Chemical and productive properties of two Sardinian milk thistle (Silybum marianum (L.) Gaertn.) populations as sources of nutrients and antioxidants

Silybum marianum (L.) Gaertn. (milk thistle), grown as a medicinal plant in several countries, is considered as a weed in pastures and cereal crops but also as an interesting plant for biomass production. As an additional contribution to the full exploitation of a such promising species, two Sardinian populations of S. marianum were investigated for chemical composition, bioactive compounds and antioxidant properties at vegetative and reproductive stages. Dry matter yield was affected by the phenogical stage and differed between populations, ranging from 148 to 246 g plant-1. Chemical composition did not differ between populations. Antioxidant capacity detected by means of ABTS [(2,2?-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt)] and by DPPH (1,1-diphenyl-2-picrylhydrazyl) methods ranged from 3.45 to 5.42 and 3.83 to 6.32 mmol/100 g dry weight of Trolox equivalent antioxidant capacity, respectively. Differences in antioxidant capacity and bioactive compound contents in the different plant organs were found and also a significant linear correlation between antioxidant capacity and total phenolics and flavonoids, at flowering compared to vegetative stage. Research highlights antioxidant capacity in different organs of milk thistle and encourages the exploitation of biomass also as functional food, source of natural antioxidants and as a complementary fodder.