Tropical Leafy Vegetables as Valuable Sources of Carotenoids and Phenolics

Abstract

Leafy vegetables play an important role as essential components of diet for rural populations in tropical Africa. This study was undertaken to provide a more comprehensive characterization of carotenoids and phenolics in these neglected plant foods. For this, 12 leafy vegetables widely consumed in Côte d’Ivoire were selected, washed and oven-dried (50°C/3 days) before High-Performance Liquid Chromatography (HPLC) analysis of carotenoids and phenolics compounds. Carotenoids contents were significantly different (p ˂ 0.05) with lutein (43.68 ± 4.89 – 513.91 ± 5.68 μg/g dw) and all trans-β-carotene (22.62 ± 1.54 – 222.61 ± 5.63 μg/g dw) as major constituents. The calculated retinol activity equivalent (RAE) of β-carotene-rich leafy vegetables in this study ranged between 1.54 and 2.52 mg/100 g. The values of total phenolics ranged from 179.66 ± 11.33 mg/100 g dw in Corchorus olitorius to 436.48 ± 1.73 mg/100g dw in Abelmoschus esculentus. Three (3) flavonoids: quercetin (0.79 – 8.36 μg/g dw), catechin (0.39 – 5.65 μg/g dw) and kaempferol (0.76 – 29.11 μg/g dw) were quantified in the selected leafy vegetables. Chlorogenic acid (0.94 – 17.01 μg/g dw) was the most quantified phenolic acid in the leaves. Antioxidant activity evaluation of the leaves showed that 2,2-Diphenyl-1-Picrylhydrazyl (DPPH) radical scavenging activity ranged between 19.63 and 65% with Solanum melongena showing the highest value (65%). For 2,2’-Azino-Bis(3-ethylbenzothiazoline-6-sulphonic acid) or ABTS scavenging activity, Myrianthus arboreus recorded the highest value (76.66%) compared to other leaves. All these results suggest that the studied leafy vegetables are potential sources of carotenoids and phenolics and their consumption in sufficient amount may contribute to human health improvement.