Evaluation of the effect of aqueous and ethanolic extraction methods on extraction yield, phenolic compounds, and antioxidant and antimicrobial activity of Stachys schtschegleevii extract

The plant Stachys schtschegleevii is used in the Iranian traditional medicine for the treatment of bacterial infections, rheumatism fever, and inflammatory diseases. In this study, the maceration extraction method with ethanol and water was used to obtain S. schtschegleevii extract, and extraction yield, total phenol content, and antioxidant and antimicrobial activity of the obtained extracts were evaluated. The extraction yield of S. schtschegleevii ethanolic extract was higher than that of aqueous extract (8.8±0.27 vs. 6.9±0.33%), and its total phenol content was also higher compared to the aqueous one (55.35±0.28 vs. 49.4±0.62 mg gallic acid/g dried extract). Antioxidant activity based on IC50 showed that the ethanolic extract, due to its higher total phenol content, has the ability to deactive and neutralize free radicals more efficiently in comparison to the aqueous extract. Antimicrobial results (disk diffusion agar, minimum inhibitory concentration and minimum bactericidal concentration) indicated that bacteria Staphylococcus aureus, Listeria innocua, Escherichia coli and Pseudomonas aeruginosa were more sensitive to the ethanolic extract, and at the same concentration of ethanolic and aqueous extracts, gram-positive bacteria (Staphylococcus aureus and Listeria innocua) had higher sensitivity than the gram-negative ones (Escherichia coli and Pseudomonas aeruginosa). Thus, S. schtschegleevii extract rich in phenolic compounds with appreciable antimicrobial and antioxidant activity could be used as an ingredient to increase nutritional value and shelf-life of food products.