Chemical Profiling of Fatty Acids and Phenolic Compounds in Thistle Seeds and Dietary Thistle Products and Evaluation of Their Bioactivity

This study aimed to characterize the fatty acid (FA) and phenolic profiles of milk thistle (Silybum marianum) seeds in comparison to seeds of other thistles native to Greece (Carlina corymbosa and Cirsium vulgare), as well as commercial dietary supplements and juices containing milk thistle alone or combined with artichoke. Free fatty acids (FFAs) were determined by LC-HRMS, total FA composition by GC-MS, and total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity and toxicity by spectrophotometric assays. Silybins A and B, the main bioactive constituents of milk thistle, were quantified using HPLC, while UHPLC-Orbitrap MS was employed for a more comprehensive phenolic profiling. Linoleic and oleic acids were the predominant FAs, both free and esterified forms, although FA distributions varied according to botanical source and formulation. Dietary supplements exhibited the highest TPC values, while the native Carlina corymbosa seed sample exhibited the highest antioxidant activity and the Cirsium vulgare seed sample exhibited the highest toxicity against V. fischeri. UHPLC-Orbitrap MS identified 32 phenolic compounds, revealing distinct profiles among the investigated matrices. In milk thistle seed samples, caftaric acid predominated; Cirsium vulgare seeds were mostly characterized by trans-chlorogenic acid, whereas Carlina corymbosa exhibited elevated p-hydroxybenzoic acid and exclusive detection of procyanidin B2. Ultimately, these results provide important insights into the lipid and phytochemical composition of native thistle seeds and commercial formulations of milk thistle, and the quantification of FFAs in such samples is reported here.