(a) Scheme of hydrolysis of glycyrrhizin (GL) into glycyrrhetinic acid 3-O-mono-β-d-glucuronide (GAMG) and glycyrrhetinic acid (GA), catalyzed by β-glucuronidase. (b to g) Structures of typical glucuronides. (b) Baicalin; (c) baicalein 7-O-β-d-glucoside; (d) quercetin 3-O-β-d-glucuronide; (e) quercetin 3-O-β-d-glucoside; (f) GAM-Glc; (g) pNP-sugar. “X” stands for glucopyranose (Glc), galactopyranose (Gal), xylopyranose (Xyl), mannopyranose (M), or glucopyranosiduronic acid (GlcA).