Antioxidant activity and phytochemical screening of Nepeta nepetella aqueous and methanolic extracts from Algeria

Abstract

labile hydrogen and the ability to scavenge the DPPH radical is related to the inhibition of lipid peroxidation (Matsubara et al., 1991) IC50 value was determined from plotted graph of scavenging activity against the different concentrations of N.nepetella extracts, ascorbic acid, and BHA. The scavenging activity was expressed by the percentage of DPPH reduction after 30 min of reaction. The measurements were duplicate and their scavenging effects were calculated based on the percentage of DPPH scavenged (Blois et al., 1958; Singh et al., 2008). The obtained results are summarized in table 2. The results show that methanolic extract leaves (1.45 ± 0.07 mg/ml), methanolic extract flowers (2.75±0.03 mg/ml), were the most potent of all studied extracts of N.nepetella. For methanolic extract stems (7.37±0.17mg/ml), aqueous extract leaves (10.435±0.61mmg/ml), aqueous extract flowers (17.7±0.14 mg/ml) and aqueous extract stems (20.16±0.23 mg/ml). These capacities of all extracts were less than that ascorbic acid (0.12±0.08 mg/ml) and BHA (0.09±0.03 mg/ml). Reducing antioxidant power assay (FRAP) The antioxidant capacity of leaf extracts was evaluated by FRAP assay because it also showed high reproducibility (Thaipong et al., 2006). Reducing power is to measure the reductive ability of antioxidant and it is evaluated by the transformation of Fe to Fe by donating an electron, Therefore, the Fe can be monitored by measuring the formation of Perl’s Prussian blue at 700 nm. However, the activity of antioxidants has been assigned to various mechanisms such as prevention of chain initiation, binding of transition-metal ion catalysts, decomposition of peroxides, and prevention of continued hydrogen abstraction, reductive capacity and radical scavenging (Diplock, 1997; Yildirim et al., 2000). Reducing power of methanolic and aqueous extracts of Nepeta nepetella and standards (BHA and TROLOX ) using the potassium ferricyanide reduction method were described in Fig 1. Methanolic extracts of N.nepetella were more potent on reducing power compared to aqueous extracts. However, the reduction power of BHA and TROLOX was relatively more pronounced than that of the different extracts N.nepetella. Table. 1: Total phenolics contents of Nepeta nepetella methanolic and aqueous extracts of leaves, flowers and stems. Parameter Leaves Flowers Stems Phenols contents* Aqueous Methanol Aqueous Methanol Aqueous Methanol 41.65±2.18 58.11± 1.24 13.18±1.04 21.42±0.96 14.98±1.07 41.725±0.38 *Expressed as mg GAE/g of dry plant material. The data are displayed with mean ± standard deviation of twice replications. Mean values followed by different superscript in a column are significantly different (p<0.05). SELADJI et al. / Journal of Applied Pharmaceutical Science 4 (02); 2014: 012-016 015 β-Carotene –linoleic acid assay In this model system, β-Carotene undergoes rapid discoloration in the absence of an antioxidant, which results in a reduction in absorbance of the test solution with reaction time. This is due to the oxidation of linoleic acid that generates free radicals that attacks the highly unsaturated β-Carotene molecules in an effort to reacquire a hydrogen atom. When this reaction occurs the b-carotene molecule loses its conjugation and, as a consequence, the characteristic orange color disappears. The presence of antioxidant avoids the destruction of the β -carotene conjugate system and the orange color is maintained. The obtained results are summarized in table 3. The results show that methanolic extract leaves (0.247 ± 0.03 mg/ml), methanolic extract flowers (0.195±0.03 mg/ml),and methanolic extract stems(0.148 ±0.003 mg/ml) were the most potent of all studied extracts of N.nepetella and are similar to high than Gallic acid (0.435±0.003 mg/ml) and Trolox (0.242±0.002 mg/ml). For aqueous extract leaves (8.02±0.15 mg/ml), aqueous extract flowers (24.815±0.26 mg/ml) and aqueous extract stems (24.815±0.26 mg/ml).