The influence of total phenol, β-carotene, and lycopene contents on antioxidant capacity in Stachys obliqua extracts

This study is designed to examine in vitro antioxidant capacity of the extracts obtained from Stachys obliqua Waldst. & Kit. and to compare this capacity with the values of total phenol, β-carotene and lycopene contents. Antioxidant capacities of the samples were investigated by three different test systems namely β-carotene/linoleic acid bleaching, DPPH radical scavenging, and metal chelating effect. The phenolic contents of S. obliqua extracts were determined using Folin-Ciocalteu's phenol reagent. The methanol extract showed higher radical scavenging ability (IC₅₀=0.011±0.000mg/ml) than the water extract (IC₅₀ =0.018±0.001mg/ml). The extracts have more effective scavenging ability on DPPH radicals than synthetic antioxidant BHT (IC₅₀=0.023±0.001mg/ml). Moreover, both of the extracts exhibited the high chelating ability and showed a notable capacity to suppress lipid peroxidation. The methanol (230.78±3.95µg/mg) and the water (171.65±4.17µg/mg) extracts were found to be rich-in phenolics. However, β-carotene and lycopene were only found in small amounts in the methanol extract and not found in the water extract. A significant relationship between the antioxidative effects and total phenolic contents were found (p<0.05). Therefore, further studies need to be directed to isolate and characterize antioxidant active compounds from the extracts which could be responsible for the high antioxidant activities.