Comparative evaluation of the nutritional composition, antioxidant capacity and inhibitory activities against α-amylase and α-glucosidase of three Nigerian leafy vegetables (Amaranthus hybridus L., Celosia argentea L. and Solanum macrocarpon L.).

BACKGROUND

Indigenous leafy vegetables are important components of diet and are recognized for their nutritional value and bioactive phytochemicals. Their antioxidant properties and ability to inhibit carbohydrate-hydrolyzing enzymes may contribute to the regulation of postprandial glucose levels and reduction of oxidative stress. This study evaluated the nutritional composition, antioxidant capacity, and inhibitory activities against α-amylase and α-glucosidase of the leaves of Amaranthus hybridus L. (AH), Celosia argentea L. (CA), and Solanum macrocarpon L. (SM), three commonly consumed Nigerian leafy vegetables.

METHOD: Proximate composition and mineral contents were determined in the dried leaves using standard analytical procedures. Methanolic leaf extracts were evaluated for total phenolic content, total flavonoid content, total antioxidant capacity, reducing power, Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, metal-chelating activity, and inhibitory activities against α-amylase and α-glucosidase enzymes.

RESULTS

AH, CA, and SM exhibited appreciable nutritional value and mineral composition, with significant differences (p < 0.05) observed for most parameters evaluated. AH contained the highest crude protein (22.08 g/100 g), crude fibre (18.02 g/100 g), ash (9.25 g/100 g), estimated metabolizable energy (275.54 kcal/100 g dry weight), and higher concentrations of most mineral elements. CA exhibited the highest total flavonoid content (5.84 mg QE/g extract), while total phenolic content ranged from 11.27 to 12.07 mg GAE/g extract with no significant differences among the vegetables. All extracts demonstrated concentration-dependent DPPH radical scavenging, metal-chelating, α-amylase inhibitory, and α-glucosidase inhibitory activities. Among the vegetables, AH exhibited the strongest overall antioxidant activity, with the lowest DPPH IC₅₀ (250.15 ± 8.45 µg/mL) and metal-chelating IC₅₀ (952.28 ± 10.56 µg/mL). Enzyme inhibitory activities also increased in a concentration-dependent manner, suggesting potential modulation of carbohydrate-digesting enzymes.

CONCLUSION

The studied vegetables possess valuable nutritional properties and exhibit antioxidant and carbohydrate-hydrolyzing enzyme inhibitory activities under in vitro conditions. These findings suggest that Amaranthus hybridus, Celosia argentea, and Solanum macrocarpon may serve as important dietary sources of nutrients and bioactive compounds with potential relevance to oxidative stress management and postprandial glycemic control. Further studies involving chromatographic characterization of individual compounds and in vivo investigations are required to confirm their biological significance.