Exploring aldehyde release in beer by 4-vinylpyridine and the effect of cysteine addition on the beer's pool of bound aldehydes

As a continuation of our previous work, which concerned the binding of aldehydes to bisulfite and cysteine, this article presents more results on the applicability of 4-vinylpyridine addition to beer prior to analysis aiming at release of aldehydes from these preformed bound states, thus making them quantifiable with the headspace solid-phase microextraction method combined with gas chromatography-mass spectrometry. This article also presents the first results on spiking beer samples with cysteine prior to forced-aging, pointing to the important role of cysteine in beer flavor stability. Both the levels in free and bound aldehydes show a relatively large degree of variation among different beers, but also between marker aldehydes. For some aldehydes (e.g., hexanal), the bound amount was shown to increase rather strongly upon forced beer aging, whereas for others (e.g., 2-methylpropanal), large amounts appeared to already be present in a bound state in the fresh samples. Spiking beer samples with cysteine prior to aging significantly lowered the aldehyde levels compared with nonspiked samples. Flavor stability of the cysteine-spiked beers was thereby greatly improved through aldehyde-cysteine adduct formation. It was further hypothesized that, in addition to efficient binding of aldehydes, cysteine also inhibits the formation of furfural during beer aging from Maillard reaction intermediates

Kombucha Tea Fermentation:A Review

Kombucha tea is made by aerobically fermenting a sweetened tea infusion with a kombucha culture, a symbiotic culture of bacteria and yeasts. The resulting beverage is usually non-alcoholic, sour and refreshing, but not naturally sparkling. Many consumers are drinking kombucha because of its alleged health effects and as kombucha tea is increasing in popularity, consumers are increasingly demanding kombucha beverages of better quality. To better adapt their products to these consumer demands, brewers are looking to the scientific knowledge about kombucha for answers. However, the scientific exploration of this complex naturally fermented beverage is still limited. This review paper presents the current state-of-the-art. To further deepen the understanding of the kombucha fermentation process and to help brewers in their search for higher-quality beverages, the microbial species diversity and its dynamics during the fermentation process should be investigated in detail, as well as the kinetics of the substrate consumption and metabolite production, and the relationship between the substrate and metabolite concentrations, and the consumer preferences for the resulting beverage

The Antecedents of Creativity Revisited: A Process Perspective

This study invokes a process view on employee creativity to uncover how the different stages of the creative process are associated with different antecedents. Specifically, we explore the role of five previously identified antecedents of organizational creativity in the different phases of the creative process within organizations: (1) personality; (2) rewards; (3) the role of co-workers; (4) leadership; and (5) organizational resources. In an analysis of 22 case studies we found that antecedents of creativity indeed have different roles in different stages of the creative process and that antecedents that are helpful in one stage of the creative process, can be detrimental for another stage. Such results highlight the importance of conceptualizing creativity as a process, rather than as an outcome variable

On the origin of free and bound staling aldehydes in beer

The chemistry of beer flavor instability remains shrouded in mystery, despite decades of extensive research. It is, however, certain that aldehydes play a crucial role because their concentration increase coincides with the appearance and intensity of "aged flavors". Several pathways give rise to a variety of key flavor-active aldehydes during beer production, but it remains unclear as to what extent they develop after bottling. There are indications that aldehydes, formed during beer production, are bound to other compounds, obscuring them from instrumental and sensory detection. Because freshly bottled beer is not in chemical equilibrium, these bound aldehydes might be released over time, causing stale flavor. This review discusses beer aging and the role of aldehydes, focusing on both sensory and chemical aspects. Several aldehyde formation pathways are taken into account, as well as aldehyde binding in and release from imine and bisulfite adducts.status: publishe

Real-time profiling of volatile malt aldehydes using selected ion flow tube mass spectrometry

The potential of selected ion flow tube mass spectrometry (SIFT-MS) to differentiate malted barley cultivars on the basis of their headspace profiles has been investigated. From a broad range of volatiles, marker aldehydes were selected because they are associated with malt quality and beer flavor stability. The authors used dynamic headspace SIFT-MS to identify the target volatiles in the different malt headspaces. The technique exhibited an increase in specificity and speed compared with the headspace solid-phase microextraction (SPME) gas chromatography MS method currently used. The unique feature of SIFT-MS to analyze sample headspaces rapidly and directly without the need for sample preparation, derivatization, or chromatographic preseparation is demonstrated

Real-time profiling of volatile malt aldehydes using selected ion flow tube mass spectrometry

The potential of selected ion flow tube mass spectrometry (SIFT-MS) to differentiate malted barley cultivars on the basis of their headspace profiles has been investigated. From a broad range of volatiles, marker aldehydes were selected because they are associated with malt quality and beer flavor stability. The authors used dynamic headspace SIFT-MS to identify the target volatiles in the different malt headspaces. The technique exhibited an increase in specificity and speed compared with the headspace solid-phase microextraction (SPME) gas chromatography MS method currently used. The unique feature of SIFT-MS to analyze sample headspaces rapidly and directly without the need for sample preparation, derivatization, or chromatographic preseparation is demonstrated

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

Further elucidation of beer flavor instability : the potential role of cysteine-bound aldehydes

The potential involvement of 2-substituted 1,3-thiazolidine-4-carboxylic acids in beer flavor stability was further investigated. The binding behavior of beer-aging aldehydes toward both cysteine and bisulfite was confirmed and compared in model solutions of varying pH values that are relevant to malting and brewing (pH 6.0, 5.2, and 4.4). It was found that binding of aldehydes increased with increasing pH, especially for binding to cysteine. Furthermore, a sample preparation approach was developed to release aldehydes from their bound-state. After binding between aldehydes and cysteine, the strong base 4-vinylpyridine (4VP) was added to the samples as a competitor of the aldehydes toward cysteine binding, and subsequent release of aldehydes was clearly observed. The same approach also resulted in a release of aldehydes from preformed bisulfite adducts. Sample treatment with 4VP was also applied to fresh pale lager beer, resulting in increased levels of free beer-aging aldehydes. Moreover, the presence of furfural-derived 1,3-thiazolidine-4-carboxylic acid in fresh pale lager beer was confirmed and quantified by a newly developed ultra-performance liquid chromatography-UV method. The insights gained in this study strengthen the hypothesis that 2-substituted 1,3-thiazolidine-4-carboxylic acids may play an important role in beer flavor stability or instability

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