Optimization of Rosmarinic Acid Extraction from Thunbergia laurifolia Leaves Using a Green Solvent and Evaluation of Its Biological Activities

Thunbergia laurifolia (TL) is a medicinal herb that has been used in ethnomedicine and possesses many biological activities. This study aimed to develop a green extraction method for rosmarinic acid (RA), a major active component of TL leaves, using stirring-assisted maceration (SAM). Butylene glycol (BG) in water was chosen as a solvent due to its safety and its ability to be incorporated directly into pharmaceutical and cosmetic formulations without requiring removal from the extract. Box-Behnken Design was employed to optimize the extraction of RA from TL leaves. The results demonstrated that the extraction time and %BG were significant variables influencing the RA yield, total phenolic content, and antioxidant activity. The optimal condition was an extraction time of 2 h, 52% BG, and stirring speed of 200 rpm. These parameters yielded 5.415 ± 0.023 mg/g TL RA yield, 2.573 ± 0.012 mg GAE/g TL total phenolic content, and 6.362 ± 0.097 mg AAE/g TL ABTS radical scavenging activity, closely to predicted values. The extract obtained under an optimal condition exhibited anti-inflammatory properties. Furthermore, RA demonstrated wound-healing activity, and a biphasic dose-response was observed regarding its anti-melanogenic effects. As a result, the TL extract holds significant potential for cosmetic and pharmaceutical applications.