Romanian Biotechnological Letters
Copyright © 2015 University of Bucharest
Vol. 20, No. 6, 2015
Printed in Romania. All rights reserved
ORIGINAL PAPER
Evaluation and Comparison of Aroma Volatile Compounds
in Hop Varieties Grown in Romania
Received for publication, August 14, 2014
Accepted, March 22, 2015
LIANA SALANȚĂ, MARIA TOFANĂ*, SONIA SOCACI, ELENA MUDURA,
CARMEN POP, ANAMARIA POP, ANCA FĂRCAȘ
Faculty of Food Science and Technology, “University of Agricultural Sciences and
Veterinary Medicine Cluj-Napoca, Romania
*Address correspondence to: University of Agricultural Sciences and Veterinary Medicine,
Cluj-Napoca, Faculty of Food Science and Technology, 3-5 Mănăştur street, 400372, ClujNapoca, Romania, phone: +04-264-596384, e-mail: [email protected]
Abstract
Hop breeding programs try to exploit the aroma potential available in hop, to develop new
cultivars, that contribute to the unique flavour and pleasant aroma of beer. The aim of this research
was to study volatile profiles and to characterize the main odour volatiles compounds of three varieties
of hop in order to determine the variability of the aroma composition among phenophases. The
essential oil of hop was analyzed by ITEX/GC-MS in order to assess the composition of volatiles during
development of cones and to evaluate the characteristic odour of principle aroma compounds. The
relative composition of essential oil data for 20 compounds (70.85-88.81% of the total essential oil)
identified as having fruity, floral, citrus, herbal and spicy/woody aromas. Principal component analysis
demonstrated that the volatile profile based on the concentrations of aroma compounds enabled good
differentiation of phenophases of each variety. This research revealed that were many similarities
between varieties, considerable qualitative and quantitative differences made each aroma profile
distinct.
Keywords: hops, essential oil, odour, GC-MS, in-tube extraction, principal component analysis
1. Introduction
Hops, scientifically known as Humulus Lupulus, belong to the family Cannabaceae, and
are native to temperate climates in Asia, Europe and North America (1). The intensely
smelling hop cones, which are botanically the mature inflourescences of the female plant of
Humulus lupulus L., have been used since mediaeval times to enhance the shelf life and
bitterness of beer (2). The lupulin glands, located on the leavs of the cones, also contain an
intensely smelling essential oil, besides the bitter tasting hop acids.
Hops can influence beer aroma in terms of floral, spicy, herbal, woody and fruity
characters. There are a large number of hop varieties commercially available with distinct odour
characteristics, which can be attributed to the different composition of their essential oils (3).
Because the composition of hop oil contributes to the aroma of beer, the essential oil profile of
hop samples contains valuable information for brewers (4). In order to remain competitive, hop
breeders must respond to the ever-changing needs of the brewing community by providing
suitable new varieties (5). Essential oil makes up between 0.5% and 3% of the composition of
the dried hop cone, varying between cultivars (6). The aroma compounds identified in hop
varieties of Lithuania, Germany, Czech, Slovenia, Romania or California are composed mainly
of esters, aldehydes, ketones, alcohols, terpenes and carboxylic acids (7, 8, 9, 10).
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
11049
LIANA SALANȚĂ, MARIA TOFANĂ, SONIA SOCACI, ELENA MUDURA,
CARMEN POP, ANAMARIA POP, ANCA FĂRCAȘ
Chromatographic fingerprint analysis of medicinal plants represents a comprehensive
qualitative approach for varieties authentication and evaluation of quality (10). Gas
chromatography and mass spectrometry are successfully employed for identification and
quantification of hop essential oil components. Over 170-200 compounds can be separated
and their quantities estimated using capillary GC analysis of hops essential oils in one run,
which is a very suitable tool performing comparative study of different plants by so called
chromatographic profiling or fingerprinting (11). However, their efficiency is limited by the
excessively long time needed to prepare a sample (4). In order to obtain hop essential oil, the
steam distillation method is commonly used (12). This method requires a relatively large
amount of sample (50-100 g) and it is rather time consuming.
The headspace sampling is a „soft” method for the analysis of natural volatile odour
compounds (13), this technique allows the analysis of a high number of samples in a relative
short time allied to rapid and simple sample preparation procedures and it is easily automated
(14,15). A novel introduced dynamic headspace sampling method is in-tube extraction (16).
This technique requires no or minimal sample preparation, allowing a simple, efficient and
rapid enrichment of volatile or semi-volatile compounds during the headspace analysis. The
assembly consists in a sorbent bed placed between the needle and the body of the headspace
syringe. After sample pre-conditioning (heating and shaking), using the plunger of the
headspace syringe, the volatile compounds from the headspace are repeatedly pumped
through the sorbent material leading to their concentration into the microtrap. The transfer of
volatiles compounds into the GC injector is then achieved by thermal desorption (14, 17).
Previous studies showed that ITEX technique can be successfully used for a rapid and
sensitive determination of volatile compounds from a wide range of matrices (18, 19, 20, 21,
22). Although several headspace techniques were used for the determination of hops volatile
compounds (12, 23, 24, 25) to our best knowledge, ITEX technique wasn’t one of them.
The hop is a important vegetable matrix for this study, because it is used extensively in
brewing. Its importance results from the fact that no other substance (natural or synthetic)
could replace lupulin to achieve physicochemical characteristics and flavour of beer. It also
has been used in medicine from ancient times for its claimed antiseptic, hypnotic, sedative,
anti diuretic, anti inflammatory, (an)aphrodisiac and stomachic properties (26, 27).
Furthmore, the estrogenic properties as well as the potential cancer chemopreventive activities
of hops have been investigated and presented in many papers (27, 28, 29, 30).
This study aimed to characterize and compare the essential oils composition of three hop
varieties: Magnum, Aroma and Hüller Bitterer cultivated in Romania, based on compounds of
essential oils which give a distinctive type of odour.
2. Materials and methods
In order to perform the goal, we investigated the evolution of volatile compounds during
development of hop cones. The data used in this study came from samples taken during the
harvest season of 2011 and 2012, respectively.
Plant material
Samples from three different varieties of the Humulus lupulus, cultivars Magnum (MG),
classified as high α-acid, Hüller Bitterer (HB) and Aroma (AR), classified as aroma (low αacid), were collected in 2011 and 2012 year crops. Magnum and Hüller Bitterer are varieties
acclimated in Romania and Aroma hop cultivar was created at UASVM (9) Cluj-Napoca
(Romania) through clonal selection from the Hüller Bitterer cultivar. The hop cultivars were
collected from the Transylvanian hilly region. The female hop inflorescence (cones) were
11050
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
Evaluation and Comparison of Aroma Volatile Compounds
in Hop Varieties Grown in Romania
picked during three phenophases of development (end of August/beginning of September). In
phenophase I (PHP I), the cones are small-scale, measuring between 2-2,5 cm. This phenophase
coincide with the period of shaping of the cone and the lupulin gland. In the phenophase II
(PHP II) cones have medium size measuring approximately 3cm and the lupulin glands are
fully formed being in full ripeness. In the last phenophase (PHP III), cones have the
technological maturity to be harvested measuring 4 cm. The cones were dried for 48 hours, in a
cool dark place for the conservation of the active principles. The pellets (P) samples were
obtained from the pelletization station. Essential oil profiles from hop pellet samples (the most
used commercial product) were used for HB and MG varieties, except for AR, for which whole
dried cones were used. All hop samples were labeled and stored until the analysis at -20ºC.
Essential oil extraction
Samples of hop essential oil were isolated by hydrodistillation as described our previous
study (31). Shortly, 50 g of ground hop cones/hop pellets (ground in a coffee mill) were
weighed into a 700 ml distillation glass. The distillation time was 3.5 hours since the
distillation begins. The obtained essential oil was collected and measured. Yield was
calculated as ml of essential oil per 100g plant material free of moisture. At the end of
extraction the obtained essential oil was collected and measured. Yield was calculated as ml
essential oil per 100g plant material free of moisture.
ITEX analysis
The extraction of volatile compounds was performed using the ITEX technique, as
described our previous study (32). The parameters for the method were: incubation
temperature: 60oC; incubation time: 20 minutes, number of strokes: 30. The other parameters
were maintained constant for all samples: syringe temperature 60ºC; agitation speed 500 rpm;
extraction volume 1000 µL; extraction speed 100 µL/s; desorption temperature 200ºC; trap
cleaning temperature 250ºC; trap cleaning time 2 min with N2. The used ITEX fibre was an
ITEX-II Trap (G23)-SilicoNert 2000, Tenax TA 80/100 mesh, ea, fibre. After incubation a
250 µL headspace sample was injected in the GC-MS injector.
GC-MS analysis
The analyses were carried out on a Shimadzu GC-MS QP-2010 (Shimadzu Scientific
Instruments, Kyoto, Japan) model gas chromatograph-mass spectrometer equipped with a
CombiPAL AOC-5000 autosampler (CTC Analytics, Zwingen, Switzerland). A Zebrone ZB5ms column of 50m x 0.32 mm i.d. and 0.25 µm film thickness was used for the analyses.
The parameters for the method were: injector temperature 250.0ºC; pressure 93.1 kPa,
linear velocity 44.0 cm/s, split ratio 1:200, carrier gas-helium 1.39mL/min, detector MS, ion
source temperature 250.0ºC, interface temperature 250.0ºC, MS mode EI, scan range 50400u, scan rate 2000u/s. The program for column oven temperature was: 60ºC (3 min) to
160ºC at 3ºC/min to 250ºC (10 min).
The acquisition of chromatographic data was performed by the comparison of the obtained
mass spectra with the ones from the mass spectra libraries, NIST27 and NIST147, from the US
National Institute of Technology and Standards (NIST) mass spectra libraries. All peaks found
in at least two of the three total ion chromatograms (TIC) were taken into account when
calculating the total area of peaks (100%) and the relative areas of the volatile compounds.
Statistical analysis
Each sample was analyzed in duplicate. The results obtained were subjected to principal
component analysis (PCA) with cross-validation (full model size and centre data). The
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
11051
LIANA SALANȚĂ, MARIA TOFANĂ, SONIA SOCACI, ELENA MUDURA,
CARMEN POP, ANAMARIA POP, ANCA FĂRCAȘ
statistical analysis were performed using Unscrambler X software Version 10.1 (CAMO
Software AS, Oslo, Norway).The statistical test were generated with GraphPad Prism version
5.03 for Windows (GraphPad Software, San Diego, CA, www.graphpad.com).
3. Results and discussion
Odour volatiles composition of hops
The comparison of compounds was done based on analysis suggested by Ĉerenak & al.,
(5) of Slovenian aroma varieties and Whittock and Koutoulis (33) of Australian aroma
varieties.The headspace ITEX/GC-MS technique was applied to characterise the composition
of volatiles and to evaluate the principle odours compounds. Myrcene (33.12-40.18%) and
caryophyllene (8.69-18.62%) were found to be the main constituents of these samples. The
Aroma headspace ITEX/GC–MS hop oils analysis is shown in Figure 1.
Figure 1. Chromatograms (TIC, Total Ion Chromatogram)
of headspace ITEX/GC-MS analysis
of volatiles from Aroma variety. The numbering of the
peaks refers to the Table 1.
The relative composition of essential oil data for 20 compounds (70.85-88.81% of the total
essential oil) identified as having fruity, floral, citrus, herbal and spicy/woody aromas are
presented in Table 1. Hop oils are made up primarily of a hydrocarbon fraction and an
oxygenated fraction (33). Compounds quantified using ITEX/GC-MS included esters (methyl
nonanoate, methyl heptanoate and methyl decadienoate), ketones (2-nonanone and 2undecanone) and alcohols (linalool) in the oxygentated group, and terpenes (myrcene and βpinene), cyclic monoterpenes (limonene and γ-terpinene), sesquiterpenes (α-copaene,
caryophyllene and α-caryophyllene) and bicyclic sesquiterpenes (γ-cadinene and β-selinene).
The oxygenated compounds present in hop essential oil tend to provide fruity and floral aromas
(5). Esters and ketones are identified with fruity odours, while the alcohols tend to be identified
with floral odours. Terpenes are associated with citrus (limonene), herbal and spicy/woody
odours (33). Compounds with fruity odours make up a higher proportion of the essential oils in
MG than in AR and HB. Methyl nonanoate was found in varieties grown in Romania, in
contrast to Ĉerenak & al., (5) who didn’t found in any of samples collected from Slovenia.
Hüller Bitterer variety have the highest proportion of floral compounds in essential oils.
Relatively high levels of linalool were observed in all varieties during phenophases, with the
lowest (1.45%) found in AR (PHP III). Comparing to the results from Australian researchers
Whitock and Koutoulis (33), Australian varieties have lower content of linalool than varieties of
hops included in our research. Linalool is a key contributor to hoppy flavour, therefore there is a
good correlation between linalool content and perceived fruity-flowery flavour (34).
Limonene and γ-terpinene compounds were determined in the category of citrus odour,
however Ĉerenak & al., (5) suggests other compounds, such as linalool, geraniol and farnesene,
who may contribute in the perception of citrus odour or flavour. High levels of limonene were
observed in AR (1.85-2.27%) and very high levels in MG (2.55-2.93%). Within the group of
11052
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
Evaluation and Comparison of Aroma Volatile Compounds
in Hop Varieties Grown in Romania
varieties investigated, γ-terpinene only occurs at levels less 1%. High levels of compounds with
herbal odours are found in all three varieties. The major contributing component is beta
selinene, high levels of which are characteristic of AR variety (1.23-3.07%). Compounds
providing a spicy/woody character make up the highest proportion of the volatil oils in all
varieties. Relatively high levels of spicy/wood odour compounds were seen in MG variety. It is
difficult to see much of a pattern in the distribution between varieties of compounds with spicy
or woody odours, due to the dominance over this fraction by myrcene (33).
Table 1. Summary of 20 odour active essential oil compounds in three varieties grown in Romania,
expressed as in average of all the samples included. All data are in relative %.
No.
Essential oil
Components
Aroma (AR)
Hüller Bitterer (HB)
Magnum (MG)
PHP I
PHP II
PHP III
PHP I
PHP II
PHP III
P
PHP I
PHP II
PHP III
P
2-nonanone
methyl
nonanoate
3
2-undecanone
4. methyl
heptanoate
5. methyl
decadienoate
Sum of fruity
0.00
0.20
0.73
0.57
0.17
0.47
Fruity
0.64
0.23
0.15
0.43
0.09
0.52
0.00
0.69
1.07
0.00
0.85
0.25
0.78
0.57
0.70
0.68
0.59
0.62
1.57
2.90
0.96
1.74
1.18
0.91
0.75
1.40
0.89
1.49
0.45
1.17
1.09
0.99
1.28
1.87
0.56
2.42
1.00
0.99
0.51
0.23
0.16
0.08
0.24
0.26
1.49
0.00
0.11
0.43
1.31
1.92
6
3.5
3.25
3.8
3.15
4.36
4.76
4.68
6.
7.
linalool
2-decanone
Sum of floral
1.58
0.44
2.02
2.28
0.33
2.61
1.45
0.66
2.11
2.38
0.45
2.83
4.10
0.35
4.45
0.81
0.13
0.94
1.16
0.48
1.64
2.36
0.25
2.61
1.71
0.56
2.27
8.
9.
limonene
γ-terpinene*
Sum of citrus
2.27
0.11
2.38
1.85
0.09
1.94
1.87
0.06
1.93
2.96
3.05
Floral
1.01
1.23
0.27
0.26
1.28
1.49
Citrus
2.75
1.70
0.09
0.06
2.84
1.76
Herbal
1.52
1.34
7.91
6.56
2.64
1.28
1.77
0.06
1.83
2.06
0.06
2.12
2.81
0.05
2.86
2.93
0.05
2.98
2.55
0.05
2.6
2.85
0.05
2.90
α-pinene
0.96
1.33
1.11
1.23
2.02
β-pinene
6.99
5.90
5.89
6.45
8.85
β1.35
1.87
1.97
1.25
1.27
phellandrene
13. β- trans1.78
0.90
0.56
0.20
0.33
0.74
0.74
ocimene
14. β-selinene
1.8
1.23
3.07
1.48
3.41
1.25
1.09
15. γ-cadinene
1.01
1.20
1.81
1.71
2.20
1.38
0.84
16. δ-cadinene
2
1.50
2.89
2.18
3.00
1.29
1.43
Sum of herbal
15.89 13.93 17.3 17.77 18.12 13.59 16.24
Spicy/Woody
17. myrcene
38.37 37.44 34.81 38.93 33.80 33.12 33.32
18. α-copaene
1.78
1.35
1.36
1.75
1.51
1.66
1.27
19. caryophyllene 17.57 15.15 8.69
9.06 14.39 14.89 13.77
20. α2.62
2.10
1.15
3.07
2.63
1.93
1.70
caryophyllene
Sum of spicy/woody 60.34 56.04 46.01 58.14 52.33 51.6 50.06
% oil accounted for 82.55 80.52 70.85 82.99 76.75 73.10 76.67
* γ-terpinene was identified and quantified in samples from 2011 only
1.67
10.58
1.51
1.72
9.26
1.91
1.75
9.53
2.12
3.01
11.31
1.91
0.56
0.24
0.15
0.13
0.90
1.31
2.17
18.7
1.04
1.50
2.47
18.14
0.41
0.91
1.46
16.33
0.31
0.66
1.49
18.82
40.18
1.01
18.62
3.35
37.97
1.06
16.43
3.43
37.05
1.01
15.05
1.85
38.61
0.94
14.75
2.08
63.16
88.81
58.89
86.01
54.96
81.26
56.38
85.05
1.
2.
10.
11.
12.
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
11053
LIANA SALANȚĂ, MARIA TOFANĂ, SONIA SOCACI, ELENA MUDURA,
CARMEN POP, ANAMARIA POP, ANCA FĂRCAȘ
The Aroma variety achieved the maximum content of odour volatiles compounds mostly
in phenophase II of vegetation, while Hüller Bitterer and Magnum varieties presents the
maximum accumulation mostly in the phenophase three of development. The fraction of
sesquiterpene hydrocarbons tend to be herbal, spicy or woody aromas, while the class of
monoterpenes is more fruity or citrusy. Esters provide additional fruity and floral
characteristics to the odour. Romanian varieties have more or less similar odour which may
gives a very pleasant, hoppy aroma to the beer.
Principal component analysis
For interpreting the results, Principal Component Analysis (PCA) was applied to
evaluate the differences among phenophases of hop varieties. The first two principal
components explained 93% of the variance of the data for AR variety, 85% for HB variety
and 98% for MG variety, showing a good discrimination between the samples (cones, pellets
and volatile oils) and phenophases, as presented in the PCA bi-plots (Figure 2). For all
varieties, the composition of the samples of volatile cones and pellets is well differentiated
from the volatile composition of the essential oil extracted by hydrodistillation. In the case of
AR and HB varieties it can be noticed a clear distinction between cones samples from
phenophases I and the other two phenophases. For the Magnum variety, the cones sample
from FN I had a close profile with those from phenophase II.
(A) Aroma variety
(B) Hüller Bitterer variety
(C) Magnum variety
Conclusions
The ITEX/GC-MS technique has enabled a comparative study of the composition of
odours volatiles in three hop varieties. The aroma profiles of hop varieties were found to
consist of a number of odours described as woody, fruity, floral and citrus along with a
number of herbal odorants. Qualitative and quantitative differences demonstrated the distinct
varietal differences in the aroma profiles of the three varieties. Principal component analysis
provided the possibility of monitoring the accumulation of odour volatiles during the crop
year, and at the same time the differentiation of the phenophases of varieties. This research
revealed that all the cultivars included have a similar type of odour and a very strong
spicy/woody character.
11054
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
Evaluation and Comparison of Aroma Volatile Compounds
in Hop Varieties Grown in Romania
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
PATZAK J, NESVADBA V, HENYCHOVA A, KROFTA K, Assessment of the genetic diversity of wild
hops (Humulus lupulus L.) in Europe using chemical and molecular analyses, Biochemical Systematics and
Ecology, 38, 136-145 (2010).
STEINHAUS M, WILHELM W, SCHIEBERLE P, Comparison of the most odour-active volatiles in
different hop varieties by application of a comparative aroma extract dilution analysis, Eur Food Res
Technol, 226, 45-55 (2007).
EYRES G, DUFOUR JP, Hop essential oil: analysis, chemical composition and odor characteristics, In Beer
in Health and Disease Prevention, Preedy VR, Editure Academic Press, San Diego, 2009, pp. 239-253.
ERI S, KHOO BK, LECH J, HARTMAN TG, Direct Thermal Desorption-Gas Chromatography and Gas
Chromatography-Mass Spectrometry Profiling of Hop (Humulus lupulus L.) Essential Oils in Support of
Varietal Characterization, J Agric Food Chem, 48, 1140-1149 (2000).
ĈERENAK A, PAVLOVIĈ M, LUSKAR MO, KOŠIR IJ, Characterisation of slovenian hop (Humulus
Lupulus L.) varieties by analysis of essential oil, Hmeljarski bilten/Hop Bulletin, 18, 27-32 (2011).
DZINGELEVIČIUS N, MARUŠKA A, RAGAŽINSKIENĖ O, OBELEVIČIUS K, Optimization of hop
essential oil extraction by means of supercritical CO2, Biologija, 57(2), 63-69 (2011).
BERTNOTIENE G, NIVINSKIENE O, BUTKIENE R, MOCKUTE D, Chemical composition of essential
oils of hop (Humulus lupulusL.) growing wild in Ausktaitjia, Cemjiia, 2, 31-36 (2004).
JELÍNEK L, ŠNEBERGER M, KARABÍN M, DOSTÁLEK P, Comparison of Czech Hop Cultivars Based
on their Contents of Secondary Metabolites, Czech J Food Sci, 28(4), 309-316 (2010).
TOFANĂ M, Substanţe amare şi de aromă din hamei, Editura Alma Mater, Cluj-Napoca, 2006, pp. 23-24,
120-160.
NANCE MR, SETZER WN, Volatile components of aroma hops (Humulus lupulusL.) commonly used in
beer brewing, Journal of Brewing and Distilling, 2(2), 16-22 (2011).
GAD HA, EL-AHMADY SH, ABOU-SHOER MI, AL-AZIZI MM, Application of Chemometrics in
Authentication of Herbal Medicines: A Review, Phytochem Anal, 24, 1-24 (2013).
LIGOR M, STANKEVIČIUS M, WENDA-PIESIK A, OBELEVIČIUS K, RAGAŽINSKIENĖ O,
STANIUS Z, MARUŠKA A, BUSZEWSKI B, Comparative Gas Chromatographic–Mass Spectrometric
Evaluation of Hop (Humulus lupulus L.) Essential Oils and Extracts Obtained Using Different Sample
Preparation Methods, Food Anal. Methods., 7, 1433-1442 (2014).
KOVACEVIC M, MILICA K, Solid-phase microextraction of hop volatiles. Potential use for determination
and verification of hop varieties, J.Chromatography. A, 918, 159-167 (2001).
SOCACI SA, SOCACIU C, TOFANĂ M, RAŢI IV, PINTEA A, In-tube Extraction and GC-MS Analysis
of Volatile Components from Wild and Cultivated sea buckthorn (Hippophae rhamnoides L. ssp. Carpatica)
Berry Varieties and Juice, Phytochem Anal 24(4), 319-328 (2013).
JORGE K, TRUGO LC, Discrimination of Different Hop Varieties Using Headspace Gas Chromatographic
Data, J Braz Chem, 14(3), 411-415 (2003).
BICCHI C, CORDERO C, LIBERTO E, SGORBINI B, RUBIOLO P, Headspace sampling of volatile
fraction of vegetable matrices, J. Chromatography. A, 1184, 220-233 (2008).
LAAKS J., LETZEL T, SCHMIDT TC, JOCHMANN MA, Fingerprinting of red wine by headspace solidphase dynamic extraction of volatile constituents, Anal. Bioanal. Chem., 403(8), 2429-2436 (2012).
JOCHMANN MA, YUAN X, SCHILLING B, SCHMID TC, In-tube extraction for enrichment of volatile
organic hydrocarbons from aqueous samples, J. Chromatogr. A 1179, 96-105 (2008).
LAAKS J, JOCHMANN MA, SCHILLING B, SCHMID TC, In-tube extraction of volatile organic
compounds from aqueous samples: an economical alternative to purge and trap enrichment, Anal Chem, 82,
7641-7648 (2010).
RASANEN I, VIINAMÄKI J, VUORI E, OJANPERÄ I, Headspace in-tube extraction gas
chromatography-mass spectrometry for the analysis of hydroxylic methyl-derivatized and volatile organic
compounds in blood and urine, J Anal Toxicol, 34(3), 113-121 (2010).
PĂUCEAN A, VODNAR DC, SOCACI SA, SOCACIU C, Carbohydrate metabolic conversions to lactic
acid and volatile derivatives, as influenced by Lactobacillus plantarum ATCC 8014 and Lactobacillus casei
ATCC 393 efficiency during in vitro and sourdough fermentation, European Food Research and
Technology, 237, 679-689 (2013).
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015
11055
LIANA SALANȚĂ, MARIA TOFANĂ, SONIA SOCACI, ELENA MUDURA,
CARMEN POP, ANAMARIA POP, ANCA FĂRCAȘ
22. ZAPATA J, MATEO-VIVARACHO L, LOPEZ R, FERREIRA V, Automated and quantitative headspace
in-tube extraction for the accurate determination of highly volatile compounds from wines and beers, J
Chromatogr A, 1230, 1-7 (2012).
23. FIELD JA, NICKERSON G, JAMES DD, HEIDER C, Determination of Essential Oils in Hops by
Headspace Solid-Phase Microextraction, J Agric Food Chem, 44, 1768-1772 (1996).
24. VAN OPSTAELE F, DE CAUSMAECKER B, AERTS G, DE COOMAN L, Characterization of novel
varietal floral hop aromas by headspace solid phase microextraction and gas chromatography-mass
spectrometry/olfactometry, J Agric Food Chem., 60(50), 12270-12281 (2012).
25. VÁZQUEZ-ARAÚJO L, RODRÍGUEZ-SOLANA R, CORTÉS-DIÉGUEZ SM, DOMÍNGUEZ JM, Use
of hydrodistillation and headspace solid-phase microextraction to characterize the volatile composition of
different hop cultivars, J Sci Food Agric., 93(10), 2568-2574 (2013).
26. AHMADI-GOLSEFIDI M, SOLEIMANI MH, AROODI M, Simultaneous determination of main effective
constituents for hops extracts, J Sci IAU (JSIAU), 18(68): 43-49 (2008).
27. VAN CLEEMPUT M, CATTOOR K, DES BOSSCHER K, HAEGEMAN G, DE KEUKELEIRE D,
HEYERICK A, Hop (Humulus lupulus)-Derived Bitter Acids as Multipotent Bioactive Compounds, J Nat
Prod, 72, 1220-1230 (2009).
28. STEVENS JF, PAGE JE, Xanthohumol and related prenylflavonoids from hops and beer: to your good
health!, Phytochemistry, 65, 1317-1330 (2004).
29. GERHÄUSER C, Beer constituents as potential cancer chemopreventive agents, European Journal of
Cancer, 41, 1941-1954 (2005).
30. ZANOLI P, ZAVATTI M, Pharmacognostic and pharmacological profile of Humulus lupulus L. Journal of
Ethnopharmacology, 116, 383-396 (2008).
31. SALANTA LC, TOFANA M, SOCACI SA, POP C, MICHIU D, FĂRCAŞ A, Determination of the
Volatile Compounds from Hop and Hop Products using ITEX/GC-MS Technique, Journal of
Agroalimentary Processes and Technologies, 18(2), 110-115 (2012).
32. SOCACI SA, SOCACIU C, MURESAN C, FARCAS A, TOFANA M, VICAŞ S, PINTEA A,
Chemometric Discrimination of Different Tomato Cultivars Based on Their Volatile Fingerprint in Relation
to Lycopene and Total Phenolics Content, Phytochem Anal, 25(2), 161-169 (2014).
33. WHITOCK S, KOUTOULIS A, New hop (Humulus lupulus L.) aroma varieties from Australia.
Proceedings of the Scientific Commission, International Hop Growers’ Convention I.H.G.C. Lublin, Poland,
2011, pp. 10-13.
34. HANKE S, Linalool-A Key Contributor to Hop Aroma, MBAA - Global Emerging Issues, 2009.
11056
Romanian Biotechnological Letters, Vol. 20, No. 6, 2015