Fats have a wide range of applications and are a major scientific and economic issue. Indeed, depending on their variety and dietary preferences, oilseeds can be consumed as a main dish, condiment, or fortifier. They thus contribute to the diversity and balance of the population’s diet or they can be used as non-food sources. They can be used in the form of medicines or dyeing and tanning products: and in cosmetics [1]. Panda oleosa Pierre of the pandaceae family is a very common tree in Gabon. These fruits envelop a thick and very hard core, characterized by a bumpy aspect containing oleaginous seeds in the shape of crescent. Its fruiting is abundant in February. It is a medicinal and food plant. The bark contains tannin. The seeds contain an edible oil [2], produced and sold locally by the populations. In Gabon, the crushed seeds are added to sauces such as Irvingia gabonensis fruit kernels [3]. The seed oil is applied to ulcers, the crushed and roasted seeds to bronchial diseases. Screening tests on the bark of Panda oleosa have shown an inhibitory activity of HIV [4] [5].

Isolona hexaloba of the annonaceae family is a plant species found in Angola, Cameroon, Congo, Gabon, Equatorial Guinea, Nigeria, CAR, DRC. It is present in evergreen and semi-deciduous forest, in primary as well as secondary forest. It is often found along rivers. Its fruits are green to black with a wrinkled-bossed surface [6]. In the Democratic Republic of Congo, the bark is used in traditional medicine as a purgative and decoctions of bark are administered to treat abdominal pain, constipation, and wounds [7]. Bisbenzylisoquinoline alkaloids, curine and cyclene, have been isolated from the root bark. Both compounds showed significant trypanocidal activity in mice infected with strains ofTrpanosoma cruzi, the protozoaire causing Chagas disease. A sesquiterpene derivative, cazolobine has also been isolated from the roots [8]. Consumable vegetable oils are essential to our nutritional balance and play a role in our health. If the knowledge surrounding oil plants is relatively well developed elsewhere, it would seem that oil seeds are very little documented in Gabon or even in the Central African sub-region.

The objective of this work is to study the phytochemical and antiradical activity of the oil seeds of two oil plants from Gabon that have not been extensively studied: Panda oleosa Pierre and Isolona hexaloba Pierre ex Engl. and Diels.

The anti-radical activity was measured by scavenging the free radical cation of 2,2’-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid] (ABTS-+) according to the method developed by Re et al. [9] and optimized by N’negue et al. [10] with gallic acid as the reference antioxidant.

In this study, we first calculated the extraction yields of the different solvents from Panda oleosa and Isolona hexaloba seeds. The results obtained indicate that cyclohexane, the first solvent used during the successive extraction and the least polar, extracts mainly liposoluble substances (oils, fats, terpenes) from the seeds of the two oleaginous plants (Table 1). The cyclohexane thus contains the important fat fractions. The yields of cyclohexane are the highest; 35.97% for Panda seeds and 16.08% for Isolena seeds. These results reflect that the seed powders were virtually de-oiled by cyclohexane. Polar solvents subsequently solubilize polar compounds such as polyphenols. The successive extraction thus combines apolar and polar solvents. It allows partitioning the extractables in different fractions facilitating the later analyses, and the sum of the extracts with each solvent gives an idea of the global content in extracts of the seeds. The overall extract content is 69.50% for Panda seeds and 34.28% for Isolena seeds (Table 1). Silou [23] studied one hundred and thirty samples of oils and fats extracted from 77 species of the Congo Basin belonging to 35 botanical families and divided them into three classes of equal magnitude between 15% and 75% fat content. The plants with low fat content have a rate between 15% and 35%; those with medium fat content have a rate between 35% - 55% and finally the plants with high fat content have a rate between 55% - 75%. According to these percentages, Panda is a high-fat plant and Isolena a low-fat plant.

The phytochemical tests (Table 2) carried out on the seeds showed the presence of alkaloids, polyphenols, reducing compounds, free anthracene derivatives, terpenoids, anthraquinones, total sugars, coumarins, free quinones, leucoanthocyanins, sterols and triterpenes, carotenoids, flavonoids and cardiac glycosides. We note in Panda seeds, the absence of leucoanthocyanins, sterols, tannins, saponins, cardiac glycosides and mucilages. While in Isolena seeds, we note only the absence of tannins and mucilages. These bioactive compounds have multiple therapeutic properties and support the use of Panda and Isolena seeds in traditional medicine in the treatment of several pathologies. Indeed, Panda is used in the Democratic Republic of Congo as an antidiabetic and Isolona as a purgative and for the treatment of abdominal pain, constipation and wounds. Several authors have demonstrated that the consumption of foods rich in polyphenols reduces the development of numerous pathologies, such as cancer, vascular diseases, hypertension, atherosclerosis [24] [25] [26]. The seeds of Panda and Isolena contain a high quantity of alkaloids. These compounds are sought after for their physiological effects and pharmacological activities that are exerted in various fields. Alkaloids also play the role of antibiotics [13]. Cardiac glycosides highlighted in phytochemical tests of Isolena seeds could be major drugs for heart failure. They exert their activity on the heart at several levels: contraction forces, frequency, conductivity. These effects are reflected in the electrocardiographic changes [27]. Sterols and triterpenic alcohols present in both types of seeds, have anti-inflammatory, antidiabetic, anticancer, antidiarrheal, antiviral and anti-HIV activities [28]. Carotenoids are well-known phytomicronutrients. Carotenoids in Panda and Isolena seeds may have pro-vitamin A activity. Vitamin A is involved in maintaining good vision and preventing diseases that could affect the eyes. Carotenoids are also known to be antioxidants. They have a potential protective effect on the prevention and progression of cancers, cardiovascular diseases and cataracts [29]. The carotenoids contained in Panda and Isolena seeds can also be used in the food industry as additives as food coloring or in cosmetic products [29] [30].

In a second step, we evaluated the anti-free radical activity of aqueous and ethanolic extracts of Panda and Isolena seeds, by scavenging the free radical ion ABTS-+ according to the method of Re et al. [9] optimized by N’negue et al. [10] with gallic acid as reference antioxidant. The results of the antioxidant activity of gallic acid (a synthetic molecule with high antioxidant activity) validate the chosen method. Moreover, the IC50 value of gallic acid deduced from our results is more or less equivalent to that obtained by Sadat et al. [31] i.e. 0.47 µg/mL and N’negue et al. [10] [32] i.e. 0.47 and 0.37 µg/mL. These authors worked under the same conditions.

The results of the evaluation of the anti-free radical activity of the aqueous and ethanolic extracts of Isolona seeds also showed a variation of anti-free radical activity with the extraction solvent. According to the results obtained (Figure 2 and Figure 3), the aqueous extract with an IC50 of 37.5 µg∙mL⁻¹ is more active than the ethanolic extract with an IC50 of 95 µg∙mL⁻¹. The IC50 of the ethanolic extract is thus 2.5 times higher than that of the aqueous extract. As with the Panda seeds, the results obtained with the Isolena seeds seem surprising. Indeed, the aqueous extracts of Isolona seeds showed after the phytochemical study an absence of polyphenols and a low level of carotenoids which are both antiradical compounds [33] [34] [35]. While the ethanolic extract presented average amounts of carotenoids and polyphenol. This can be explained by the fact that during the successive extraction by maceration, the level of antioxidant compounds (polyphenol and carotenoids) present in the ethanol may be lower than the level of saponosides (antiradical compounds) strongly present in the aqueous extract. On the other hand, the aqueous extract may contain an unidentified polar anti-radical compound.

A comparison of the antiradical activity of the two oil plants shows that the aqueous extracts of the two seeds have quite similar antiradical activities, with however a slight advantage for the aqueous extract of Isolona. (IC50 = 37.5 µg∙mL⁻¹ against 40 µg∙mL⁻¹ for the aqueous extract of Panda). This can be explained by the presence in the Isolena aqueous extract of carotenoids and saponins, absent in the Panda aqueous extract. The comparison of the antiradical activities of the ethanolic extracts of the two oleaginous plants shows a more important activity for the Panda extract. Indeed, the IC50 of the ethanolic extract of Panda is equal to 60 µg∙mL⁻¹, and that of the Isolena extract 95 µg∙mL⁻¹. This result could be explained by the presence of a type of polyphenolic compounds much more active in the ethanolic extract of Panda seed.

The comparison of the free radical scavenging activity of Panda and Isolena oil seeds with that of gallic acid (IC50 = 0.37 µg∙mL⁻¹), a pure chemical compound “reference antioxidant”, shows that gallic acid is about 10 times more active than the aqueous extracts of the two seeds, 16 times more active than the ethanolic extract of Panda and 25 times more active than the ethanolic extract of Isolena. Indeed, the active principle responsible for the antiradical activity representing only about 10% of the total compounds of the extract, IC50 of 37.5; 40 µg∙mL⁻¹; 60 µg∙mL⁻¹ or 95 µg∙mL⁻¹ of the total extract, would be equivalent to IC50 of 3.7 µg∙mL⁻¹; 4 µg∙mL⁻¹; 6 µg∙mL⁻¹ or 9.5 µg∙mL⁻¹ of the active principle. The aqueous extracts of the seeds would thus be more active than the ethanolic extracts.

The work showed that the extraction rates of Panda oleosa and Isolona hexaloba seeds varied from one solvent to another. Extraction yields were highest with cyclohexane, water and trichloroethylene for Panda seeds and with cyclohexane for Isolena seeds. Panda is a highly oleaginous plant as its global extract rate was 69.5%, and Isolena a low oleaginous plant with a global extract rate of 34.28%. The phytochemical tests carried out showed that these oleaginous seeds contain major chemical groups such as alkaloids, polyphenols, sterols, triterpenes, carotenoids, tannins, reducing compounds, total sugars, saponins, coumarins and terpenoids, leucoanthocyanins, flavonoids, free anthracene derivatives, and cardiac glycosides. These bioactive compounds having multiple therapeutic properties, these seeds could thus be used in traditional medicine, in the treatment of several pathologies. Aqueous and ethanolic extracts of Panda and Isolena seeds have antiradical activity. Aqueous extracts have a higher antiradical activity than ethanolic extracts. Gallic acid, the “reference antioxidant”, is about 10 times more active than the aqueous extracts of both seeds, 16 times more active than the ethanolic extract of Panda and 25 times more active than the ethanolic extract of Isolena. A number of studies have revealed the important role that antioxidants play in our body. The extracts with strong anti-free radical activity of Panda and Isolena, due to their antioxidant properties, would therefore have preventive potential in the fight against pathologies associated with oxidative stress (cardiovascular diseases, aging, diabetes, cancer, inflammation, neuronal or genetic diseases). Moreover, these extracts could be used as natural antioxidants fighting against oxidation in food, pharmaceutical and cosmetic industries.

The authors declare no conflicts of interest regarding the publication of this paper.

N’negue ép Mezui-Mbeng, M.-A., Medza, D., Edou Engonga, P., Lié, O.B., Mengome, L., Engone, N. and Sophie, A. (2022) Phytochemical Study and Evaluation of the Antiradical Activity of Extracts of Oleaginous Seeds of Panda oleosa and Isolona hexaloba from Gabon. Food and Nutrition Sciences, 13, 165-180. https://doi.org/10.4236/fns.2022.132015