Abstract: Waste liquid from glycyrrhizic acid extraction was extracted with n-hexane, chloroform, ethyl acetate and n-butyl alcohol sequentially. The inhibitory effects of the resulting extracts on α-glucosidase were studied compared to identify the one with the highest inhibitory effect. The inhibition type was evaluated based on the Lineweaver-Burk plot and synergistic interaction between the selected extract and acarbose was analyzed by combination index. The chemical structure and amounts of the major components of the extract were determined using ultra-high performance liquid chromatography-diode array detection-mass spectrometry following acid hydrolysis by comparison with standards. The results showed that the ethyl acetate extract had the strongest inhibitory activity against α-glucosidase through competitive inhibition with an half maximal inhibitory concentration value of 0.152 9 g/L and an inhibition constant (Ki) value of 0.085 1 g/L, and synergistic effect existed between acarbose and the ethyl acetate extract. The major constituents of the extract were monoglucosides and diglucosides of glycyrrhizin, naringenin, isoliquiritigenin and formononetin. The contents of the flavonoids glycyrrhizin, naringenin, isoliquiritigenin and formononetin were 28.08%, 2.95%, 11.80% and 4.38% respectively. The content of total flavonoids was 47.21%.

Key words: waste liquid from glycyrrhizic acid extraction, α-glucosidase, inhibition, licorice flavonoids, synergistic effect