Citrus limonoids – bitter principle and anticarcinogenic activity

H. Schmandke, Bergholz-Rehbrücke

Citrus limonoids are furan containing, highly oxidized tetracyclic triterpenoids, present as bitter aglycones and non-bitter 17-ß-D-glucopyranosides. Plant biosynthesis starts with nomilin which, via obacunone and ichangin, is finally transformed into limonin.

In mature fruit tissue, glucosides, predominantly limonin glucoside, accumulate while in seeds both aglycones and glucosides, predominantly nomilin glucoside, are found. Hence fresh tissue and freshly squeezed juice do not taste bitter. However, seeds crushed during juice production release bitter aglycones and glucosidases hydrolyzing limonoid glucosides to bitter aglycones. Citrus juice turns bitter during storage. This delayed bitterness is caused by limonin and nomilin forming from monolactones. Commercial citrus juices contain the following limonoid glucoside concentrations: navel orange 180 ppm, grapefruit 120 ppm and lemon 54 ppm. Commercial citrus molasse, a byproduct, contains 3 400 ppm.

Oral administration of limonin glucoside at doses of up to 2 g to healthy subjects has been found to elevate the limonin plasma level; absorption was dependent upon doses. Hamsters fed diets containing either 0.05 % or 0.5 % of a natural limonoid-glucoside mixture revealed no toxic symptoms. Limonin and nomilin have been found non-mutagenic in Ames tests.

In-vivo tests in rats, mice and hamsters have shown that limonoids and their glucosides inhibit carcinogen-induced tumor growth in different organs. They also enhance the activity of the carcinogen-metabolizing enzyme glutathione S-transferase in the liver and mucosa of the small intestine. The growth of human breast cancer cells in cell cultures is inhibited by some aglycones.

Some limonoids, but not glucosides, decrease cholesterol release in cultured human liver cells. This effect is not due to an inhibition of cholesterol synthesis, however. EU11/03

Keywords: Citrus limonoids / bitter principle / and anticarcinogenic activity

Sie finden den Artikel in deutscher Sprache in Ernährungs-Umschau 11/03 ab Seite 432.