The Antibacterial Effect of Humulus lupulus (Hops) against Mycobacterium bovis BCG: A Promising Alternative in the Fight against Bovine Tuberculosis?

The female flowers of the Humulus lupulus plant or Hops have been used extensively within the brewing industry for their aroma and bitterness properties. It was also found that beer that contained hops was less likely to spoil, thus revealing the antimicrobial potential of these plants. One species of bacteria, Mycobacterium spp., is of particular interest as it is the causative agent of both human and animal forms of tuberculosis (TB). In this study an aqueous extraction process was employed to analyse the antibacterial properties of 50 hop extracts (45 individual variants); against M. bovis BCG. Using an agar well diffusion assay we found that all hops exhibited a level of inhibitory activity which ranged from 1.2 mm (+/− 0.08 mm) in the case of hop variant; Target, to 15.7 mm (+/− 0.45 mm) in the case of hop variant Citra. The Citra variant had a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 16% v/v. This is the first study to analyse a wide range of hops for their antimicrobial potential against M. bovis BCG and recommends that further research focuses on other Mycobacteria spp., the potential for antimicrobial synergy and the antibacterial effect of individual components.

Hop Tannins as Multifunctional Tyrosinase Inhibitor: Structure Characterization, Inhibition Activity, and Mechanism

The application of hops could be extended to obtain higher commercial values. Tannins from hops were assessed for their tyrosinase inhibition ability, and the associated mechanisms were explored. Nuclear magnetic resonance (NMR) and high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (HPLC–ESI–MS/MS) revealed that the hop tannins were characterized as condensed tannins with (epi)catechin and (epi)gallocatechin as subunits and an average polymerization degree of 10.32. Tyrosinase inhibition assay indicated that hop tannins had an IC₅₀ = 76.52 ± 6.56 μM. Kinetic studies of the inhibition processes indicated the tannins provided inhibition through competitive–uncompetitive mixed reactions. In silico molecule docking showed that tannins were bound to the active site of tyrosinase via hydrogen and electrovalent bonds. Circular dichroism (CD) observed the structural variation in the tyrosinase after reacting with the tannins. Fluorescence quenching analysis and free radical scavenging assays indicated that the tannins had copper ion chelating and antioxidant activities, which may also contribute to inhibition. The intracellular inhibition assay revealed that the melanin was reduced by 34.50% in B16F10 cells. These results indicate that these tannins can be applied as whitening agents in the cosmetics industry.

The Effect of Dry Hopping Efficiency on β-Myrcene Dissolution into Beer

The production of heavily hopped beers, such as Indian Pale Ale (IPA) styles, has been gaining momentum in recent years in the Central European markets. To this end, the dry hopping process is becoming increasingly popular, mostly in microbreweries, but also with larger manufacturers. In our research, we investigated the dissolution rate of the main volatile component of hops, β-myrcene with a modified dry hopping method. Following the primary fermentation, we applied the dry hopping process, where the weighed hops were chopped and blended into a container with 0.5 L of beer and later added to the young beer. During the dry hopping process, we determined various important parameters of the beer, and we repeated the same measurements for the bottled beer. In the first 96 h of the dry hopping process, we monitored the concentration of β-myrcene so that we managed to determine the dissolution rate constant (k = 0.1946 h^-1). The β-myrcene concentration stabilizes after 44 h in the fermenter. At the same time, measurements were conducted for bitterness, pH, CO₂ and alcohol content, extract and density during the process. Our experiment demonstrates that a new method of dry hopping provides a much higher concentration of β-myrcene (215 μg/L) than other methods indicated in former studies in the field. A health and safety assessment of β-myrcene was also made and we determined what the safe amount of β-myrcene ingested with IPA beer is. Our modified process was successful, we were able to determine the dissolution rate of β-myrcene, and the recommended daily intake of IPA beer with particular reference to β-myrcene.