Subcritical water extraction of betulinic acid from birch bark

An alternative and green method for extraction of betulinic acid (BA) from birch bark is here proposed as Subcritical Water Extraction (SWE). Using response surface methodology (RSM), optimization was conducted on reaction parameters for maximum extraction yield of BA. Optimal modifying conditions are as follows: extraction time of 27.37 min, extraction temperature at 184.52 °C and a solvent/solid ratio of 59.60 mL/g. Under optimal conditions, the maximum BA yield was 28.03 mg/10 g birch bark. Extracts by different methods (leaching extraction, reflux extraction, ultrasonic extraction, and SWE) were comparatively and quantitatively analyzed, using High Performance Liquid Chromatography (HPLC). Results show BA yields by SWE are higher than those obtained using ethanol, a traditional extraction method, plus the extract contained fewer impurities. Furthermore, the extraction processes for all four of the above methods were modeled and reviewed individually.