For the study of biochemical characteristics, three batches of water lily seeds were constituted: a batch of black seeds and a batch of red seeds of Nymphaea lotus, and the third batch of seeds of Nymphaea micrantha. The first two lots (Lot 1) and (Lot 2) were collected from three tributaries of the Senegal River: “Ndiaye”, “Mboudom” and “Ndiandane” (Figure 1). The third lot of N. micrantha seeds (Lot 3) was collected from two tributaries: “Saint-Louis” and “Ross-bethio” (Figure 1).

The antioxidant activity was evaluated with 2,2 diphenyl-1-pycrilhydrazyl (DPPH) following the method described by Oliveira et al. (2009) [15].

All assays were performed in duplicate and statistical treatments were performed with R software. Statistical differences were considered significant with a probability less than 0.05 (P < 0.05).

The screening reveals three major elements that are common to all analyzed water lily seeds, showing that they have an identical phytochemical profile (Table 1).

The two groups of tannins (hydrolyzable tannins and non-hydrolyzable condensed tannins), alkaloids and flavonoids are present in large quantities in all three types of seeds.

Cardiotonic heterosides are present but in lesser quantities.

Saponosides and anthracene compounds are not identified in the samples analyzed.

Flav: flavonoids; Hydr: hydrolysable; Cond: condensed; Sap: saponins; Alc: alkaloids; A.D: Anthracene derivatives; C.G: Cardiac glycosides; ++: Very positive reaction (large quantity); +: Moderately positive reaction (small quantity); − Negative reaction (no reaction).

The presence of tannins, alkaloids, flavonoids as well as cardiotonic compounds would partly explain the use of seeds of N. lotus and N. micrantha species in the diet of diabetics in the delta and lower valley of the Senegal River [16]. These elements were also reported in the species Nymphaea lotus by Nicodème et al. (2016) [16].

These phytochemicals have many health benefits. Indeed, tannins have an astringent effect and manifest properties of vitamin P. They strengthen blood vessels and contribute to the accumulation of vitamin C in the body [5]. Some alkaloids enhance cardiac activity, excite the central nervous system, symptomatic nerves and stimulate blood circulation [17]. Flavonoids are well known as antioxidants [18] [19]. They are also anti-ulcer, anti-tumor, anti-spasmodic, anti-secretory and anti-diarrheal [20], anti-allergic, anti-inflammatory, hypotensive and protect against cancer and cataract [21]. They also have aphrodisiac properties [22]. Polyphenols have a potassium retention effect and therefore have a diuretic activity [23]. Cardiac glycosides have a fundamental therapeutic action which is the increase of cardiac output [11]. The presence of all these elements supports the hypothesis that the use of seeds would be good in the diet of diabetics. The extracts from N. lotus would act in the regulation of blood pressure [6]. Thus, this additional information would encourage efforts to promote the widespread use of water lily seeds, at least in endemic areas.

Quantitative estimation of some phytochemicals present in the methanolic extract of N. lotus and N. micrantha shows according to Table 2, that tannins are the highest (38.12 ± 0.021 to 118.13 ± 0.034 EAT/g DM) followed by flavonoids (24.06 ± 0.113 to 31.97 ± 0.087 mg EC/g DM) and total polyphenols are the lowest (0.54 ± 0.054 to 1.95 ± 0.120 mg EAG/g DM).

Tannin determination revealed statistically variable amounts among seed types (p value < 0.05%) (Table 2). Black and red N. lotus seeds had the highest values (118.132 ± 0.034 mg EAT/g DM and 89.904 ± 0.037 mg EAT/1 g DM, respectively). These results agree with the studies of Mourtala et al. (2019) [24] who found a content of 90.00 ± 0.50 mg/g in the methanolic extract of N. lotus

a, b, c: In the same column, means followed by a different letter are significantly different at the p < 5% threshold (Newman and Keuls method). DM: Dry Matter.

rhizome. This bioactive compound is known to have potential antiviral activity [25] as well as potential prophylactic and therapeutic effect against cancer cells [26]. The high amounts found in this study would justify the antibacterial effects [27] and cytotoxic effects on cancer cells reported in N. lotus species by Ashidi et al.(2010) [28].

Total polyphenols are in almost similar amounts in the three types of seeds, with values ranging from 0, 54 ± 0.054 to 1, 95 ± 0.120 mg EAG/g DM. Compared to the results obtained with dates, considered rich in phenolic compounds (566 mg/100g) [29] and those of grape seeds (750 to 4040 mg/100g) [30], it is easy to say that the seeds of Nymphaea sp. are quite rich in total polyphenols. Polyphenols are considered a major group of compounds that contribute to the antioxidant activities of plants as free radical scavengers due to their hydroxyl groups [31].

A high amount of flavonoid was found in all three types of seeds tested but varying considerably among seed types (Table 2). The highest value was found in red N. lotus seeds (31.970 ± 0.087 mg EC/g DM) while black N. lotus seeds had the lowest value (24.057 ± 0.113 mg EC/g DM). N. micrantha seeds had a content of 27.026 ± 0.074 mg EC/g DM. However, these values are lower than those from the work of Murtala et al. (2009) [24] who found a flavonoid content of 80.0 mg EC/g in the rhizome of N. lotus. This difference could be due to the difference in the organ tested. Flavonoids have many useful properties. They generally serve as flavoring ingredients in plants [24] and are also expressed in plants in response to microbial infection, suggesting their antimicrobial activity [32]. Flavonoids are also antioxidants such as those in tea that are believed to reduce oxidation of low-density lipoproteins and lower blood cholesterol and triglyceride levels [33].

The methanolic extracts show a notable antioxidant potential, regardless of the type of seed with a non-significant variation (Table 3). All the inhibition percentages are high ranging from 83.92% ± 1.40% to 87.67% ± 0.16%. However, black N. lotus seeds have significantly the highest antioxidant activity compared

to the other two seed types. These differences appear to be correlated with genotypic and phenotypic differences [34]. The synergistic action of tannins, total phenols, flavonoids found would explain the antioxidant power of plant extracts [35]. Previous work by Aliyu et al. (2018) on the in vitro antioxidant potential of oils extracted from the seeds of Nymphaea lotus and Nymphaea pubescens has prompted their use in the treatment of diseases caused by oxidative stress.