Improving Free Radical Scavengers in Vernonia amygdalina (Bitter leaf) through Soil Amendment with Organic Fertilizer

Abstract

Free radical scavengers (antioxidants) are essential micronutrients required for maintenance of good health. Except for fruits, leafy vegetables are the major sources of the free radical scavengers which play the critical roles in the normal metabolic activity for the survival of cells and the entire organism. Adequate intake of dietary free radical scavengers help in the maintenance of good health and prevention of chronic diseases. The concentrations of these compounds in most Nigerian leafy vegetables are generally low due to impoverished soil occasioned by continuous use of the soil for cultivation of crops and poor agricultural practices. It is against this background that this research was designed to evaluate the influence of organic fertilizer (Craseonycteris thonglongyai droppings) on the improvement of some dietary free radical scavengers (ascorbic acid, tocopherol, β-carotene, carotenoid, lycopene, chlorophyll, flavonoids and total phenol) in the leaf of Vernonia amygdalina. The leaves of V. amygdalina grown with organic fertilizer (C. thonglongyai droppings) and chemical fertilizer (commercial reference) in a pot experiment were harvested at market maturity and the concentrations of tocopherol, lycopene, chlorophyll, β-carotene, carotenoid, flavonoid and phenol were evaluated by spectrophotometric method whereas ascorbic acid was determined by titrimetric technique. The results showed that treatment with both chemical and organic fertilizers significantly increased (p < 0.05) the concentrations of lycopene, vitamin E, carotenoid and flavonoid in V. amygdalina, however; the concentration of lycopene, carotenoid and flavonoid were significantly higher (p < 0.05) in the vegetable treated with the organic fertilizer when compared with chemical fertilizer. While the concentrations of carotene, chlorophyll and phenol in the leaf of V. amygdalina increased significantly with the application of organic fertilizer, treatment with chemical fertilizer had no significant effect on the concentrations of these parameters in the vegetable. Similarly, the application of organic and chemical fertilizers significantly decreased the vitamin C in the vegetable, however, the vitamin C content in the V. amygdalina treated with chemical fertilizer was significantly higher than in the vegetable treated with the organic fertilizer. The study suggests that soil amendment with the organic manure generally enhances the bioaccumulation of free radical scavengers in the leaf of V. amygdalina when compared with the synthetic fertilizer (commercial reference).