Assessment of Various Pretreatment and Extraction Methods for the Extraction of Bioactive Compounds from Orthosiphon stamineus Leaf via Microstructures Analysis

摘要

The impacts of various methods such as mechanical grinding, ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), and also sample pretreatments using acid and alkali on the microstructure of plant sample were studied for the extraction of bioactive compounds from Orthosiphon stamineus leaf. From scanning electron microscopy (SEM) analysis of the extracted sample, UAE and MAE induced significant disruption on glandular trichomes structure, which is the main site for biosynthesis of plant secondary metabolites. This improves the diffusion of bioactive compound and resulted in approximately 86-95% of the total extraction yield quantified by conventional Soxhlet extraction. Chemical pretreatments generally imparted weaker microstructures disruption thus slight improvement on the extraction yields was observed. In this case, acid reagent is more suitable for the pretreatment as the presence of alkali decomposes the bioactive compounds. In a nutshell, the performance of an extraction strongly depends on its degree of disruption on the plant sample microstructure.