Distribution of Phytochemicals and Bioactivity in Different Parts and Leaf Positions of Stevia Rebaudiana (Bertoni) Bertoni- a Non-caloric, Natural Sweetener

Abstract

Stevia rebaudiana (Bertoni) Bertoni (Asteraceae) is a small perennial herb which is widely cultivated for its sweet leaves and possesses 250-300 times the sweetness than sucrose due to the presence of steviol glycosides (mainly stevioside and rebaudioside). It is commonly known as candy leaf, sweet leaf and sugar leaf. Even though, this plant has been studied extensively for its sweetness, information on therapeutically important active components presence in stevia is scattered or lacking. Therefore, the present study was undertaken to determine the distribution of Total Phenolic Content (TPC), Total Flavonoid Content (TFC) and Total Antioxidant Capacity (TAC) of different parts and different leaf positions of S. rebaudiana. Leaf fresh weight, dry weight and leaf area at different leaf positions were recorded. The TAC, TPC and TFC were determined using Ferric Reducing Antioxidant Power Assay (FRAP), modified Folin-Ciocalteu colorimetric method and calorimetric method respectively. Leaf fresh weight and leaf dry weight were increased with the maturity. All tested plant parts demonstrated the presence of TPC, TFC and TAC. The significantly higher TPC, TFC and TAC were reported in leaves than other parts of plant. The order of increase of active components was leaf>flower>stem>branch>root. TPC, TFC and TAC of different leaf positions revealed that TAC, was decreased gradually from immature to mature leaf (1st leaf>2nd leaf>3rd leaf>4th leaf>5th leaf). Moreover, all tested phytochemicals (phenolics and flavonoids) and antioxidant capacity were significantly higher in extracts prepared from the first leaf. Interestingly, a strong significant correlations were observed between TAC and tested secondary metabolites (TFC, R2=0.85). The results of the present study are vital important in cultivation, harvesting and quality control aspects of S. rebaudiana.