Effect of liquid vehicles on the enhancement of rosmarinic acid and carvacrol release from oregano extract liquisolid compacts

Spraying and freeze-drying of various herbal extracts is often used for industrial dry herbal powder preparation. However, it is possible to produce a better quality powder applying liquisolid compact technique with the simpler preparation process. The aim of this study was to evaluate the influence of liquisolid and freeze-drying techniques on physicochemical properties of Oregano powder and the yield of its active compounds-rosmarinic acid and carvacrol. The quantities of active compounds were determined by UPLC method. The accelerated and long-term stability studies of all formulations have also been evaluated. The physicochemical characteristics and the morphology of the dry powder were evaluated using X-ray diffraction, UPLC-ESI-MS and scanning electron microscopy. The results showed that Oregano powder obtained by freeze-drying was hygroscopic and showed passable flow properties, with the angle of repose 43.00 +/- 0.87 degrees and flowability 0 g/s. The X-ray diffraction method showed amorphous state of the active ingredients in the liquisolid formulations. Furthermore, the dissolution tests in vitro confirmed that liquisolid systems released 2.2-2.8-fold more rosmarinic acid and 2.9-fold more carvacrol compared to the Oregano powder obtained by freeze-drying (p < .05). The stability studies showed that physicomechanical properties, the dissolution profiles, rosmarinic acid and carvacrol content of liquisolid formulations were not significantly affected by ageing. In conclusion, the use of liquisolid compacts could be a promising tool to increase the solubility of Oregano extract active compounds. The liquisolid technology is especially promising for herbal drugs preparation because of the simple manufacturing process, low production costs and the possibility of industrial manufacture due to the good flow and compaction properties, and the ability to protect the active compounds from oxidation.