The air-dried leaves of
S. rebaudiana
(50g) were powdered and
then extracted with 500ml of distilled water by merceration pro-
cess. The crude extract was filtered and evaporated under reduced
pressure to give a viscous mass with a percentage yield of 8.0%
(w/w). The extract was stored at 4
◦
C for further use. This aque-
ous leaf extract of
S. rebaudiana
(ALES) was reconstituted in known
amount of water and used for the assessment of antioxidant activ-
ity.
2.4. Determination of total phenolic content
Total soluble phenolics in the leaf aqueous extract of
S. rebau-
diana
were determined with Folin-Ciocalteau reagent according
to the method using gallic acid as a standard phenolic compound
(
Slinkard and Singleton, 1977
). 1.0ml of extract solution contain-
ing 1.0g extract in a volumetric flask was diluted with 46ml of
distilled water. 1.0ml of Folin-Ciocalteau reagent was added and
mixedthoroughly.Threeminuteslater,3.0mlof2%sodiumcarbon-
ate was added and the mixture was allowed to stand for 3h with
intermittent shaking. The absorbance of the blue color that devel-
oped was measured at 760nm. The concentration of total phenoliccontentwasexpressedasmg/gofdryextracts.Theconcentrationof
total phenolic content in the extract was determined as
g of gallic
acid equivalent using an equation obtained from the standard gallic
acid graph: