Hop Beta Acids Research Articles

Cell Envelope Modifications Generating Resistance to Hop Beta Acids and Collateral Sensitivity to Cationic Antimicrobials in Listeria monocytogenes.

Hop beta acids (HBAs) are characteristic compounds from the hop plant that are of interest for their strong antimicrobial activity. In this work, we report a resistance mechanism against HBA in the foodborne pathogen Listeria monocytogenes. Using an evolution experiment, we isolated two HBA-resistant mutants with mutations in the mprF gene, which codes for the Multiple Peptide Resistance Factor, an enzyme that confers resistance to cationic peptides and antibiotics in several Gram-positive bacteria by lysinylating membrane phospholipids. Besides the deletion of mprF, the deletion of dltA, which mediates the alanylation of teichoic acids, resulted in increased HBA resistance, suggesting that resistance may be caused by a reduction in positive charges on the cell surface. Additionally, we found that this resistance is maintained at low pH, indicating that the resistance mechanism is not solely based on electrostatic interactions of HBA with the cell surface. Finally, we showed that the HBA-resistant mutants display collateral sensitivity to the cationic antimicrobials polymyxin B and nisin, which may open perspectives for combining antimicrobials to prevent resistance development.

Hop beta acids – from cones to beer

Hop beta acids – from cones to beer

Activation of membrane-located Ca2+ channels by hop beta acids and their tricyclic transformation products

Beta-bitter acids of hops (lupulones) revealed sedative and antidepressant–like effects in animal studies. Transformation of β-acids during beer brewing leads to the formation of tricyclic transformation products, which have a close structural analogy to hyperforin. The latter compound is responsible for the antidepressant activity of St. John’s wort by activation of TRPC6 cation channels in neuronal-like cells leading to Ca2+ influx. In this study, nortricyclolupones, dehydrotricyclolupones, and tricyclolupones were isolated from a wort-boiling model and their structures were elucidated by UHPLC–DAD, UHPLC–ESI−-MS/MS and 1D/2D-NMR spectroscopy. Beta-bitter acids and their transformation products induced Ca2+ influx in PC12 cells to the same extent as hyperforin. Application of a Ca2+-free environment abolished the Ca2+ elevation, indicating that the increase is mediated by influx across the plasma membrane. Thus, activation of neuronal-like Ca2+-channels by lupulones and tricyclolupones represent a novel mechanism contributing to the antidepressant activity of hops.

Hops (Humulus lupulus L.) Bitter Acids: Modulation of Rumen Fermentation and Potential As an Alternative Growth Promoter.

Antibiotics can improve ruminant growth and efficiency by altering rumen fermentation via selective inhibition of microorganisms. However, antibiotic use is increasingly restricted due to concerns about the spread of antibiotic-resistance. Plant-based antimicrobials are alternatives to antibiotics in animal production. The hops plant (Humulus lupulus L.) produces a range of bioactive secondary metabolites, including antimicrobial prenylated phloroglucinols, which are commonly called alpha- and beta-acids. These latter compounds can be considered phyto-ionophores, phytochemicals with a similar antimicrobial mechanism of action to ionophore antibiotics (e.g., monensin, lasalocid). Like ionophores, the hop beta-acids inhibit rumen bacteria possessing a classical Gram-positive cell envelope. This selective inhibition causes several effects on rumen fermentation that are beneficial to finishing cattle, such as decreased proteolysis, ammonia production, acetate: propionate ratio, and methane production. This article reviews the effects of hops and hop secondary metabolites on rumen fermentation, including the physiological mechanisms on specific rumen microorganisms, and consequences for the ruminant host and ruminant production. Further, we propose that hop beta-acids are useful model natural products for ruminants because of (1) the ionophore-like mechanism of action and spectrum of activity and (2) the literature available on the plant due to its use in brewing.

The development of HopGuard® as a winter treatment against Varroa destructor in colonies of Apis mellifera

The development of new veterinary medicinal products to control Varroa destructor is very important for the successful management of honey bee colonies. We tested natural plant compounds (hop acids) as active ingredients for a new veterinary drug for Varroa control. Tolerability of bees and efficacy against mites was tested in the laboratory and in the field. In laboratory tests, hop beta acids were proven to be safe for bees (5 % mortality) and effective against mites (93.3 % mortality); there is a six-fold safety margin for bees after individual dermal application compared to the lowest dosage highly toxic to mites. In a clinical study, these results were confirmed: bee colonies tolerated the treatment (<10 % mortality), while most of the mites were killed (efficacy up to 88 %). The treatment did not affect the adult bee population and winter survival of colonies.

Beta kyseliny chmele, význam a využití.

Význam a využití beta kyselin chmele, významné složky chmelových pryskyřic, se odvíjí ve třech rovinách, pivovarské, antimikrobiální a fyziologické. V pivovarství je určující vlastností beta kyselin nízká rozpustnost ve vodných roztocích a schopnost oxidace na rozpustnější produkty. Oxidace probíhá při zpracování a skladování chmele a v malé míře při výrobě piva. Piva chmelená pre-oxidovanými beta kyselinami mají výraznou senzorickou hořkost, hořčící vydatnost oxidačních produktů beta kyselin chmele dosahuje přibližně 35-40 % hořkosti iso-alfa kyselin. Byla shromážděna řada důkazů o biologických a farmakologických účincích chmelových hořkých kyselin a speciálně účincích beta kyselin. Chmelové kyseliny jsou potenciálním zdrojem pro léčbu anebo prevenci řady onemocnění včetně rakoviny, diabetu, osteoporózy, kardiovaskulárních chorob, zánětlivých procesů a metabolických poruch. Významné jsou antimikrobiální účinky beta kyselin proti řadě různých mikroorganismů, které již našly využití v cukrovanictví, lihovarství a chovu hospodářských zvířat. Tento přehledový článek shrnuje dosavadní poznatky o beta kyselinách chmele jak z hlediska působení v pivovarském procesu, tak z hlediska jejich bioaktivních účinků.

Vliv oxidačních produktů beta kyselin chmele na hořkost piva.

Určující vlastností beta kyselin je jejich nestabilita a sklon k oxidaci v závislosti na podmínkách . Uvedená vlastnost se projevuje jak při skladování chmele, tak při použití v procesu výroby piva . V čistém stavu se na vzduchu při pokojové teplotě rozloží po měsíci zhruba polovina původního množství . Po 6 měsících činí míra degradace více než 90 % . V hlávkových chmelech je dynamika degradace značně pomalejší, zejména v prvních 6 měsících skladování . Změny beta kyselin v průběhu stárnutí vysvětlují jednu z příčin, proč hořčící potenciál starších chmelů neklesá úměrně s poklesem obsahu alfa kyselin . Významný podíl degradačních produktů tvoří látky, které vznikají cyklizací bočních isopentenylových řetězců beta kyselin (tricyklolupulony a hydroxytricyklolupulony) . Piva chmelená oxidačními produkty beta kyselinami v dávce 20 g/hl vykazovala zřetelnou senzorickou hořkost, která nebyla v žádném případě nepříjemná a ulpívající . Hořčící vydatnost oxidačních produktů beta kyselin chmele dosahuje přibližně 35-40 % hořkosti iso-alfa kyselin

STABILITY OF HOP BETA ACIDS AND THEIR DECOMPOSITION PRODUCTS DURING NATURAL AGEING

Instability and tendency to oxidation depending to conditions is a dominant property of hop beta acids. Mentioned property has an impact both on hop storage and beer brewing process. Approximately half amount decomposes at room temperature under open air conditions in the course of one month. After 6 months the rate of degradation is more than 90%. Dynamics of decomposition is much slower in leaf hops, primarily during first 6 months of storage. Beers hopped by partially oxidized beta acids showed perceptible sensorial bitterness. Bitterness was pleasant and not clinging. Changes of beta acids in the course of ageing explain that bittering potential of old hops does not declines proportionally to alpha acid loss. A large share of degradation products are formed by cyclization of prenyl side chains of beta acids as arises from mass spectra analysis (tricyclolupulones and hydroxytricyclolupulones). Comparison of decomposition products mass spectra emerging during natural ageing and laboratory wort boiling shows discovery of several unpair fragments beside of many identical ones. It indicates that decomposition products of beta acids established during natural ageing and wort boiling process are not fully idetical.

The effects of beta acids from hops (Humulus lupulus) on mortality of Varroa destructor (Acari: Varroidae)

Hop (Humulus lupulus L.) beta acids (HBA) were tested for miticidal effects on varroa destructor Anderson and Trueman, a parasitic mite of the honey bee (Apis mellifera L.). When varroa were placed on bees that had topical applications of 1 % HBA, there was 100 % mite mortality. Bee mortality was unaffected. Cardboard strips saturated with HBA and placed in colonies resulted in mite drop that was significantly greater than in untreated hives. HBA was detected on about 60 % of the bees in colonies during the first 48 h after application. Mite drop in colonies lasted for about 7 days with the highest drop occurring in the first 2–3 days after treatment. There was a reduction in the percentages of bees with HBA and in the amounts on their bodies after 7 days. Bee and queen mortality in the colonies were not affected by HBA treatments. When cardboard strips saturated with HBA were put in packages of bees, more than 90 % of the mites were killed without an increase in bee mortality. HBA might have potential to control varroa when establishing colonies from packages or during broodless periods.

Application of plant-based antimicrobials for the growth inhibition of clostridia in pressed beet pulp silage

In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated pressed sugar beet pulp silages was investigated. Hop beta acids are natural substances which display their effect at low concentrations. Fresh pressed beet pulp material was mixed with soil to artificially contaminate it with clostridia. Laboratory silos were filled with the substrate, stored at 25 °C and opened for sampling at 0, 2, 8, 15, 30, 60, and 90 days. The impact on clostridial growth during silage fermentation was monitored by determination of the pH value and dry matter content, as well as chemical analysis of the fermentation products. Throughout the experiments, the effect of a commercial silage inoculant based on lactic acid bacteria (LAB) and hop-resistant LAB were examined with and without the combination of plant-based antimicrobials. Results indicate that in contaminated silage samples without any additives high butyric acid contents occurred due to clostridial growth. This spoilage could not be suppressed by the application of LAB, whereas the combined application of LAB and hop beta acids significantly improved silage quality, which was reflected by favourable organic acid composition (P < 0.05). The experimental data indicate that the application of hop beta acids improves the preservation effect of LAB in suppressing clostridial growth in silages and thus demonstrates some potential for the combined use of plant-based antimicrobials and LAB.

Protective effect of hop ?-acids on microbial degradation of thick juice during storage

This study assessed the value of a commercial alkaline solution of hop beta-acids (HBA) for prevention of microbial degradation of thick juice, a concentrated intermediate product in the production of beet sugar. The antimicrobial effect of different concentrations of HBA against microbial degradation of thick juice was tested in a pilot-scale storage experiment. Chemical, biochemical and microbial parameters were monitored during thick juice storage. Thick juice degradation, indicated as a decrease in pH, was generally accompanied by an increase in the count of fastidious bacteria (FB) on Columbia Agar with Sheep Blood (CAwSB), which were mainly identified as Tetragenococcus halophilus. Addition of HBA delayed juice acidification and the development of FB in a concentration-dependent manner. The susceptibility of FB to HBA was determined by plating degraded thick juice (FB > 10(5) CFU ml(-1) on CAwSB plates with different concentrations of HBA (0-160 ppm). None of the HBA concentrations tested reduced the number of FB colonies formed, but increasing HBA concentrations extended the lag time of colony formation. HBA produce no measurable bactericidal effect, but retard the development of FB in thick juice. Moreover, HBA do not prevent the thick juice from deteriorating, but significantly delay its degradation. These results indicate that adding a commercially available HBA formulation can prolong the storage life of thick juice in the sugar industry, although degradation cannot be eliminated. Future research will focus on the detailed characterization of FB consistently isolated from degraded thick juice and on determining their role in thick juice degradation.

The Control of Selected Micro-Organisms During the Malting Process

The micro-organisms associated with malt have an important influence on quality parameters. Although it was not possible to eliminate the growth of micro-organisms entirely during the malting process, it was possible to control particular groups by applying some simple procedures. A three steep schedule was associated with increased fungal growth which was not observed when a two steep schedule was used. Fungal proliferation could also be reduced by the use of hop beta-acids. The use of sodium hypochlorite, potassium hydroxide, hydrochloric acid and hop beta-acids reduced or eliminated E. coli. The most effective means of controlling total micro-flora was an alternate acid/alkaline wash. There was no evidence that a correlation existed between growth site and microbial loading for the years studied. Furthermore, whilst many of the barley associated micro-organisms were able to secrete brewing related enzymes, the activities of these were too low to have any significant effect during mashing.