Phytochemical and antioxidant properties of unconventional leafy vegetables consumed in southern Africa

Abstract

Indigenous leafy vegetables possess high horticultural potential based on their long utilisation history by local communities across Africa. Phytochemical and antioxidant properties of 50% aqueous methanol and water extracts of three indigenous as well as two commercial leafy vegetables commonly consumed in southern Africa were evaluated. The total extractable phenolic content was highest for Amarathus dubius (5.16 ± 0.12. mg GAE/g DW) followed by Cleome gynandra (3.94 ± 0.09. mg GAE/g DW). Total flavonoid concentration was highest for A. dubius (3.89 ± 0.28. mg CE/g DW) followed by C. gynandra (2.19 ± 0.11. mg CE/g DW) and Cucurbita maxima (1.55 ± 0.04. mg CE/g DW). No proanthocyanidins were detected in C. maxima and Brassica napus cv Covo whereas low concentrations were recorded in other vegetables. Total saponins were variable across the evaluated extracts, with the highest concentrations recorded for B. napus cv Covo (83.2 ± 16.58. mg DE/g DW). Total iridoid content was highest for C. gynandra (9.14 ± 0.20. mg HE/g DW). More potent DPPH radical scavenging activities were exhibited by 50% aqueous methanol extracts compared to water extracts. A similar trend was observed in the ferric-reducing antioxidant power assay. The antioxidant activity based on the rate of β-carotene bleaching was higher for water extracts compared to 50% aqueous methanol extracts. The indigenous vegetables evaluated in this study had higher levels of phytochemicals and also exhibited more potent antioxidant activity compared to the commercial varieties. These findings not only suggest the importance of the indigenous vegetables in a healthy diet, but also provide a motivation for exploring their horticultural potential. © 2012 South African Association of Botanists.