The hop plant is seasonal, but beer production continues throughout the whole year. The quality of hops begins to decrease immediately after harvesting; therefore, maintaining the highest possible ...quality is important. A good indicator of hop freshness is the hop storage index (HSI). In this study, three different varieties of hops with five different HSI values, from 0.3 to 0.7, were used for brewing with the dry hopping technique. The main goal was to evaluate the impact of the HSI value on beer quality in terms of hop aroma and bitterness. Alpha acids, iso-alpha acids, humulinones, bitterness units and hop aroma compounds were chemically analysed. Sensorial analysis was also conducted on all samples. Decreases in the intensity and quality of hop aroma were detected with increasing HSI. The quality of bitterness was also reduced. High HSI also led to undesirable gushing. Beers brewed with hops with HSI values greater than 0.4 had deviations in aroma and bitterness when compared with beers brewed with fresh hops.
Hops are an indispensable ingredient in beer, and the differences in their chemical composition impart the various tastes and aromas associated with different beers. However, during storage, hops ...undergo changes in their chemical composition. Here, the changes in aroma and bitterness of kettle-hopped beers were evaluated in an experiment conducted on three different hop varieties (Aurora, Celeia and Styrian Wolf) with five different hop storage index (HSI) values (0.3-0.7). Hops were added to boiling wort for 5, 45 and 90 min. Alpha-acids, iso-alpha-acids, humulinones, bitterness units and hop aroma compounds in the samples were chemically analysed. All samples also underwent sensorial analysis. The old hops were not problematic in terms of bitterness or early hopping time. However, later additions of old hops reduced the quality and intensity of the hop aroma. The limit value for use without negative consequences for kettle hopping was set at HSI 0.5 for Aurora and Celeia and HSI 0.6 for Styrian Wolf.
Hop essential oil, in addition to alpha-acids, is one of the most valuable parameters for brewers, since it is responsible for beer aroma. The hop oil content and hop oil chemical composition deliver ...various aromas to beer. During storage, the hop chemical composition undergoes many physical and chemical changes that impact its quality. The main purpose of our study was to evaluate the changes occurring in hop oil content and its chemical composition during two years of storage under four different conditions (anaerobic, aerobic, cold room (4 °C), and room temperature) in the form of cones and pellets, supplied by local suppliers in Slovenia. Hop oil content and composition were determined by steam distillation and GC-FID. The greatest decrease in hop essential oil content occurred when the hops were stored under aerobic conditions and at room temperature. Monitoring of eight hop oil compounds under various conditions revealed different behaviors of the changes. The best storage conditions were anaerobic at low temperatures. Oxygen resistance was lower for pellets than for hop cones, whereas high temperature was more devastating for hop cones. In addition to the storage conditions, the hop variety and form were important factors regulating the extent of changes in hop oil content and chemical composition.
The stability of alpha-acids, beta-acids and hop storage index (HSI) values under different conditions (aerobic/anaerobic, 4 °C/room temperature) was studied in a two-year trial. Six different ...varieties (Celeia, Aurora, Bobek, Styrian Gold, Savinjski Golding and Styrian Wolf) were used in the form of cones and pellets. Alpha- and beta-acids were determined by HPLC and HSI by spectrophotometry. Anaerobic conditions at 4 °C were best for alpha-acids, beta-acids and HSI values; however, 10-35% of the alpha-acids were still lost after two years. The decline was greater (63-99%) under aerobic conditions and at room temperature. Alpha-/beta-acid ratios increased in hop cones and decreased in hop pellets, whereas HSI values increased in all storage conditions. Overall, the performance was better for pellets than for hop cones. Storage conditions, storage form and hop variety had significant effects on the stability of hop resins.
In a laboratory experiment, we studied the insecticidal effects of invasive alien plants on the rice weevil. The research was carried out in two parts. In the first part, we studied the insecticidal ...properties of seven different plant species, namely, Bohemian knotweed (Fallopia × bohemica), Japanese knotweed (Fallopia japonica), false indigo-bush (Amorpha fruticosa), tree of heaven (Ailanthus altissima), staghorn sumac (Rhus typhina), Canada goldenrod (Solidago canadensis), and giant goldenrod (Solidago gigantea). Mixtures of powders and wheat were prepared in two different concentrations, namely, 2.5 w% and 1.25 w%. The experiment was performed at temperatures 20 °C and 25 °C and at two humidity levels, 55% R.h. and 75% R.h. Very low mortality (below 8%) was found when using combinations with the higher relative humidity. No significant differences were observed between the effects of these concentrations. In the second part of the experiment, Norway spruce wood ash and diatomaceous earth (product SilicoSec®) were added to the powder obtained by milling leaves of four different invasive plant species (Canada goldenrod, staghorn sumac, tree of heaven, false indigo). In the independent application, wheat was added to the powder at a concentration 2.5 w%. In the treatments that involved mixtures of powder and wood ash/diatomaceous earth, we applied 1.25 w% plant powder and 1.25 w% wood ash or 1.25 w% plant powder and 450 ppm of a SilicoSec® preparation. The positive control was carried out as two separate treatments with 2.5 w% wood ash of Norway spruce and 900 ppm of the SilicoSec® product, while untreated wheat represented the negative control. The experiment was performed at two temperatures (20 °C and 25 °C) and two R.h. values (55 and 75% R.h.). The mortality of beetles was recorded on the 7th, 14th, and 21st day after the start of the experiment. Higher mortality rates of rice weevil adults were found at the higher relative humidity, and an important factor of mortality was also the day of exposure, as a higher mortality was found when the exposure of individuals to the tested substances was for a longer time period. After 21 days at 25 °C and 55% R.h., the combinations in which the lower concentration of Norway spruce wood ash was added to the powder of invasive alien plants achieved more than 90% mortality of beetles. By adding the plant powder of invasive alien plants to wood ash, we achieved a greater insecticidal efficacy of invasive plants and lower concentrations of wood ash. Nevertheless, the results of our research do not indicate any great usefulness of the plant powder of invasive plants in suppressing the rice weevil. Additional studies should primarily focus on the insecticidal efficacy of powder from the genus Solidago, which in our study, displayed the greatest insecticidal potential among the tested invasive plants.
Hmelj (Humulus lupulus L.) je dvodomna trajnica, ki obrodi enkrat letno, njegova uporaba, ki je omejena predvsem na pivovarsko industrijo, pa poteka skozi celotno leto. Zaradi navedenega je uporaba ...svežega hmelja skozi leto praktično nemogoča, zato je izjemnega pomena ohraniti kakovost hmelja na kar se da visoki ravni. V sklopu doktorske disertacije smo ovrednotili vpliv različnih pogojev skladiščenja (anaerobno/aerobno, 4 °C/sobna T) na vsebnost alfa-kislin, beta-kislin, eteričnega olja, komponent eteričnega olja in na vrednost HSI-ja, v šestih različnih sortah (Celeia, Aurora, Bobek, Styrian Gold, Savinjski golding in Styrian Wolf), v obliki storžkov in peletov. Navedene parametre smo spremljali dve leti, s čimer smo objavili prve tako obširne in dolgo trajajoče študije o stabilnosti hmelja pod različnimi pogoji na svetu. Prav tako smo s poskusom varjenja piva preučili vpliv postaranega hmelja na kakovost in intenzivnost arome ter grenčice piva in tudi tukaj objavili eno prvih raziskav na področju vpliva postaranega hmelja na kakovost piva.Vsebnost alfa- in beta-kislin, vsebnost eteričnega olja, sestavo eteričnega olja, grenčico in HSI smo analizirali po že vpeljanih metodah, za analizo hmeljne arome piva ter vsebnosti humulinonov in izo-alfa-kislin pa smo vpeljali nove analizne metode. Validacija navedenih metod je predstavljena v sklopu doktorske disertacije.Pri preučevanju vplivov skladiščenja smo ugotovili, da s pogoji skladiščenja vplivamo na kakovost hmelja, ter da s primernim skladiščenjem upočasnimo procese staranja. Za najprimernejše so se izkazali anaerobni pogoji pri nizkih temperaturah (4 °C), za najmanj primerne pa aerobni pogoji pri sobni temperaturi. Pri beta-kislinah in HSI-ju je na njuno vsebnost vplivala tudi oblika hmelja, peleti so se izkazali za obstojnejše. Odstotek vsebnosti n-humulona v alfa-kislinah se skozi skladiščenje ni spreminjal, se je pa spreminjala vsebnost n-lupulona v beta-kislinah v peletih. Razmerje med alfa- in beta-kislinami je pri neoptimalnih pogojih skladiščenja v storžkih naraščalo, v peletih pa se je nižalo. HSI je z naraščanjem časa eksperimenta naraščal, s čimer smo potrdili naraščanje oksidacijskih produktov alfa- in beta-kislin.Naraščanje oksidacijskih produktov se je odražalo tudi v pivu; višji kot je bil HSI hmelja uporabljenega za pripravo piva, nižja je bila kakovost piva. Pri hladno hmeljenem pivu se je, z naraščanjem HSI-ja pri hmelju uporabljenemu za hmeljenje, zniževala intenzivnost in kakovost arome, prav tako vsebnost komponent eteričnega olja. Zniževala se je tudi kakovost grenčice, pri uporabi hmelja s HSI-jem višjim od 0,6 pa smo zaznali prekomerno penjenje. Pri tradicionalnem postopku hmeljenja postaran hmelj manj vpliva na samo kakovost piva, sploh kadar imamo dolg čas vrenja hmelja. Se pa predvsem na aromi zazna prisotnost oksidacijskih produktov, ki v pivo vnesejo vonj po postaranem in oksigeniranem. Na podlagi rezultatov smo tako postavili mejo za kakovosten hmelj, ki ne vpliva negativno na aromo in grenčico piva. Pri hladnem hmeljenju je ta meja 0,4 pri Aurori in Celei ter 0,5 pri Styrian Wolfu, pri tradicionalnem hmeljenju pa je ta meja 0,5.Doktorsko delo tako predstavlja obsežen vpogled v spremembe kemijske sestave pri različnih načinih skladiščenja in spremembe na aromi in grenčici piva pripravljenega s postaranim hmeljem.
Hop cones (Humulus lupulus L.), or more specifically the lupulin glands, hold the reason for the specific, pleasant aroma of hops - its essential oil. The hops themselves, or the extracted oil, are ...used almost exclusively in beer production. The essential oil is an indispensable part of beer and is responsible for its characteristic aroma. However, hop essential oil (HEO) also has a broad range of positive effects on human health and is a potential natural pesticide that has no harmful impacts on humans. This review summarizes basic information about HEO, including its chemical composition and methods for extraction and analysis, while also providing a comprehensive overview of the contribution to beer aroma, health, and insecticide applications for this versatile essential oil.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•Extracts and essential oils of four different hops varieties from the territory of Slovenia were obtained.•Monoterpnenes and sesquiterpene hydrocarbons were dominant components in isolated essential ...oils.•All obtained extracts and oils were characterized by strong antimicrobial activity.•All extracts and essential oils were selective towards normal cells.
Hydrophilic, lipophilic extracts and essential oil of four hops varieties from Slovenia were examined in this study. Lipophilic extracts were obtained by supercritical extraction (SFE), while for hydrophilic extracts ultrasound and microwave extraction were employed. Essential oils were isolated by the hydrodistillation process. The lipophilic composition of essential oils and lipophilic extracts was determined by GC–MS analysis. Monoterpenes and sesquiterpene hydrocarbons were the most abundant class of compounds in oils (62.27–79.65 %), with myrcene being the most abundant constituent. Limonene and trans-caryophyllene were two terpenes determined in all essential oils while only trans-caryophyllene was detected in SFE samples. Antioxidant, antimicrobial, and cytotoxic activity, determined by applying in vitro assays, was more influenced by extraction technique than by varieties. Molecular docking was carried out to gain insight into the potential cancer protein targets BCL-2 and MMP9, whereby humulene epoxide II displayed good binding configuration within the cavities of the two proteins.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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