Idant capacity in vitro, but no single assay is capable to determine the total antioxidant ability of a studied sample. Previous studies [20,21] indicated that more than one antioxidant capacity measurement is needed in order to take into account the various modes of antioxidants’ actions. Thus, the antioxidant activity of L. indica leaf extracts were evaluated by employing three different established testing systems, such as scavenging activity on DPPH radicals, reducing power assay and SOD activity assay. These three assays have been widely used to assess the antioxidant abilities of studied sample as they required relatively standard equipment and reproducible results.Scavenging activity of L. indica leaf extracts on DPPH radicalsThe quantification for total phenolic GLPG0187 web content in the L. indica leaf extracts, expressed as mg of GAEs/g of extract is shown in Table 1. All extracts contained a considerable amount of phenolic metabolites from 1.27 to 37.29 mg of GAEs/g of extract. The highest amount was found in the fractionated water extract (37.29 mg of GAEs/g of extract), followed by ethanol (19.15 mg of GAEs/g of extract), ethyl acetate (15.61 mg of GAEs/g of extract) and hexane (1.27 mg of GAEs/g of extract) extracts in the decreasing order. The hexane extract showed the lowest phenolic content although the yield of hexane extract was the highest among the fractionated extracts (refer to the section `preparation of extracts’). The significantly higher (p < 0.05) phenolic content in the fractionated water extract than in the crude ethanol extract was probably due to the concentration of phenolic compounds in this fractionated extract. In the previous study reported by Srinivasan et al. [6], gallic acid which is a strong naturally occurring antioxidant was identified in the leaf extract. The high phenolic content in the fractionated water extract might contribute towards the antioxidant activities and curative ability adsorbing and neutralising free radicals.Table 1 Total phenolic content of L. indica extractsExtracts Ethanol Hexane Ethyl acetate Water Ascorbic acid* Concentration of total phenolics (mg of GAEs/g of extract) 19.15 ?2.66c 1.27 ?0.09a 15.61 ?2.12b 37.29 ?3.52d 45.03 ?2.15eFree radical scavenging is one of the known mechanisms by which antioxidants inhibit lipid oxidation. DPPH is a nitrogen-centered free radical which stable in room temperature. The reducing capability of the DPPH is determined by the reduction in its absorbance measured at 520 nm induced by antioxidants. The decrease PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/26024392 in the absorbance of DPPH caused by antioxidants is due to the reaction between antioxidant molecules and radical, which results in the scavenging of the radical by electron transfer. In the DPPH scavenging assay, leaf extracts of L. indica were investigated through the free radical scavenging activity via their reaction with the stable DPPH radicals. The radical scavenging activity (EC50) values of the extracts are shown in Table 2. Low EC50 value indicates strong ability of the extract to act as DPPH scavenger. A high EC50 value indicates low scavenging activity of the scavengers as more amounts of the scavengers were required to achieve 50 scavenging reaction. This means, the scavengers are less effective in scavenging the DPPH radicals. Among the four extracts, the fractionated water extract (EC50 48 g/ml) showed the strongest scavenging activity compared with the standard ascorbic acid, followed by ethanol (EC50 60 g/ml) and ethyl aceta.