Antioxidant Properties and Total Phenolic Content of Selected Traditional Thai Medicinal Plants

Abstract

Objectives: In accordance with traditional local wisdom, medicinal plants from north-eastern Thailand are used for the treatment of dermatitis-related inflammations. This study aimed to investigate the antioxidant activity and total phenolic content (TPC) of the bark of thirteen medicinal plants. Methods: The study plants included Stephania venosa (Blume) Spreng, Smilax perfoliata Lour., Dolichandrone stipulata, Glochidion coccineum,  Xantolis cambodiana, Dalbergia cultrata, Bauhinia sirindhorniae K., Knema angustifolia, Tristaniopsis burmanica, Ficus hirta Vahl, Capparis zeylanica, Amphineurion marginata (Roxb.) G. Don. and Microsorum pteropus (Blume) Copel. The antioxidant properties were determined by means of three approaches namely 1,1-diphenyl-1-princylhydrazyl (DPPH) radical scavenging assay at 517 nm, ferric-reducing antioxidant power (FRAP) assay at 593 nm and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid  (ABTS) assay at 734 nm. The TPC of the plants was determined via the Folin-Ciocalteu method. The correlation between each of the antioxidant activity value with TPC was tested using the Pearson’s correlation coefficient (r). Results: The antioxidant properties and TPC differed significantly among the plants.  In each of the methods, S. venosa (Blume) Spreng., X. cambodiana, B. sirindhorniae, K. angustifolia and C. zeylanica consistently exhibited the most potent antioxidant property ranging from 70% to 100%. This further suggested their potential rich source of natural antioxidants. Coincidentally, these plants contained the highest TPC (38,113 - 9,989 mg GAE/g). Significant positive correlations were found between antioxidant activity (ABTS·+ and FRAP assays) and the TPC with r = 0.987 and 0.956, respectively. Conclusion: Thirteen medicinal plants contained antioxidant activity which was related to the phenolic content. The active ingredients and other biological activities of these herbal plants merit further investigations. Keywords: Thai medicinal plants, antioxidant activity, total phenolic content