Microbial production of glycyrrhetic acid 3-O-mono-b-D-glucuronide from glycyrrhizin by Aspergillus terreus

Among seven fungi (three Aspergilli and four Penicilli) have been screened for production of glycyrrhetic acid 3-O-mono- b-D-glucuronide (GAMG) from glycyrrhizin (GL), Aspergillus terreus was found to be the most potent GAMG producer. This strain was capable of expressing two intracellular b-D-glucuronidase forms, one responsible for partial hydrolysis of GL to GAMG and the other one for hydrolysis of GL to glycyrrhetic acid (GA). The highest yield of GAMG was achieved when the reaction mixture was incubated at pH 6 at 40 °C for 1 h using GL (0.1%, w/v) as a substrate. The maximum hydrolytic activity for production of GAMG (396 U/mL) was obtained using production medium composed of (g%, w/v): corn steep liquor 2.5, soybean flour 3.5, glucose 0.5 and CaCO3 0.5; pH 6.0. The medium was inoculated with 15% (v/v) inoculum and incubated at 27 °C for 3 days. Under these optimal conditions, GAMG yield became about 2 times higher than GA yield and the cells bioconversion efficiency increased from 24.6 to 78.3%.