DPPH in its non-radical form. The smaller the IC50 value, the more the extract has a strong antioxidant activity. The different IC50 obtained are shown in Table 4. Table 4. DPPH radical hard inhibitor power of extracts, fractions and standards. Plants Extracts/ fractions IC50 (µg/ml) Daniella oliveri Hydroéthanolicextract 0,51±0,08def Ethyl acetate fraction 0,71±0,2bcdef butanolic Fraction 0,63±0,04bcdef Sclerocarya Birrea Hydroethanolicextract 0,87±0,14abcd Ethyl acetate fraction 0,59±0,06cdef butanolic Fraction 0,73±0,20bcdef Maranthes Polyandra Hydroethanolicextract 1,08±0,15ab Ethyl acetate fraction 0,47±0,12ef butanolic Fraction 0,81±0,03bcde Ptelopsis Suberosa Hydroethanolicextract 0,36±0,19f Ethyl acetate fraction 0,96±0,14abc butanolic Fraction 0,53±0,23def Standards Quercétin 0,93±0,02 Gallic acid 0,60±0,01 The results presented by the different letters are significantly different at P <0.0001. 102 Kagambega et al. Int. J. Biosci. 2020 The results expressed in IC 50 of the anti-radical activity (Table 4) reveal that all the extracts and fractions tested as well as the standard compounds exhibit an antioxidant activity. The hydroethanol macerate of Ptelopsis suberosa exhibited the highest anti-radical activity (0.36 ± 0.19 μg / ml) followed by the fraction of ethyl acetate of Maranthes polyandra (0.47 ± 0.12). μg / ml) and lastly the hydroethanolic extract of Maranthes Polyandra (1.08 ± 0.15 μg /mL).Most of the anti-radical activities of the extracts and fractions are more pronounced than those of quercetin and gallic acid, which are synthetic compounds used as references in this study. These results are similar to those of Koudoro et al. (2015), who found that the trunk bark of Daniella olivera had good antioxidant activity. Radical cation reduction ABTS ● + Anti-radical activity using the ABTS method as described by Re et al. (1999) was used to determine the antioxidant potency of hydroethanol macerates and the fractions of Daniella olivera, Sclerocarya birrea, Maranthes polyandra, Ptelopsis suberosa. Fig. 1. Inhibitory potency of the ABTS radical of the extracts, fractions and reference compound. In our study, concentrations were determined against a trolox reference curve whose regression equation is as follows: y = -0.0016x + 0.6546; R2 = 0.9903. The values of the antioxidant capacity obtained ranged from 28.75 ± 1.02 (hydroethanolic macerate) to 30.17 ± 0.47 mg ET /g (butanolic fraction) for Daniella oliveri, from 29.04 ± 0.65 to 30.42 ± 0.65 mg ET /g (ethyl acetate fraction) for Sclerocarea bierra, from 25.57 ± 0.97 (macerated hydroethanol) to 34.81 ± 0.68 mg ET/g (ethyl acetate fraction) for Maranthes polyandra and finally from 22.71 ± 0.54 (ethyl acetate fraction) to 32.28 ± 0.68 mg ET/g (hydroethanolic macerate) for Ptelopsis suberosa (Figure 1). The anti-radical activity ABTS● + obtained in this study shows that our plants are rich in compounds capables of yielding electrons or hydrogens. It is mainly the fractions (ethyl acetate and butanol) which have the best antiradical powers compared to the mother extracts (hydroethanol). These anti-free radical powers are superior to that of quercetin which is a pure compound (15.32 ± 0.25 mg ET/g) used here as a reference. In view of these results, the barks of Daniella olivera, Sclerocarya birrea, Maranthes polyandra, Ptelopsis suberosa could be exploited for the preservation of human health through their antioxidant activity. Indeed, the 103 Kagambega et al. Int. J. Biosci. 2020 cellular and oxidative lesions linked to free radicals or to ROS appear today as one of the main causes of several human diseases involving hypertension, cancer, arteriosclerosis, rheumatism, Alzheimer's disease, heart disease, autoimmune diseases, disorders of the digestive system such as peptic ulcer, intestinal and intestinal inflammations, neurodegenerative disorders, diabetes and viral infections (Bonnefoy et al., 2002; Huang et al. 2005; Li et al., 2009). These free radicals, which naturally occur in the normal metabolism of living organisms, can be captured through chemo-prevention using the antioxidant compounds found in human nutrition and medicinal plants (Kubola et al., 2008; Verma et al., 2009). Conclusion In the present work, different aspects of Daniella oliveri, Sclerocarya birrea, polyandra Maranthes, Ptelopsis suberosa were studied: a quantitative study of phenolic compounds and the antioxidant activity of crude extracts and fractions.Extraction and fractionation of the bark of plants yielded different yields depending on the solvents used. Quantification of phenolic compounds, to know total phenolics and total flavonoids, made it possible to note that the hydroethanolic extract and the ethyl and butanolic acetate fractions of Ptelopsis Suberosa had the highest levels of total phenolics and flavonoids. The study of the antioxidant activity of the extracts and fractions of the four plants showedthat all the extracts and fractions have an interesting antioxidant power, in this case the hydroethanol macerate of Ptelopsis suberosa and the fraction of ethyl acetate of Maranthes polyandra which respectively gave the best antioxidant potentials (DPPH and ABTS). 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