Effect of milling on physicochemical properties of usnic acid isolated from usnea sp.

Abstract

Usnic acid is the secondary metabolite found in lichens, particularly Usnea sp which has considerable pharmacological activities. However, the used of usnic acid is still limited due to poorly soluble in water. The aim of this study was to investigate the impact of milling process to physicochemical properties of usnic acid. Usnic acid was isolated from Usnea sp by soxhlet extraction method. The crystal of usnic acid was then milled in three different times: 30, 60 and 90 minutes. The characterization of intact and milled usnic acid were conducted using powder X-ray diffraction (PXRD), infra-red spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Solubility test was conducted in water for 24 h and the amount of usnic acid was determined by UV spectrophotometry. The X-ray diffractogram showed a decline in peak intensity of usnic acid after milling process. The infra-red spectrum showed no shift of wavenumber of usnic acid after milling process. Thermal analysis showed a decline in melting point and heat energy of usnic acid after milling process. The photomicrograph of SEM depicted the changes in habit crystal of milled usnic acid. The solubility of intact usnic acid was 51 µg/ml, while the milled usnic acid increased fourfold compared to intact usnic acid.There was no significant difference of milling time on solubility (p>0.05). In conclusion, the milling process influence the physicochemical properties of usnic acid which indicated by crystallinity, melting point, crystal habit and solubility.