The plant material for this study consists of the fruit and vegetables, presented in Table 1 and Table 2, which were, on the one hand, harvested in the “ex-Tele zone” in the first district Makélékélé of Brazzaville and, on the other hand, purchased at the “Total market” in the second district and the “Lycée Thomas Sankara market” in the ninth district of Brazzaville. The different plants were identified by Dr. Jean Marie MOUTSAMBOTE from the National Institute for Research in Exact and Natural Sciences (IRENS) of Brazzaville (Congo).

2,2-diphenyl-1-picrylhydrazyl (DPPH), Quercetin and Folin-Ciocalteu were purchased from Sigma Aldrich. Gallic acid was obtained from Merck.

The different fruit and vegetables collected were carefully washed with tap water and the organs used were: pulp and seeds for fruit, leaves and seedling for vegetables. The organs of the different fruit were then dried in an oven at 40˚C and those of the vegetables at room temperature away from light for 7 days until their mass had stabilized. The dried organs were crushed and the powder obtained was stored before the various analyses.

The extracts for determining of total polyphenols and flavonoids, and antiradical activities were obtained by mixing 30 g of the plant material in 2 × 150 mL of the hydro-ethanol solution of a 50% (v/v). The mixture was stirred for 72 hours, and then filtered. The filtrate obtained was concentrated dry from a rotary evaporator and stored in a cold place (+4˚C) awaiting analysis [25].

The determination of total polyphenol content (TPC) was carried out using Folin-Ciocalteu colorimetric method described by Muanda et al. [26]. This quantitative assay was performed by mixing in an Eppendorff tube 0.1 mL of the hydroethanolic extract (2 mg/mL), 0.9 mL of distilled water and 0.9 mL of the Folin-Ciocalteu reagent (1N), and then immediately following 0.2 mL of a 20% sodium carbonate (Na₂CO₃) was added. The absorbance of the obtained mixture was measured at 760 nm employing a spectrophotometer after incubation for 40 min at room temperature in the dark against a methanol solution used as a blank. Quantification was conducted on the basis of a standard curve of gallic acid analyzed under the same conditions as the samples. Results are expressed as milligrams of gallic acid equivalent (GAE) per 100 grams of dry weight (GAE/100 g DW).

The total flavonoid content (TFC) was determined using the colorimetric method described by Muanda et al. [26]. For this purpose, 250 μL of the hydro-ethanol extract and 1 mL of water were introduced successively into a 10 mL flask. At the initial time (0 minutes), 75 μL of a 5% sodium nitrite solution was added. After 5 minutes, 75 μL of a 10% aluminium trichloride solution was added. At 6 min, 500 μL of sodium hydroxide (1N) was added to the mixture. Immediately, 2.5 mL of distilled water was added to the mixture. The absorbance of the mixture obtained was measured at 510 nm with the UV-visible spectrophotometer. A calibration curve was drawn up using standard solutions of quercetin prepared at different concentrations. The TFC was calculated and expressed as a quercetin equivalent [milligrams of quercetin equivalent (QtE) per 100 grams of dry weight (QtE/100 g DW)].

The DPPH radical scavenging activity was determined using the method described by Hennebelle [27] The test solution was performed by mixing 10 mL of a 10 mg/250 ml of 2,2-diphenyl-1-picrylhydrazyl (DPPH) solution with 100 µL of the test extract at different concentrations (5 to 50 mg/mL). The activity was then measured at 517 nm employing a spectrophotometer UV-visible after a 30 minute-incubation in the dark. The percentage of inhibition of DPPH was calculated by the following relationship:

% i n h i b i t i o n = ( A B l a n k − A S a m p l e ) ( A B l a n k ) × 1 0 0

ABlank: Absorbance of Blank; ASample: Absorbance of sample.

The IC50 was determined by evaluating the free radical scavenging activity of several dilutions of each sample and interpolating the extract concentration whose inhibition percentage reached 50%. The IC50 value was calculated from the graph plotting the scanning activity for the selected fruits and vegetables.

All tests were performed in triplicate. The statistical analyses were carried out with R software version 3.3.3. The Pearson’s Chi-squared test was used to compare two by two the measured parameters (TPC, IC50 and TFC) of fruit and vegetables. All tests had a significance level of 5%.

The regression equation from calibration curve of galic acid was of Y = 3.9089x + 0.1257, with a correlation coefficient: R² = 0.9989. The TPC expressed in mg GAE/100 g DW are shown in Figure 1. These results show that TPC vary in different vegetable extracts.

In Figure 1, we can see that the highest TPC values were found in the extracts of I. batatas and C. pepo, which were respectively 536.02 ± 0.01 and 533.60 ± 0.05 mg of GAE/100 g DW, and they are statistically identical (P > 0.05). Followed of the extracts of H. sabdariffa (421.02 ± 0.015 mg of GAE/g DW) and S. negrum 1 (412.10 ± 0.05 mg of GAE/g DW), that are also statistically identical (> 0.05). Ours values were generally higher than the ones reported by Yadav et al. [15], especially in methanolic, ethanolic and butanolic extracts of C. pepo which were respectively 519.81 ± 2.35, 336.25 ± 1.52 and 272.01 ± 1.57 mg of GAE/100 g DW, and in the ethanol extracts of six other varieties of gourd leaves, i.e. Cucurbita maxima (56.11 ± 0.69 mg of GAE/100 g DW), Trichosanthes dioica (118.82 ± 1.11 mg of GAE/100 g DW), Luffa acutangula (156.23 ± 2.02 mg of GAE/100 g DW), Lageneria siceraria (463.64 ± 1.37 mg of GAE/100 g DW), Momordica. charantia (440.79 ± 2.12 mg of GAE/100 g DW) and Lageneria cylindrica (300.06 ± 2.51 mg of GAE/100 g DW). Extracts of Amanranthus (194.79 ± 0.03

mg of GAE/100 g DW) and S. oleacea (196.79 ± 0.03 mg of GAE/100 g DW) had mean TPC that were statically identical (P > 0.05), while those of S. negrum 2 (120.09 ± 0.03 mg of GAE/100 g DW), S. melongena (147.30 ± 0.11 mg of GAE/g DW), B. campestris (97.78 ± 0.17 mg of GAE/100 g DW) and D. liebrechtsiana De Wild (124.7 ± 0.01 mg of GAE/100 g DW) had relatively low TPC and did not show significant differences (P > 0.05).

Results showing the total polyphenol contents (TPC) determined in the hydroethanolic extracts of edible fruits are presented in Figure 2. Regarding this Figure, the extract TPC of C. lacourtianum (532.79 ± 0.19 mg of GAE/100 g DW) and the seeds of A. alboviolaceum (469.38 ± 0.28 mg of GAE/100 g DW) were much higher than those of any other fruit under study. However, the extract of C. lacourtianum showed significantly (P < 0.05) higher value of TPC than the one of A. alboviolaceum. It should be noted that those values were considerably higher than the ones of Ficus carica (331.93 ± 51.19 mg/100 g MS), Prunus armenidca (304.63 ± 38.84 mg/100 g MS), Phoenix dactylifera (241.61 ± 50.48 mg/100 g MS) and Prunus amygdalus (109.07 ± 15.96 mg/100 gMS) dry fruit of commonly consumed in India reported by Vijaya Kumar Reddy et al. [14], and similar to those found in fruit regularly consumed in the Malaysia such as Baccaurea polyneura (546.25 ± 15.70 mg of GAE/100 g), Mangifera odorata (487.00 ± 8.23 mg of GAE/100 g) and Syzygium jambos (555.57 ± 28.33 mg of GAE/100 g) published by Ikram et al. [28], and to other dried fruit consumed in Algeria, such as apricots and figs, with values of 630 mg GAE/100 g DW and 520 mg GAE/100 g DW, respectively [29].

In addition, we noted not negligible TPC in extracts of C. reticulata, P. quadrangularis and A. alboviolaceum (P + S), with values 186.89 ± 0.05, 106.12 ±0.07 and 93.23 ± 0.11 mg of GAE/100 g DW, respectively. The value for C. reticulata is

statistically different from two other extracts (P-value < 0.05), which are statistically identical (P-value > 0.05).

The low TPC were obtained with extracts of A. muricata (54.24 ± 0.13 mg GAE/100 g DW), A. gigantum pulp and seed (59.65 ± 0.09 mg GAE/100 g DW), S. senegalensis (35.46 ± 0.15 mg GAE/100 g DW), A. gensisEngl (46.75 ± 0.2 mg GAE/100 g DW) and F. capensis (47.56 ± 0.15 mg GAE/100 g DW). We observed a significant variation (P < 0.05) between the mean of S. senegalensis and those of A. muricata and A. gigantum, which are statistically identical (P-value > 0.05) to the ones of A. gensisEngl and F. capensis. In addition, the TPC value of S. senegalensis pulp is very low compared to that obtained by Lamien-Meda et al. [7] on the acetone (872.33 mg GAE/100 g) and methanol (505.83 mg GAE/100 g) extracts from the same fruit. This difference could be explained by the climate as well as the extraction solvent used.

The regression equation from calibration curve of quercetin was of Y = 1.6954x + 0.2816, with a correlation coefficient: R² = 0.9955. The TFC of the extracts of the different vegetables expressed in mg QtE/100 g DW are presented in Figure 3.

In this figure, we observe that the extract of I. batatas (486.46 ± 0.10 mg of QtE/100 g DW) had a far (P < 0.05) higher TFC than the other extracts. Followed by C. pepo (303.72 ± 0.10 mg of QtE/100 g DW) and S. negrum 1 (292.10 ± 0.14 mg of QtE/100 g DW) extracts, and finally H. sabdariffa (243.49 ± 0.10 mg of QtE/100 g DW). The extracts of S. melongena L, D. liebrechtsiana De Wild, Amaranthus, S. nigrum L2, B. campestris and S. oleracea presented the lowest TFC, with values of 95.08 ± 0.04; 74.24 ± 0.12; 59.70 ± 0.10; 52.43 ± 0.20;

50.36 ± 0.10 and 27.52 ± 0.10 mg of QtE/100 g DW, respectively. Nevertheless, our values were higher than or similar to the ones found by Yadav et al. [15] on the ethanol extracts of seven varieties of squash with values between 3.73 ± 0.22 and 84.85 ± 0.35 mg of QtE/100 g DW.

The results were expressed as quercetin equivalents using the regression equation from the standard curve of quercetin, Y = 1.6954x + 0.2816; R² = 0.9955. Figure 4, presenting the TFC results of the extracts of the different selected fruit, shows that the highest TFC was observed in the extract of C. lacourtianum (380.55 ± 0.10 mg of QtE/100 g DW), with significant variations (P-value < 0.05) than the other fruit, followed of the extract of A. alboviolaceum seeds (107.27 ± 0.10 mg of QtE/100 g DW). Extracts from C. reticulata L (64.89 ± 0.03 mg EQt/100 g DM) and P. quadrangularis (59.70 ± 0.01 mg EQt/100 g DM) revealed low TFCs which were significantly different (P < 0.05), with non-significant variations (P > 0.05). In addition, lowest TFC values with not significant variations (P > 0.05) were recorded for A. gigantum, A. muricata L, A. gensisEngl, A. alboviolaceum (P + S), F. capensis and S. senegalensis, with values of 36.86 ± 0.03; 34.78 ± 0.05; 31.70 ± 0.03; 31.67 ± 0.01; 28.55 ± 0.1 and 23.36 ± 0 mg of QtE/100 g DW, respectively. When comparing with the work by Benmeddour et al. [30] on the TFCs of ten Algerian date cultivars, this study showed that, exception the C. lacourtianum fruit which had a high value, the other fruit presented TFC values within the value range of those ten date varieties (15.22 to 299.74 mg QE/100 g DW).

These results direct us towards the regular consumption of vegetables such as I. batatas, C. pepo, H. sabdariffa and S. negrum 1, and fruit such as A. alboviolaceum and C. lacourtianum, which are rich in total polypenolic compounds and total flavonoid. These fruit and vegetables could help to avoid disorders related to oxidative stress such as degenerative diseases [31], and provide protection

against oxidation at the cellular level by interfering in enzyme activity, chelation of redox active metals and free radical scavenging [32]. Dietary polyphenols may provide indirect protection by activating endogenous defence systems and modulating cell signaling processes such as NF-кB activation, AP-1 DNA binding, glutathione biosynthesis and various biochemical processes involved in the activation of carcinogenesis [33] [34]. In addition, phenolic compounds such as flavonoids are powerful free radical scavengers in fruit and vegetables. They protect lipids and vital cells from oxidative damage, participate in the prevention of coronary heart disease, and have antiproliferative or anticancer activities [35] [36] [37].

The results of the anti-radical activity of extracts from vegetables are presented in Figure 5.

From the analysis of Figure 5, it appears that extracts of S. nigrum L1, H. sabdariffa, I. batatas, S. oleracea and C. pepo better inhibit free radicals with low inhibitory concentrations (IC50) of 12.33 ± 0.01; 12.86 ± 0.04; 14.20 ± 0.02; 18.27 ± 0.02 and 18.28 ± 0.02 mg/mL, respectively, followed by extracts of S. nigrum L2 (21.83 ± 0.1 mg/mL) and D. liebrechtsiana De Wild (23.06 ± 0.01 mg/mL), with not significant variations (P > 0.05). While extracts of S. melongena, Amaranthus and B. campestris inhibit less free radicals with the strengths of IC50 of 28.28 ± 0.08; 36.23 ± 0.04 and 42.08 ± 0.34 mg/mL, respectively, with not significant differences (P > 0.05).

Figure 6 presents the results of the antiradical activity of the studied fruit.

It can be seen that extracts of F. capensis, A. alboviolaceum and A. gigantum strongly inhibit free radicals with respective IC50 of 11.47 ± 0.07 and 11.84 ± 0.07; 18.91 ± 0.11 mg/mL, followed by the extracts of C. reticulata L (24.21 ± 0.11 mg/mL), A. gensisEngl (28.90 ± 0.21 mg/mL) and A. muricata L (29.76 ± 0.20 mg/mL). The lowest anti-radical activity was observed with extracts of S. senegalensis (38.34 ± 0.20 mg/mL), C. lacourtianum (40.03 ± 0.03 mg/mL), P. quadrangularis (51.36 ± 0.02 mg/mL) and A. alboviolaceum (58.68 ± 0.08 mg/mL).

The results of this study show that vegetables such as S. nigrum L1, H. sabdariffa, I. batatas, S. oleracea and C. pepo, on the one hand, and fruit such as F. capensis, A. alboviolaceum and A. gigantum on the other hand, reduce free radicals better. This strong inhibition of free radicals could be justified by the relatively high concentrations of total polyphenols and flavonoids quantified in this study. Indeed, polyphenolic compounds are reputed to be powerful compounds with the ability to reduce free radicals [25]. The results obtained correlate clearly with the total polyphenol content and strongly advocate for the consumption of these fruit and vegetables as potential natural additives in the food instead of synthetic compounds [14] [25] [38] [39].