Antimicrobial Activity of Chemical Hop (<em>Humulus</em> <em>lupulus</em>) Compounds: A Systematic Review and Meta-Analysis
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Humulus lupulus, commonly known as hop, is a climbing plant whose female cones impart beer’s characteristic bitterness and aroma and also serve as a preservative. In this study, we conducted a meta-analysis to investigate the antimicrobial activity of hop compounds and extracts against various microorganisms by statistically synthesizing Minimum Inhibitory Concentration (MIC) values. Our comprehensive literature search retrieved 2,553 articles, of which 18 met the inclusion criteria, encompassing 45 individual studies that reported MIC values for six hop compounds and three extract types tested against 55 microbial strains. MIC values corresponded to 24- and 48-hour incubation periods with the compounds or extracts. Results indicate that xanthohumol (a flavonoid) and lupulone (a bitter acid) exhibit potent antimicrobial activity against most tested microorganisms, particularly food spoilage bacteria. Furthermore, hydroalcoholic extracts demonstrated greater efficacy compared to supercritical CO₂ (SFE) extracts, which showed limited antimicrobial effects against both probiotic and non-probiotic strains. These findings underscore the need for standardized, evidence-based protocols—including uniform microbial panels and consistent experimental procedures—to reliably evaluate the antimicrobial properties of hop-derived compounds and extracts.