Stevia rebaudiana ( Bertoni ) have genus of about 200 species of herbs and shrubs in the sunflower family and grows up to 1 m tall(P. Mishra, Singh, R., Kumar, U., & Prakash, V 2010). Stevia is a perennial herb with an extensive root system and their significantly economic value due to its high content of natural, dietetically valuable sweeteners in its leaves(Kinghorn, 2002) (K. S. Ramesh, V.; Megeji, N. W., 2006).Dried Stevia leaves have been used as natural sweeteners in many years. These leaves contain about eight different steviol glycoside diterpenes (Wallin, 2007.). Mainly steviol glycosides found in stevia leave are stevioside and rebaudioside A (“Reb A”), which can compile up to 20% of dry leaf weight in some strains, and are approximately 250–300 times sweeter than sucrose. (Chaturvedula et al., 2011; Lemus-Mondaca, Vega-Gálvez, Zura-Bravo, & Ah-Hen, 2012). The leaves also present in lower concentrations of other diterpene glycosides such as steviolbioside, rebaudioside B, C, D, F, dulcoside A , and rubusoside(Yadav & Guleria, 2012) .The non-caloric stevia sweeteners, extract from leaves, have been used in soft drinks, soju, soy sauce, yogurt, and other foods specially in Japan, Koreaand Brazil (N. C. Kim & Kinghorn, 2002) .In addition, stevia include carbohydrates, crude fiber, protein, and essential amino acids (Lemus-Mondaca et al., 2012).Moreover, Stevia leaves have a high amount of phenolic compounds, vitamin C, carotenoids, flavonoids, alkaloids, xanthophylls, acids (caffeic, chlorogenic, etc.), as well as oligosaccharides chlorophyll (Wallin, 2007.) .
Stevia leaf extract have possessed many medicinal properties such as lowering of blood sugar, increased urination, and dilation of blood vessels which in turn help lowering blood pressure, anti-inflammatory activity, and wound .The leaf extract have been reported the effect of antibacterial, antifungal, anti-inflammatory, antimicrobial, antiviral, antiyeast, cardiotonic, diuretic, and anti- hyperglycemic(Curi R., 1986). S. rebaudiana leaves extract cause for the effects on cardiovascular , renal systems and affects hypertension and hyperglycemia. Since, these activities may be interacted with the presence of antioxidant compounds, extracts of S. rebaudiana leaves were evaluated for their total phenols, flavonoid contents and total antioxidant capacity (TAC) which have a positive effect on human health and also can be used for the treatment of many diseases(Madan, 2010).
Phenolic compounds are crucial in the plants for plant growth development and defense against infection and injury. These compounds in injured plants have an important impact on the oxidative stability antimicrobial safety(Abouarab, Abouarab, & Abusalem, 2010). Phenolics, is a biologically active substances specially found in plants, are known to possess potential antioxidant properties (S Shukla, Mehta, Mehta, & Bajpai, 2012). The most efficient way to exclude and decrease the action of free radicals which cause the oxidative stress to a defense mechanisms. Antioxidant possess the ability to neutralize free radicals and prevent oxidative damage caused by free radicals and have free radical chain reaction breaking properties(Veeru, 2009). They can interfere with the oxidation process, chelating catalytic metal sand also act as oxygen scavengers. Antioxidant-based drug formulations can be used for the prevention and treatment of complex diseases like atherosclerosis, stroke, diabetes, Alzheimer’s disease and cancer(Ramya, Manogaran, Joey, Keong, ; Katherasan, 2014).