Averrhoa carambola is employed traditionally in Nigeria to treat diabetes, vomiting, cough, chickenpox, ringworm, aphthous stomatitis, high blood pressure, eczema, diarrhea, and kidney dysfunction.. This study investigated the bioactive compounds, antioxidant and antidiabetic activities of the stem bark of Averrhoa carambola using standard methods. The antioxidant properties were assessed using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing power (FRAP) assay and the metal chelating (MC) activity. The phytochemical analysis of the extract indicated the presence of flavonoids, saponins, alkaloids, tannins, and cardiac glycosides. The total phenolic and flavonoid content ranged from 4.46 ± 0.19 to 51.25 ± 0.52 mg of GAE/g and from 441.00 ± 5.98 to 2285.00 ± 11.13 mg of QE/g, respectively. Antioxidant study revealed IC50 range for DPPH (26.47 to 29.64 µg/mL), FRAP (26.51 to 51.30 µg/mL) and MC (69.53 to 60.66 µg/mL). The acute toxicity test of Averrhoa carambola stem bark extract showed a mean lethal dose (LD50) of 3872.98 mg/kg. The extract’s effect on α-amylase and α-glucosidase enzymes in rats, at doses of 155, 310 and 6200 mg/kg showed a significant reduction in blood glucose levels (p < 0.05). Gas chromatography-mass spectrometry (GC-MS) analysis of ethyl acetate fraction indicated several compounds, including 5-(2-Amino-phenyl)-[1,3,4]thiadiazo-2-yl-p-tolyl-amine, 2-hydroxymethoxybenzaldehyde, tert-butyldimethylsilyl ether, phenol, 4-[2,3-dihydro-7-methoxy-3-methyl-5-(1-propenyl)-2-benzofuranyl]-2-methoxy, thiazolo[3,2-a]2enzimidazole-3(2H)-one,2-(2-fflorobenzylideno)-7,8-dimethyl, squalene, phenol 2-methoxy-4-(2-propenyl)-, acetate, 2-(2,5-dimethoxy-4-propylphenyl) ethanamine, isoquinoline,1,2,3,4-tetrahydro-8-amino-2-methyl-4-phenyl-, phenol, 2,6-dimethoxy-4-(2-propenyl)-. This research suggests that Averrhoa carambola stem bark possesses antioxidative activity and inhibits the enzymes α-amylase and α-glucosidase in rats, probably due to the presence of its bioactive constituents.
Averrhoa carambola, stem bark extract, antioxidant activity, diabetes, bioactive compounds
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