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Publication Title | Solid-phase microextraction of hop volatiles Potential use for determination and verification of hop varieties

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Journal of Chromatography A, 918 (2001) 159–167

Solid-phase microextraction of hop volatiles Potential use for determination and verification of hop varieties

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Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1111 Ljubljana, Slovenia

Received 11 October 2000; received in revised form 20 February 2001; accepted 27 February 2001

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Institute of Hop Research and Brewing Zalec, Zalskega tabora 2, SI-3310 Zalec, Slovenia

Miroslav Kovacˇevicˇa ,*, Milica Kacˇa,b

www.elsevier.com / locate / chroma

Abstract

The composition of hop essential oil is an important tool for evaluation of hop quality. As each hop variety has a typical essential oil pattern (fingerprint), hop oil analyses can be used to distinguish between hop varieties. The headspace solid-phase microextraction (SPME) method as described in this contribution is a simple sample preparation technique and represents an alternative procedure for essential oil fingerprint determination. Different SPME parameters (extraction temperature, extraction time and sample mass) were studied and the results were compared with those obtained by the routine distillation method. It is shown that SPME results can be used for determination and verification of varieties grown in Slovenia by means of principal components analysis.  2001 Elsevier Science B.V. All rights reserved.

Keywords: Hop; Essential oils; Headspace analysis; Prinicple components analysis; Humulus lupulus

1. Introduction

Hops, cones of the hop plant (Humulus lupulus L.), are used in brewing to add bitterness and aroma to beer. The quality of the final product — beer — depends on the hop variety used in the process. Those breweries that still use traditionally aromatic hops, tend to buy hops of known variety and origin. As each hop variety has a typical essential oil pattern

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Presented at the Sixth International Symposium on New Achievements in Chromatography, Plitvice Lakes, 11–13, Oc- tober, 2000.

*Corresponding author. Tel.: 386-3-71-21-600 or 386-3- 71-21-608; fax: 386-3-71-21-620.

E-mail address: miroslav.kovacevic@guest.arnes.si (M. Kovacˇevicˇ).

(the so-called fingerprint of the variety), hop oil analyses are used for identification of hop varieties and determination of aroma properties [1 – 10].

Dry hops contains 0.5 – 2% of essential oil. It contains mainly terpene hydrocarbons and their oxidation products. About 400 peaks can be regis- tered in capillary GC chromatograms and more than 200 components have been identified. The most important constituents are the monoterpene myrcene and the sesquiterpenes -humulene and - caryophyllene, which together represent about 80– 90% of the total [11]. The routine method for hop essential oil analysis is based on oil isolation by steam distillation followed by gas chromatographic separation [12]. This requires a relatively large amount of sample (50–100 g) and is a time consum- ing procedure (3–4 h of distillation). The essential

0021-9673/01/$ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)00719-1

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