Silymarin (Batch 32621/M5) was obtained from Indena (Milan, Italy). Detailed quantitative analysis revealed a flavonolignan content of 62.81% w/w, with the most abundant components being silybin B (13.8%) and silybin A (9.3%), and the presence of a polymer fraction accounting for 36.6%. The stock solution was prepared at a concentration of 10 mg mL -1 in DMSO (dimethylsulfoxide; Sigma-Aldrich, Prague, Czech Republic) and kept at 4 °C. A working solution of concentration 2 mg mL -1 was prepared by mixing the stock solution with fermentation medium. The concentration of silymarin in each 2 mL well during the incubations was 50 µg mL -1 .