Antioxidant Activity and Phenolic Compounds in Medicinal Plants: A Comparison of Organic and Conventional Mentha piperita, Melissa officinalis, Salvia officinalis, and Urtica dioica

The study was conducted to determine whether the origin of medicinal plants (conventional vs. organic cultivation) may affect the content of selected bioactive ingredients. This work complements the current state of knowledge on this subject by analysing the content of selected groups of bioactive compounds in four popular herb species (<i>Mentha piperita</i>, <i>Melissa officinalis</i>, <i>Salvia officinalis</i>, <i>Urtica dioica</i>). The aim of the study was to compare the total polyphenol (TPC) and flavonoid (TFC) content, antioxidant activity (AA) and phenolic compound profile in herbal extracts of organic and conventional origin. For all species examined, it was demonstrated that water-ethanol extracts from organically grown herbs contain statistically (<i>p</i> << 0.05) significantly more TPC, TFC and AA than water-ethanol extracts from conventionally grown herbs. Among the analysed extracts, the highest TPC was found in organic <i>M. officinalis</i> (7023.3 mg GAE/100 g d.m.), while the extract of this species from conventional cultivation contained only 3679.4 mg GAE/100 g d.m. TFC in the extracts of organic and conventional <i>M. piperita</i> was 1607.6 and 499.4 mg QE/100 g d.m., respectively. Based on GC-MS analysis, between 15 and 25 phenolic compounds were identified, depending on the species of herbal plant. Almost all the identified compounds were phenolic acids. The studies conducted indicate a statistically significantly higher content of antioxidant compounds in herbs from organic farming compared to conventionally grown herbs, and thus their greater health-promoting potential.