Recent Advances in the Extraction and Purification of Ethyl p-Methoxycinnamate from Kaempferia galanga L. Rhizomes

Abstract

Ethyl p-methoxycinnamate (EPMC) is the principal bioactive ester of Kaempferia galanga L. rhizomes, a Zingiberaceous herb long used across South and Southeast Asia for inflammatory, respiratory and dermatological complaints. Interest in EPMC has grown substantially over the past decade because of its anti-inflammatory, antiangiogenic, antituberculosis, antimelanoma, hypopigmentary and vasorelaxant activities, alongside its established role as a cosmetic and food flavouring agent. This review critically examines the methods used to extract and purify EPMC from K. galanga rhizomes, tracing the transition from classical solvent-based approaches such as maceration, Soxhlet extraction and steam or hydrodistillation towards greener and more selective alternatives, including supercritical carbon dioxide extraction, ultrasound- and microwave-assisted extraction, and deep eutectic solvent systems. Downstream purification strategies are considered in parallel, spanning solvent-mediated crystallisation, column and preparative chromatography, and molecularly imprinted polymer-based solid-phase extraction, now demonstrated for EPMC itself. Analytical standardisation practices, including validated high-performance liquid chromatography and gas chromatography-mass spectrometry methods, are reviewed with attention to the influence of rhizome age, harvest season and storage conditions on EPMC yield and purity. The review further addresses formulation challenges arising from the poor aqueous solubility of EPMC and the pharmaceutical strategies, such as co-crystallisation, polymorph engineering and nanoscale confinement, that have been proposed to overcome them. Persistent gaps are identified in process scale-up, environmental impact assessment and regulatory harmonisation of extraction protocols, and priorities for future research are outlined accordingly.