Thunbergia laurifolia (TL) Linn., a Thai medicinal herb, has been used as a herbal tea for detoxification of poisons and antipyretic purpose. Its antioxidant activity and related biological effects have also been reported. The active markers of the TL tea were caffeic acid (CA) and rosmarinic acid (RA). Although this tea has been used for decades, the information relating to its optimal infusion condition was limited. Therefore, this study was aimed to preliminary investigate the effect of

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... ion variables which were infusion time, water temperature and volume, on the CA and RA contents transferred into the tea solutions. To evaluate the efficiency of extraction methods, the marker contents obtained by infusion and aqueous extraction process were compared. Furthermore, the infusion variables were optimized to obtain maximum antioxidant activity by using response surface methodology (RSM). The 2,2diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity was used as a model response. The results demonstrated that the contents of CA and RA in the tea solutions varied considerably according to the infusion conditions, which may be critical for the therapeutic efficacy of the tea. More importantly, after infusion, the major portion of active markers remained in the tea powder implying low efficiency of the infusion method. By using RSM, it was successfully found that the maximum DPPH activity was obtained when infusing the TL tea in 200 mL of boiling water for 15 min. The results of this study can help further understanding of the maximal health benefits to be attained through consumption of TL tea.