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Publication Title | Occurence of glycosidically bound flavour

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Original File Name Searched: Occurence_of_glycosidically_bound_flavour_compounds_in_hops__hop_products_and_beer_-_H._Kollmannsberger__M._Biendl__S._Nitz_-_Monatsschrift_Brauwissenschaft_2006.pdf | Google It | Yahoo | Bing



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83 May / June 2006

© 2007 Fachverlag Hans Carl GmbH

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Kopieren, Vervielfältigung und Verbreitung nur mit Genehmigung des Verlages.

H. Kollmannsberger, M. Biendl and S. Nitz

Occurence of glycosidically bound flavour

compounds in hops, hop products and beer

Glycosidically bound flavour compounds of hops are considered to contribute to the hop flavour in beer. Therefore, diffe- rent hop varieties and hop products were analyzed for their glycoside content. During extraction with supercritical CO2 almost all of the hop glycosides remain in spent hops. After ethanol extraction, glycosides could be detected in both the etha- nol tannin extract and the ethanol pure resin extract. In all examined varieties an enrichment of the sensorially important glycosides of monoterpene alcohols (e.g. linalool) and nor-carotenoids could be observed in the ethanol pure resin extracts. Some of these glycosides could be detected in hopped beer, where they could act as precursors for the organoleptically acti- ve linalool. This could be confirmed by a rise in free linalool in a stored beer brewed with a re-extracted ethanol pure resin extract containing linalyl glycoside, compared to a beer brewed with a glycoside-free hop preparation. The strongly flavour- active ß-damascenone could also be liberated from hop glycosides, but hops seem not to be the only source for this ketone.

Descriptors: Humulus lupulus, hops, glycosides, aglycones, pure resin extract, glycosidically bound flavour compounds

1 Introduction

Glycosides are odourless compounds, containing a sugar-moiety (usually ß-D-glucose) and a non-sugar-moiety (= aglycone). Nu- merous glycosides of aliphatic alcohols, phenols, terpene alcohols and nor-carotenoids have been recently identified in hops (1-4). From these glycosides, odoriferous aglycones like ß-damascenone or linalool could be liberated by thermal or enzymatic cleavage of their glycosides (see Fig. 1).

The orthonasal odour threshold of ß-damascenone in water is 4 ng/L (5). The odour threshold of the natural isomer (R)-linalool in hops was determined to be 0,14 μg/L in water (5) and 2,2 μg/L in beer (6). Because of these low threshold values, ß-damascenone and linalool show the highest calculated odour activity values in pilsner-type beers (5) along with typical fermentation-derived compounds like ethanol and some ethyl esters.

Linalool was identified as one of the most potent flavour com- pounds in fresh and dried hops (7), strongly contributing to the floral flavour note of hopped beer (5, 8, 9). As its concentration is considered to be useful to predict flavour intensity of hopped beers (10), linalool can be regarded as a quality indicator for hopped beer (6). A >95% decrease of the linalool concentration was observed during wort boiling (10, 11). During storage, lina- lool rapidly disappears from beer brewed with hop oil (12) and carbon dioxide extract (13). Linalool also disappears rapidly in the first 2 of 8 weeks storage in a beer spiked with pure linalool (14). In contrast to these findings, an increase in linalool during fermentation and aging was observed in beer brewed with hop pellets (10, 15, 16). Liberation of linalool from glycosides was considered to be responsible for this increase (10, 15).

Authors: Hubert Kollmannsberger, Lehrstuhl für Chemisch-Techni- sche Analyse und Chemische Lebensmitteltechnologie, Technische Universität München, D-85350 Freising-Weihenstephan, Germany, e-mail: kollma@wzw.tum.de;

Dr. Martin Biendl, Hopsteiner - Hallertauer Hopfenveredelungs- gesellschaft m.b.H., D-84048 Mainburg, Germany, e-mail: martin. biendl@hhv.net;

Prof. Dr. Siegfried Nitz, Lehrstuhl für Chemisch-Technische Analyse und Chemische Lebensmitteltechnologie, Technische Universität Mün- chen, D-85350 Freising-Weihenstephan, Germany e-mail: nitz@wzw. tum.de

Tables and Figures see Appendix

The concentration of ß-damascenone increases during and after wort boiling (11) and during artificial aging of beers (17). A high ß-damascenone content seems to be important to the flavour of aged beer (18). As high yields of ß-damascenone are obtained at lower pH values and after addition of ß-glucosidase to the fresh beer, the increase in ß-damascenone was explained partially by acid hydrolysis of glycosides (17, 18).

The aim of this study was to investigate different hop varieties and hop products for their composition of glycosides and to support the assumption that these glycosides can also be found in fres- hly brewed beer and give rise to hop-glycoside-derived flavour compounds in beer.

2 Material and methods

Dried hops (Czech Saazer CSA, Hallertauer Tradition HHT, Haller- tauer Mittelfrüh HHA, Hallertauer Hersbrucker HHE, Hallertauer Magnum HHM), hop pellets (Type 90), ethanol pure resin extract, ethanol tannin extract, carbon dioxide extract, spent solids (each of Hallertauer Perle HPE), ethanol pure resin and tannin extracts (of Hallertauer Perle PE, Hallertauer Tradition HT and Spalter Select SE) were obtained from HHV, D-84048 Mainburg. The hemicellulase preparation Rapidase was a gift of B. Heimann, DSM Food specialities, D-44319 Dortmund.

A detailed description of the isolation of glycosides and analysis of liberated aglycones in hops was published recently (3). In short, glycosides were extracted with hot water or methanol-water (4:1), after addition of the internal standard phenyl-ß-D-glucoside. The extracts were decanted, treated with Polyclar (PVPP), filtrated and concentrated to dryness. Volatile compounds were removed by extraction with pentane-dichloromethane (2:1). After frac- tionation on Amberlite XAD-2 resin, the methanol eluate was concentrated to dryness and the glycosidic fraction was incubated with ß-glucosidase or the hemicellulase preparation Rapidase (3) in a phosphate-citrate buffer (pH 5) at 40 °C for 1 or 3 days. Liberated aglycones were extracted with ether and investigated by gas chromatography - mass spectrometry (GC-MS). Measured peak areas are corrected by considering the area of the internal standard. Values are given for 500 ml beer, 25 g dried hops, 100 g hop pellets, 75 g spent hops, 25 g carbon dioxide extract, 25 g ethanol pure resin extract, 25 g ethanol tannin extract.

Additionally, three different pilsner beers have been brewed in a pilot brewery. Apart of the hop products, all ingredients and

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