Quantitative estimation of the polyphenolics of S. malaccense studied is presented in
. Plant derived antioxidants are regarded as effective in controlling the effects of oxidative damage, and hence had influence in what people eat and drink (Viana et al., 1996; Sun et al., 2002; Pinder and Sandler, 2004). The antioxidative effect is mainly due to phenolic components, such as flavonoids (Pietta, 1998), phenolic acids, and phenolic diterpenes (Shahidi et al., 1992). The total phenolic content in the methanolic extract was 108.08 ± 12.03 mg/g while total flavonoid content was 76.25 ± 4.68 mg/g., the phenolic and flavonoid contents in the aqueous extract showed 82.07 ± 8.09 mg/g and 49.36 ± 5.27 mg/g. The compounds such as flavonoid contain hydroxyls are responsible for the radicals scavenging effects in plants.
Estimation of total phenols and flavonoids
Antioxidant Activities of Extracts
Polyphenolic compounds such as flavonoids, phenolic acids and tannins are considered to be the major contributors to the antioxidant activity of medicinal plants, fruits and vegetables. The antioxidant activities of polyphenols were attributed to their redox properties, which allow them to act as reducing agents, hydrogen donators and singlet oxygen quenchers, as well as their metal chelating abilities (Pereira 2009, Rice Evan 1996, Sanda et al., 2011). Therefore, in the present study four different assays were employed in order to determine and compare the antioxidant properties of selected Syzygium malaccense as well as elucidate their mode of action.
The DPPH assay has been widely used to evaluate the free radical scavenging effectiveness of various antioxidant substances. Antioxidants upon interaction with DPPH either transfer an electron or hydrogen atom to DPPH, thus neutralizing its free radical character. The colour of the reaction mixture changes from purple to yellow with a decrease of the 517 nm absorbance. The degree of discolouration indicates the scavenging potential of the antioxidants [Villano et al., 2007, Foti et al]., 2004]. shows the percent inhibition of DPPH with tested S.malaccense leaf methanolic and aqueous extracts at different concentrations (20-100μg /ml). The higher inhibitory effect was noticed in the methanolic leaf extracts. (78.73% at100μg /ml).The IC50 value of the methanolic extract was 25.74 μg /ml.
DPPH Scavenging Activity of Methanol and Water Leaf Extracts of
The hydroxyl radical scavenging ability of S.malaccense methanolic and aqueous extracts and a reference antioxidant are presented in the . The hydroxyl radical is an extremely reactive oxygen species, capable of modifying several biologically important molecules in the living cells. This radical is able to cause DNA damages leading to carcinogenesis, mutagenesis and cytotoxicity. (Sanda et al., 2011).
Hydroxyl Radical Scavenging Assay of Methanol and Water Leaf Extracts of
When S. malaccense leaf extract was added to the reaction mixture, it removed the hydroxyl radicals from the sugar and prevented the reaction. The leaf methanolic extracts showed higher inhibitory activities on the hydroxyl radical formation in a concentration dependent manner when compared to the aqueous extract. The IC50 values of the methanolic extract and standard in this assay were 16.25 μg /ml and 7.94 μg /ml respectively. The IC50 value of the aqueous extract is 21.25 μg /ml and the gallic acid is 2.70 μg /ml.
The reducing power assay measures the electron donating ability of antioxidants using the potassium ferricyanide reduction method. Antioxidants cause the reduction of the Fe3+/ferricyanide complex to the ferrous form and activity is measured as the increase in the absorbance at 700 nm. In this assay, the yellow colour of the test solution changes to various shades of green and blue depending on the reducing power of antioxidant samples [Gulcin 2006, 2008 and Prasad et al., 2009].
shows the plot of reducing power of S.malaccense leaf methanolic and aqueous extracts in comparison with BHA and Gallic acid as a reference antioxidant. At tested concentrations (20-100 μg/mL) all samples possessed the ability to reduce iron(III) ions. The reducing power of the plant extracts increased with increasing concentrations in a strongly linear manner. In this assay, methanolic leaf extract exhibited once again the most powerful effect but lowest effect at 100 μg/mL when compared to Gallic acid.
Reducing Power of Methanol and Water Leaf Extracts of Syzygium malaccense