Factors influencing silymarin content and composition in variegated thistle (Silybum marianum)

Abstract

Variegated or milk thistle (Silybum marianum) was grown in various field trials in New Zealand, and the seed analysed for silymarin content and composition. The trials were a time of sowing trial with a New Zealand line and a German cultivar, an analysis of plant parts of the German cultivar, a time of seed harvest trial with the German and a Polish cultivar, and a comparison of seed of 25 ecotypes of the New Zealand line from a range of sites, either as collected, or after growing together on one site. Sowing date had a small effect on silymarin concentration, but not on silymarin composition. There were large differences between cultivars in seed silymarin content and composition. The New Zealand line had 18g/kg of silymarin, whereas the German cultivar had 6g/kg. The New Zealand line had a significantly higher percentage of silychristin A, and silybins A and B than the German cultivar, but lower isosilybins and no silydianin. Silymarin content and composition between parts of the plant ranged from none in the stems and leaves up to 14.7 k/kg in the seeds. Silymarin in the roots and flowers was made up of only silychristin B and silybin B, whereas in the green seed head and seeds, silydianin made up over 30% of the silymarin. Seed silymarin content increased as the seed matured, but at a decreasing rate. In the German line, the percentage of silychristin A and both silybins increased significantly as the seed matured, while silydianin decreased significantly, whereas in the Polish line, the converse was true. The range in silymarin content of the 25 ecotypes decreased from 10 to 43 g/kg as collected in the wild to 22–38g/kg when grown together, with very little change in silymarin composition.