Phytochemical screening, in vitro Antioxidant, and Antimicrobial Efficacy of Humulus lupulus L. flowers (Newport and Comet varieties) from Thailand

Abstract

Humulus lupulus L. (hop) has a rich history in beer brewing, prized for its contributions to flavor, aroma, and preservation qualities. Polyphenols in hops have been reported for various activities, especially antioxidant, anti-inflammatory antibacterial and anti-cancer properties. This study aims to explore the effects of flowers extracts of the Comet and Newport varieties of H. lupulus L. on antioxidant and antibacterial potential. Ethanolic hop extracts were prepared, and their antioxidant activity was assessed using the 2,2-diphenyl-1-picryhydrazyl (DPPH), ferric ion reducing antioxidant power (FRAP), and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical cation decolorization assays. Total phenolic and flavonoid contents were quantified via the Folin–Ciocalteu and colorimetric aluminum chloride assays, respectively. Antibacterial efficacy was evaluated using the microdilution method. Additionally, the chemical composition of hops from various varieties included in our investigation was analyzed using liquid chromatography-mass spectrometry (LC-MS). Ethanolic extracts from the Newport and Comet varieties of H. lupulus L. contained total phenolics content about 36.98±2.38 and 66.66±7.96 mg QE/g extract, respectively. Total flavonoid content of the Newport and Comet were 5.26±0.04 and 8.20±0.65 mg QE/g extract, respectively. Chemical analysis revealed phenolic and prenylflavonoid compounds in the extracts. Both varieties exhibited strong antioxidant activity, with DPPH assay IC50 values of 0.67 and 0.24 mg/mL, and ABTS assay IC50 values of 0.54 and 0.16 mg/mL, respectively. Additionally, the FRAP assay showed antioxidant capacity of 28.02 and 19.88 mgTE/g extract for Newport and Comet. Furthermore, the Newport and Comet extracts displayed significant antibacterial activity against Stapphylococcus aureus with MIC 0.061 and 0.146 mg/mL, respectively and Cutibacterium acnes with MIC 0.061 and 0.073 mg/mL, respectively. This study represents the first investigation into the phytochemical and biological activity of H. lupulus L. varieties in Thailand, revealing promising antioxidant and antibacterial properties in both Newport and Comet varieties against S. aureus and C. acnes.