A comparative study of antioxidant potentials of some leafy vegetables : emphasis on African leafy vegetable and exotic vegetables.

Abstract

Due to malnutrition and food insecurity problem around the globe, mainly in developing countries, cheap nutritional food sources are required. In South Africa, a large proportion of the population is considered “poor” and with limited resources. However, South Africa as a whole is rich in indigenous leafy vegetables which have the capacity to help mitigate the problem of malnutrition and food insecurity. Amaranthus hybridus, an African indigenous leafy vegetable was tested for seed quality and potential essential antioxidants. Exotic (to Africa) leafy vegetables (Brassica oleracea and Brassica oleracea var. capitata f. rubra) were used as references for potential antioxidants. Amaranthus hybridus seed quality was tested using two different coloured seeds, red and white gold. Seed viability and vigor were tested using germination, electrolyte leakage and antioxidant content. Data recorded indicated better seed quality for red seeds than white gold seeds; therefore red coloured seeds were planted along with purchased Brassica oleracea and Brassica oleracea var. capitata f. rubra for quantifying antioxidant content. Selected antioxidant types were measured on weekly harvests of the studied vegetables. From the results it was evident that the indigenous leafy vegetable amaranth with total antioxidants [FRAP(3174.91 mmol Fe2 SO4 100g-1 DW) and DPPH(8.3 mmol trollox 100g-1)], proteins (6.88 mg.g-1 DW), total phenols ( 345 mg 100g-1 DW), flavonoids (79 mg 100g-1 DW), Chlorophyll and carotenoids (2.8 mg 100g-1 DW), ascorbic acid (86 mg 100g-1 DW) and soluble sugars (1.07 Brix %), could be used in conjunction with available commercial leafy vegetables to combat malnutrition and food security problems. Further, these results indicate that in resource limited regions this vegetable can act as a main source of nutrients and a supplement in resource abundant regions of the country and/or continent. Further, analysis of selected enzymatic antioxidants was carried-out on leaf material of the studied vegetable to evaluate the capability of indigenous leafy vegetables to protect themselves against oxidative damage. Indigenous leafy vegetables exhibited high antioxidant activity against lipid peroxidation at early stages of growth and high antioxidant enzyme activity at similar stages thus high capability of mitigating ROS effect. Data obtained from the study indicated that indigenous vegetables are a good source of essential antioxidants which are beneficial to human health; therefore the intensity of their use needs to be increased, especially in areas of high prevalence of malnutrition and diseases.