High performance liquid chromatography fingerprinting and chemometric analysis of antioxidant quality of Thunbergia laurifolia leaves

High performance liquid chromatography (HPLC) method was optimized using Design of Experiment (DOE) process and validated for quantitative analysis of caffeic acid and rosmarinic acid contents in extracts from Thunbergia laurifolia leaves collected from 10 different locations in Thailand. Antioxidant qualities of all extracts were evaluated by various chemometric analysis methods from the results of HPLC analysis both fingerprints and active component contents, in vitro antioxidant activities determined by 2,2-diphenyl-1-picrylhydrazyl scavenging assay and total phenolic and total flavonoid contents determined by Folin-Ciocaltue and aluminium chloride methods, respectively. It was found that HPLC fingerprints of T. laurifolia leaf extracts analyzed by similarity analysis and chemical pattern recognition had moderate similarity (r = 0.76) with the same 11 major peaks. Total phenolic contents calculated as both caffeic acid equivalent (CAE) and rosmarinic acid equivalent (RAE) showed the highest correlation to antioxidant effects of T. laurifolia leaf extracts (R² > 0.9). This study is the first demonstration of the analytical method for simultaneous quantitative analysis of 2 active component contents in leaf decoction extract from T. laurifolia and the uses of chemometric methods to evaluate and compare the quality, especially the chemical and biological qualities of raw materials collected from different locations.