A comparative study on extraction processes of Stevia rebaudiana leaves with emphasis on antioxidant, cytotoxic and nitric oxide inhibition activities

In this paper, the extraction conditions yielding the highest steviol glycosides from the leaves of Stevia rebaudiana were determined using microwave (MAE) and ultrasonically assisted extraction (UAE) and biological activities of the extracts along with analyses of the residue from the extraction process were investigated. Under optimum conditions, 21.21 mg glycosides/g dried leaf in MAE and 14.90 mg glycosides/g dried leaf in UAE were quantified by HPLC analyses. After extraction, total chlorophyll, carotenoid contents and total dietary fibers were quantified as 15.14 mg/100 g, 2.93 mg/100 g and 6.5% in the raffinate phase. The total phenols were determined as 80.13 and 86.47 mg gallic acid/g extract, whereas the total flavonoids were 111.16 and 126.70 mg quercetin/g extract and DPPH radical scavenging activities were 91.39 and 92.40%, respectively. The extracts exhibited no cytotoxicity against healthy cell line and macrophage RAW 264.7 cells. The IC50 values were 68 mu g/ml and >100 mu g/ml for MAE and UAE. Overall, obtained results suggest that stevia extracts and its residue can be utilized holistically on industrial scale. (C) 2015 Elsevier B.V. All rights reserved.