Evaluation of Nitrite Radical Scavenging Properties of Selected Zimbabwean Plant Extracts and Their Phytoconstituents

Oxidative stress resulting from accumulation of reactive oxygen species has been associated with disease. The search for natural antioxidants of plant origin is necessitated by the side effects associated with synthetic antioxidants currently available. The objective of the study was to determine the antioxidant activity of Combretum zeyheri, Combretum platypetalum, and Parinari curatellifolia extracts by determining nitrite radical scavenging ability. The nitrite radical scavenging assay was used to evaluate the antioxidant potential of the extracts. The total flavonoid content of P. curatellifolia methanol extract was determined by the aluminium calorimetric method. The aqueous and ethanolic leaf extracts of C. zeyheri, C. platypetalum, and P. curatellifolia extracts exhibited nitrite radical scavenging activity. The results show the scavenging activity in the order of potency: P. curatellifolia > C. platypetalum > C. zeyheri with concentration values of 103？μg/mL, 158？μg/mL, and 188？μg/mL for the ethanol extracts and 92.5？μg/mL, 97.5？μg/mL, and 198？μg/mL for the water extracts, respectively. P. curatellifolia ethanol extract was the most potent and the total flavonoid content was estimated to be 0.4 ± 0.05？mg/g quercetin and could account for the activity. Thus, our findings provide evidence that C. zeyheri, C. platypetalum, and P. curatellifolia leaf extracts could be potential sources of natural antioxidants. 1. Introduction Oxidation in living organisms is essential for the generation of energy during catabolism but these metabolic processes result in the continuous production of free radicals and reactive oxygen species (ROS) in vivo. Free radicals or more generally ROS are highly reactive species that are generated by cells during respiration and cell-mediated immune functions [1]. Free radicals are also generated through environmental pollutants, cigarette smoke, automobile exhaust, radiation, and pesticides [2]. The instability and reactivity of free radicals due to the lone electron in the outer shell can cause them to attack specific biomolecules in the body such as protein and lipids [3]. Normally, there is a balance between the quantity of free radicals generated in the body and the antioxidant mechanisms which scavenge/quench these free radicals preventing them from causing deleterious effects in the body [2]. The antioxidant mechanisms include endogenous and exogenous systems such as catalase and vitamin antioxidants, respectively. When the generation of free radicals exceeds the scavenging capacity of the cell’s endogenous systems, the