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Določanje pristnosti hmelja (Humulus lupulus L.) in analiza aromatičnih sestavin hmelja v pivu
Ocvirk, Miha (Author), Košir, Iztok Jože (Mentor) More about this mentor... This link opens in a new window, Poklar Ulrih, Nataša (Co-mentor)

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Abstract
Namen raziskave je bil določiti botanično pristnost hmelja (Humulus lupulus L.). Z analizo vsebnosti in sestave eteričnega olja in vsebnosti in razmerij alfa- in beta-kislin, ki so genetsko pogojena smo s pomočjo multivariantne statistike med sabo uspešno ločili pet najpogosteje gojenih sort v Sloveniji. Geografsko poreklo smo določali na 77 vzorcih hmelja, zbranih iz vseh svetovno najpomembnejših področij pridelave. Izmerjena razmerja stabilnih izotopov smo uporabili kot prstni odtis posamezne geografske regije pridelovalke hmelja. Z veliko zanesljivostjo smo iz vrednosti δ15N in δ34S določili klasifikacijo vzorcev glede na njihovo geografsko poreklo, medtem ko smo z vrednostmi δ13C uspeli nakazati razlikovanje slovenskih sort glede na botanično pristnost. Grupiranje piv na primerne in tiste, ki imajo v aromi manjša odstopanja smo izvedli na podlagi rezultatov analiz hlapnega profila piva in vsebnosti višjih alkoholov in estrov v kombinaciji s kemometrijo. Iz rezultatov sklepamo, da v pivovarskem procesu ne prihaja do konstantne, ponavljajoče napake, saj so bili vzorci z odstopanji v grafu narejenem z metodo glavnih osi raztreseni okrog primernih in niso tvorili samostojne skupine. Najvišji izkoristek izomerizacije (19 %) smo dosegli po 100 minutah kuhanja hmelja v pivini. Daljši čas kuhanja povzroči razpad izo-alfa-kislin. S časom se v vreli pivini koncentracije komponent eteričnega olja močno znižujejo, tudi do vrednosti, ki so pod mejo zaznavnosti. Z diferencialno dinamično kalorimetrijo zaznani fazni prehodi med segrevanjem in ohlajanjem hmeljnih ekstraktov, čeprav so ti sestavljeni iz približno 70 % alfa- in beta-kislin, niso posledica reakcije izomerizacije alfa-kislin.

Language:Slovenian
Keywords:hmelj, Humulus lupulus L., hmeljni ekstrakt, alfa-kisline, eterično olje, pivo, hmeljenje, aroma, avtentičnost, geografsko poreklo, botanična pristnost, izotopska razmerja, kemometrija
Work type:Dissertation (m)
Tipology:2.08 - Doctoral Dissertation
Organization:BF - Biotechnical Faculty
Year:2018
Publisher:[M. Ocvirk]
UDC:633.791:663.4:543.2/.9
COBISS.SI-ID:4917112 Link is opened in a new window
Views:496
Downloads:348
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Secondary language

Language:English
Title:Determination of hop (Humulus lupulus L.) authenticity and analysis of hop aroma compounds in beer
Abstract:
The aim of this study was to determine the botanical origin of hops (Humulus lupulus L.), from the results of analysis of the amount and contents of essential oil and contents of alpha- and beta-acids, which are genetically influenced. With the use of multivariant statistics, we have successfully distinguish between the five most common cultivars grown in Slovenia. For the determination of geographical origin, we have collected 77 samples of hop cones which are representative of the major hop-growing regions of the World. Isotopic ratios can act as fingerprints for different growing regions from around the world and we observe clustering of hop samples based on significant differences between growing regions based on δ15N and δ34S values. The δ13C values which are the least discriminative in determination of geographical origin, proved to be the most discriminative in determination of botanical origin of four Slovenian varieties. We made a clustering of beer samples on appropriate ones and ones with some minor deviations, based on the results of analysis of aroma profile and contents of higher alcohols and esters in combination with chemometrics. Our results show that these deviations in beer aroma are not a consequence of a permanent repeatable error in the brewing process, because the samples with deviations are not forming their own unique group, but are scattered around appropriate ones. The optimal time of hopping with intent to achieve high bitterness is no longer, than 100 min. Cooking longer leads to degradations of iso-alpha-acids. During wort boiling, great reductions of hop essential oil components are noticed, even to the bellow detection limit. We have shown that, even though hop extracts consist of around 70 % of alpha- and beta-acids, isomerization process of alpha-acids are not responsible for the observed thermal transitions.

Keywords:hop, Humulus lupulus L., hop extract, alpha-acids, essential oil, beer, hopping, aroma, authenticity, geographical origin, botanical origin, stable isotope ratio, chemometrics

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