Comparative Proximate, Vitamin and Mineral Composition of Leaves of Four Selected Tropical Vegetable Plants Namely: Ocimum gratissimum, Piper guineense, Gongronema latifolium and Vernonia amygdalina

Abstract

Aim: The aim of the study was to carry out a comparative analysis of the proximate, vitamin and mineral composition of the leaves of four selected tropical vegetable plants namely: Ocimum gratissimum, Piper guineense, Gongronema latifolium and Vernonia amygdalina. Methodology: Fresh leaves of each vegetable were washed and air dried at room temperature for two weeks. The dried leaves were pulverized using a mechanical grinder. Measured amounts were subjected to quantitative proximate, vitamin and mineral analysis. Results: For all four plants, carbohydrates was the major macronutrient constituents (range 49.61-64.09% dry wt.) followed by fats (15.06-29.43%), Protein (7.28-12.53%), ash (1.81-14.82%) and fiber (2.92-7.53%) in that order. G. latifolium had the highest carbohydrate (64.09±0.09% dry weight) and protein (12.53±0.10%) composition while V. amygdalina had the highest fat (29.43±0.03%) composition. Results of Ash analysis of the four leaves showed P. guineense to have the highest total mineral content (14.82±0.12% dry wt.) followed by V. amygdalina (10.75±0.01%), O. gratissimum (4.60±0.04%) and G. latifolium (1.81±0.01%) in that order. O. gratissimum and P. guineense had the highest composition of fiber (7.53±0.02% and 7.22±0.02% respectively) closely followed by G. latifolium (6.03±0.02%) and V. amygdalina (2.92±0.02%). Vitamin analysis revealed that leaves of the four vegetable plants contained high levels of vitamin C (range 18.1-43.4 mg/100 g) and appreciable quantities of vitamins A (0.3-1.2 mg/100 g) and E (0.67-0.9 mg/100 g). V. amygdalina leaf contained the highest concentration of vitamin C (43.4±0.01 mg/100 g) and A (1.2±0.9 mg/100 g) while O. gratissimum had the highest vitamin E content (0.9 mg/100 g). The mineral assay indicated that the leaves of the plants contain high levels of Magnesium (Mg)(3.6-24.8 mg/100 g), Phosphorus (P) (2.8-34.3 mg/100 g), Calcium (Ca) (12.1-19.0 mg/100 g) and copper (Cu) (5.8-18.5 mg/100 g) relative to their Zinc (Zn) (1.1-2.1 mg/100 g), Potassium (K) (2.1-6.9 mg/100 g)  and Sodium (Na) (4.3-8.1 mg/100 g) contents. Conclusion: In conclusion, these plants were shown to be rich in carbohydrates, proteins and fats, vitamins and minerals justifying their use in diets. That the plants were particularly rich in vitamins and mineral with antioxidant properties could explain the therapeutic uses of the various preparations of these leafy vegetables, in traditional medicine, for the treatment and management of diseases that have their etiology and pathophysiology in free radical generation and oxidative stress.