How do grinding and sieving impact on physicochemical properties, polyphenol content, and antioxidant activity of Hieracium pilosella L. powders?

In this work, phytochemical properties of Hieracium pilosella L. powders of different particle sizes were assessed. Four granulometric classes with 180, 315, and 500 µm sieves, as well as the unsieved plant powder were studied for that purpose. Antioxidant activity was determined by DPPH scavenging activity assay and the main bioactive compounds found in H. pilosella L. were quantified by LC-PDA-ESI/MS. The highest antioxidant activity was obtained for the 180-315 µm and 315-500 µm fractions, with 22.5 and 22.3 mg Trolox equivalents per gram of dried matter, respectively. The major bioactive compounds of H. pilosella L., including phenolic acids, flavonoids, and umbelliferone, were evidenced in hydromethanolic extracts. Their maximum content was reached for the same granulometric classes as for maximal antioxidant activity. These results highlighted the interest of grinding and sieving for improving phytochemical properties such as antioxidant activity and bioactive compound content of plants.