Characterization of volatiles in unhopped wort

chuyen de ve cong nghe san xuat bia, giai doan dun soi voi hoa hops la rat quan trong, day la nghie cuu moi ve qua trinh dun soi o cong doan nau bia mot trong nhung cong doan rat quan trong den chat luong cua bia thanh pham

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/5310324 Release and Evaporation of Volatiles during Boiling of Unhopped Wort Article in Journal of Agricultural and Food Chemistry · August 2008 Impact Factor: 2.91 · DOI: 10.1021/jf800610x · Source: PubMed CITATIONS READS 10 75 7 authors, including: David Paul De Schutter Daan Saison Anheuser Busch Inbev AB-Inbev 18 PUBLICATIONS 384 CITATIONS 29 PUBLICATIONS 455 CITATIONS SEE PROFILE SEE PROFILE Guy Derdelinckx Freddy R Delvaux University of Leuven University of Leuven 83 PUBLICATIONS 1,624 CITATIONS 101 PUBLICATIONS 2,637 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately SEE PROFILE Available from: David Paul De Schutter Retrieved on: 20 May 2016 Identification of Volatiles in Unhopped Wort DAVID P DE SCHUTTER1*, DAAN SAISON1, FILIP DELVAUX1, GUY DERDELINCKX1, DELVAUX1 JEAN-MARIE ROCK², HEDWIG NEVEN³, FREDDY R University of Leuven Kasteelpark Arenberg 22 box 02463, 3001 Heverlee, Belgium ²Brasserie d’Orval S.A., 6823 Villers-devant-Orval, Belgium 10 Centre for Malting and Brewing Science, Faculty of Bioscience Engineering, Catholic ³Brewery Duvel Moortgat N.V., Breendonkdorp 58, 2870 Puurs, Belgium 11 12 * tel: +32 (0)16 321413; fax: +32 (0)16 321576; 13 David.DeSchutter@biw.kuleuven.be 14 15 TITLE RUNNING HEADER 16 Volatiles in unhopped wort 17 18 ABSTRACT 19 The volatile fraction of wort components was studied during boiling Not less than 118 20 volatile compounds were identified when un-hopped pilsner wort was boiled and samples 21 of wort and condensed vapors were analyzed with headspace SPME-GC/MS, of which 54 22 were confirmed with reference compounds The wort samples contained 61 identifiable 23 compounds, while the vapor condensate yielded 108 different compounds Almost 30 24 known compounds were found that have not been described before in un-hopped pilsner 25 wort, while one previously unknown aldol reaction product was tentatively identified as 26 2-phenyl-2-octenal The detection of branched 2-alkenals underlines the importance of 27 the aldol condensation in Maillard-type reactions, while the tentative identification of 28 alkyloxazoles and alkylthiazoles could once more accentuate the central role of α- 29 dicarbonyl compounds, aldehydes and amino acids in flavor generation The 30 condensation of wort vapors joined with the SPME-GC/MS technique has proven to be a 31 useful tool in volatile analysis 32 33 KEYWORDS 34 Keywords: wort boiling, volatiles, evaporation, condensate, aldehydes, ketones, 2- 35 alkenals, 2-phenyl-2-octenal, oxazoles, thiazoles, furans, Maillard reaction, flavor 36 compounds 37 38 INTRODUCTION 39 In the world of brewing technology, no topic is more controversial than wort boiling The 40 reason for this is simple: wort is a complex mixture of sugars, amino acids, lipids, 41 proteins and polyphenols Hundreds of reactions occur simultaneously, such as Maillard 42 reactions, lipid oxidation reactions, the thermal decomposition of S-methylmethionine to 43 dimethylsulfide and the isomerization of hop α-acids into iso-α-acids Unfortunately, it is 44 not yet known to which extent every single reaction accounts for the quality of the final 45 product and the flavor stability of the beer during storage 46 Brewing researchers agree that the reduction of thermal load during wort boiling 47 improves beer flavor stability (1,2) Apart from that, the evaporation of dimethylsulfide is 48 often the sole quality criterion used by suppliers to prove the value of their wort boiling 49 system Progress in this field can only be made through a more profound knowledge of 50 the presence of the volatiles in wort and the chemical background of these compounds In 51 the past, analysis of volatiles has already been carried out on malt extract (3), ale malt 52 (4), caramel malts (5), roasted malts (6), ale wort (7) and on pilsner-type beer (8,9) Other 53 papers focused primarily on odor-active compounds of hops in beer (10) or described 54 new techniques to identify more than 120 different compounds in hop oil, while probably 55 over 1,000 compounds are still waiting to be discovered in the hop oil fraction (11) 56 The presence of these abundant hop volatiles in wort could impede a proper detection and 57 identification of the malt-derived and boiling process related volatiles Therefore, it was 58 decided to investigate the flavor profile of un-hopped pilsner wort together with the 59 condensate of the vapors generated while boiling The advantage of the analysis of vapor 60 condensates is obvious: volatiles are generally enriched in the vapor phase, depending on 61 the volatility of the particular compound If this flavor-rich mixture is combined with a 62 very sensitive analysis technique, such as solid-phase micro-extraction (SPME) in 63 combination with GC/MS (12,13), a powerful identification tool is created The increased 64 sensitivity offers opportunities for the detection of new compounds in wort and 65 consequently, fur unraveling new reaction pathways that may occur during boiling As 66 the volatility of every volatile compound is determined and expressed by its vapor-liquid 67 equilibrium (14), there must be a strict correlation between the presence of a compound 68 in the condensate and in the wort Variations in wort will therefore be reflected in the 69 vapor condensate 70 The purpose of the present study is the identification of a broad range of volatiles in order 71 to obtain a better understanding of the chemical background of unhopped wort A crucial 72 factor in this identification is obtaining an increased sensitivity for the identification of 73 novel compounds Therefore the SPME GC/MS technique is combined with the analysis 74 of wort vapor condensate, a combination that should greatly enhance the analysis 75 sensitivity 76 In the present study, we used the SPME-GC/MS technique for the detection and 77 identification of volatiles in un-hopped pilsner wort and vapor condensates of the same 78 wort The chemical background of some of the detected compounds is further 79 investigated and a comparison is made with data found in literature New compounds 80 found in the un-hopped wort are discussed in detail 81 MATERIALS AND METHODS 82 Chemicals 83 Methyl isobutyl ketone RECTAPURTM was bought from VWR International (West 84 Chester, PA) The compounds 2-pentylfuran (98 %) and (E,E)-2,4-decadienal (90 %) 85 were obtained from Alfa Aesar GmbH (Karlsruhe, Germany) All other chemicals were 86 acquired from Sigma-Aldrich (St Louis, MO, USA): isobutyraldehyde, 2-phenyl-2- 87 butenal, (E)-2-nonenal, 5-hydroxymethyl-2-furfural (HMF), decanal, 5-methyl-2-furfural, 88 3-methylthiopropionaldehyde, 89 dimethyltrisulfide (DMTS), 2-ethyl-3,5(or 6)-dimethylpyrazine, 5-methyl-2-phenyl-2- 90 hexenal, 4-methyl-2-phenyl-2-pentenal, 2-acetylfuran, 2-isopropyl-5-methyl-2-hexenal, 91 2-methylpyrazine, 92 diacetyl, 2,3-pentanedione, β-myrcene, dimethylsulfide, β-damascenone, 4-vinylguaiacol, 93 hexanal, 2-heptanol, phenylethylalcohol, 3-methylbutanol, 1-hexanol, isovaleric acid, 2- 94 furfural, heptanal, propanal, furfuryl alcohol, pentanal, benzaldehyde, 2-methylbutanal, 95 octanal, butanal, isoamyl acetate and γ-nonalactone 96 Wort production 97 Wort production was performed in the pilot scale (5 hl) brewery of the Centre for Malting 98 and Brewing Science (Heverlee, Belgium) An amount of 80 kg milled pilsner malt 99 (Dingemans, Stabroek, Belgium) was added to 220 liters of water at 55°C The pH was 100 adjusted to 5.5 with lactic acid and the mash was subjected to a rest of 10 Next, the 101 temperature was raised to 63°C (35 of rest) and the saccharification temperature of 102 72°C (20 min) After the saccharification rest, the mash was heated up to 78°C and 103 subsequently transferred to the lauter tun, in which the separation of spent grains and 104 sweet wort takes place The filtered sweet wort was collected in the boiling kettle, where 105 it was heated up to 90°C At 90°C, the wort was taken in 1.5L containers and nonanal, (E)-2-hexenal, 2,3-diethyl-5-methylpyrazine, 3-methylbutanal, phenylacetaldehyde, α-linalool, 106 immediately cooled down to room temperature Hereafter the containers with sweet wort 107 were frozen at -25°C Prior to the boiling experiments, the wort was defrosted; the 108 density was adjusted to 12°P and the pH was adjusted to 5.2 with sulfuric acid 109 Lab-scale boiling 110 The boiling device consisted of a 6L stainless steel vessel, equipped with a wort sample 111 valve, a paddle stirrer and a temperature sensor, which was immersed in the wort A glass 112 cover was used with inlets for the paddle stirrer, the temperature sensor and an outlet 113 chimney for wort vapors A Liebig-cooler (cooling water at 2°C) was placed on the outlet 114 in order to condense the produced vapors This condensate was collected in 50 ml tubes 115 on ice The heating device consisted of a stainless steel plate with an integrated 116 temperature sensor and feed back temperature regulation was performed with the 117 immersed temperature sensor While boiling, the heating plate temperature was kept 118 constant to guarantee uniform heating during the boiling experiment, while continuous 119 stirring ensured a homogenous heat distribution 120 Sample preparation and Solid-Phase Micro-Extraction (SPME) 121 A 20 mL headspace vial was filled with a 10 mL aliquot of wort or vapor condensate, 122 together with 3.5 g NaCl (analytical grade) and 50 µL of a 200 ppm 2-heptanol solution, 123 used as an internal standard The vial was placed in the tray of the CombiPAL (CTC 124 Analytics, Zwingen, Switzerland), where it was pre-incubated at 40°C for 10 minutes 125 Hereafter a carboxen-polydimethylsiloxane-divinylbenzene fiber (CAR-PDMS-DVB, 126 Supelco, Bellefonte, PA) was used for extraction of volatiles in the headspace of the vial 127 during 20 at 40°C 128 GC/MS analysis 129 The injection of the CAR-PDMS-DVB fiber was performed in a split/splitless injector of 130 a Trace GC Ultra (Thermo, Waltham, MA) and desorption was executed for minutes at 131 250°C in split mode (with a split ratio of 8) The used columns were of the type RTX- 132 200MS (30m, 0.25mm ID, 0.5µm df) and of the type RTX-5SilMS (60m, 0.25mm ID, 133 1.0µm df), both from Restek (Bellefonte, PA) A constant flow of 1.5 ml He per minute 134 was applied in both cases The following temperature program was used with the RTX 135 200MS column: 30°C for min, followed by a 3°C/min increase to 120°C, then a 136 10°C/min rise to 200°C, and finally with a 30°C/min rise to 260°C with a hold 137 The following temperature program was used with the RTX 5SilMS column: 30°C for 138 min, then a rise to 70°C at a rate of 10°C/min with hold, followed by a rise up to 139 200°C at a rate of 4°C/min, and finally up to 270°C at a rate of 20°C/min, with a 140 hold After separation, the volatiles were analyzed with a Dual Stage Quadrupole (DSQ) 141 MS (Thermo, Waltham, MA), which was set to detect positive ions with a mass to charge 142 ratio (m/z) of 33-260 in the electron-impact mode The data were analyzed using 143 Xcalibur software (Thermo, Waltham, MA) 144 Identification of volatiles 145 The identification of wort volatiles was performed by GC-MS spectral analysis and their 146 Kovat’s retention indices were calculated for a RTX-200MS column and a RTX-5MS 147 column Where possible, chemical standards were injected and compared with identified 148 compounds 149 Aldol condensation reactions 150 De-ionized water was supplemented with 500 ppb of each reagent The pH was adjusted 151 to pH 5.2 with lactic acid and 20 ml of the solution was incubated in sealed pyrex tubes 152 for hour in a water bath at 100°C (in duplicate) After incubation, the samples were 153 cooled on ice and prepared for SPME-GC/MS analysis as described above 154 RESULTS AND DISCUSSION 155 Headspace SPME GC/MS is a very sensitive technique for trace compound analysis in 156 the headspace of beverages, without the need for preliminary extraction and 157 consequently, without the risk of losing information with time-consuming extraction 158 procedures (13) The only consideration that has to be made is the choice of the 159 appropriate fiber In this case, a 3-phase CAR-PDMS-DVB fiber was chosen in order to 160 obtain the broadest extraction spectrum of volatiles 161 When wort is boiled, an important concern of the brewer is the quality of the wort after 162 boiling The evaporated fraction of the wort is of minor importance, except for energy 163 recuperation by condensation However, wort vapors contain high levels of volatiles due 164 to the higher volatility of those compounds in comparison with the volatility of water 165 Therefore, the condensed vapors contain volatiles in levels that are related of the levels of 166 those volatiles in the remaining wort Hertel and coworkers have determined the vapor- 167 liquid equilibrium of dimethylsulfide as 75.6, whereas the vapor-liquid equilibrium of 168 phenylacetaldehyde is no more than 5.6 (14) Hence analyzing the condensed vapor 169 fraction of the wort reveals more information than analysis of the same wort The 170 difference in sensitivity is illustrated in Error! Reference source not found.1 While only 171 peaks have an intensity of more than 107 in wort (Chromatogram A), there are more 172 than 20 peaks with the same intensity in the condensate (Chromatogram B) Therefore it 173 was chosen to take samples from pilsner wort during boiling, as well as from the vapors 174 produced during the same wort boiling The vapors were collected in subsequent 175 fractions, the first condensate fraction containing the highest total concentration of 176 volatiles as a mirror of the high content of volatiles in the un-boiled wort 177 The volatiles that were identified in the wort and vapor condensates are shown in Table 178 In the un-hopped wort, it was possible to identify 61 volatile compounds: sulfur 179 compounds, 10 furans, 11 linear aldehydes, esters, 14 ketones, alcohols, branched 180 2-alkenals, pyrazines, a terpenoid compound, an acid, a lactone and a phenolic 181 compound On the other hand, analysis of the vapor condensate revealed 114 identifiable 182 compounds: sulfur compounds, 14 furans, 13 linear aldehydes, esters, 18 ketones, 14 183 alcohols, 19 2-alkenals, 13 pyrazines, terpenoids, oxazoles, thiazoles, lactone and 184 a phenolic compound Some of these compounds have never been reported before as part 185 of the volatile fraction of un-hopped wort or even in beer One previously unidentified 186 compound, 2-phenyl-2-octenal, was identified by mass spectral analysis and confirmed 187 by experiments with a model solution This compound was never reported before in 188 literature, to the best of our knowledge 189 190 Sulfur compounds Methanethiol is generated from the degradation of methional or 191 methionine by a retro-Michael reaction and two molecules of methanethiol can further 192 associate to yield dimethyldisulfide (15) The compound dimethylsulfide is one of the 193 most important quality parameters for brewers while boiling It is formed by the thermal 194 decomposition of S-methylmethionine (16) The flavor threshold of this compound is 195 around 50 ppb and in high concentrations it has an unpleasant, cooked cabbage flavor 196 Thiophene is obtained as a result of the reaction of cysteine with Maillard reaction 197 products (17) Dimethyltrisulfide was easily detected in both wort and condensate, 424 Vanderhaegen, B.; 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Haffenden, L J W Mechanism of imidazole and oxazole formation 534 in C-13-2 -labelled glycine and alanine model systems Food Chem 2003, 81, 403-409 24 535 44 Elmore, J S.; Mottram, D S.; Enser, M.; Wood, J D Novel Thiazoles and 3- 536 Thiazolines in Cooked Beef Aroma J Agric Food Chem 1997, 45, 3603-3607 537 45 Elmore, J S.; Mottram, D S Investigation of the Reaction between Ammonium 538 Sulfide, Aldehydes, and -Hydroxyketones or a-Dicarbonyls To Form Some Lipid- 539 Maillard Interaction Products Found in Cooked Beef J Agric Food Chem 1997, 45, 540 3595-3602 541 46 Coghe, S.; Benoot, K.; Delvaux, F.; Vanderhaegen, B.; Delvaux, F R Ferulic Acid 542 Release and 4-Vinylguaiacol Formation during Brewing and Fermentation: Indications 543 for Feruloyl Esterase Activity in Saccharomyces Cerevisiae J Agric Food Chem 2004, 544 52, 602-608 545 47 Maga, J A The Chemistry of Oxazoles and Oxazolines in Foods Crc Critical 546 Reviews in Food Science and Nutrition 1981, 14, 295-307 547 548 ACKNOWLEDGEMENTS 549 The authors wish to thank the Shelf High Chair and the Belgian breweries Duvel- 550 Moortgat and Orval for the financial support of this research 25 Figure Formation of 2-butylfuran and 2-ethylfuran from their precursors (based on the formation pathway of 2-pentylfuran as proposed by Hidalgo et al (24)) Figure Mass spectrum of 2-phenyl-2-octenal Figure Proposed spectral fragmentation pattern for 2-phenyl-2-octenal Figure Formation of branched 2-alkenals by aldol condensation of Strecker aldehydes The reaction products are 5-methyl-2-phenyl-2-hexenal (1), 2-isopropyl-5-methyl-2hexenal (2), 4-methyl-2-phenyl-2-hexenal (3), 4-methyl-2-phenyl-2-pentenal (4) 2phenyl-2-butenal (5) and 2-phenyl-2-octenal (6) Figure Possible reaction pathway for the formation of 4,5-dimethyl-2- isopropyloxazole (1) and 4,5-dimethyl-2-isobutyloxazole (2) The imine intermediate, straight from the Strecker degradation of valine or leucine with diacetyl or via the reaction of an α-aminoketone with 2-methylpropanal or 3-methylbutanal, undergoes cyclization and subsequent oxidation, yielding the respective oxazoles 26 FIGURES Figure OH OH O O H H 4-hydroxy-2-hexenal 4-hydroxy-2-octenal OH OH OH OH H H -H2O O 2-butylfuran -H2O O 2-ethylfuran 27 Figure 28 Figure m/z 91 m/z 173 m/z 173 H + CHO H H + -CHO -CH2CH3 -(CH2-H) + m/z 104 m/z 202 m/z 159 H + + H -CH2CH2CH3 H CHO + CHO H H -(CH2-H) -CH2CH2CH2CH3 m/z 117 -CH2 m/z 131 m/z 145 -(CHO-H) H H H CHO + H CHO H + + 2-phenyl-2-butenal ion 29 Figure CHO CHO CHO CHO CHO 3-methylbutanal 2-methylpropanal CHO CHO 2-methylbutanal phenylacetaldehyde acetaldehyde CH3CHO CHO hexanal CHO CHO CHO 30 Figure H H2N O R COOH O H H COOH N OH R N O O O H H N -CO2 O R H OH R imine intermediate H H N N H O O2 O R H R H -H2O N O R NH2 H + RCHO O -H2O R = CH(CH3)2 N O R N O N R = CH2CH(CH3)2 O 31 TABLES Table Volatile compounds identified in wort and vapor condensate a Detection Kovat's RI No RTX 200MS Compound RTX 5SilMS wort cond Identificationb SULFUR COMPOUNDS methanethiol [...]... detected in the pilsner 339 wort as well Hence, the concentration of the pyrazines appeared to be low in most cases, 340 as the majority was not detectable in the pilsner wort Pyrazines are characteristic 341 compounds of roasted cocoa beans (27,40,41), coffee (40,42) and roasted malt (4,40), 342 often characterized by nutty and roasted flavors The presence of these pyrazines in 343 pilsner wort indicates... Formation of Amines and Aldehydes from 494 Parent Amino Acids during Thermal Processing of Cocoa and Model Systems: New 495 Insights into Pathways of the Strecker Reaction J Agric Food Chem 2006, 54, 1730- 496 1739 497 29 Meilgaard, M.; Ayma, M.; Ruano, J I A Study of Carbonyl Compounds in Beer IV 498 Carbonyl Compounds Identified in Heat-Treated Wort and Beer American Society of 499 Brewing Chemists... found in wort and vapor 380 condensate respectively The peach-like flavored γ-nonalactone is known as an important 381 beer aging compound (33) The phenolic compound 4-vinylguaiacol (smoked, dentist- 382 like flavor), was detected in wort and vapor condensate with increasing intensity during 383 the wort boiling process It is formed by thermal decarboxylation of ferulic acid, which is 384 released during... % of the sum of the two peak areas in case of 5- 308 methyl-2-phenyl-2-hexenal Apparently the formation of every time the same isomer is 309 strongly favored during the reaction This could be explained by sterical hindrance of the 310 bulky phenyl of isopropyl side chains, favoring either the cis- or the trans-configuration 311 However, it is unclear whether the cis or the trans-configuration dominates... T.; Ogawa, Y.; Ohkochi, M Influence of wort boiling and wort 422 clarification conditions on aging-relevant carbonyl compounds in beer Tech Q Master 423 Brew Assoc Am 2006, 43, 121-126 19 424 2 Vanderhaegen, B.; Neven, H.; Verstrepen, K J.; Delvaux, F R.; Verachtert, H.; 425 Derdelinckx, G Influence of the Brewing Process on Furfuryl Ethyl Ether Formation 426 during Beer Aging J Agric Food Chem 2004,... generating benzaldehyde and formaldehyde Phenylethylamine can be formed out of 239 phenylalanine Consequently, direct formation of benzaldehyde from phenylalanine could 240 occur analogously with an additional decarboxylation step 241 The linear alkanals have already been described many times in wort (29) and beer (30) 242 They originate from the enzymatic oxidation of fatty acids during the mashing process... released during the mashing process However, the contribution of the thermal 385 decarboxylation to the total formation of 4-vinylguaiacol in beer is low compared with 386 the enzymatic production of 4-vinylguaiacol during fermentation (46) 387 388 Conclusion The combination of Headspace SPME-GC/MS combined with vapor 389 condensate analysis was a successful tool for the detection of new volatile compounds... the complete identification of the wort volatile fraction 412 However, quantitative measures have not been taken, nor has there been a follow up op 413 volatiles during wort boiling Further research will therefore pay attention at the 414 evolution of the identified compounds in the course of wort boiling 415 416 ABBREVIATIONS 417 CAR-PDMS-DVB Carboxen-polydimethylsiloxane-divinylbenzene 418 SPME Solid... immediate reaction 362 of diacetyl with valine and leucine, respectively This oxazole formation could also be 363 obtained immediately from the Strecker degradation pathway, starting from 364 tautomerization of the imine intermediate The hypothetical formation pathway of the 365 detected oxazoles is depicted in Figure 5 After the reaction of the Strecker aldehyde 366 with the α-aminoketone, a Schiff base... as aging-relevant compounds and are frequently used as 233 indicators for wort boiling performance (1) The parent amino acids of the Strecker 234 aldehydes are easy to determine, except for benzaldehyde, as there is no direct correlation 235 between benzaldehyde and any available amino acid Granvogl et al (28) suggested an 236 imine-enamine 237 methylglyoxal, followed by the oxidation of the intermediate