Antioxidant activity of Stevia rebaudiana Bert. Leaves from Bangladesh Ismet Ara Jahan 1* , Mohammad Mostafa 1 , Hemayet Hossain 1 , Ishrat Nimmi 1 , Abdus Sattar 2 , Abdul Alim 2 and Syed M. Iqbal Moeiz 2 1 Chemical Research Division, Bangladesh Council of Scientific and Industrial Research Dr. Qudrat-E- Khuda Road, Dhaka-1205, Bangladesh. 2 Dhaka College, National University, Mirpur Road, Dhaka-1205, Bangladesh. Abstract The in vitro antioxidant potential of different extractives of Stevia rebaudiana Bert. was evaluated in the present study. Four complementary test systems; namely DPPH free radical scavenging, reducing power, total phenolic and total flavonoids concentrations were used for this study. IC 50 values of 80% ethanol extract (at room temp.) and its 1-butanol and water soluble fractions were found to be 8.02±0.874, 23.60±0.763 and 43.81± 0.459 μg/mL, respectively and that for methanol and water hot extracts were observed as 44.61±0.821 and 23.70±0.861 μg/mL, respectively. Ascorbic acid, the standard compound exhibited the IC 50 value 4.21±0.861. In reducing power test the maximum absorbance for 80% ethanol extract and its, n-hexane, dichloromethane, 1-butanol and water soluble fractions were found to be upto 1.0717±0.0017, 0.5684±0.0013, 0.8191±0.0017, 0.9819±0.0014 and 1.5552±0.0015, respectively and that for hot extracts, n-hexane, dichloromethane, methanol and water were upto 0.5894±0.0014, 0.9498±,0.0015, 0.9086±0.0018 and 0.9972±0.0029, respectively compared to the absorbance of ascorbic acid as standard (1.3741±0.0031). Total phenolic concentrations in 80% ethanol extract (at room temp.) and its different fractions were ranged from 25.36±0.34 - 65.21±0.97 and that in different hot extracts were observed in the range 15.33 ±0.78,36.95±0.09 mg gm -1 gallic acid equivalent, respectively. The total flavonoids concentration of 80% ethanol extract and its fractions were ranged from 34.26±0.79 -125.64±1.07 and the range for hot extracts was 23.56±0.89 - 76.94±0.35 mg gm -1 quercetin equivalent per gm of dry extract, respectively. The results revealed that 80% ethanol extract exhibited most significant antioxidant activity followed by its water and 1-butanol extracts and hot methanol and water extracts. This clearly indicates that Stevia rebaudiana leaves from Bangladesh has a significant potential to use as a natural antioxidant. Key words: Stevia rebaudiana Bert. Antioxidant activity, DPPH free radical scavenging, Reducing power, Total phenolic and Total flavonoids Introduction * Author for Correspondence: Ismet Ara Jahan, Chemical Research Division, Bangladesh Council of Scientific and Industrial Research, Dr. Qudrat-E Khuda Road, Dhaka-1205, Bangladesh. E-mail: ismet0103@yahoo.com Oxidation is essential to human beings to fuel biological processes for the production of energy. During metabolism, molecular oxygen is reduced to water; yet the stepwise transfer of electrons generates free reactive oxygen species (ROS), including superoxide radicals (O 2 • -), hydrogen peroxide (H 2 O 2 ), and hydroxyl radicals (OH • ). Other radicals such as alkyl (R • ), alkoxyl (RO • ), and peroxyl (ROO • ) radicals may also be produced endogenously (Simic et al., 1989). The uncontrolled production of oxygen derived free radicals is involved in onset of many diseases such as aging, immunodeficiencies, neurologic disorders, inflammation, arthritis, ischemia, arteriosclerosis, coronary heart disease, stroke, diabetes mellitus, Parkinson’s disease, Alzheimer’s disease and certain cancers (Sies, 1991; Gutteridge, 1993; Kehrer, 1993; Aruoma, 1994; Cook et al., 1996; Scandalios, 1997; Kumpulainen et al., 1999; Halliwell et al, 1999; Parejo et al., 2002; Hou et al., 2003;). Allmost all organisms are well protected against free radical damage by enzymes such superoxide dismutase and catalase, or compounds such as ascorbic acid, tocopherols and glutathione (Mau et al., 2002). When the mechanism of antioxidant protection becomes unbalanced by factors such as aging, Bangladesh Pharmaceutical Journal; Vol. 13, No. 2, July 2010 67 ISSN 0301-4606