Recovery of bioactive molecules from Hypericum perforatum L. dust using microwave-assisted extraction

Microwave-assisted extraction (MAE) conditions were optimized to improve extract quality of medicinal herb - Hypericum perforatum L. (St. John's wort) dust. Response surface methodology was applied initially to obtain the highest concentration of total polyphenols in extract solids (MAE-e). St. John's wort was mixed with 30% ethanol in 50 mL/g solvent to solid ratio, and treated with 170 W microwave power for 40 s to yield an extract with 411.26 +/- 6.21 mg GAE/g of polyphenols. This extract contained a significantly higher content of polyphenols (42.50%) and had significantly higher antioxidant activity than the macerate obtained by using European Medicines Agency (EMA) recommended procedure. The advantage of the EMA procedure was the higher yield of extract per gram of plant material. Therefore, another set of MAE conditions was defined to maximize the yield of polyphenols per gram of plant material (MAE-p). The MAE-p extract was produced by using 30% ethanol, 10 mL/g solvent to solid ratio, and 170 W microwave power for 100 s, which was, again, a markedly shorter period than 72 h of maceration. The MAE-p extract had a slightly, but significantly higher yield (5.2%), more polyphenols (8.8%), and improved antioxidant activity compared to the EMA macerate. Antimicrobial activity against several pathogens was stronger for the MAE extracts. The chemical composition of extracts was slightly different and MAE favored extraction of glycosides, in particular, rutin (quercetin-3-O-rutinoside), while the EMA macerate contained quercetin aglycon in the highest concentration. Our study demonstrates that statistically planned experiments allow for significant improvement of the extraction process, which application could facilitate better use of natural resources and deliver more potent extracts than those obtained by currently recommended procedures.