Analysis of silymarin in milk thistle extracts

Dry extract of milk thistle (Silybum marianum) is listed in the European Pharmacopeia and other monographs as a component of herbal preparations indicated for the symptomatic treatment of functional digestive disorders of hepatic origin, including acute or chronic hepatitis and cirrhosis of the liver, induced by alcohol, medicines or toxins. Silymarin is the main bioactive constituent of milk thistle extract and contains a mixture of different flavonolignan isomers: silybinin (syn. silybin) A and B, isosilybinin A and B, silychristin A and B, and silydianin. Silybin is the component with the highest biological activity, accounting for 40-65% of the silymarin extract, and is the most studied flavonolignan. The content of silymarin in raw materials and extracts is usually expressed as the sum of the contents of silibinin A and silibinin B, calculated with reference to the total silymarin. The nominal content of silymarin ranges from 30% m/m to 65% m/m (anhydrous extract).

Silymarin content

Treatment with herbal preparations of milk thistle is recognized as safe and well tolerated at recommended doses and specified conditions of use, with a low incidence of adverse effects compared to placebo. A variety of dietary supplements are available in different formulations, including tablets, capsules, or standardized extracts. However, alarming discrepancies have been found between declared and detected content of silymarin in these products. Several authors found significant differences in silymarin content (measured vs. declared content) between individual products, but also substantial inter-batch differences in silymarin content and alarming levels of mycotoxins, the presence of various pesticide residues, and microbiological contamination. For example, a study of six milk thistle extracts on the European market showed that silymarin content ranged between 17.21 to 63.96% and varied widely between batches from the same manufacturers.

While the silymarin content in milk thistle seeds is highly dependent on the geographic location of cultivation and agronomic conditions, according to the recent report, 30% to 50% of commercially available milk thistle extracts do not conform to labelled claims, up to 28.6% of do not contain silymarin, while there is evidence of adulteration in up to 46%. This raises serious safety concerns, as the presence of contaminants (e.g., heavy metals, pesticides, mycotoxines) or suspected adulterants is associated with a higher incidence of liver injuries.

HPLC method for the analysis of silymarin

Although many testing and quality monitoring strategies have been developed to characterize the composition of products containing silymarin and to check for possible adulterants, HPLC is recommended as a technique of choice in the monographs of the European Pharmacopeia and the United States Pharmacopeia.

In our laboratory, we have developed and validated an HPLC method for the analysis of silymarin in raw materials, extracts, dietary supplements, and other herbal preparations.

For analysis of the active ingredients or contaminants (pesticides, heavy metals, mycotoxins) and further information, please Contact us.