Investigation of the chemical properties and antimicrobial activities of Humulus lupulus extract on Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Enterobacter aerogenes in vitro

In this study, the ethanolic extract of Humulus lupulus was prepared by the maceration method. Its antimicrobial effect was evaluated against pathogenic bacteria (Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Enterobacter aerogenes) through disk diffusion agar, well diffusion agar, minimum inhibitory concentration, and minimum bactericidal concentration. Total phenol and flavonoid contents of the extract were measured by Folin-Ciocalteu and aluminum chloride colorimetric methods, respectively. The antioxidant activity of the ethanolic extract was also measured by DPPH and ABTS free radical scavenging methods. The highest and lowest inhibition zones in disk diffusion agar (16.9 mm vs. 12.5 mm) and well diffusion agar (17.6 mm vs. 13.9 mm) methods were accounted for S. aureus and E. aerogenes, respectively. Gram-positive bacterial species were more sensitive to H. lupulus ethanolic extract compared to Gram-negative ones. Total phenol and flavonoid contents of the extract were found to be 96.47 mg GAE/g and 28.5 mg QE/g, respectively. The antioxidant effects of the H. lupulus ethanolic extract, based on DPPH and ABTS radical scavenging activities, were 58.63% and 66.5%, respectively. Based on the results, the ethanolic extract of H. lupulus could be used as a natural antimicrobial and antioxidant agent to inhibit the growth of pathogenic bacteria and lipid oxidation progression in various food products.