Enhanced production of glycyrrhetic acid 3-O-mono-β-d-glucuronide by fed-batch fermentation using pH and dissolved oxygen as feedback parameters

Glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG), the major functional ingredient in licorice, has widespread applications in food, pharmacy and cosmetics industry. The production of GAMG through Penicillium purpurogenum Li-3 cultivation was for the first time performed through both batch and fed-batch processes in bioreactors. In batch process, under optimal conditions (pH 5.0, temperature 32 °C, agitation speed 100 r·min^{- 1}), 3.55 g·L^{- 1} GAMG was obtained in a 2.5 L fermentor. To further enhance GAMG production, a fine fed-batch process was developed by using pH and DO as feedback parameters. Starting from 48 h, 100 ml 90 g·L^{- 1} substrate Glycyrrhizin (GL) was fed each time when pH increased to above 5.0 and DO was increased to above 80%. This strategy can significantly enhance GAMG production: the achieved GL conversion was 95.34% with GAMG yield of 95.15%, and GAMG concentration was 16.62 g·L^{- 1} which was 5 times higher than that of batch. Then, a two-step separation strategy was established to separate GAMG from fermentation broth by crude extraction of 15 ml column packed with D101 resin followed by fine purification with preparative C18 chromatography. The obtained GAMG purity was 95.79%. This study provides a new insight into the industrial bioprocess of high-level GAMG production.