Itharat A, Sayompark S, Hansakul P and Dechayont B
Dried stems and leaves of Yha-nang dang (Bauhinia strychnifolia Craib.) have long been used in Thailand to make tea for promoting health and for detoxification of the body. The objectives of this study were to investigate antioxidant activities of B. strychnifolia dried stem and leaf extracts obtained by different extraction methods. The antioxidant power of B. strychnifolia extracts and water extracts of green tea leaves (Camellia sinensis) were evaluated using four different methods: DPPH radical scavenging assay, Ferric reducing antioxidant power (FRAP) assay, and Superoxide radical scavenging by NBT dye reduction assay, and measurement of total phenolic contents by the Folin-Ciocalteu colorimetric method. The 95% ethanolic extract of B. strychnifolia stems exhibited the strongest DPPH radical scavenging activity, with an EC50 value of 4.2 μg/ml. This was in agreement with results from the Ferric reducing antioxidant power assay, which showed that this extract had the highest FRAP value and TEAC (Trolox equivalent antioxidant capacity) values of 1481.2 mg Fe(II)/g and 421.4 mg Trolox/g, respectively. The 50% ethanolic extracts of B. strychnifolia stems showed the highest superoxide radical scavenging activities with an EC50 value of 85.7 μg/ml. The total phenolic contents of all extracts ranged from 143.7 to 390.1 mg GAE/g. The 95% ethanolic extract of B. strychnifolia stems had the highest total phenolic contents (390.1 mg GAE/g). Green tea water extracts showed less antioxidant activity than 95% ethanol B. strychnifolia stem extracts, by all assays, except by the DPPH assay. The results from this study indicate that ethanolic extracts of B. strychnifolia stems are rich in phenolic content and demonstrate as good, or better antioxidant activities compared to green tea. This lends scientific support for the use of these extracts for detoxification by Thai traditional medicine practitioners, and suggests that they could be further developed into commercial detoxification products.