Assessment of optimal infusion condition for Thunbergia laurifolia tea by using response surface methodology

According to the National List of Essential Medicines of Thailand, the Thunbergia laurifolia (TL) tea is categorized as antipyretic and detoxifying herbal medicine. This tea has also been used for the treatment of drug addiction and smoking cessation. However, suggested infusion conditions were varied which may result in variations in extracted active contents and bioactivities. In this study, the infusion condition that maximized extraction of caffeic acid (CA) and rosmarinic acid (RA), the major markers of TL tea, was assessed by using response surface methodology (RSM). The contents of markers were analyzed by a validated high-performance liquid chromatographic method. To evaluate the extraction efficiency, the marker contents obtained by preparing the tea under the optimal condition were compared to those obtained by aqueous extraction process. The results demonstrated that the marker contents varied considerably according to infusion variables; time, temperature and volume. By using RSM, it was successfully found that the optimal condition for the tea (3 g) was as follows: 200 mL of boiling water and infusion time of 10 min. More importantly, by using infusion method, the major portion of markers remained in the tea powder implying poor extraction efficiency of the method. This result suggested that the use of TL extract would be benefit in terms of quality and efficacy. The optimal infusion condition could be utilized in clinical studies to find an effective oral dose range of markers. Ultimately, the obtained information could be used as support information for determining the oral dose of TL extract.