Inclusion complexes of trans-iso-alpha-acids with beta-cyclodextrin : preparation of highly enriched cis- and trans-iso-alpha-acids

Separation of cis-iso-alpha-acids from trans-iso-alpha-acids, starting from the commercial isomerised hop extract, was successfully carried out by complex formation of the trans-iso-alpha-acids with beta-cyclodextrin. The separation was performed on laboratory scale permitting the quantitative dosage of cis-iso-alpha-acids resp. trans-iso-alpha-acids to 50 L of fermented beer, addition rate 25 mg/L. The methodology consists of two successive complex formation steps with a saturated solution of beta-CD in water. The precipitate from the first complex formation step is enriched in trans-isomers, which can be recovered from the beta-CD inclusion complexes. The collected first supernatant is already enriched in cis-isomers, but in order to obtain a higher enrichment in cis-isomers in this fraction, it was incubated again with beta-CD for a second complex formation step. The cis-isomers were then isolated from the second supernatant by solid phase extraction. The final cis-and trans-isomers fractions were highly enriched in respectively cis-iso-alpha-acids (98 %) and trans-iso-alpha-acids (90 %), as opposed to common isomerised hop extracts with a typical ratio of 70 % cis-iso-alpha-acids and 30 % trans-iso-alpha-acids. The established methodology for the isolation of cis-iso-alpha-acids and trans-iso-alpha-acids from a commercial isomerised hop extract allows highly advanced beer bittering on pilot scale and represents an innovative tool to further investigate both the cis-and trans-specific bitter acids degradation in beer in relation to flavour stability

Sufficient formation and removal of dimethyl sulfide (DMS) without classic wort boiling

The formation and removal of dimethyl sulfide (DMS) was studied during a new method for wort production, without classic wort boiling. This was compared with classic brewing trials comprising one hour of wort boiling. The new wort production method consists of fine milling of malt under water to minimize LOX reactions, mashing-off at 95 degrees C, membrane assisted thin bed filtration, in-line injection of clean steam in the filtered wort and stripping of the wort while entering the combination vessel ('boiling' kettle/decantor), optional clean steam injection during filling of the combination vessel, and finally decantation of the hot trub in the same combination vessel. Oversized chimneys with condensate traps are installed on both the mash vessel and the combination vessel to promote removal and prevent re-entrance of unwanted volatiles, including DMS. Like in classic wort production, the contents of DMS precursor and DMS were sufficiently reduced when applying the new brewing method and DMS presented no flavour problem in the finished beer. The processing time of the innovative wort production method until the end of filling of the combination vessel and optional stripping of the wort was only 2.5 hours as compared to at least 3.5 hours for classic brewing using the same brewing line. Therefore, application of the proposed innovative wort production method allows for preparation of significantly more brews per day with sufficient removal of unwanted volatiles

Influence of pH on the stability of 2-substituted 1,3-thiazolidine-4-carboxylic acids in model solutions

© 2018, © 2018 American Society of Brewing Chemists, Inc. Upon beer storage, the levels of staling aldehydes increase, which coincides with the appearance of characteristic off-flavors. Bound-state aldehydes have been reported as potential sources of off-flavor appearance in aging beer. This study investigated the stability of cysteinylated aldehydes, also referred to as 2-substituted 1,3-thiazolidine-4-carboxylic acids, and the release of aldehyde compounds from cysteine adducts in model solutions at different pH values that are relevant in malting and brewing. The cysteinylated aldehydes were initially synthesized for their use as reference compounds in model solutions. Confirmation of their chemical structure was obtained by 1 H-NMR. The results from the stability tests showed that degradation of cysteine-bound aldehydes results in concomitant release of the free aldehydes. The rate of degradation is highly dependent on the 2-substitution pattern of the thiazolidine ring, as well as on the pH of the model solution. At malting and brewing relevant pH values (pH 4.4, 5.2, 6.0), degradation of cysteine-bound aldehydes is observed, in particular at pH 4.4, which is representative of the beer pH.status: Published onlin

Monitoring the evolution of free and cysteinylated aldehydes from malt to fresh and forced aged beer

During storage, beer staling coincides with a gradual increase in the concentrations of aldehydes resulting in the appearance of undesirable flavours. Cysteinylated aldehydes, also referred to as 2-substituted 1,3-thiazolidine-4carboxylic acids, have been proposed as potential precursors of this increase. This study aimed to further understand the origin of aldehydes in aged beer, by monitoring both free and cysteinylated aldehydes throughout the brewing process, from the raw materials until the stored product. Quantification of free and cysteinylated aldehydes was performed for two different brews via headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS), respectively. All selected marker aldehydes were quantified in malt, wort, and the resulting fresh and aged beer samples. Cysteinylated aldehydes were quantifiable in malt and up to the wort boiling phase. The highest levels of free aldehydes were found in malt, whereas cysteinylated aldehydes showed highest levels at mashing-in pointing to their formation during both malting and subsequent mashing-in. During beer ageing, an increase in all free aldehydes was measured. In particular, a rise in 2-methylpropanal and furfural is most striking. Although the presented experimental data obtained on malt and brewery samples do support the concept of bound-state aldehydes, cysteinylated aldehydes cannot be consider as the cause of increasing levels of staling aldehydes during beer ageing

Influence of pH on the Stability of 2-Substituted 1,3-Thiazolidine-4-Carboxylic Acids in Model Solutions

Upon beer storage, the levels of staling aldehydes increase, which coincides with the appearance of characteristic off-flavors. Bound-state aldehydes have been reported as potential sources of off-flavor appearance in aging beer. This study investigated the stability of cysteinylated aldehydes, also referred to as 2-substituted 1,3-thiazolidine-4-carboxylic acids, and the release of aldehyde compounds from cysteine adducts in model solutions at different pH values that are relevant in malting and brewing. The cysteinylated aldehydes were initially synthesized for their use as reference compounds in model solutions. Confirmation of their chemical structure was obtained by 1H-NMR. The results from the stability tests showed that degradation of cysteine-bound aldehydes results in concomitant release of the free aldehydes. The rate of degradation is highly dependent on the 2-substitution pattern of the thiazolidine ring, as well as on the pH of the model solution. At malting and brewing relevant pH values (pH 4.4, 5.2, 6.0), degradation of cysteine-bound aldehydes is observed, in particular at pH 4.4, which is representative of the beer pH. © 2018, © 2018 American Society of Brewing Chemists, Inc

Validation of an ultra-high-performance liquid chromatography-mass spectrometry method for the quantification of cysteinylated aldehydes and application to malt and beer samples

status: accepte

Validation of an ultra-high-performance liquid chromatography-mass spectrometry method for the quantification of cysteinylated aldehydes and application to malt and beer samples

This paper describes the method validation for the simultaneous determination of seven cysteinylated aldehydes, i.e. 2-substituted 1,3-thiazolidines-4-carboxylic acids, using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC–MS). Authentic reference compounds were first synthesized for identification and quantification purposes. Moreover, nuclear magnetic resonance (1H NMR and 13C NMR) was applied for verification of their structure, while ultra-high-performance liquid chromatography–mass spectrometry (UHPLC–MS) was applied for estimation of the purity. The method for quantification of cysteinylated aldehydes in model solutions has been validated according to the criteria and procedures described in international standards. The synthesized compounds were successfully identified via UHPLC–MS by comparing retention time and MS spectra with the commercial reference compounds. Method validation revealed good linearity (R2 > 0.995) over the range of 0.4–2.2 µg/L to approximately 1000 µg/L, depending on the analyte. The limits of quantification varied from 0.9 to 4.3 µg/L depending on the nature of the compound. Furthermore, evaluation of the method showed good accuracy and stability of the standard solutions. Reported chromatographic recoveries ranged from 112 to 120%. Consequently, the currently described method was applied on malt and beer samples. For the first time, quantification of cysteinylated aldehydes was obtained in malt. In contrast, in fresh beers unambiguous identification of these compounds was not achieved.</p

Validation of an ultra-high-performance liquid chromatography-mass spectrometry method for the quantification of cysteinylated aldehydes and application to malt and beer samples

This paper describes the method validation for the simultaneous determination of seven cysteinylated aldehydes, i.e. 2-substituted 1,3-thiazolidines-4-carboxylic acids, using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC–MS). Authentic reference compounds were first synthesized for identification and quantification purposes. Moreover, nuclear magnetic resonance (1H NMR and 13C NMR) was applied for verification of their structure, while ultra-high-performance liquid chromatography–mass spectrometry (UHPLC–MS) was applied for estimation of the purity. The method for quantification of cysteinylated aldehydes in model solutions has been validated according to the criteria and procedures described in international standards. The synthesized compounds were successfully identified via UHPLC–MS by comparing retention time and MS spectra with the commercial reference compounds. Method validation revealed good linearity (R2 > 0.995) over the range of 0.4–2.2 µg/L to approximately 1000 µg/L, depending on the analyte. The limits of quantification varied from 0.9 to 4.3 µg/L depending on the nature of the compound. Furthermore, evaluation of the method showed good accuracy and stability of the standard solutions. Reported chromatographic recoveries ranged from 112 to 120%. Consequently, the currently described method was applied on malt and beer samples. For the first time, quantification of cysteinylated aldehydes was obtained in malt. In contrast, in fresh beers unambiguous identification of these compounds was not achieved.</p

Validation of an ultra-high-performance liquid chromatography-mass spectrometry method for the quantification of cysteinylated aldehydes and application to malt and beer samples

This paper describes the method validation for the simultaneous determination of seven cysteinylated aldehydes, i.e. 2-substituted 1,3-thiazolidines-4-carboxylic acids, using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC–MS). Authentic reference compounds were first synthesized for identification and quantification purposes. Moreover, nuclear magnetic resonance (1H NMR and 13C NMR) was applied for verification of their structure, while ultra-high-performance liquid chromatography–mass spectrometry (UHPLC–MS) was applied for estimation of the purity. The method for quantification of cysteinylated aldehydes in model solutions has been validated according to the criteria and procedures described in international standards. The synthesized compounds were successfully identified via UHPLC–MS by comparing retention time and MS spectra with the commercial reference compounds. Method validation revealed good linearity (R2 &gt; 0.995) over the range of 0.4–2.2 µg/L to approximately 1000 µg/L, depending on the analyte. The limits of quantification varied from 0.9 to 4.3 µg/L depending on the nature of the compound. Furthermore, evaluation of the method showed good accuracy and stability of the standard solutions. Reported chromatographic recoveries ranged from 112 to 120%. Consequently, the currently described method was applied on malt and beer samples. For the first time, quantification of cysteinylated aldehydes was obtained in malt. In contrast, in fresh beers unambiguous identification of these compounds was not achieved. © 201