Étude des traits morphologiques, des caractéristiques nutritionnelles et phytochimiques, ainsi que l’évaluation de l’activité antioxydante des graines de Vigna unguiculata (L.) Walp.

Abstract

Vigna unguiculata (L.) Walp., commonly known as cowpea, is a leguminous plant whose seeds are widely consumed due to their nutritional value and biological properties. The present study aimed to investigate the morphological, biometric, nutritional, and phytochemical characteristics, as well as the antioxidant activity, of two cowpea seed varieties: black and white. Morphological analysis showed that both varieties exhibited an oblong or D-shaped form with a smooth and shiny surface. Biometric measurements revealed differences in seed width, sphericity index, and weight, with the white variety displaying the highest values. Nutritional composition analysis indicated that black seeds contained higher levels of proteins (28.91%), lipids (1.14%), carbohydrates (58.61%), and ash (3.34%) than white seeds. Soxhlet extraction using 85% aqueous methanol provided the highest extraction yields, particularly for black seeds (3.92%), whereas hexane extracts showed lower yields (<1.2%). Colorimetric analysis revealed that methanolic extracts were the richest in polyphenols and flavonoids. The highest concentrations were recorded in the methanolic extract of black seeds, with 128.04 µg GAE/mg extract of total polyphenols and 5.37 µg QE/mg extract of total flavonoids. The antioxidant activity of the extracts was evaluated using several assays, including total antioxidant capacity (TAC), DPPH, ABTS, and FRAP. The results demonstrated that the methanolic extract of black seeds (BSME) exhibited the strongest antioxidant activity, with a TAC value of 169.80 ± 1.08 µg AAE/mg extract. Moreover, BSME showed a strong free-radical scavenging activity against DPPH and ABTS radicals, with IC₅₀ values of 58.89 µg/mL and 494.57 ± 13.34 µg/mL, respectively. Furthermore, the FRAP assay revealed a greater reducing power for methanolic extracts, particularly BSME, which exhibited an A₀.₅ value of 451.72 ± 13.02 µg/mL. In conclusion, the findings highlight the nutritional and therapeutic potential of Vigna unguiculata (L.) Walp. seeds, especially the black variety, which is distinguished by its higher content of bioactive compounds and its remarkable antioxidant activity.