Secondary Metabolites and Antioxidant Activity of Different Parts of the Baobab Fruit (<i>Adansonia digitata</i> L.)

Abstract

The objective of this study was to determine the polyphenol, flavonoid and tannin content and the antioxidant power of methanolic extracts from the different parts of the Senegalese baobab fruit. Phytochemical screening revealed the presence of saponosides, tannins, alkaloids, sterols, flavonoids, coumarins and total sugars in all extracts from the fruit parts. The total polyphe nol content was determined by the folin-ciocalteu method. This method is based on the quantification of the total concentration of hydroxyl groups present in the extract. In an alkaline medium, the reagent of folin-ciocalteu, oxidizes the phenols to ion phenolates and partially reduces its hetero-polyacids , hence the formation of a blue complex. The absorbance is read at 765 nm against a control. The Flavonoids vere determined using aluminum trichloride and sodium hydroxide. Aluminum trichloride forms a yellow complex with flavonoids and sodium hydroxyde forms a pink complex absorbing in the visible range at 510 nm. The alternative colorimetric method based on reactions with vanillin in an acidic medium made it possible to determine the tannin content. Absorbances were measured at 500 nm. The results show that the methanolic extracts of the fibers and shell have very high polyphenol, flavonoid and tannin contents. In fact, the polyphenol contents of the fiber (159.00 ± 0.93 μg EAG/mg extract) and shell (155.39 ± 0.89 μg EAG/mg extract) were much higher than those of the pulp (27.21 ± 0.26 μg EAG/mg extract) and seeds (18.36 ± 0.07 μg EAG/mg extract). In addition, the flavonoid contents of the fibers (97.64 ± 0.40 μg EQ/mg) and of the shell (86.18 ± 0.46 μg EQ/mg) were higher than those of the seeds (12.82 ± 0.04 μg EQ/mg) and pulp (5.66 ± 0.18 μg EQ/mg). The tannin contents of the fibers (256.65 ± 1.45 μg EC/mg) and of the shell (196.05 ± 25 μg EC/mg) are higher than those of the pulp (103.09 ± 0.62 μg EC/mg extract) and seeds (1.09 ± 0.04 μg EC/mg extract). The antioxidant activity of extracts from different parts of the baobab fruit has Also been achieved using two different methods (DPPH and FRAP). The trapping capacity of the DPPH radical is very advantageous for the fibers (IC50 = 2.27 μg/mL) and the shell (IC50 = 1.52 μg/mL). The FRAP test has shown that the extracts from the shell (18.47 μg/mL) and fibers (20.00 μg/mL) have a greater iron reduction capacity than that of the standard ascorbic acid (45.64 μg/mL).