Improvement of antioxidant activity and polyphenol content of Hypericum perforatum and Achillea millefolium powders using successive grinding and sieving

• Polyphenol-rich fine powders were produced from H. perforatum and A. millefolium aerial parts.
• The impact of plant grinding and sieving on antioxidant activity and polyphenol content was studied.
• Antioxidant activity and polyphenols contents are related to particle size.
• Optimal fractions were of intermediate size, between 100 and 315 μm.

This work aims at evaluating the effect of successive grinding and sieving processes on the polyphenol content of plants. Powders of particle size ranging from 20 to 500 μm and over were produced from aerial parts of Hypericum perforatum and Achillea millefolium. The evaluation of total phenolic content and antioxidant activity, as well as the identification and quantification of some bioactive compounds by LC-ESI/MS were performed. The highest antioxidant activity was obtained for the 100–180 μm fraction: IC50 of 0.43 and 0.51 mg/mL for H. perforatum and A. millefolium, respectively. LC-ESI/MS analyses evidenced that two intermediate granulometric classes, 100–180 μm and 180–315 μm, allowed achieving the highest polyphenol content. These results show that fine grinding and sieving lead to a differential distribution of bioactive compounds according to particle size.

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