Glycyrrhiza glabra L. (Licorice)

Distribution and Importance of the Plant

The genus Glycyrrhiza contains 30 species native to hot temperate or subtropical regions such as the Mediterranean Basin. Among these various kinds of licorice plants, few are of industrial interest, for example, Glycyrrhiza glabra L., G. glabra L. var. glandulifera Rgl. et Herd., G. uralensis D.C. and G. echinata L. This chapter describes only the results for G. glabra L. the licorice material most employed in industry for its aromatic and sweetener properties.

G. glabra L. is a perennial plant belonging to the subfamily Papilion-oideae of the family Leguminosae, common around the Mediterranean Sea. It is a herb which can reach 1.50 in height, the most important part being underground. The roots are held by a subterranean stem or rhizome, which are very ramified with long and thick branches. The upper shoot, with a sometimes scabrid and pubescent stem, is erect, with long (5 to 20 cm) imparipinnate leaves, each with 9 to 17 elliptical leaflets.

The hanging, elongate racemes, surrounded by their subtending leaves, contain 20 to 30 flowers, which are relatively short (corolla 8-12 mm with five whitish purple petals) and characterized by a horseshoe-shaped opening of the anthers at the end of the ten stamens. The fruit, up to 30 mm, is compressed, glabrous or glandular-setose, with three to five small (2-3 mm) seeds.

In the species G. glabra L., three varieties are generally distinguished:

  • G. glabra L. var. typica called Spanish Licorice after the country where it has long been cultivated over great areas. In 1930, 1648 ha were reported to be cultivated with this variety. It has been found in many neighboring countries in the Mediterranean zone such as Portugal, Italy, Greece, Turkey, and the Caucasus.
  • G. glabra L. var. glandulifera Rgl. et Herd, or Russian Licorice. In this variety, the stolons are missing. It develops best in Hungary, Iran, and Spain.
  • G. glabra L. var. violacea, wrongly called Iran Licorice, is not found in Iran, and is encountered mainly in Iraq.

Economical Aspects

Glycyrrhizae Radix is an important commercial product. It is used:

  • — in the tobacco industry, where licorice powder gives a sweet aromatic perfume, and also protects tobacco from desiccation,
  • — in the food industry, where licorice is used as an aromatic raw material in sweets or in mixtures in which the sweetening effect needs its aromatic taste,
  • — in the pharmaceutical industry for the anti-inflammatory and antiulcerative activity of glycyrrhizin, the main component of licorice.

Conventional Practices for Propagation, the Production of Glycyrrhizin, and the Demand in the World Market

Licorice plants can grow only in limited regions in the world around the Mediterranean Sea, and therefore the production of licorice root and industrial reprocessing has necessarily been regionally restricted.

Propagation is performed by cutting. Small pieces of rhizomes, 10 to 15 cm long, cut from the mother plant, contain two to three buds. These buds develop rapidly and later adventitious roots appear on the short rhizome. Licorice plantation is carried out in early spring in deep, light soils.

In France, one of the authors succeeded in cultivation by directly sowing seeds previously treated with concentrated sulfuric acid for 2 h following the technique of Shukurullaev and Khamdamov (1976). The soil had to be perfectly free of weeds for the first 2 years after planting or sowing. Five liter/ha Etazine is spread on the cuttings after planting and 11/ha Sinbar on the sowing bed just before drilling.

After 3 years of growth, 26 t/ha of a mixture of roots and rhizomes were extracted from the soil. The glycyrrhizin contents increased with subsequent growth periods: 11.02% were obtained the first year, 11.50% the second, 14.14% the third, and 15.20% the fourth.

The main countries producing licorice are Turkey, Syria, Iran, Iraq, the U.S.S.R., and China, but Greece, Italy, and Spain come very soon after. The U.S.A. are the main importer, with 20,000 tons of root-rhizome mixture handled by only one company, which imports the roots and rhizomes either directly from Syria, Turkey, and the U.S.S.R., or after a first extraction performed in China (Bozzi M., EVD Company, Marseille, France, Division of MacAndrew and Forbes Company, U.S.A., pers. commun.).

In France, 3500 t are imported each year and transformed for either the pharmaceutical or food industry.

Micropropagation of licorice is actually the only technique which can be used in industry. Given the difficulty of multiplying this plant by classical methods, it represents important progress. Until now, undifferentiated cultures of licorice failed to regenerate the plant, or to produce metabolites in vitro. Further investigations are necessary to elucidate the induction of the embryogenesis and the regulation of the biosynthesis of secondary products.

 

Selections from the book: “Medicinal and Aromatic Plants III”, 1991.