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

• Stevia leaves were extracted with microwave (MAE) and ultrasonically assisted extraction (UAE).
• About 21.21 and 19.90 mg glycosides/g dried leaf were obtained in MAE and UAE.
• The biological, cytotoxic and iNOS activities of the extracts were investigated.
• The extracts were not toxic to healthy cell line (HEK) at a dose of 50 μg/ml.
• The raffinate phase was characterized to determine the utilization possibilities in industry.

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 μg/ml and >100 μg/ml for MAE and UAE. Overall, obtained results suggest that stevia extracts and its residue can be utilized holistically on industrial scale.

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