Metabolomics reveals the differential regulatory mechanisms of quality and flavonoid biosynthetic pathways during the drying process of varieties licorice

Abstract

Flavonoids are one of the major chemical components in licorice. However, during the drying process, their chemical stability, content, and biological activity can all change. Moreover, the impact of different varieties on these aspects is still not clear. This study employed hot air-drying technology at 45-65 °C to examine the effect of drying temperature on the drying flavonoids, total phenolics, and antioxidant activity and other quality aspects in Glycyrrhiza uralensis and Glycyrrhiza inflata from the Xinjiang Uygur Autonomous Region, China. Results showed that the optimal drying temperature was 60 °C, at which the total phenolic content of both varieties of licorice reached its peak, with G. inflata achieving 2.42 mg GAE/g and G. uralensis reaching 2.46 mg GAE/g. However, drying significantly reduced the antioxidant activity of licorice. Additionally, there were 24 differential flavonoid metabolites between the dried samples of G. inflata and G. uralensis, among which 19 were up-regulated and 5 were down-regulated. G. uralensis retained better overall quality than G. inflata after drying. These findings provide insights into flavonoid metabolite and antioxidant regulation under drying stress, and valuable information for primary processing in licorice-producing areas.

Keywords: Antioxidant capacity; Drying; Flavonoid; Licorice; Metabolism.

Graphical abstract

Fig. 1

Determination of basic quality and antioxidant capacity of licorice samples under different treatment methods. A: Drying kinetics curve and drying time of Glycyrrhiza uralensis. B: Drying kinetics curve and drying time of Glycyrrhiza inflata. C: Total phenol content in licorice samples under different treatment methods of G. uralensis and G. inflata. D: Determination of antioxidant capacity of G. uralensis using the DPPH, ABTS, and FRAP methods. E: Determination of antioxidant capacity of G. inflata using the DPPH, ABTS, and FRAP methods.

Fig. 2

A: Total ion current map of metabolite detection of licorice samples. B: Clustering analysis diagram of licorice samples. (W-Fresh: Fresh sample of G. uralensis; Z-Fresh: Fresh sample of G. inflata; W-Drying: Dried sample of G. uralensis; Z-Drying: Dried sample of G. inflata.)

Fig. 3

Principal component analysis and orthogonality partial least squares-discriminant analysis of licorice group samples. A: PCA score map of quality spectrum data for licorice group samples. B–E: Orthogonality partial least squares–discriminant analysis of licorice group samples.

Fig. 4

A: Venn diagram of differences among groups of licorice samples. B: Volcanic map of different substances among groups of licorice samples. C–F: Difference multiples bar chart of licorice group samples.

Fig. 5

KEGG classification diagram and enrichment analysis diagram of differential metabolites in licorice group samples.

Fig. 6

Schematic diagram of the change mechanism of liquiritin.