Characterization of the Migration of Hop Volatiles into Different Crown

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Characterization of the Migration of Hop Volatiles into Different Crown Cork Liner Polymers and Can Coatings Philip Ché Wietstock, Richard Glattfelder, Leif-Alexander Garbe, and Frank-Jürgen Methner J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b00031 • Publication Date (Web): 20 Mar 2016 Downloaded from http://pubs.acs.org on March 28, 2016

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Journal of Agricultural and Food Chemistry

Revised manuscript ID jf-2016-00031j 1.

Title: Characterization of the Migration of Hop Volatiles into Different Crown Cork Liner Polymers and Can Coatings.

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Corresponding author: Dipl.-Ing. Philip C. Wietstock, Technische Universität Berlin, Department of Food Technology and Food Chemistry, Chair of Brewing Science, Seestrasse 13, 13353 Berlin, Germany, [email protected].

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–

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Coauthors list: B.Sc. Richard Glattfelder, Technische Universität Berlin, Department of Food Technology and Food Chemistry, Chair of Brewing Science, Seestrasse 13, 13353 Berlin, Germany, [email protected]

Prof. Dr. Leif-Alexander Garbe, Fachbereich Agrarwirtschaft und Lebensmittelwissenschaften, Hochschule Neubrandenburg, Brodaer Str. 2 D, 17033, Neubrandenburg, Germany, [email protected]

Prof. Dr.-Ing. Frank Jürgen Methner, Technische Universität Berlin, Department of Food Technology and Food Chemistry, Chair of Brewing Science, Seestrasse 13, 13353 Berlin, Germany, [email protected].

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Significance: Scalping of volatile hop aroma compounds by crown cork liner polymers and by beer can coatings was characterized in buffered model systems and in beer using solvent assisted flavor evaporation (SAFE)GC/MS. The work provides new information regarding the degree of scalping and the rate by which scalping of hop volatiles occurs. Migration of certain hop aroma compounds was shown to be strongly dependent on the polaritiy of the hop volatile measured and to a lesser extent on the closure or packaging used. A short exposure time to the packaging material already yielded a high migration of certain compounds which alters the original balance of the flavor compounds and thus results in flavor loss and flavor deterioration. This is the first time that the scalping of hop volatiles in beer systems was described by Fick’s second law of diffusion. Outcomes from this study point to the importance of scalping in beer systems and will therefore help improving closures and to ‘rethink’ experimental designs when assessing hop aroma.

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Characterization of the Migration of Hop Volatiles into Different Crown Cork Liner Polymers and Can Coatings. Philip C. Wietstock1*, Richard Glattfelder1, Leif-Alexander Garbe2, Frank-Jürgen Methner1

1

Technische Universität Berlin, Department of Food Technology and Food Chemistry, Chair

of Brewing Science, Seestrasse 13, 13353 Berlin, Germany. 2

Hochschule Neubrandenburg, Department of Agriculture and Food Sciences, Brodaer Str. 2,

17033 Neubrandenburg, Germany.

* Corresponding author: Philip C. Wietstock, Seestr. 13, D-13353 Berlin, Phone: +4930-31427505, Fax: +493031427503, Email: [email protected]

2 ACS Paragon Plus Environment

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ABSTRACT

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Absorption of hop volatiles by crown cork liner polymers and can coatings was investigated

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in beer during storage. All hop volatiles measured were prone to migrate into the closures and

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the absorption kinetic was demonstrated to fit well Fick’s 2nd law of diffusion for a plane

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sheet. The extent and rate of diffusion was significantly dissimilar and was greatly dependent

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on the nature of the volatile. Diffusion coefficients in cm2/day ranged from 1.32×e-5

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(limonene) to 0.26×e-5 (α-humulene). The maximum amounts absorbed into the material at

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equilibrium were in the order limonene > α-humulene > t-caryophyllene > myrcene >>

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linalool > α-terpineol > geraniol. Applying low-density polyethylene (LDPE) liners with

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oxygen scavenging functionality, oxygen barrier liners made up from high-density

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polyethylene (HDPE), or liner polymers from a different manufacturer had no significant

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effect on the composition of hop volatiles in beers after prolonged storage of 55 days;

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however, significantly higher amounts of myrcene and limonene were found in the oxygen

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barrier-type crown cork while all other closures behaved similarly. Can coatings were

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demonstrated to absorb hop volatiles in a similar pattern as crown corks but to a lesser extent.

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Consequently, significantly higher percentages of myrcene were found in the beers.

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Keywords: Scalping, crown cork liner polymers, hop volatiles, can coatings, hop aroma.



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INTRODUCTION

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Flavor scalping is referred to as the loss of aroma substances in food containers due to

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migration into the packaging materials. This process can occur in both directions and product

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volatiles can either migrate into the packaging or or substances from the packaging material

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can migrate into the product as e.g. bisphenols do in canned beers1,2, or chloranisoles3,4 in

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wine . Most knowledge about flavor sorption today originates from the food industry, where

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aroma migration of volatiles from juices or other citrus fruit containing beverages and

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foodstuffs were studied.5,6 But also wine closures were studied intensively and were shown to

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have a significant impact on the quality of the product.7,8 The sorption kinetics for these

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reactions are from great interest because they allow deductions for the rate at which sorption

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occurs, give indication of over-all rate of uptake, and open of a large field of modeling

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complex applications.

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A wide range of plastics are nowadays used for food packaging including homo-polymers or

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co-polymers from low to high density polyethylene. Preferably polyethylene (PE) and

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polypropylenes (PP) are used if plastics are in contact with foodstuffs because of their good

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chemical resistance, inertness to most foods, good barrier properties to water, and

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thermostability.9 To minimize oxygen permeation, thus increasing shelf-life and organoleptic

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properties of the product, additional scavenging or barrier material may be introduced into the

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compound polymer. The extent of flavor absorption is influenced by the chemical

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composition of the polymer, the molecular properties of the aroma compounds and external

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factors.10-12

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Today more than 400 single hop oil components are identified in hops and discovery of new

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compounds is still ongoing.13 The most abundant fractions are the hydrocarbons which are

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constituted of small isoprene units forming the monoterpenes or sesquiterpenes. In fresh hops,

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myrcene makes up to 69 %14 of the total hop oil composition and it has been reported by 4 ACS Paragon Plus Environment

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Schieberle and Steinhaus15 to be one of the most potent hop odorants. The terpenoids or

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terpene alcohols are oxygenated terpenes which feature a much higher solubility in beer.16

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Terpenoids may either be formed via oxidation of their corresponding terpenes17, are

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enzymatically converted18,19 or released.20 Major components of the terpenoid fraction are

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linalool, geraniol, and α-terpineol, all of which are believed to be an important contributor for

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a floral hop aroma.16,21 The group of the oxygenated sesquiterpenes are claimed to be the

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source of the traditional spicy and herbal ‘noble-hop’ or ‘kettle-hop’ aroma.22 Substances

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frequently associated with these aromas are oxidation products of α-humulene and t-

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caryophyllene.23 Furthermore, recent research focused on sulfur-containing compounds in hop

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oils which are present at much lower concentrations than the other fractions but concomitantly

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have very low flavor thresholds.16

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Hop volatiles in beer usually are rather low in concentration which makes it particularly

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difficult to quantitate those substances. The volatile nature of essential oils enables relatively

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simple enrichment and separation using steam distillation, as described in ASBC24 and EBC25

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manuals or the simultaneous extraction distillation (SED) described by Likens and

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Nickerson.26 Solid-phase micro-extraction (SPME) coupled with a suitable measuring devices

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and detectors such mass spectrometers (MS) are used nowadays by many laboratories.27-29

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Purge-and-trap30, head-space trap31, or thermal desorption32 are further alternatives.

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To achieve a beer rich in hop aroma, hops are added later on during whirlpool rest or during

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late boil, in the cold part of the brewery mostly during secondary fermentation or maturation,

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or even in the form of distinct hop oil rich products downstream. Once the beer is bottled, the

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hop aroma changes rapidly during storage and only little is known about the origin of these

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flavor alterations. While storage conditions such as e.g. temperature certainly have a strong

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impact on the rate and type of flavor changes in the product, closures also play a key role

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because they not only determine oxygen exposure of the product but moreover scalping of 5 ACS Paragon Plus Environment


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flavor compounds as Peacock and Deinzer11 indicated. However, also racemization33, acid-

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catalyzed isomerization34-36 or acid hydrolysis11 may explain the transitory nature of hop

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aroma in bottled beer. Only little work on aroma scalping and sorption kinetics in beer

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systems is available thus far. Peacock and Deinzer11 studied scalping of crown liners

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containing polyvinylchloride (PVC) and found particularly high absorptions of hydrocarbons

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along with varying extents of other beer constituents, not only those derived from hops. PVC

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features great flexibility when used in combination with plasticizers such as phthalates but

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because of safety concerns is today mainly used in nonfood packaging applications.37 In 2013,

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Van Opstaele et al.38 reported a decrease of hop volatiles in beer and ascribed it partly to

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scalping into crown cork liners but also to adsorption to haze formed during ageing. The

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composition and material of the crown corks used in this study were not mentioned, though.

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Information as related to absorption of aroma-active beer constituents by different ‘modern’

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PE beer bottle closures and can coatings as well as the concurrent uptake-rate of hop volatiles

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into crown cork liners is thus far lacking in published literature. The goal of this study was

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consequently to elucidate these issues. Hence, for the first time, time-dependent uptake rates

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and diffusion coefficients for a hop volatile-LDPE liner system in beer during storage were

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deduced using Fick’s 2nd law of diffusion. Additionally, the effects of using liners from

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different manufacturers, crown corks with oxygen scavenging or oxygen barrier functionality,

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or storing beers in cans on hop volatile concentration in PE liner polymers, can linings, and

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corresponding beers after prolonged storage were analyzed. Solvent-assisted flavor

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evaporation (SAFE) coupled with GC/MS was used to quantitate hop volatiles in beers or

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packaging because this procedure ensures a gentle sample treatment and an appropriate

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detection of the target analytes.39 This work provides novel information regarding the extent

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of scalping of hop volatiles in beer systems and the rate by which scalping occurs. Outcomes

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from this study therefore allow deductions on the loss of certain volatiles to the closures or 6 ACS Paragon Plus Environment

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packaging tested and therefore point to a disturbance of the original balance between beer

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aroma compounds eventually altering the beer’s aroma perception.

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MATERIALS AND METHODS

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Chemicals.

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Acetic acid, geraniol, α-humulene, limonene, linalool, myrcene, 4-octanol, and trans-

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caryophyllene were obtained from Sigma-Aldrich (Steinheim, Germany). Ethanol, sodium

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acetate, sodium carbonate, and sodium sulphate were ordered from Merck (Darmstadt,

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Germany). Diethyl ether was obtained from VWR (Leuven, Belgium). All chemicals were of

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analytical grade or highest possible purity.

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Beer analysis according to MEBAK.40

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The beer analyses carried out were as follows: original extract (2.9.6.3); alcohol (2.9.6.3); pH-

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value (2.13); color (2.12.2).

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Quantitation of hop volatiles in beer.

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Hop volatiles were quantitated following a modified procedure described by Engel, Bahr and

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Schieberle.39 This procedure uses the solvent assisted flavor evaporation (SAFE) technique

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and GC combined with MS analysis. Beer samples were filtered (funnel and filter sheet) to

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remove CO2 and an aliquot of 100 mL was spiked with 4-octanol such that a 1 mL addition

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achieved a final concentration of 25 µg/L in the sample. The sample was subsequently

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extracted twice with 150 mL diethyl ether and placed into a SAFE-apparatus. After high

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vacuum distillation, the sample was washed twice with a 0.5 M Na2CO3 solution and

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bidistilled water, then dried over Na2SO4 for one hour, and concentrated to 5 mL using a

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vigreux column at a temperature of 46-48 °C. A sample (1 µL) of the concentrated distillate

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was introduced into the GC via a cold injection system (Gerstel GmbH & Co. KG, Mühlheim

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an der Ruhr, Germany) in 20:1 split mode to a GC 6890 (Agilent Technologies, Waldbronn,

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Germany) fitted with a capillary column (VF-5 MS, 60 m x 0.25 mm, 0.25 µm film, Varian, 8 ACS Paragon Plus Environment

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Darmstadt, Germany). The following temperature program was used for the GC oven: after 12

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min at 35 °C, the oven temperature was raised to 150 °C at a rate of 12 °C/min and then to

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250 °C at 30 °C/min where it was held for 5 min. The flow rate of helium carrier gas was 0.6

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mL/min. Mass spectra in the electron impact mode (MS/EI) were generated at 70 eV using an

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MSD 5973 (Agilent Technologies, Waldbronn, Germany) in selected ion monitoring (SIM)

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mode. The analytes’ retention times and m/z ratios are depicted in Table 1. A six-point

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external calibration (r2 > 0.99) was carried out to quantitate the target molecules. The

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method’s limit of quantitation (LOQ) was 1 µg/L for all analytes. The calculated

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concentrations in µg/L were divided by the volume of the initial sample to obtain the total

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amounts of analytes in the samples.

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Quantitation of hop volatiles in crown cork liner polymers and can linings.

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Crown corks with liners were removed from buffer solutions or beer bottles, washed three

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times with 12 mL of bidistilled water, and any liquid residues were carefully dried off with a

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tissue. Crown cork liner polymers were then extracted with 100 mL of diethylether over 24

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hours at room temperature and an amount of 4-octanol was added as an internal standard to

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achieve a final concentration of 25 µg/L in the sample. Beer cans were cut into small pieces

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and were subsequently washed with 800 mL of bidistilled water. The extraction procedure

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was then analogous to the crown liner extraction. The diethylether extracts from crown liner

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materials, beer cans, or water were then analyzed as described above. There is a possibility

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that analytes are removed by water during the washing step. The potential washing-off effect

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was therefore tested by adding 200 mL of water to already rinsed can material and shaking it

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for 5 min vigorously. The water was then separated from the can material and extracted twice

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with 150 mL diethylether prior to analyzing it as described above.

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Migration of hop volatiles into crown liner materials in buffered model solutions.

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A preliminary experiment was conducted to assess principal migration of hop volatiles in

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crown cork liner polymers. Low-density polyethylene crown corks were therefore incubated

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for 24 and 72 hours in 130 mL of buffered model solutions (acetate buffer, 0.01 M, pH 4.3,

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5 vol.-% EtOH) which was spiked with 130 µg of myrcene, limonene, linalool, α-terpineol,

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geraniol, t-caryophyllene, and α-humulene prior to adding the crown corks. The incubation

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flasks were filled with minimized headspace in order to minimize the diffusion of hop

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volatiles into the gaseous phase. The amount of volatiles in the liner polymer was then

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analyzed as described above.

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Aroma sorption kinetics during beer storage.

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30 L of a commercially available pilsner beer (original gravity: 11.84 % wt./wt.; alc.: 5.2 %

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v/v; bitter units: 28; carbon dioxide: 5.1 g/L; pH: 4.38, color: 6.38 °EBC; hop dosage solely

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CO2 extract at the beginning of wort boiling; all values were measured according to

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MEBAK40) low in hop aroma (all hop constituents < 5 µg/L as measured by SAFE-GC/MS)

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was spiked with a mixture of myrcene, limonene, linalool, α-terpineol, geraniol, t-

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caryophyllene, and α-humulene such that a final amount in the beer of 250 µg for each

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compound was achieved. All compounds were solved in 10 mL of ethanol prior to spiking

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directly into the keg. The keg remained open as short as possible during spiking to minimize

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oxygen uptake. The beer was mixed well and was immediately filled in 0.5 L standard brown

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glass bottles using a H4 filler (JS Maschinen GmbH, Nandlstadt, Germany). The bottles were

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pre-flushed three times with CO2 prior to filling and were directly sealed using low-density

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polyethylene (LDPE) pry-off crown corks. Oxygen levels in packaged beer after filling were

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< 50 µg/L as measured using a DIGOX 6.1 (Dr. Thiedig GmbH & Co KG, Berlin, Germany)

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apparatus. During storage at room temperature, the spiked beers’ amounts of hop volatiles 10 ACS Paragon Plus Environment

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were measured directly after filling, after 21 days, and after 55 days of storage, respectively.

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The crown cork liner polymers were analyzed after 0, 1, 3, 8, 21, and 55 days of storage. Each

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specified day, three bottles were taken out of the storage experiment and were analyzed

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separately. The aroma sorption kinetics were modeled additionally using eq. 1:

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Mt 8 = 1− 2 M∞ π

n =∞

1

∑ (2n + 1)

2

{

exp − D ( 2n + 1) 2 π 2 t / l 2

}

(1)

n =0

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where: Mt is the total amount of components absorbed by the sheet at time t, expressed as µg

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of aroma component, M∞ the equilibrium absorbed mass which is theoretically attained after

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infinite time, expressed as µg of aroma component, D is the diffusion coefficient, expressed

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as cm2/day, and l is the film thickness of the polymer, expressed as cm.

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Eq. 1 is derived from Fick’s 2nd law.41 The application of eq. 1 is based on the assumption of

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an instantaneous pressure change of sorbing compounds above a homogenous thin film made

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of a dense polymer which remains constant afterwards. For simplification, the crown liner

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material was assumed to be a plane sheet which does not swell and the polymer was

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considered to be initially free of sorbing compounds. Assuming the diffusion coefficient to be

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constant did not yield satisfactory results because clearly, the diffusion coefficient is

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concentration dependent and increases as the concentration of the migrating molecule

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increases. The concentration-dependent diffusion coefficients Dc were therefore deduced

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separately from observations of the time-dependent rate of uptake of the individual hop

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volatiles into the liner material. Final D values given represent then the mean of the variable

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diffusion coefficients averaged over the range of concentration. In the case of t-caryophyllene

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and α-humulene, the equilibrium sorption was not reached during the experiment and their

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mean diffusion coefficients could thus not be derived. Therefore, their diffusion coefficients

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were approximated by non-linear fitting of the experimental data to eq. 1. 11 ACS Paragon Plus Environment


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Characterization of aroma migration in different liner polymers.

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The same beer and sample preparation as in the previous trial was applied but in this trial four

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different pry-off crown cork liner materials were used: ‘standard’ LDPE liner from a

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manufacturer A, ‘standard’ LDPE liner from a manufacturer B, oxygen barrier high-density

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polyethylene (HDPE) liner, and oxygen scavenger LDPE liner with Na2SO3 as the reactant in

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the liner material. The bottles were stored for 55 days at room temperature and three crown

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corks or three bottles, respectively, were analyzed individually on their amounts of hop

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volatiles.

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Comparison of hop volatile migration into crown cork liner materials and can coatings.

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A highly-hopped ale-type beer (dry-hopped, 5.6 vol.-% EtOH) from Scotland was available in

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both 0.33 L cans and 0.33 L bottles (capped with pry-off LDPE crown cork liners with

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oxygen scavenging functionality). It was ensured that the beers were from the same

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maturation tank. Storage was then conducted in the dark at room temperature for 46 days and

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hop volatiles in beers and packaging materials were subsequently quantitated by SAFE-

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GC/MS from three individual samples.

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Data Analysis.

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Statistical analysis was performed using XLSTAT (Ver. 2014.5.03.), Addinsoft, USA. Data

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were analyzed using analysis of variance (ANOVA). Means were used to compare differences

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and Tukey’s honestly significant difference (HSD) test was applied to compare the mean

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values. The significance level for the ANOVA analyses was p < 0.05. Additionally, an

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unpaired Student’s t-test was used to compare sample means between beers filled in cans and

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filled in bottles at a confidence level of 95 %.


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RESULTS AND DISCUSSION

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A bottle or canned beer can be considered a system comprising gaseous and liquid phases.

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Directly after filling and sealing, the system is not in equilibrium and molecules strive from

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the liquid phase into the gaseous phase or backwards. The compounds’ distribution in both

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phases at equilibrium is defined by their distribution factor kL,G42 (eq. 2) and by the system’s

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conditions such as e.g. the temperature:

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k L ,G =

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where: kL,G is the (thermal) distribution factor between the liquid and the gaseous phase, cG is

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the molar concentration of a component in the gas phase, and cL is the molar concentration of

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a component in the liquid phase.

cG cL

(2)

230 231

If scalping occurs, e.g. in beer bottles, this system is disturbed because molecules migrate

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from the gaseous phase or headspace into the packaging material or crown cork liner material

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thus lowering the concentration in the gaseous phase. The over-all migration in the packaging

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is defined by a second partition coefficient kG,P between the product side; here, the gaseous

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phase or headspace, and the packaging’s polymer material at equilibrium (eq. 3).9

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kG ,P =

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where: kG,P is the partition coefficient between the headspace and the packaging polymer, cP is

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the concentration of a component in the packaging polymer, and cG is the concentration of a

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component in the gaseous phase or headspace.

cP cG

(3)

240 241

When migration into packaging polymers occurs, the component’s concentration in the

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gaseous phase is lowered and consequently, molecules strive again for equilibrium and diffuse

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from the liquid phase into the gaseous phase as defined by their kL,G value. If a component is 13 ACS Paragon Plus Environment


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volatile (kL,G > 1), the limiting factor for the over-all rate of a component sorbing into the

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packaging must therefore be kG,P because the headspace’s ‘reservoir’ is always ‘filled up’

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again; at least as long as the component is not completely exhausted in the liquid.

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However, it shouldn’t be neglected that the packaging material is not a closed system but is

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‘connected’ to the environment, and also permeation from the packaging into the environment

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may occur. Ultimately, aroma is lost and/or is altered continuously, not only because aromatic

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molecules migrate into the packaging material via the headspace but also because the

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equilibrium state is never reached when permeation occurs. Within this study’s scope, the

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determination of kG,P was not possible because the component’s kL,G values were not known

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and concentrations in the headspace were not measured. However, this information is still

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essential to understand and interpret this study’s results.

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Migration of hop volatiles from buffered model solutions into LDPE crown cork liner

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materials.

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In a first test series of this study, LDPE crown cork liners without any barrier or scavenging

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materials added to the liner polymer were screened on their tendency to scalp a selection of

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hop volatiles. Additional to investigating the liner materials’ scalping tendencies, it was tested

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if the 24 hour extraction procedure via diethylether was sufficient to extract the analytes from

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the liner material. As analytical markers, two monoterpenes (myrcene, limonene), two

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sesquiterpenes (α-humulene, t-caryophyllene), and three monoterpenoids (linalool, geraniol,

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and α-terpineol) commonly found in beer and hops were selected because they not only are

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odor-active constituents in beer but also represent different chemical characteristics, e.g.

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polarities.

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In individual trials, crown corks were incubated for 24 hours or 72 hours in ‘beer-like’

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buffered model solutions which were spiked with hop volatiles prior to adding the caps. A 24 14 ACS Paragon Plus Environment

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hour extraction with diethylether and subsequent SAFE-GC/MS analysis revealed that in

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terms of the hydrocarbon fraction 8.4 µg myrcene, 9.1 µg limonene, 7 µg t-caryophyllene,

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and 7.7 µg α-humulene were absorbed by the liner polymer. The migration of terpenoids was

272

lesser and only 2 µg of linalool, 1.6 µg of α-terpineol, and 2.6 µg of geraniol were found

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(Table 2). Incubating the crown corks for 72 hours at the same experimental conditions

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yielded a further extraction of maximum 4.5 % for the hydrocarbon fraction while the

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terpenoid fraction showed only very little changes (< 0.3 µg).

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A second diethylether extraction of the same crown cork liner materials for 24 hours in

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diethylether yielded very minor amounts of hydrocarbons (< 0.1 µg) while no further

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terpenoids were detected in the concentrated extracts. The extraction for 24 hours was

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therefore considered sufficient and was used for all the trials.

280 281

Hop volatile sorption into an LDPE liner polymer as a function of storage time.

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A storage trial was prepared in which a commercial Pilsner type beer was spiked with 250 µg

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of hop volatiles per 500 mL of beer. The beers were capped with ‘standard’ LDPE crown

284

caps, and the beers’ and liners’ content of hop volatiles were measured at certain time points.

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Figure 1 depicts the content of hop compounds as detected in the liner materials directly after

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bottling, as well as after 1, 3, 8, 21 and 55 days of storage. The drawn through lines in the

287

figure were obtained by applying eq. (1) to the data. Already after one day of storage, hop

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volatiles were present in the liner material in contents ranging from < 0.5 µg (geraniol) to

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40.7 µg (limonene). Until day 21, a distinct increase was observed which leveled off for

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myrcene as well as limonene, while a further increase was seen for t-caryophyllene and α-

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humulene. Linalool, geraniol, and α-terpineol showed a similar behavior and curve shape as

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myrcene and limonene but at a much lower rate. From all substances measured, from initially

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250 µg spiked amount in the bottles, the following order of sorption into the LDPE-liner 15 ACS Paragon Plus Environment


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polymer from highest to lowest was found: limonene (105.7 %) > α-humulene (91.4 %) > t-

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caryophyllene (74.2 %) > myrcene (53.1 %) >> linalool (1.4 %) > α-terpineol (0.6 %) >

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geraniol (0.4 %).

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Directly after spiking, the rates of terpenes and sesquiterpenes found in the beers were low

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and ranged from 10.9 % (myrcene) to 20.4 % (t-caryophyllene) as related to their initially

300

spiked amount while the terpene alcohols’ rates were higher and ranged from 71.9 %

301

(linalool) to 81.7 % (α-terpineol) (Figure 1). The gaseous phase is not obtained analytically

302

when doing a liquid-liquid extraction which is the first step when doing the SAFE-analysis.

303

One reason for the low amounts of terpenes and sesquiterpenes detected after the initial

304

spiking may be that they accumulated in the gaseous phase or bottle headspace as based on

305

their individual kL,G value and therefore were not extracted when performing the diethylether

306

extraction process. Myrcene is less polar than e.g. linalool because of its more aliphatic

307

character. Therefore, it presumably has a higher kL,G value in an aqueous system (e.g. beer)

308

than linalool and thus, at equilibrium, myrcene molecules are present to a higher extent in the

309

bottle headspace than e.g. linalool molecules. Consequently, less myrcene is detected when

310

doing the liquid-liquid extraction.

311

This hypothesis is supported by the observation that all more polar compounds measured with

312

a concurrent lower kL,G value and higher solubility in beer such as linalool, geraniol, and α-

313

terpineol were found to a higher extent in the beer after spiking while all hop constituents

314

measured with a more aliphatic character and concomitantly lower kL,G were detected at lower

315

levels. Unfortunately, no data is available on the distribution coefficients of hop volatiles in

316

beer systems which would allow predicting their concentration in the headspace. Linalool is

317

the only compound where little is known and in wort, a kL,G-value of 37.2 at a temperature of

318

72 °C was determined.42 The kL,G-values are dependent on the temperature, the pressure and 16 ACS Paragon Plus Environment

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319

the composition of the gasous and liquid phases.42 In beer at room temperature, the

320

compounds’ distribution coefficients (kL,G) are presumably lower because of the lower

321

temperature and the beers’ ethanol content; however, they must still be greater 1 because they

322

are considered to be volatiles.

323

Adding up the amounts found in the crown cork liner materials and the beers after the 55 days

324

of storage revealed that the terpenes’ ‘total’ amounts increased over time, and in sum, the

325

following rates as related to the initial spiking amount were detected at the end of storage:

326

myrcene, 56.6 %; limonene, 114 %; t-caryophyllene, 78.9 %; α-humulene, 96.4 %.

327

Concomitantly, the terpene alcohols’ rates increased or decreased only marginally (linalool,

328

74.3 %; α-terpineol, 73.6 %; geraniol, 69.9 %). The increase of the terpenes’ or

329

sesquiterpenes’ ‘total’ content found in liner and beer over storage time may again be traced

330

back to and support the hypothesis given before: the terpenes’ or sesquiterpenes’ initially

331

accumulated in the bottle headspace at an amount as defined by their kL,G value directly after

332

bottling, and from there, subsequent slow diffusion into the crown cork liner material

333

occurred during storage as defined by their diffusion coefficients until an equilibrium was

334

reached.

335

This hypothesis, however, cannot fully explain the observations, and in addition, the low rates

336

detected in liner and beer, in particular for myrcene where still ‘only’ 56.6 % were found at

337

the end of storage, may also be originated from losses of analytes during sample preparation

338

such as e.g. during the filtration step of the beers before the diethylether extraction. Also,

339

losses of analytes during the bottling process cannot be fully excluded.

340

Ultimately, sorption in the liner materials results consequently in a lowering of the

341

concentrations in the headspace which, in turn, provokes that volatiles diffuse yet again in the

342

headspace striving for equilibrium. The observation that the terpenes and sesquiterpenes

343

showed reciprocal curve shapes in liner and beer over storage is therefore an indication that 17 ACS Paragon Plus Environment


344

the scalping in fact is the cause for their depletion in the beers. Linalool, geraniol, and α-

345

terpineol, however, showed only little accumulations in the liner material and their

346

concentration changes during beer storage thus must be derived from other reactions. Linalool

347

is known to be relatively stable over storage which is in accordance to the results from this

348

study; however, there is evidence that racemization from the (R)- into the less aroma-active

349

(S)-enantiomer can occur.43 Geraniol and α-terpineol are reported to undergo certain

350

isomerization reactions34-36 and their decrease or increase, respectively, may thus be

351

originated from those transformations.

352 353

The absorption kinetic was modeled by fitting Fick’s second law (eq. 1) to the experimental

354

data. Table 3 lists the model parameters as calculated from eq. 1. The ratios between RMSE

355

and Mmax ranged from 2.3 to 19.1 % which was judged satisfactory. The substances t-

356

caryophyllene and α-humulene did not reach the equilibrium state during the 55 day storage

357

and the diffusion coefficients were therefore derived from fitting eq. 1 to the experimental

358

data by using non-linear regression analysis. ANOVA analysis of the results at p < 0.05

359

indicated a significant difference between the diffusion coefficients and a clustering into four

360

groups. The clustering as related to the substances implies that the different kinetics in

361

diffusing into the LDPE-film may be derived from the different chemical properties of the

362

volatiles such as most probably the polarity and the molecular size. The different Mmax values

363

observed can also only be partly ascribed to the different diffusion kinetics but are derived

364

from the compounds’ different affinities to react with the LDPE-polymer. The ‘polar’ terpene

365

alcohols linalool, α-terpineol, and geraniol clearly formed one group according to Tukey’s

366

HSD, while myrcene, limonene, α-humulene, and t-caryophyllene did not.

367

Taken these data together, the results suggest that all substances measured diffuse into the

368

LDPE-crown liner material according to Fick’s law which was also reported by other authors 18 ACS Paragon Plus Environment

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369

for e.g. limonene44-46 or linalool.7,47 However, diffusion coefficients for the limonene-LDPE

370

system as reported in 46 or linalool-LDPE system as reported in 7 differed markedly from our

371

results which can most probably be traced back to the difference in the experimental

372

conditions used.

373 374

Hop volatile scalping characteristics of different crown cork liners.

375

In a separate trial, the migration of hop volatiles into four different crown cork liners and the

376

effect of their functionalities on the composition of hop volatiles in beer were tested. In

377

addition to the LDPE crown cork liner from manufacturer A, which was also used in the trial

378

before, a second LDPE crown cork liner from another manufacturer (manufacturer B), an

379

LDPE oxygen scavenging crown cork, and an HDPE oxygen barrier crown cork liner, both

380

again from manufacturer A, were examined. The amounts found in the different liners after 55

381

days of storage are shown in Figure 2.

382

As expected, the same scalping characteristics of the liner materials as in the previous trial

383

were observed, and hop terpenes and sesquiterpenes were found at high levels while the more

384

‘polar’ terpene alcohols were only present at very low levels. Interestingly, all liners displayed

385

similar scalping tendencies with the exception of the oxygen barrier liner where myrcene and

386

limonene were found at significantly higher levels. These results are contradicting findings

387

from 6 or 46 who reported that HDPE generally absorbs constituents to a lesser extent.

388

In the beers, none of the applied crown cork liner materials yielded significantly different

389

amounts of the constituents (Figure 3), and in accordance with the previous trial, the terpene

390

alcohols linalool, α-terpineol, and geraniol were found at elevated levels ranging from 140

391

(geraniol) to 182 µg (α-terpineol) while terpenes and sesquiterpenes were lower and ranged

392

from 7 (myrcene) to 15 µg (limonene).



393

As related to this, it should be noted that the oxygen barrier crown cork scalped significantly

394

higher amounts of myrcene and limonene but still no significant differences were found in the

395

beers. In this regard, also, the ‘total’ rate for limonene was found to be 149.8 % for the

396

oxygen barrier crown cork and it was therefore suspected that limonene was already present

397

in the HDPE liner material. Though, no contamination of the crown corks with the analytes

398

was supposed, all crown corks were still extracted individually and were tested on the

399

potential presence of hop volatiles in the liner materials to exclude this possibility. Yet, the

400

analysis revealed that none of the analytes were discovered at detectable levels in the liners.

401

The high recovery rates for limonene can therefore not be explained.

402

The crown corks’ oxygen scavenging and the oxygen barrier functions are assumed to

403

diminish the effects of oxygen in the bottled beer by binding oxygen which is already present

404

in the bottles after filling or by forming a physical barrier for oxygen entry through diffusion,

405

respectively. There is evidence that myrcene is readily oxidized when oxygen is present17 and

406

there is a possibility for the oxidation of myrcene in bottled beer. Yet, the observation that

407

both, the oxygen scavenger crown cork and the oxygen barrier crown cork, did not yield

408

significantly different amounts of hop volatiles in the bottled beers suggests that oxygen only

409

plays an inferior role for the changes of the hop volatile composition in beer after bottling,

410

though. It should however be emphasized that this outcome is only valid for this study’s scope

411

such as the limited storage time of 55 days and the constituents tested. For instance,

412

humuluene diepoxides are claimed to be important contributors to hop aroma48 which can be

413

lost by oxidation or acid hydrolysis.11 As discussed earlier, it is possible that hop volatiles are

414

present at high levels in the bottle headspace because of their volatility. One explanation for

415

the higher amounts of myrcene found in the oxygen barrier liner materials may therefore be

416

that the oxidation of myrcene as present in bottle the headspace was diminished because

417

oxygen diffusion through the crown cork liner was minimized thus yielding more myrcene to 20 ACS Paragon Plus Environment

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418

migrate into the liner material. Aside from all that, diminishing oxygen exposure of beer or

419

other food systems is indispensable for preserving product freshness as it is also involved in

420

many flavor deterioration reactions.49,50

421 422

Scalping of hop volatiles in crown cork liner materials and can coatings.

423

The extent of flavor migration of hop volatiles into crown liner polymer and can coating

424

material was also investigated and beer from the same bright beer tank was filled in bottles or

425

cans prior to storing it for 46 days. The results from this trial are depicted in Table 4. In all

426

beers and liner materials or can coatings, low levels of limonene, t-caryophyllene, and α-

427

humulene were observed which may be traced back to the hop bill used for beer production. It

428

is therefore difficult to draw conclusions for these constituents. However, data still suggests

429

that the scalping was in accordance with the previous trials for crown cork liner materials.

430

Hop mono terpenes and sesquiterpenes were found at high levels in the crown cork liner

431

materials and high losses were thus detected in the beers. The terpene alcohols reacted

432

inversely and only small losses to the packaging material were observed. With regards to the

433

respective percentages of hop constituents scalped (Table 4), the can coatings were found to

434

be also liable to absorb hop mono terpenes and sesquiterpenes but exhibited a significantly

435

lower migration of myrcene (p < 0.05) into the packaging than the LDPE-polymer of the

436

crown corks. Trans-caryophyllene formed an exception and was only detected in the

437

packaging of both, LDPE-liners and can coatings while no t-caryophyllene was found in the

438

beers. Relative to the total amounts found in polymers and beers, the canned beers contained

439

as a consequence of the scalping characteristics significantly higher amounts of particularly

440

myrcene at a confidence level of 95 %, also because this was the only hop mono terpene

441

tested which arose at higher levels. It is noteworthy to mention that a 0.33 L beer can

442

possesses a total coating surface area of ca. 31.26 cm2 while a crown cork lining has a surface 21 ACS Paragon Plus Environment


443

area of ca. 2.25 cm2. When taking the surface to volume ratios into consideration, it can be

444

stated that the total amounts of hop volatiles scalped per cm2 are considerably lower in the

445

beer can than in the crown cork liner. It should also be noted that the sum of all individual hop

446

volatiles in both the packaging (can coating or crown cork liners) and the beers (bottled or

447

canned beer) revealed significant differences at a 95 % confidence level. Myrcene, limonene,

448

linalool, α-terpineol, and α-humulene were higher in the bottled beer plus crown cork liner

449

polymers while the amount of t-caryophyllene was higher in the canned beer plus can

450

coatings. Geraniol formed an exception and no significant difference at the 95 % confidence

451

level was found (Table 4).

452

The possibility that analytes are removed by the extensive washing step of the cans was tested

453

in a separate trial. The washing step was therefore done according to the normal procedure to

454

rinse-off all adhesive analytes. Subsequently, the rinsed can material was washed with water

455

thoroughly again and the water from the second washing-step was extracted using

456

diethylether and analyzed. None of the analytes were identified in the concentrated extracts at

457

detectable levels. The washing-step is consequently most likely not responsible for the lower

458

‘total’ amounts of most analytes in the canned beer (plus coating) than in the bottled beers

459

(plus liner). A reasonable explanation for this observation can therefore not be given.

460 461

The series of experiments presented clearly demonstrated that hop volatiles are prone to

462

migration into beer packaging but to a deviant degree. In all closures tested within the scope

463

of this study, scalping of constituents occurred to a high extent, and differences between the

464

closures were only little relative to the degree of losses. The shelf-life of beer is correlated

465

with the preservation of its original aroma. Scalping causes the loss of certain volatiles thus

466

provoking a disturbance of the original balance between the aroma compounds. Linalool and

467

geraniol may have a key role for hop aroma perception in beer21 and were hardly lost to the 22 ACS Paragon Plus Environment

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468

packaging, but particularly in aromatic beers, many aroma-active constituents make up the

469

characteristic flavor and aroma in a complex interplay. It is very likely that in addition to the

470

compounds monitored in this investigation, also other beer constituents are being scalped and

471

lost to the packaging as e.g. reported in.11 The impacts of this study’s outcomes on aroma

472

alterations are therefore undeniable. Deductions from this thus relate to the role of flavor

473

scalping and point to the importance to improve closures to enhance aroma consistency and

474

stability of packaged beer. Also, there is a need for awareness when assessing aroma in food

475

systems as key aroma compounds may be depleted before being analyzed.

476 477

ABBREVATIONS USED

478

HDPE, high-density polyethylene; LDPE, low-density polyethylene; PE, polyethylene; PP,

479

polypropylene; PVC, poly vinyl chloride.

480 481

ACKNOWLEDGEMENT

482

The authors wish to thank Pelliconi & C. S.p.A. for providing crown corks for this study.

483



484

REFERENCES

485 486

1.

487 488

Howe, S.; Borodinsky, L.; Lyon, R., Potential exposure to bisphenol a from foodcontact use of epoxy coated cans. J.Coatings Technol. 1998, 70, 69-74.

2.

Zech, J.; Manowski, A.; Malchow, S.; Rettberg, N.; Garbe, L.-A., Determination of

489

bisphenols, bisphenol A diglycidyl Ether (BADGE), BADGE chlorohydrins and

490

hydrates from canned beer by high-performance liquid chromatography tandem mass

491

spectrometry. BrewingScience 2015, 68, 102-109.

492

3.

Capone, D. L.; Skouroumounis, G. K.; Barker, D. A.; McLean, H. J.; Pollnitz, A. P.;

493

Sefton, M. A., Absorption of chloroanisoles from wine by corks and by other

494

materials. Aust. J. Grape Wine R. 1999, 5, 91-98.

495

4.

Özhan, D.; Anli, R. E.; Vural, N.; Bayram, M., Determination of chloroanisoles and

496

chlorophenols in cork and wine by using HS-SPME and GC-ECD detection. J. Inst.

497

Brew. 2009, 115, 71-77.

498

5.

499 500

Sadler, G. D.; Braddock, R. J., Absorption of Citrus Flavor Volatiles by Low Density Polyethylene. J. Food Sci. 1991, 56, 35-37.

6.

Charara, Z. N.; Williams, J. W.; Schmidt, R. H.; Marshall, M. R., Orange flavor

501

absorption into various polymeric packaging materials. J. Food Sci. 1992, 57, 963-

502

968.

503

7.

Licciardello, F.; Del Nobile, M. A.; Spagna, G.; Muratore, G., Scalping of

504

ethyloctanoate and linalool from a model wine into plastic films. LWT - Food Sci.

505

Technol. 2009, 42, 1065-1069.

506

8.

Capone, D.; Sefton, M. A.; Pretoius, I. S.; Høj, P. B., Flavour 'scalping' by wine bottle

507

closures – the 'winemaking' continues post vineyard and winery. Aust. NZ Wine Ind. J.

508

2003, 18, 16-20. 24 ACS Paragon Plus Environment

Page 24 of 38

Page 25 of 38

509


9.

510 511

Sajilata, M. G.; Savitha, K.; Singhal, R. S.; Kanetkar, V. R., Scalping of flavors in packaged foods. Compr. Rev. Food Sci. F. 2007, 6, 17-35.

10.

Nielsen, T. J.; Jägerstad, M. I.; Öste, R. E., Study of factors affecting the absorption of

512

aroma compounds into low-density polyethylene. J. Sci. Food Agric. 1992, 3, 377-

513

381.

514

11.

515 516

Brew. Chem. 1988, 46, 104-107. 12.

517 518

Peacock, V. E.; Deinzer, M. L., Fate of Hop Oil Components in Beer. J. Am. Soc.

Leufvén, A.; Hermansson, C., The sorption of aroma components from tomato juice by food-contact polymers. J. Sci. Food Agric. 1994, 64, 101-105.

13.

Nijssen, L. M.; Vissher, C. A.; Maarsse, H.; Willemsens, L. C.; Boelens, M., Volatile

519

compounds in food. Qualitative and quantitative data: hop oil; Wiley-VCH:

520

Weinheim, Germany, 1996; Vol. 62.

521

14.

Rettberg, N.; Thörner, S.; Labus, A. B.; Garbe, L.-A., Aroma-active monocarboxylic

522

acids - origin and analytical characterization in fresh and aged Hops. BrewingScience

523

2014, 67, 33-45.

524

15.

Steinhaus, M.; Schieberle, P., Comparison of the most odor-active compounds in fresh

525

and dried hop cones (Humulus lupulus L. variety Spalter Select) based on GC-

526

olfactometry and odor dilution techniques. J. Agric. Food. Chem. 2000, 48, 1776-

527

1783.

528

16.

Kishimoto, T.; Wanikawa, A.; Kono, K.; Shibata, K., Comparison of the odor-active

529

compounds in unhopped beer and beers hopped with different hop varieties. J. Agric.

530

Food. Chem. 2006, 54, 8855-8861.

531 532

17.

Dieckmann, R. H.; Palamand, S. R., Autoxidation of some constituents of hops. I. Monoterpene hydrocarbon, myrcene. J. Agric. Food. Chem. 1974, 22, 498-503.



533

18.

Takoi, K.; Koie, K.; Itoga, Y.; Katayama, Y.; Shimase, M.; Nakayama, Y.; Watari, J.,

534

Biotransformation of hop-derived monoterpene alcohols by lager yeast and their

535

contribution to the flavor of hopped beer. J. Agric. Food. Chem. 2010, 58, 5050-5058.

536

19.

537 538

lager yeasts. FEMS Yeast Res. 2003, 3, 53-62. 20.

539 540

Kollmannsberger, H.; Biendl, M.; Nitz, S., Occurence of glycosidically bound flavour compounds in hops, hop products and beer. Monatsschr. Brauwiss. 2006, 5/6, 83-89.

21.

541 542

King, A. J.; Dickinson, J. R., Biotransformation of hop aroma terpenoids by ale and

Peacock, V. E.; Deinzer, M. L.; Likens, S. T.; Nickerson, G. B.; McGill, L. A., Floral hop aroma in beer. J. Agric. Food Chem. 1981, 29, 1265-1269.

22.

Praet, T.; Van Opstaele, F.; De Causmaecker, B.; Bellaio, G.; de Rouck, G.; Aerts, G.;

543

De Cooman, L., De novo formation of sesquiterpene oxidation products during wort

544

boiling and impact of the kettle hopping regime on sensory characteristics of pilot-

545

scale lager beers. BrewingScience 2015, 68, 130-145.

546

23.

547 548

Peacock, V. E.; Deinzer, M. L., Chemistry of hop aroma in beer. J. Am. Soc. Brew. Chem. 1981, 39, 136-141.

24.

American Society of Brewing Chemists, Hops-13: Total essential oils in hops and hop

549

pellets by steam distillation. In Methods of Analysis, 9th ed.; American Society of

550

Brewing Chemists: St. Paul, MN, 2009.

551

25.

552 553

European Brewery Convention, Section 7: Hops, Methods 7.10, 7.12. In AnalyticaEBC, Hans Carl Getränke Fachverlag: Nürnberg, Germany, 2006.

26.

Likens, S. T.; Nickerson, G. B., Identification of hop varieties by gas chromatographic

554

analysis of their essential oils. Constancy of oil composition under various

555

environmental influences. J. Agric. Food. Chem. 1967, 15, 525-530.


Page 26 of 38

Page 27 of 38

556


27.

Field, J. A.; Nickerson, G.; James, D. D.; Heider, C., Determination of essential oils in

557

hops by headspace solid-phase microextraction. J. Agric. Food. Chem. 1996, 44, 1768-

558

1772.

559

28.

Kovacevic, M.; Kac, M., Solid-phase microextraction of hop volatiles: Potential use

560

for determination and verification of hop varieties. Journal of Chromatography A

561

2001, 918, 159-167.

562

29.

Steinhaus, M.; Fritsch, H. T.; Schieberle, P., Quantitation of (R)- and (S)-linalool in

563

beer using solid phase microextraction (SPME) in combination with stable isotope

564

dilution assay (SIDA). J. Agric. Food. Chem. 2003, 51, 7100-7105.

565

30.

Kleinová, J.; Klejdus, B., Determination of volatiles in beer using solid-phase

566

microextraction in combination with gas chromatography/mass spectrometry. Czech J.

567

Food Sci. 2014, 3, 241-248.

568

31.

Aberl, A.; Coelhan, M., Determination of volatile compounds in different hop varieties

569

by headspace-trap GC/MS in comparison with conventional hop essential oil analysis.

570

J. Agric. Food. Chem. 2012, 60, 2785-2792.

571

32.

Eri, S.; Khoo, B. K.; Lech, J.; Hartman, T. G., Direct thermal desorption-gas

572

chromatography andg chromatography-mass spectrometry profiling of hop (Humulus

573

lupulus L.) essential oils in support of varietal characterization. J. Agric. Food. Chem.

574

2000, 48, 1140-1149.

575

33.

576 577

Fritsch, H. Untersuchung zum Hopfenaroma in Pilsner Bieren. Dissertation, Technische Universität München, München, Germany, 2001.

34.

Rapp, A.; Güntert, M.; Ullemeyer, H., Über Veränderungen der Aromastoffe während

578

der Flaschenlagerung von Weißweinen der Rebsorte Riesling. Z. Lebensm Unters.

579

For. 1985, 180, 109-116.



580

35.

Ohta, T.; Morimitsu, Y.; Sameshima, Y.; Samuta, T.; Ohba, T., Transformation from

581

geraniol, nerol and their glucosides into linalool and α-terpineol during shochu

582

distillation. Journal of Fermentation and Bioengineering 1991, 72, 347-351.

583

36.

Baxter, R. L.; Laurie, W. A.; McHale, D., Transformations of monoterpenoids in

584

aqueous acids: The reactions of linalool, geraniol, nerol and their acetates in aqueous

585

citric acid. Tetrahedron 1978, 34, 2195-2199.

586

37.

587 588

Marsh, K.; Bugusu, B., Food Packaging-Roles, Materials, and Environmental Issues. J. Food Sci. 2007, 72, R39-R55.

38.

Van Opstaele, F.; Van Holle, A.; Van Nieuwenhove, J.; Naudts, D.; De Keukeleire,

589

D.; Aerts, G.; De Cooman , L., Characterisation of fresh and aged single-hop beers via

590

hop oil constituents fingerprinting and sensory assessment. Presented at the 34th

591

Congress of the European Brewery Convention [Online], Luxembourg, Luxembourg,

592

May 26-30, 2013. Brewers of Europe website http://www.ebc2013lux.org/tl_files/dl/

593

abstracts/Poster_Abstracts.pdf (accessed March 03, 2016).

594

39.

Engel, W.; Bahr, W.; Schieberle, P., Solvent assisted flavour evaporation – a new and

595

versatile technique for the careful and direct isolation of aroma compounds from

596

complex food matrices. Eur. Food Res. Technol. 1999, 209, 237-241.

597

40.

598 599

Freising-Weihenstephan, Germany, 2002; Vol. 4. 41.

600 601 602

Miedaner, H., Brautechnische Analysemethoden, Band II. Selbstverlag der MEBAK

Crank, J., The definition and measurement of diffusion coefficients. In The Mathematics of Diffusion, second edition. Clarendon Press: Oxford, England, 1975.

42.

Hertel, M., Das Ausdampfverhalten von Aromastoffen während der Würzekochung. Dissertation, Technische Universität München, München, Germany, 2007.


Page 28 of 38

Page 29 of 38

603


43.

Kaltner, D.; Steinhaus, M.; Mitter, W.; Biendl, M.; Schieberle, P., (R)-Linalool als

604

Schlüsselaromastoff für das Hopfenaroma in Bier und sein Verhalten während der

605

Bierlagerung. Monatsschr. Brauwiss. 2003, 11/12, 192-196.

606

44.

Sadler, G. D.; Braddock, R. J., Oxygen permeability of low density polyethylene as a

607

function of limonene absorption: an approach to modeling flavor “scalping”. J. Food

608

Sci. 1990, 55, 587-588.

609

45.

Mauricio-Iglesias, M.; Peyron, S.; Chalier, P.; Gontard, N., Scalping of four aroma

610

compounds by one common (LDPE) and one biosourced (PLA) packaging materials

611

during high pressure treatments. J. Food Eng. 2011, 102, 9-15.

612

46.

613 614

polyethylene. Food Addit. Contam. 2006, 23, 738-746. 47.

615 616

Limm, W.; Begley, T. H.; Lickly, T.; Hentges, S. G., Diffusion of limonene in

Van Willige, R. W. G. Effects of flavour absorption on foods and their packaging materials. Dissertation, Wagening University, Wagening, The Netherlands, 2002.

48.

Lam, K. C.; Deinzer, M. L., Tentative identification of humulene diepoxides by

617

capillary gas chromatography/chemical ionization mass spectrometry. J. Agric. Food.

618

Chem. 1987, 35, 57-59.

619

49.

620 621 622

Kaneda, H.; Kobayashi, N.; Takashio, M.; Tamaki, T.; Shinotsuka, K., Beer staling mechanism. Tech. Q. Master Brew. Assoc. Am. 1999, 36, 41-47.

50.

Narziß, L.; Miedaner, H.; Eichhorn, P., Untersuchungen zur Geschmacksstabilität des Bieres (Teil 2). Mschr. Brauwiss. 1999, 5/6, 80-85.



623

Figure captions

624 625

Figure 1: Hop monoterpene, sesquiterpene and terpene alcohol concentrations absorbed into

626

an LDPE liner polymer and concentrations in beer as a function of storage time; a: myrcene;

627

b: limonene; c: linalool; d: α-terpineol; e: geraniol; f: t-caryophyllene; g: α-humulene. ()

628

amounts in liner, experimental data; () fit of the Fickian model to the amounts found in the

629

liner. () amounts in beer, experimental data. Data points with asterisks were below the limit

630

of quantification. Mean values are presented and error bars represent ± 1 standard deviation, n

631

= 3.

632 633

Figure 2: Comparison of the accumulation of hop volatiles in four different crown cork liner

634

materials after 55 days of storage. White bars: LDPE-liner from manufacturer A; hatched

635

bars: LDPE-liner from manufacturer B; light grey bars: LDPE-oxygen scavenging liner; dark

636

grey bars: HDPE-oxygen barrier liner. Results from linalool, α-terpineol, and geraniol are

637

magnified to ease visibility of the bars. Bars with asterisks were below the limit of

638

quantification. Mean values are presented and error bars represent ± 1 standard deviation,

639

letters above bars indicate statistical significance at p < 0.05, n = 3.

640 641

Figure 3: Influence of four different crown cork liner materials on the composition of hop

642

volatiles in beer after 55 days of storage. White bars, LDPE-liner from manufacturer A;

643

hatched bars, LDPE-liner from manufacturer B; light grey bars, LDPE-oxygen scavenging

644

liner; dark grey bars, HDPE-oxygen barrier liner. Mean values are presented and error bars

645

represent ± 1 standard deviation, letters above bars indicate statistical significance at p < 0.05,

646

n = 3.


Page 30 of 38

Page 31 of 38


Tables

Table 1: Retention times and m/z ratios used for analyzing hop volatiles by SAFE-GC/MS. Substance

tR [min]

m/z

myrcene

23.87

93

4-octanol

23.96

73

limonene

24.92

68

linalool

26.27

93

α-terpineol

28.16

59

geraniol

29.44

69

t-caryophyllene

34.18

93

α-humulene

35.05

93

tR = retention time.



Page 32 of 38

Table 2: Hop volatiles in liner polymer after 24 and 72 hours incubation at room temperature. The incubation for 24 hours was done in a duplicate trial and values are given as the mean. The incubation for 72 hours was done as a single trial. incubation for 24 hours

incubation for 72 hours

liner [µg]

% in liner

liner [µg]

% in linera

LDPE-myrcene

8.4

6.5

11.3

8.7

LDPE-limonene

9.1

7.0

13.4

10.3

LDPE-linalool

1.8

1.4

2.1

1.6

LDPE-geraniol

1.5

1.2

1.6

1.2

LDPE-α-terpineol

2.5

1.9

2.7

2.1

LDPE-t-caryophyllene

6.2

4.8

10.5

8.1

compound

a

LDPE-α-humulene 7.2 5.5 13.0 10.0 a : percentages were calculated based on the absolute amount in the solutions of 130 µg.


Page 33 of 38


Table 3: Model parameters as deduced Fick’s second law (eq. 1). The D-values of tcaryophyllene and α-humulene were derived from non-linear fitting of eq. 1 to the experimental data. All values shown are calculated.

Polymer-volatile

D ± Std. Dev. [cm2/day]

Mmax ± Std. Dev. [µg]

t0.99 [days]

RMSE/Mmax ×100 [1/µg]

LDPE-myrcene

1.17 e-5 ± 0.19 e-5 a

144.0 ± 18.5 a

21.6 ± 3.9

13.3

LDPE-limonene

1.32 e-5 ± 0.16 e-5 a

275.8 ± 29.3 b

LDPE-linalool

-5

-5 b

-5

-5 bc

0.84 e ± 0.07 e

LDPE-α-terpineol

0.72 e ± 0.07 e

LDPE-geraniol

0.49 e-5 ± 0.09 e-5 cd -5

-5 d, 1

-5

-5 d, 1

LDPE-t-caryophyllene 0.32 e ± 0.11 e

18.7 ± 2.4

19.1

3.9 ± 0.3

c

29.6 ± 2.4

3.1

1.6 ± 0.1

c

34.3 ± 3.3

2.3

50.5 ± 9.1

6.0

78.0 ± 27.1

9.7

1.1 ± 0.0 c 184.4 ± 3.7

d e

LDPE-α-humulene 0.26 e ± 0.06 e 227.0 ± 5.9 96.2 ± 24.8 9.7 : diffusion coefficients were determined using non-linear fitting. D = diffusion coefficient;

1

Mmax = amount of volatile in the liner material at equilibrium; RMSE = root mean square deviation of the modeled data from the experimental data; t0.99 = time at which 99 % of Mmax was reached. Mean values ± 1 standard deviation are present and letters in apex indicate statistical significance at p < 0.05, n = 3.



Page 34 of 38

Table 4: Amount of hop volatiles found and percent absorption in bottled beer, crown cork liner materials, canned beer, and can coatings after 46 days of storage. bottled beer beer [µg]

crown liner [µg]

canned beer

% in beer a

myrcene

8.9 ± 1.0

279.4 ± 34.8

3.1 ± 0.3

limonene

0.3 ± 0.0

2.3 ± 0.2

12.1 ± 1.1 a

200.9 ± 8.9

1.2 ± 0.2

α-terpineol

6.0 ± 0.1

geraniol

% in liner

can coating [µg]

% in beer

% in coating b

71.2 ± 9.1 b

41.0 ± 1.1

101.6 ± 13.0

28.8 ± 0.8

87.9 ± 6.6 a

0.5 ± 0.0

0.6 ± 0.0

46.3 ± 4.2 b

53.7 ± 2.7 b

99.4 ± 4.4 a

0.6 ± 0.1 a

169.4 ± 7.7

0.7 ± 0.1

99.6 ± 4.5 a

0.4 ± 0.1 a

< 0.3

100 ± 1.6 a

n.d. a

5.6 ± 0.4

< 0.3

100 ± 6.4 a

n.d.

71.5 ± 4.5

0.8 ± 0.2

98.9 ± 6.3 a

1.1 ± 0.2 a

69.2 ± 6.7

0.5 ± 0.4

99.3 ± 9.7 a

0.7 ± 0.6 a

t-caryophyllene

< 0.3

1.3 ± 0.1

n.d.

100.0 ± 7.8 a

< 0.3

8.7 ± 0.2

n.d.

100.0 ± 2.7 a

α-humulene

< 0.3

5.3 ± 0.1

n.d.

100.0 ± 2.3 a

0.4 ± 0.0

0.8 ± 0.1

35.0 ± 2.0 b

65.0 ± 8.1 b

linalool

96.9 ± 12.1

beer [µg] a

n.d. = not detected. Mean values ± 1 standard deviation are presented. Letters in apex indicate significant difference of mean percentages between canned beers and bottled beers, and can coatings and crown cork closures, respectively, by a Student’s t-test at the 95 % confidence level, n = 3.

34


Page 35 of 38


Figures

0

75

50

0

60

10

20

30

40

50

150

1 0

0

0

storage [days] 1.2

2

125 0

60

10

40

50

190

0.9

180 0.6 170

*

160

0.0

150 10

20

30

40

storage [days]

50

60

f

200

60

150

45

100

30

50

15

0

0 0

10

200 0.5

175

*

0.0

60

150 0

10

20

30

40

50

60

storage [days]

Figure 1

35


20

30

40

storage [days]

200

e

0

30

225 1.0

storage [days]

storage [days]

0.3

20

α-humulene in liner [µg]

40

175

t-caryophyllene in beer [µg]

30

t-caryophyllene in liner [µg]

20

15

geraniol in beer [µg]

10

30

3

250

1.5

g

250

60

200 45 150 30

100

15

50 0

0 0

10

20

30

40

storage [days]

50

60

50

60

α-terpineol in beer [µg]

150

0 0

45

200

275

d

α-humulene in liner [µg]

10

225

4

2.0

α-terpineol in liner [µg]

50

60

225

c

linalool in beer [µg]

20

300

5

75

b

linalool in liner [µg]

100

limonene im liner [µg]

30

myrcene in beer [µg]

150

375

limonene in beer [µg]

40

a

geraniol in liner [µg]

myrcene in liner [µg]

200


Page 36 of 38

400

b

amount in liner [µg]

a

a

300

a

a

a

b

200

a

a a

a a

a

4

a

3

a a

a

b b

2

100

c

1

a ab

b c

0

a b* bc * * c

linalool α-terpineol geraniol

0 myrcene

limonene

linalool

α-terpineol

geraniol

Figure 2


t-caryophyllene

α-humulene

Page 37 of 38


300

a a

amount in beer [µg]

250

a 200

a a

a a a a a a a

150

100

50

a a a a

a a a a

a a a a

a a a a

t-caryophyllene

α-humulene

0 myrcene

limonene

linalool

α-terpineol

geraniol

Figure 3



TOC Graphic


Page 38 of 38

Characterization of the Migration of Hop Volatiles into Different Crown

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