Optimization of rosmarinic acid extraction from Thunbergia laurifolia leaves using a green solvent and evaluation of its biological activities

Thunbergia laurifolia Lindl. (TL) is a medicinal herb belonging to the Acanthaceae family. It has been used in ethnomedicine and possesses many biological activities. This study aimed to optimize the extraction of rosmarinic acid (RA), a major active component of TL leaves, using an aqueous green solvent via stirring-assisted maceration (SAM). Butylene glycol (BG) was selected as the green solvent due to its safety and its ability to be incorporated directly into pharmaceutical and cosmetic formulations without requiring removal from the extract. A Box-Behnken design was employed to optimize the extraction of RA from TL leaves. The results demonstrated that extraction time and BG concentration 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 a 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 the predicted values. The extract obtained under the optimal condition exhibited anti-inflammatory properties. Furthermore, RA demonstrated wound-healing activity, and a biphasic dose-response was observed regarding its anti-melanogenic effects. These findings suggested the potential of the TL extract as a ready-to-use active ingredient for skincare and pharmaceutical formulations.