Effect of Steam Explosion on Conversion and Extraction of Glycyrrhizic Acid from Glycyrrhiza uralensis

In this paper,steam explosion(SE)technology was innovatively applied to treat Glycyrrhiza uralensis. The physical-chemical properties of Glycyrrhiza uralensis after SE,including morphological characterization,chemical composition and functional groups were characterized;the distribution and extraction kinetics of glycyrrhizic acid(GL)and its conversion products were determined to clarify the hydrothermal conversion and extraction promotion of glycyrrhizic acid from Glycyrrhiza uralensis by SE. Results showed that SE combined the thermal and mechanical modification to break the dense structure in cell wall,cell and tissue scales of Glycyrrhiza uralensis. It removed the hemicellulose content of 64.03%,increased the acid soluble lignin by 1.59 times and water extraction content to 31.29%,which was beneficial to the dissolution and release of GL and its converted products. SE accelerated the proton attack to the O-glycoside group in GL,in order to rapidly hydrolyze its glycosidic bond to form glycyrrhetinic acid 3-O-mono-β-D-glucuronide(GAMG)and β-glycyrrhetinic acid(GA). The conversion rate of GL reached 24.23% and the production rates of GAMG and GL were 6.58% and 31.55%,respectively. Their extraction yields reached the maximum value within 2 h during the extraction process,and their extraction equilibrium time was shortened by more than 80% after SE. The study was aimed to provide technical support and theoretical basis for the development of high-intensity sweeteners for glycyrrhizic glycosides and the high-value utilization of their conversion products.