Michael Dresel - Academia.edu (original) (raw)

Papers by Michael Dresel

Research paper thumbnail of Extinction following separate-phase acquisition: Effects of shifts in reinforcement percentage and N-length

Bulletin of the Psychonomic Society, 1977

Research paper thumbnail of Evolution of the aroma of single-hopped worts and beers

Although the annual world beer production is steadily increasing, the hop production is decreasin... more Although the annual world beer production is steadily increasing, the hop production is decreasing. A reason is the technological progress made on the conversion rate leading to a better utilization of the α-acids towards the iso-α-acids during beer production. However, scientific data on the evolution of the hoppy aroma of beer is rare and the hop-derived aroma of beer, or more precisely the volatile composition of hops, is significantly influenced by the brewing process. In order to introduce unique flavor profiles into beer, huge amounts of hops are still necessary. For this reason, this study traces the changes of the hop-derived volatiles occurring during beer manufacturing of single hopped beers with and without additional dry hopping.

Research paper thumbnail of Struktur und sensorischer Beitrag von Hopfenhartharzen zum Bittergeschmack von Bier sowie zellbasierte Studien zu deren Resorption und Metabolismus

Structure and sensorial contribution of the hard resins of hops on the bitter taste of beer as we... more Structure and sensorial contribution of the hard resins of hops on the bitter taste of beer as well as cell-based studies on their resorption and metabolism This dissertation describes the identification of key bitter compounds in the hard resin of hops by the use of instrumental-analytic technics. Besides the influence of the hop variety, the oxygen independent storage, the storage under forced conditions as well as the influence of the beer style and the beer storage on the concentration of these bitter compounds were examined. Last but not least, in vitro studies using cell-based systems examined the cytotoxicity, the resorption and the metabolism of selected compounds.

Research paper thumbnail of The hard resin of hops - A valuable source of healthy flavonoids

Research paper thumbnail of Comparison of the quality parameters of hop hard resins

This research project was funded by the The results obtained from this project show that in gener... more This research project was funded by the The results obtained from this project show that in general the hard resin rich extract has brewing applications. Although it is still necessary to improve the hard resin solubility, the produced beers had a good quality. In the sensory profiling, the panelist described the hard resin bitterness as mild and pleasant. Additionally, the beers brewed with hard resins were well rounded, the produced bitterness had a good harmony and the perceived bitterness was high. Finally, it is possible to state that hard resins contribute to taste and the microbiological stability of beers.

Research paper thumbnail of Hop Resin-Based Substance

The present invention relates, among other things, to a hop resin-based substance, in which the s... more The present invention relates, among other things, to a hop resin-based substance, in which the soft resin has been, at least substantially, removed such that the hard resin is present in an enriched state, the hard resin is enriched in terms of the water-insoluble constituents and the xanthohumol has been, at least substantially, removed. The novel substance allows both very balanced bitterness to be adjusted and it does not constitute any optical impairment of beer due to insoluble matter caused by xanthohumol.

Research paper thumbnail of Influence of raw materials and extraction methods on the antibacterial potential of hops

M-EtOH-hr M-Pllt-hr M-gh-hr T-EtOH-hr MIC (µg/ml) hop fraction TMW 1.6 TMW 1.1369 TMW1.465 TMW 1.... more M-EtOH-hr M-Pllt-hr M-gh-hr T-EtOH-hr MIC (µg/ml) hop fraction TMW 1.6 TMW 1.1369 TMW1.465 TMW 1.313 Figure 3. Minimum inhibitory concentrations of hard resin (hr) prepared from ethanol extracts (EtOH), hop pellets (Pllts) and green hops (gh), respectively, determined for four beer spoiling L. brevis strains (TMW 1.6, TMW 1.1369, TMW 1.465, TMW 1.313) after 72h incubation at 30°C in modified MRS medium. Applied hop varieties "Hallertau Hallertauer Magnum" (M) and "Tradition" (T). MIC-values above c max =286.3µg/ml depicted as 500µg/ml.

Research paper thumbnail of Comparison of the analytical profiles of volatiles in single-hopped worts and beers as a function of the hop variety

BrewingScience

Being one of the most consumed beverages in the world, much effort has been made to reveal the st... more Being one of the most consumed beverages in the world, much effort has been made to reveal the structures responsible for the sensorial characteristics of beer. Yet, the knowledge on the precise contribution of hop-derived volatiles towards the hoppy aroma of beer is rather fragmented. For a long time, the aroma of fresh beer was believed to be mainly imparted by single compounds. However, increasing evidence showed that sensorial perception of the hoppy aroma of beer is more complex than originally assumed. Moreover, the factors responsible for the perceivable differences originating from distinct hop varieties used for late and dry hopping have not been fully revealed. In order to understand how the choice of the hop variety affects the final aroma of beer, we investigated in a previous study with four different hop varieties how the analytical composition of the volatile fraction changes throughout the brewing process and how that affects the composition of late and dry hopped be...

Research paper thumbnail of The quest to hoppy aroma: Formation and behavior of oxygenated sesquiterpenoids

Fermentation and Brewing Technology (EFBT) | T +32 9 265 86 13 | F +32 9 265 87 24 | tatiana.prae... more Fermentation and Brewing Technology (EFBT) | T +32 9 265 86 13 | F +32 9 265 87 24 | tatiana.praet@biw.kuleuven.be

Research paper thumbnail of Investigation of the impact of the hop variety and the hopping technology on the analytical profile of single-hopped worts and beers

BrewingScience

Beer is one of the most consumed beverages in the world due to its alluring taste and aroma, and ... more Beer is one of the most consumed beverages in the world due to its alluring taste and aroma, and much effort has been made to reveal the structures responsible for the sensory sensation. However, the precise contribution of hop-derived volatiles towards the hoppy aroma of beer is far from being understood. For a long time, the aroma of fresh beer was believed to be mainly imparted by a few single compounds. Yet, studies revealed that sensorial perception of the hoppy aroma of beer is more complex than originally thought. Furthermore, the factors that are causing the individual varietal perceivable differences originating from distinct hop varieties used for late and dry hopping have not been revealed yet. To gain insights into the way hoppy aroma develops throughout beer manufacturing, one should first understand the impact of the different brewing process steps on the analytical composition of the volatile fraction of intermediate worts and final beers. Therefore, in this study, sa...

Research paper thumbnail of From wort to beer: The evolution of hoppy aroma of single hopped beers produced by early kettle hopping, late kettle hopping and dry hopping

) and immediately stored at -20°C until analysis. Semi-quantitative determinations of hop oil-der... more ) and immediately stored at -20°C until analysis. Semi-quantitative determinations of hop oil-derived constituents were performed using HS-SPME in combination with GC-MS operating in both full scan and selected ionmonitoring mode. The sensomics heatmap was calculated using the heatmap function of GENE-E (Version 3.0.12). Therefore, z-scores were calculated and the dendrogram was constructed by means of Kendall's Tau agglomerative linkage algorithm. Comparative and descriptive sensory analyses were performed to assess flavour impressions according to DIN 10954 (1997) und DIN 10964 (1996).

Research paper thumbnail of Evolution des Hopfenaromas von Single Hop-Bieren

http://www.brauwelt.de/index.php?inc=article&view=85304

Research paper thumbnail of Sensomics Analysis of Key Bitter Compounds in the Hard Resin of Hops (Humulus lupulus L.) and Their Contribution to the Bitter Profile of Pilsner-Type Beer

Journal of agricultural and food chemistry, Jan 27, 2015

Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fra... more Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fraction of hop. Aiming at the discovery of these compounds, hop's ε-resin was separated by means of a sensory guided fractionation approach and the key taste molecules were identified by means of UV/vis, LC-TOF-MS, and 1D/2D-NMR studies as well as synthetic experiments. Besides a series of literature known xanthohumol derivatives, multifidol glucosides, flavon-3-on glycosides, and p-coumaric acid esters, a total of 11 bitter tastants are reported for the first time, namely, 1″,2″-dihydroxanthohumol F, 4'-hydroxytunicatachalcone, isoxantholupon, 1-methoxy-4-prenylphloroglucinol, dihydrocyclohumulohydrochinone, xanthohumols M, N, and P, and isoxanthohumols M, N, and P, respectively. Human sensory analysis revealed low bitter recognition threshold concentrations ranging from 5 (co-multifidol glucopyranoside) to 198 μmol/L (trans-p-coumaric acid ethyl ester) depending on their chemical...

Research paper thumbnail of Analysis of beers from an 1840s' shipwreck

Journal of agricultural and food chemistry, Jan 11, 2015

Two bottles of beer from an about 170-year-old shipwreck (M1 Fö 403.3) near the Åland Islands in ... more Two bottles of beer from an about 170-year-old shipwreck (M1 Fö 403.3) near the Åland Islands in the Baltic Sea were analyzed. Hop components and their degradation compounds showed that the bottles contained two different beers, one more strongly hopped than the other. The hops used contained higher levels of β-acids than modern varieties and were added before the worts were boiled, converting α-acids to iso-α-acids and β-acids to hulupones. High levels of organic acids, carbonyl compounds, and glucose indicated extensive bacterial and enzyme activity during aging. However, concentrations of yeast-derived flavor compounds were similar to those of modern beers, except that 3-methylbutyl acetate was unusually low in both beers and 2-phenylethanol and possibly 2-phenylethyl acetate were unusually high in one beer. Concentrations of phenolic compounds were similar to those in modern lagers and ales.

Research paper thumbnail of Metabolism of Hop-Derived Bitter Acids

Journal of Agricultural and Food Chemistry, 2013

In this study, in vitro metabolism of hop-derived bitter acids was investigated. Besides their we... more In this study, in vitro metabolism of hop-derived bitter acids was investigated. Besides their well-known use as bitter compounds in beer, in several studies, bioactive properties have been related to these types of molecules. However, scientific data on the absorption, distribution, metabolism, and excretion aspects of these compounds are limited. More specific, in this study, α-acids, β-acids, and iso-α-acids were incubated with rabbit microsomes, and fractions were subjected to LC−MS/MS analysis for identification of oxidative biotransformation products. Metabolism of β-acids was mainly characterized by conversion into hulupones and the formation of a series of tricyclic oxygenated products. The most important metabolites of α-acids were identified as humulinones and hulupones. Iso-α-acids were found to be primarly metabolized into cis-and trans-humulinic acids, next to oxidized alloiso-α-acids. Interestingly, the phase I metabolites were highly similar to the oxidative degradation products in beer. These findings show a first insight into the metabolites of hop-derived bitter acids and could have important practical implications in the bioavailability aspects of these compounds, following ingestion of hop-based food products and nutraceuticals.

Research paper thumbnail of Identification of Beer Bitter Acids Regulating Mechanisms of Gastric Acid Secretion

Journal of Agricultural and Food Chemistry, 2012

Beer, one of the most consumed beverages worldwide, has been shown to stimulate gastric acid secr... more Beer, one of the most consumed beverages worldwide, has been shown to stimulate gastric acid secretion. Although organic acids, formed by fermentation of glucose, are known to be stimulants of gastric acid secretion, very little is known about the effects of different types of beer or the active constituents thereof. In the present study, we compared the effects of different beers on mechanisms of gastric acid secretion. To investigate compound-specific effects on mechanisms of gastric acid secretion, organic acids and bitter compounds were quantified by HPLC-DAD and UPLC-MS/MS and tested in human gastric cancer cells (HGT-1) by means of a pH-sensitive fluorescent dye which determines the intracellular pH as an indicator of proton secretion. The expression of relevant genes, coding the H + /K + -ATPase, ATP4A, the histamine receptor, HRH2, the acetylcholine receptor, CHRM3, and the somatostatin receptor, SSTR2, was determined by qPCR. Ethanol and the organic acids succinic acid, malic acid, and citric acid were demonstrated to contribute to some extent to the effect of beer. The bitter acids comprising α-, β-, and iso-α-acids were identified as potential key components promoting gastric acid secretion and up-regulation of CHRM3 gene expression by a maximum factor of 2.01 compared to that of untreated control cells with a correlation to their respective bitterness.

Research paper thumbnail of Extinction following separate-phase acquisition: Effects of shifts in reinforcement percentage and N-length

Bulletin of the Psychonomic Society, 1977

Research paper thumbnail of Evolution of the aroma of single-hopped worts and beers

Although the annual world beer production is steadily increasing, the hop production is decreasin... more Although the annual world beer production is steadily increasing, the hop production is decreasing. A reason is the technological progress made on the conversion rate leading to a better utilization of the α-acids towards the iso-α-acids during beer production. However, scientific data on the evolution of the hoppy aroma of beer is rare and the hop-derived aroma of beer, or more precisely the volatile composition of hops, is significantly influenced by the brewing process. In order to introduce unique flavor profiles into beer, huge amounts of hops are still necessary. For this reason, this study traces the changes of the hop-derived volatiles occurring during beer manufacturing of single hopped beers with and without additional dry hopping.

Research paper thumbnail of Struktur und sensorischer Beitrag von Hopfenhartharzen zum Bittergeschmack von Bier sowie zellbasierte Studien zu deren Resorption und Metabolismus

Structure and sensorial contribution of the hard resins of hops on the bitter taste of beer as we... more Structure and sensorial contribution of the hard resins of hops on the bitter taste of beer as well as cell-based studies on their resorption and metabolism This dissertation describes the identification of key bitter compounds in the hard resin of hops by the use of instrumental-analytic technics. Besides the influence of the hop variety, the oxygen independent storage, the storage under forced conditions as well as the influence of the beer style and the beer storage on the concentration of these bitter compounds were examined. Last but not least, in vitro studies using cell-based systems examined the cytotoxicity, the resorption and the metabolism of selected compounds.

Research paper thumbnail of The hard resin of hops - A valuable source of healthy flavonoids

Research paper thumbnail of Comparison of the quality parameters of hop hard resins

This research project was funded by the The results obtained from this project show that in gener... more This research project was funded by the The results obtained from this project show that in general the hard resin rich extract has brewing applications. Although it is still necessary to improve the hard resin solubility, the produced beers had a good quality. In the sensory profiling, the panelist described the hard resin bitterness as mild and pleasant. Additionally, the beers brewed with hard resins were well rounded, the produced bitterness had a good harmony and the perceived bitterness was high. Finally, it is possible to state that hard resins contribute to taste and the microbiological stability of beers.

Research paper thumbnail of Hop Resin-Based Substance

The present invention relates, among other things, to a hop resin-based substance, in which the s... more The present invention relates, among other things, to a hop resin-based substance, in which the soft resin has been, at least substantially, removed such that the hard resin is present in an enriched state, the hard resin is enriched in terms of the water-insoluble constituents and the xanthohumol has been, at least substantially, removed. The novel substance allows both very balanced bitterness to be adjusted and it does not constitute any optical impairment of beer due to insoluble matter caused by xanthohumol.

Research paper thumbnail of Influence of raw materials and extraction methods on the antibacterial potential of hops

M-EtOH-hr M-Pllt-hr M-gh-hr T-EtOH-hr MIC (µg/ml) hop fraction TMW 1.6 TMW 1.1369 TMW1.465 TMW 1.... more M-EtOH-hr M-Pllt-hr M-gh-hr T-EtOH-hr MIC (µg/ml) hop fraction TMW 1.6 TMW 1.1369 TMW1.465 TMW 1.313 Figure 3. Minimum inhibitory concentrations of hard resin (hr) prepared from ethanol extracts (EtOH), hop pellets (Pllts) and green hops (gh), respectively, determined for four beer spoiling L. brevis strains (TMW 1.6, TMW 1.1369, TMW 1.465, TMW 1.313) after 72h incubation at 30°C in modified MRS medium. Applied hop varieties "Hallertau Hallertauer Magnum" (M) and "Tradition" (T). MIC-values above c max =286.3µg/ml depicted as 500µg/ml.

Research paper thumbnail of Comparison of the analytical profiles of volatiles in single-hopped worts and beers as a function of the hop variety

BrewingScience

Being one of the most consumed beverages in the world, much effort has been made to reveal the st... more Being one of the most consumed beverages in the world, much effort has been made to reveal the structures responsible for the sensorial characteristics of beer. Yet, the knowledge on the precise contribution of hop-derived volatiles towards the hoppy aroma of beer is rather fragmented. For a long time, the aroma of fresh beer was believed to be mainly imparted by single compounds. However, increasing evidence showed that sensorial perception of the hoppy aroma of beer is more complex than originally assumed. Moreover, the factors responsible for the perceivable differences originating from distinct hop varieties used for late and dry hopping have not been fully revealed. In order to understand how the choice of the hop variety affects the final aroma of beer, we investigated in a previous study with four different hop varieties how the analytical composition of the volatile fraction changes throughout the brewing process and how that affects the composition of late and dry hopped be...

Research paper thumbnail of The quest to hoppy aroma: Formation and behavior of oxygenated sesquiterpenoids

Fermentation and Brewing Technology (EFBT) | T +32 9 265 86 13 | F +32 9 265 87 24 | tatiana.prae... more Fermentation and Brewing Technology (EFBT) | T +32 9 265 86 13 | F +32 9 265 87 24 | tatiana.praet@biw.kuleuven.be

Research paper thumbnail of Investigation of the impact of the hop variety and the hopping technology on the analytical profile of single-hopped worts and beers

BrewingScience

Beer is one of the most consumed beverages in the world due to its alluring taste and aroma, and ... more Beer is one of the most consumed beverages in the world due to its alluring taste and aroma, and much effort has been made to reveal the structures responsible for the sensory sensation. However, the precise contribution of hop-derived volatiles towards the hoppy aroma of beer is far from being understood. For a long time, the aroma of fresh beer was believed to be mainly imparted by a few single compounds. Yet, studies revealed that sensorial perception of the hoppy aroma of beer is more complex than originally thought. Furthermore, the factors that are causing the individual varietal perceivable differences originating from distinct hop varieties used for late and dry hopping have not been revealed yet. To gain insights into the way hoppy aroma develops throughout beer manufacturing, one should first understand the impact of the different brewing process steps on the analytical composition of the volatile fraction of intermediate worts and final beers. Therefore, in this study, sa...

Research paper thumbnail of From wort to beer: The evolution of hoppy aroma of single hopped beers produced by early kettle hopping, late kettle hopping and dry hopping

) and immediately stored at -20°C until analysis. Semi-quantitative determinations of hop oil-der... more ) and immediately stored at -20°C until analysis. Semi-quantitative determinations of hop oil-derived constituents were performed using HS-SPME in combination with GC-MS operating in both full scan and selected ionmonitoring mode. The sensomics heatmap was calculated using the heatmap function of GENE-E (Version 3.0.12). Therefore, z-scores were calculated and the dendrogram was constructed by means of Kendall's Tau agglomerative linkage algorithm. Comparative and descriptive sensory analyses were performed to assess flavour impressions according to DIN 10954 (1997) und DIN 10964 (1996).

Research paper thumbnail of Evolution des Hopfenaromas von Single Hop-Bieren

http://www.brauwelt.de/index.php?inc=article&view=85304

Research paper thumbnail of Sensomics Analysis of Key Bitter Compounds in the Hard Resin of Hops (Humulus lupulus L.) and Their Contribution to the Bitter Profile of Pilsner-Type Beer

Journal of agricultural and food chemistry, Jan 27, 2015

Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fra... more Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fraction of hop. Aiming at the discovery of these compounds, hop's ε-resin was separated by means of a sensory guided fractionation approach and the key taste molecules were identified by means of UV/vis, LC-TOF-MS, and 1D/2D-NMR studies as well as synthetic experiments. Besides a series of literature known xanthohumol derivatives, multifidol glucosides, flavon-3-on glycosides, and p-coumaric acid esters, a total of 11 bitter tastants are reported for the first time, namely, 1″,2″-dihydroxanthohumol F, 4'-hydroxytunicatachalcone, isoxantholupon, 1-methoxy-4-prenylphloroglucinol, dihydrocyclohumulohydrochinone, xanthohumols M, N, and P, and isoxanthohumols M, N, and P, respectively. Human sensory analysis revealed low bitter recognition threshold concentrations ranging from 5 (co-multifidol glucopyranoside) to 198 μmol/L (trans-p-coumaric acid ethyl ester) depending on their chemical...

Research paper thumbnail of Analysis of beers from an 1840s' shipwreck

Journal of agricultural and food chemistry, Jan 11, 2015

Two bottles of beer from an about 170-year-old shipwreck (M1 Fö 403.3) near the Åland Islands in ... more Two bottles of beer from an about 170-year-old shipwreck (M1 Fö 403.3) near the Åland Islands in the Baltic Sea were analyzed. Hop components and their degradation compounds showed that the bottles contained two different beers, one more strongly hopped than the other. The hops used contained higher levels of β-acids than modern varieties and were added before the worts were boiled, converting α-acids to iso-α-acids and β-acids to hulupones. High levels of organic acids, carbonyl compounds, and glucose indicated extensive bacterial and enzyme activity during aging. However, concentrations of yeast-derived flavor compounds were similar to those of modern beers, except that 3-methylbutyl acetate was unusually low in both beers and 2-phenylethanol and possibly 2-phenylethyl acetate were unusually high in one beer. Concentrations of phenolic compounds were similar to those in modern lagers and ales.

Research paper thumbnail of Metabolism of Hop-Derived Bitter Acids

Journal of Agricultural and Food Chemistry, 2013

In this study, in vitro metabolism of hop-derived bitter acids was investigated. Besides their we... more In this study, in vitro metabolism of hop-derived bitter acids was investigated. Besides their well-known use as bitter compounds in beer, in several studies, bioactive properties have been related to these types of molecules. However, scientific data on the absorption, distribution, metabolism, and excretion aspects of these compounds are limited. More specific, in this study, α-acids, β-acids, and iso-α-acids were incubated with rabbit microsomes, and fractions were subjected to LC−MS/MS analysis for identification of oxidative biotransformation products. Metabolism of β-acids was mainly characterized by conversion into hulupones and the formation of a series of tricyclic oxygenated products. The most important metabolites of α-acids were identified as humulinones and hulupones. Iso-α-acids were found to be primarly metabolized into cis-and trans-humulinic acids, next to oxidized alloiso-α-acids. Interestingly, the phase I metabolites were highly similar to the oxidative degradation products in beer. These findings show a first insight into the metabolites of hop-derived bitter acids and could have important practical implications in the bioavailability aspects of these compounds, following ingestion of hop-based food products and nutraceuticals.

Research paper thumbnail of Identification of Beer Bitter Acids Regulating Mechanisms of Gastric Acid Secretion

Journal of Agricultural and Food Chemistry, 2012

Beer, one of the most consumed beverages worldwide, has been shown to stimulate gastric acid secr... more Beer, one of the most consumed beverages worldwide, has been shown to stimulate gastric acid secretion. Although organic acids, formed by fermentation of glucose, are known to be stimulants of gastric acid secretion, very little is known about the effects of different types of beer or the active constituents thereof. In the present study, we compared the effects of different beers on mechanisms of gastric acid secretion. To investigate compound-specific effects on mechanisms of gastric acid secretion, organic acids and bitter compounds were quantified by HPLC-DAD and UPLC-MS/MS and tested in human gastric cancer cells (HGT-1) by means of a pH-sensitive fluorescent dye which determines the intracellular pH as an indicator of proton secretion. The expression of relevant genes, coding the H + /K + -ATPase, ATP4A, the histamine receptor, HRH2, the acetylcholine receptor, CHRM3, and the somatostatin receptor, SSTR2, was determined by qPCR. Ethanol and the organic acids succinic acid, malic acid, and citric acid were demonstrated to contribute to some extent to the effect of beer. The bitter acids comprising α-, β-, and iso-α-acids were identified as potential key components promoting gastric acid secretion and up-regulation of CHRM3 gene expression by a maximum factor of 2.01 compared to that of untreated control cells with a correlation to their respective bitterness.