Investigations on the Maillard reaction of dextrins during aging of Pilsner type beer

Insights into the effects of steaming on organoleptic quality of salmon (Salmo salar) integrating multi-omics analysis and electronic sensory system

The effect of steaming treatment on salmon quality was explored by different multi-omics and electronic sensory system in this study. A comparison between conventional steaming (CS) and anaerobic steaming (AS) was conducted in organoleptic quality of salmon. Twelve key volatile compounds were identified, which contributed to the flavor difference. The concentrations of hexanal, (E)-2-octen-1-al, and decanal in AS salmon were significantly lower than in CS salmon, which account for 68.9-80.5 % of the latter. During steaming, the fatty acids and diacylglycerols decreased significantly by 37.4 % and 57.9 %, respectively. Anaerobic steaming limited the degradation of some oxidized lipids, further reduced some volatile secondary oxidation products. Nucleotides and derivatives, succinic acid, glutamic acid, hydroxyproline and betaine contributed to the saltness, umami, richness of steamed salmon. Metabolomics data revealed that the higher creatinine, Ala-Ala and Ala-Leu provided more umami and less bitterness to AS salmon.

Selected Maillard Reaction Products and Their Yeast Metabolites in Commercial Wines

During beer and wine production, Maillard reaction products (MRPs) are formed, which have a particular influence on the taste and aroma of the fermented beverages. Compared to beer, less is known about individual Maillard compounds and especially corresponding yeast metabolites in wine. In this study, 36 selected wines (Amarone, Ripasso, red, and white wines) were analyzed by HPLC-UV and GC-MS concerning the amounts of 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), methylglyoxal (MGO), glyoxal (GO), 5-hydroxymethylfurfural (HMF), and furfural (FF). 3-DG was found to be the dominant compound with values from 3.3 to 35.1 mg/L. The contents of 3-DGal, MGO, GO, HMF, and FF were in a single digit range. In addition to MRPs, the yeast metabolites originating from 3-DG, namely, 3-deoxyfructose and 3-deoxy-2-ketogluconic acid, 2,5-bis(hydroxymethyl)furan and 5-formyl-2-furancarboxylic acid, both formed from HMF, and the FF metabolites furfuryl alcohol and furan-2-carboxylic acid were detected and quantitated in wines for the first time. The amounts were between 0.1 and 53.5 mg/L with especially high contents of the oxidation products. Differences between red and white wines indicate that enological parameters like grape variety, production method, and aging may have an influence on the MRP contents in wines.

Archeochemistry reveals the first steps into modern industrial brewing

A historical beer, dated to the German Empire era, was recently found in northern Germany. Its chemical composition represents a unique source of insights into brewing culture of the late nineteenth century when pioneer innovations laid the foundations for industrial brewing. Complementary analytics including metabolomics, microbiological, sensory, and beer attribute analysis revealed its molecular profile and certify the unprecedented good storage condition even after 130 years in the bottle. Comparing its chemical signature to that of four hundred modern brews allowed to describe molecular fingerprints teaching us about technological aspects of historical beer brewing. Several critical production steps such as malting and germ treatment, wort preparation and fermentation, filtration and storage, and compliance with the Bavarian Purity Law left detectable molecular imprints. In addition, the aging process of the drinkable brew could be analyzed on a chemical level and resulted in an unseen diversity of hops- and Maillard-derived compounds. Using this archeochemical forensic approach, the historical production process of a culturally significant beverage could be traced and the ravages of time made visible.

The Effect of Microwave Baking Conditions on the Quality of Biscuits and the Control of Thermal Processing Hazards in the Maillard Reaction

To reduce thermal processing hazards (TPHs), microwave baking has been extensively used in food thermal processing. In this study, the influence of microwave power and microwave time on the formation of TPHs and their precursors was explored in microwave-baked biscuits. The results indicated that the content of acrylamide, 5-hydroxymethylfurfural, methylglyoxal, and 3-deoxyglucosone increased linearly with the extension of microwave time (2, 2.5, and 3 min) and microwave power (440, 480, and 520 W). There was a significant correlation between the four TPHs. 3-Deoxyglucosone may directly or indirectly participate in the formation of the other three TPHs. The relationship between TPH levels with some heat-induced sensory characteristics was analyzed. The correlation between the sensory characteristics and the content of TPHs is L* > a* > hardness > Water activity (AW). The correlation coefficients between L* value and the four TPHs are −0.950, −0.891, −0.803, and −0.985. Furthermore, the content of TPHs produced by traditional baking and microwave baking under the same texture level was compared. Compared with traditional baking (190°C, 7 min), microwave baking at 440 W for 3 min successfully decrease methylglyoxal, 3-Deoxyglucosone, acrylamide, and 5-hydroxymethylfurfural content by 60.75, 30.19, 30.87, and 61.28%, respectively. Traditionally baked biscuits, which had a more obvious color, as characterized by lower L* value, larger a* and b* values, are more susceptible to the formation of TPHs. Therefore, microwave baking can reduce the generation of TPHs.

A Novel Approach to Develop Lager Yeast with Higher NADH Availability to Improve the Flavor Stability of Industrial Beer

Flavor stability is important for beer quality and extensive efforts have been undertaken to improve this. In our previous work, we proved a concept whereby metabolic engineering lager yeast with increased cellular nicotinamide adenine dinucleotide hydride (NADH) availability could enhance the flavor stability of beer. However, the method for breeding non-genetically modified strains with higher NADH levels remains unsolved. In the current study, we reported a novel approach to develop such strains based on atmospheric and room temperature plasma (ARTP) mutagenesis coupled with 2,4-dinitrophenol (DNP) selection. As a result, we obtained a serial of strains with higher NADH levels as well as improved flavor stability. For screening an optimal strain with industrial application potential, we examined the other fermentation characteristics of the mutants and ultimately obtained the optimal strain, YDR-63. The overall fermentation performance of the strain YDR-63 in pilot-scale fermentation was similar to that of the parental strain YJ-002, but the acetaldehyde production was decreased by 53.7% and the resistance staling value of beer was improved by 99.8%. The forced beer aging assay further demonstrated that the favor stability was indeed improved as the contents of 5-hydroxymethylfurfural in YDR-63 was less than that in YJ-002 and the sensory notes of staling was weaker in YDR-63. We also employed this novel approach to another industrial strain, M14, and succeeded in improving its flavor stability. All the findings demonstrated the efficiency and versatility of this new approach in developing strains with improved flavor stability for the beer industry.

A Comprehensive Evaluation of Flavor Instability of Beer (Part 2): The Influence of De Novo Formation of Aging Aldehydes

Flavor instability of beer is affected by the rise of aroma-active aldehydes during aging. Aldehydes can be either released from bound-state forms or formed de novo. This second part of our study focused on the de novo formation of aldehydes during the Maillard reaction, Strecker degradation, and oxidation reactions. Key precursor compounds for de novo pathways are free amino acids. This study varied the potential for reactions by varying free amino acid content in fresh beer using different proteolytic malt modification levels (569–731 mg/100 g d. m. of soluble nitrogen) of the used malt in brewing trials. Overall, six pale lager beers were produced from three malts (different malt modification levels), each was made from two different barley varieties and was naturally and forcibly aged. It was found that higher malt modification levels in fresh beer and during beer aging increased amino acid and dicarbonyl concentrations as aging precursors and Strecker aldehyde contents as aging indicators. Dicarbonyls were degraded during aging. Advanced glycation end products as possible degradation products showed no consistent formation during aging. Therefore, Strecker reactions were favored during beer aging. No alternative oxidative formation of Strecker aldehydes from their corresponding alcohols could be confirmed. Along with the preceding part one of our investigation, the results of this study showed that de novo formation and release occur simultaneously. After 4 months of natural aging, aldehyde rise is mainly accounted for by de novo formation.

Reduction of 5-Hydroxymethylfurfural and 1,2-Dicarbonyl Compounds by Saccharomyces cerevisiae in Model Systems and Beer

Glycation and caramelization reactions in malt lead to the formation of 1,2-dicarbonyl compounds, which come in contact with yeast during fermentation. In the present study, the metabolic fate of 5-hydroxymethylfurfural (HMF) and 1,2-dicarbonyl compounds (3-deoxyglucosone, 3-deoxygalactosone, 3-deoxypentosone, 3,4-dideoxyglucosone-3-ene) was assessed in the presence of Saccharomyces cerevisiae. HMF is degraded very fast by yeast with the formation of 2,5-bis(hydroxymethyl)furan (BHMF). By contrast, only 7-30% of 250 μM dicarbonyl compounds is degraded within 48 h. The respective deoxyketoses, 3-deoxyfructose (3-DF), 3-deoxytagatose, 3-deoxypentulose, and 3,4-dideoxyfructose, were identified as metabolites. While 17.8% of 3-deoxyglucosone was converted to 3-deoxyfructose, only about 0.1% of 3-deoxypentosone was converted to 3-deoxypentulose during 48 h. Starting with the parent dicarbonyl compounds, the synthesis of all deoxyketose metabolites was achieved by applying a metal-catalyzed reduction in the presence of molecular hydrogen. In a small set of commercial beer samples, BHMF and all deoxyketoses were qualitatively detected. 3-DF was quantitated in the four commercial beer samples at concentrations between 0.4 and 10.1 mg/L.

Comprehensive Analyses of Carbohydrates, 1,2-Dicarbonyl Compounds, and Advanced Glycation End Products in Industrial Bread Making

The technology of bread making is characterized by three major steps: dough mixing, proofing, and baking. To follow the course of Maillard processes in an authentic food matrix, the complete manufacturing process of wheat bread rolls was assessed along all production steps with the quantitation of sugars, furfurals, 1,2-dicarbonyl compounds, and advanced glycation end products (AGEs). As a result, the AGE profile was significantly enlarged to more than 12 structures, and comprehensive mechanistic insights were provided. The analyses of five major German bread types including wheat, brown, rye bread, pumpernickel, and crispbreads led to AGE contents of 69-149 mg/kg bread or 984-1857 mg/kg protein. Major lysine protein modifications were carboxymethyl, carboxyethyl, and formyl lysine and pyrraline. Arginine was mainly modified by methylglyoxal (MGO) to give imidazolinones. A major part of MGO was confirmed to stem from microbial metabolism.

Quantification of N6-formylated lysine in bacterial protein digests using liquid chromatography/tandem mass spectrometry despite spontaneous formation and matrix effects

RATIONALE

N⁶-Formyl lysine is a well-known modification of histones and other proteins. It can also be formed as a damaged product from direct formylation of free lysine and accompanied by other lysine derivatives such as acetylated or methylated forms. In relation to the activity of cellular repair enzymes in protein turnover and to lysine metabolism, it is important to accurately quantify the overall ratio of modified lysine to free lysine.

METHODS

N⁶-Formyl lysine was quantified using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with data collected in a non-targeted manner using positive mode electrospray ionization on a Q-Exactive HF⁺ Orbitrap mass spectrometer. Studies were performed with lysine and deuterated lysine spiked into protein digests and solvents to investigate the extent of spontaneous formation and matrix effects of formation of N⁶-formyl lysine.

RESULTS

We show that N⁶-formyl lysine, N²-formyl lysine, N⁶-acetyl lysine, and N²-acetyl lysine are all formed spontaneously during sample preparation and LC/MS/MS analysis, which complicates quantification of these metabolites in biological samples. N⁶-Formyl lysine was spontaneously formed and correlated to the concentration of lysine. In the sample matrix of protein digests, 0.03% of lysine was spontaneously converted into N⁶-formyl lysine, and 0.005% of lysine was converted into N⁶-formyl lysine in pure run solvent.

CONCLUSIONS

Spontaneous formation of N⁶-formyl lysine, N⁶-acetyl lysine, N²-formyl lysine, and N²-acetyl lysine needs to be subtracted from biologically formed lysine modifications when quantifying these epimetabolites in biological samples.

Maillard Reaction Products in Different Types of Brewing Malt

Individual Maillard reaction products (MRPs), namely, free and protein-bound glycated amino acids as well as dicarbonyl compounds, were quantitated in various types of brewing malt using chromatographic means. Among the protein-bound glycated amino acids, which were analyzed following enzymatic hydrolysis, N-ε-fructosyllysine was the dominating compound in light (EBC < 10) and dark (10 < EBC < 500) malts, accounting for up to 15.9% of lysine derivatization, followed by N-ε-maltulosyllysine (light malts, up to 4.9% lysine derivatization) or pyrraline (dark malts, up to 10.4% lysine derivatization). Roasting of malt led to the degradation of most of the protein-bound glycated amino acids. The same trends were visible for free glycated amino acids. A novel MRP-derived Strecker aldehyde, namely, 5-(2'-formyl-5'-hydroxymethylpyrrol-1'-yl)-pentanal (pyrralinal), was detected in dark malt. The most abundant 1,2-dicarbonyl compound in malt samples was 3-deoxyglucosone (up to 9 mmol/kg), followed by 3-deoxymaltosone (up to 2 mmol/kg). Only few MRPs such as 5-hydroxymethylfurfural, furfural, the dicarbonyl compounds glyoxal, methylglyoxal, and diacetyl as well as protein-bound rhamnolysine and MG-H1 correlated with the malt color. A comparison of MRPs present in malt with corresponding amounts in beer points to neoformation of MRPs such as MG-H1 and 3-deoxygalactosone during the brewing process.

Insights into chemical and sensorial aspects to understand and manage beer aging using chemometrics

Beer chemical instability remains, at present, the main challenge in maintaining beer quality. Although not fully understood, after decades of research, significant progress has been made in identifying "aging compounds," their origin, and formation pathways. However, as the nature of aging relies on beer manufacturing aspects such as raw materials, process variables, and storage conditions, the chemical profile differs among beers. Current research points to the impact of nonoxidative reactions on beer quality. The effect of Maillard and Maillard intermediates on the final beer quality has become the focus of beer aging research, as prevention of oxidation can only sustain beer quality to some extent. On the other hand, few studies have focused on tracing a profile of whose compound is sensory relevant to specific types of beer. In this matter, the incorporation of "chemometrics," a class of multivariate statistic procedures, has helped brewing scientists achieve specific correlations between the sensory profile and chemical data. The use of chemometrics as exploratory data analysis, discrimination techniques, and multivariate calibration techniques has made the qualitatively and quantitatively translation of sensory perception of aging into manageable chemical and analytical parameters. However, despite their vast potential, these techniques are rarely employed in beer aging studies. This review discusses the chemical and sensorial bases of beer aging. It focuses on how chemometrics can be used to their full potential, with future perspectives and research to be incorporated in the field, enabling a deeper and more specific understanding of the beer aging picture.

Decomposing the molecular complexity of brewing

The compositional space of a set of 120 diverse beer samples was profiled by rapid flow-injection analysis (FIA) Fourier transform ion cyclotron mass spectrometry (FTICR-MS). By the unrivaled mass resolution, it was possible to uncover and assign compositional information to thousands of yet unknown metabolites in the beer matrix. The application of several statistical models enabled the assignment of different molecular pattern to certain beer attributes such as the beer type, the way of adding hops and the grain used. The dedicated van Krevelen diagrams and mass difference networks displayed the structural connectivity of the annotated sum formulae. Thereby it was possible to provide a base of knowledge of the beer metabolome far above database-dependent annotations. Typical metabolic signatures for beer types, which reflect differences in ingredients and ways of brewing, could be extracted. Besides, the complexity of isomeric compounds, initially profiled as single mass values in fast FIA-FTICR-MS, was resolved by selective UHPLC-ToF-MS² analysis. Thereby structural hypotheses based on FTICR’s sum formulae could be confirmed. Benzoxazinoid hexosides deriving from the wheat’s secondary metabolism were uncovered as suitable marker substances for the use of whole wheat grains, in contrast to merely wheat starch or barley. Furthermore, it was possible to describe Hydroxymethoxybenzoxazinone(HMBOA)-hexosesulfate as a hitherto unknown phytoanticipin derivative in wheat containing beers. These findings raise the potential of ultrahigh resolution mass spectrometry for rapid quality control and inspection purposes as well as deep metabolic profiling, profound search for distinct hidden metabolites and classification of archeological beer samples.

Healthy eating recommendations: good for reducing dietary contribution to the body's advanced glycation/lipoxidation end products pool?

The present review aims to give dietary recommendations to reduce the occurrence of the Maillard reaction in foods and in vivo to reduce the body's advanced glycation/lipoxidation end products (AGE/ALE) pool. A healthy diet, food reformulation and good culinary practices may be feasible for achieving the goal. A varied diet rich in fresh vegetables and fruits, non-added sugar beverages containing inhibitors of the Maillard reaction, and foods prepared by steaming and poaching as culinary techniques is recommended. Intake of supplements and novel foods with low sugars, low fats, enriched in bioactive compounds from food and waste able to modulate carbohydrate metabolism and reduce body's AGE/ALE pool is also recommended. In conclusion, the recommendations made for healthy eating by the Spanish Society of Community Nutrition (SENC) and Harvard University seem to be adequate to reduce dietary AGE/ALE, the body's AGE/ALE pool and to achieve sustainable nutrition and health.

Determination of optimal sample preparation for aldehyde extraction from pale malts and their quantification via headspace solid-phase microextraction followed by gas chromatography and mass spectrometry

Aldehydes originating from malt play an important role in beer flavour deterioration. In order to better understand the influence of malting process on beer staling, it is necessary to acquire a reliable analytical methodology for determination of beer staling aldehydes in malt. Therefore, the aim of this study was to evaluate extraction parameters, which allow quantification of beer staling aldehydes present in pale malts. The method was validated with respect to linearity (R > 0.9988), limit of detection (0.28 - 0.99 μg/L), limit of quantification (0.92 - 3.31 μg/L), accuracy (± 5%), repeatability (1.3 - 5.3%) and intermediate precision (>20%). The following parameters of sample preparation were evaluated: sample amount, extraction time and temperature, ultrasonication time and oxygen level. Consequently, the best extraction conditions were successfully applied on pale malts. After extraction, the samples were analysed by headspace solid-phase microextraction (HS-SPME) with on fibre carbonyl derivatisation followed by gas chromatography and mass spectrometry (GC-MS). In addition, the salting-out effect during HS-SPME was studied. The method application allowed to identify significant differences (p ≤ 0.05) in the levels of aldehydes among various industrial scale, pale malts. The optimised method could give the information on the aldehyde content introduced into the brewing process and its potential contribution to the overall beer quality.

Higher NADH Availability of Lager Yeast Increases the Flavor Stability of Beer

Flavor stability is a significant concern to brewers as the staling compounds impart unpleasant flavor to beer. Thus, yeasts with antistaling ability have been engineered to produce beer with improved flavor stability. Here, we proposed that increasing the NADH availability of yeast could improve the flavor stability of beer. By engineering endogenous pathways, we obtained an array of yeast strains with a higher reducing activity. Then, we carried out beer fermentation with these strains and found that the antistaling capacities of the beer samples were improved. For a better understanding of the underlying mechanism, we compared the flavor profiles of these strains. The production of staling components was significantly decreased, whereas the content of antistaling components, such as SO₂, was increased, in line with the increased antistaling ability. The other aroma components were marginally changed, indicating that this concept was useful for improving the antistaling stability without changing the flavor of beer.

Spiroalanpyrroids A and B, sesquiterpene alkaloids with a unique spiro-eudesmanolide–pyrrolizidine skeleton from Inula helenium

Two sesquiterpene alkaloids with an unprecedented eudesmanolide–pyrrolizidine spiro[5.5] framework, together with two new sesquiterpene-amino acid adducts were isolated from the roots of Inula helenium.

Mitigation of 3-deoxyglucosone and 5-hydroxymethylfurfural in brown fermented milk via an alternative browning process based on the hydrolysis of endogenous lactose

During the conventional production of brown fermented milk (BFM), unhealthy substances (3-deoxyglucosone (3-DG), methylglyoxal (MGO), and 5-hydroxymethylfurfural (HMF)) are generated during the Maillard browning step. Here, an alternative browning process based on the hydrolysis of endogenous lactose was established. Compared with the conventional process, 3-DG and HMF were decreased by 5.91 mg kg-1 and 0.39 mg kg-1 in the brown milk base under the alternative browning process, and thereafter, 3-DG and HMF were decreased by 54.5% and 65.0% in BFM. Investigation into the formation of 3-DG, MGO, and HMF in different chemical models showed that different sugars lead to different Maillard reaction products and browning rates, contributing to the mitigation of 3-DG and HMF. Apart from the mitigation of unhealthy Maillard compounds, hydrolyzing lactose and avoiding the addition of external glucose make the alternative browning process a theoretical and practical basis for improving the quality and safety of BFM.

Formation of α-Dicarbonyls from Dairy Related Carbohydrates with and without Nα-Acetyl-l-Lysine during Incubation at 40 and 50 °C

α-Dicarbonyls are reactive intermediates formed during Maillard reactions and carbohydrate degradation. The formation of seven α-dicarbonyls was characterized in solutions containing dairy related carbohydrates (galactose, glucose, lactose, and galacto-oligosaccharides (GOS)) during incubations at 40 and 50 °C with and without Nα-acetyl-l-lysine at pH 6.8 for up to 2 months. The concentrations of α-dicarbonyls in samples of monosaccharides with Nα-acetyl-l-lysine were found to be 3-deoxyglucosone (3-DG) > 3-deoxygalactosone (3-DGal) > glyoxal > glucosone, galactosone > methylglyoxal > diacetyl. The presence of Nα-acetyl-l-lysine resulted in up to 100-fold higher concentrations of C6 α-dicarbonyls but lesser formation of glyoxal in the monosaccharide-containing models compared to what was observed in the absence of Nα-acetyl-l-lysine. Galactose incubated with Nα-acetyl-l-lysine generated the highest concentrations of 3-DGal (up to 130 μM), glyoxal (up to 100 μM), and methylglyoxal (up to 9 μM) compared to the other carbohydrates during incubation. Surprisingly, 3-DG (1500 μM) and 3-DGal (80 μM) were formed at levels of 2 orders of magnitude higher in solutions of GOS in the absence of Nα-acetyl-l-lysine as compared to the other carbohydrates at 40 °C, while GOS generated the lowest levels of glyoxal. GOS are widely used as an ingredient in various types of foods products, and it is therefore of importance to consider the risk of generating high levels of the reactive C6 α-dicarbonyl, 3-DG, in these types of products. This study contributes to the understanding of major α-dicarbonyl formation as affected by the presence of primary amines in GOS-, lactose-, and galactose-containing solutions under moderate heating in liquid foods.

Formation of 3-deoxyglucosone in the malting process

3-Deoxyglucosone (3-DG) is a metabolite from sugar degradation obtained by the Maillard reaction. It is an important precursor compound in Strecker reactionism that directly leads to known beer aging indicators and can influence the final sensory beer quality. However, the conditions of 3-DG formation in the malting process have not yet been described. To investigate the reaction pathways of 3-DG formation, we varied the composition of reactants (sugars, amino acids) by using different malting modification levels (germination time 5-7 d; steeping degree 42-45%; germination temperature 12-14 °C); final kilning temperature (60 °C to 100 °C). After its derivatization with ortho-phenylenediamine, we analyzed 3-DG with HPLC-UV. 3-DG concentration was between 5 and 120 µmol/100 g dry weight. The formation of 3-DG increased for high malt modification levels and high final kilning temperature. The abundant formation of 3-DG in the malting process is already comparable to the occurred brewing process concentration.

Effective Mechanism of (-)-Epigallocatechin Gallate Indicating the Critical Formation Conditions of Amadori Compound during an Aqueous Maillard Reaction

The formation conditions of the Amadori compound (ARP) N-(1-deoxy-d-xylulos-1-yl)-alanine were determined in an aqueous Maillard reaction between l-alanine and d-xylose under a two-step temperature rising process with (-)-epigallocatechin gallate (EGCG) as an indicator followed by browning intensity detection of the final Maillard reaction products (MRPs). To clarify the mechanism of EGCG indication on the ARP formation, the change in the concentration of some key products generated during the Maillard reaction with EGCG addition was investigated. Results showed an inhibition effect of EGCG on the browning precursor formation through the generation of ARP-EGCG adducts and deoxyosone-EGCG adducts, which was proposed as an important pathway to inhibit browning during the Maillard reaction and to indicate ARP formation.

Formation and Alterations of the Potentially Harmful Maillard Reaction Products during the Production and Storage of Brown Fermented Milk

To improve the quality and safety of brown fermented milk (BFM), the formation and alterations of potentially harmful Maillard reaction products (MRPs), including 3-deoxyglucosone (3-DG), methylglyoxal (MGO), 5-(hydroxymethyl)-2-furfural (HMF), acrylamide and flavour components were investigated during the browning, fermentation and commercial storage. MRPs were shown to be produced mainly during the browning stage. The levels of different substances varied during the fermentation and commercial storage stage. The proportion and type of carboxylic acids in the flavour components significantly increased during the fermentation stage. Browning index of milk during the browning stage was shown to be positively associated with the 3-DG (Pearson's r = 0.9632), MGO (Pearson's r = 0.9915), HMF (Pearson's r = 0.9772), and acrylamide (Pearson's r = 0.7910) levels and the total percentage of the flavour components from four different categories (Pearson's r = 0.7407). Changes in physicochemical properties of BFM during production not only contribute to predict the formation of potentially unhealthy MRPs, but also Lactobacillus species used for the fermentation should be carefully selected to improve the quality of this product.

Parameters affecting 5-hydroxymethylfurfural exposure from beer

5-Hydroxymethylfurfural (HMF) is generated during food and beverage heating processes and/or storage. Its daily intake, estimated as 4-10 mg day^-1, is several orders of magnitude higher than other process contaminants. Beer can be of relevance to the evaluation of HMF exposure; however, the information concerning its occurrence in different types of beer and during product storage is scarce. Therefore, the major goal of this work was to assess the amounts of HMF in different commercial beers, as well as the impact of storage, to deepen knowledge about the contribution of beer to HMF exposure. Blonde beers presented a mean content of 4.29 ± 1.05 mg L^-1, which was significantly lower (P ≤ 0.05) than those obtained for amber (6.84 ± 0.75 mg L^-1) and dark beers (6.99 ± 0.52 mg L^-1). Additionally, to study kinetic of HMF formation, fresh pilsner beers were stored at 30, 40 and 50°C during 40 days; a zero-order reaction was observed. The dependence of the rate constant on temperature was described by the Arrhenius equation and calculated activation energy was 101.85 kJ mol^-1. Storage can increase drastically HMF content, which means higher exposure for consumers. Thus, beer contribution to HMF exposure should not be neglected, since the intake of 1 L of beer entails a consumption of 4-7 mg of HMF or even more, depending on storage time and temperature.

Forced into aging: Analytical prediction of the flavor-stability of lager beer. A review

Despite years of research, sensory deterioration during beer aging remains a challenge to brewing chemists. Therefore, sensorial and analytical tools to investigate aging flavors are required. This review aims to summarize the available analytical methods and to highlight the problems associated with addressing the flavor-stability of beer. Carbonyls are the major contributors to the aroma of aged pale lager beer, which is especially susceptible to deterioration. They are formed via known pathways during storage, but, as recent research indicates, are mainly released from the bound-state during aging. However, most published studies are based on model systems, and thus the formation and breakdown parameters of these adducts are poorly understood. This concept has not been previously considered in previous forced-aging analysis. Only weak parallels can be drawn between forced and natural aging. This is likely due to the different activation energies of the chemical processes responsible for aging, but may also be due to heat-promoted release of bound aldehydes. Thus, precursors and their binding parameters must be investigated to make appropriate technological adjustments to forced-aging experiments. In combination with sophisticated data analysis, the investigation of volatile indicators and non-volatile precursors can lead to more reliable predictions of flavor stability.

A stimuli-responsive fluorescence platform for simultaneous determination of d-isoascorbic acid and Tartaric acid based on Maillard reaction product

An activatable fluorescence monitoring platform based on a novel Maillard reaction product from d-glucose and L-arginine was prepared through a facile one-pot approach and applied for simultaneous detection of d-isoascorbic acid and tartaric acid. In this work, the new Maillard reaction product GLA was first obtained, and its fluorescence intensity can be effectively quenched by KMnO₄, resulting from a new complex (GLA-KMnO₄) formation between GLA and KMnO₄. Upon addition of d-isoascorbic acid or tartaric acid, an enhanced fluorescence was observed under the optimumed experimental conditions, indicating a stimuli-responsive fluorescence turn on platform for d-isoascorbic acid or tartaric acid can be developed. The corresponding experimental results showed that this turn on fluorescence sensing platform has a high sensitivity for d-isoascorbic acid or tartaric acid, because the detection limits were 5.9μM and 21.5μM, respectively. Additionally, this proposed sensing platform was applied to simultaneously detection of d-isoascorbic acid and tartaric acid in real tap water samples with satisfactory results.

Probing Protein Glycation by Chromatography and Mass Spectrometry: Analysis of Glycation Adducts

Glycation is a non-enzymatic post-translational modification of proteins, formed by the reaction of reducing sugars and α-dicarbonyl products of their degradation with amino and guanidino groups of proteins. Resulted early glycation products are readily involved in further transformation, yielding a heterogeneous group of advanced glycation end products (AGEs). Their formation is associated with ageing, metabolic diseases, and thermal processing of foods. Therefore, individual glycation adducts are often considered as the markers of related pathologies and food quality. In this context, their quantification in biological and food matrices is required for diagnostics and establishment of food preparation technologies. For this, exhaustive protein hydrolysis with subsequent amino acid analysis is the strategy of choice. Thereby, multi-step enzymatic digestion procedures ensure good recoveries for the most of AGEs, whereas tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode with stable isotope dilution or standard addition represents “a gold standard” for their quantification. Although the spectrum of quantitatively assessed AGE structures is continuously increases, application of untargeted profiling techniques for identification of new products is desired, especially for in vivo characterization of anti-glycative systems. Thereby, due to a high glycative potential of plant metabolites, more attention needs to be paid on plant-derived AGEs.

Role of α-Dicarbonyl Compounds in the Inhibition Effect of Reducing Sugars on the Formation of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

The effect of reducing sugars on formation of PhIP in fried pork was investigated, and the underlying mechanisms were revealed by studying the reaction pathways between α-dicarbonyl compounds (α-DCs) and PhIP. The addition of reducing sugars (such as glucose) greatly reduced the amount of PhIP in fried pork from 15.5 ng/g to less than 1.0 ng/g. The amount of PhIP decreased significantly with an increasing level of added α-DCs in model systems. Similarly, the addition of methylglyoxal (MGO) decreased significantly the levels of phenylalanine (Phe) and creatinine (Crn) but increased significantly the level of phenylacetaldehyde (PEA). 2-Amino-1-methyl-5-(2-oxopropylidene)-imidazol-4-one and N-(1-methyl-4-oxoimidazolidin-2-ylidene) amino propionic acids were identified in MGO/Crn and MGO/Crn/Phe model systems and fried pork with glucose. These results revealed that the degradation products of reducing sugars-α-DCs-play an important role in inhibiting formation of PhIP by reacting with key precursors of PhIP and itself.

Formation of Reactive Intermediates, Color, and Antioxidant Activity in the Maillard Reaction of Maltose in Comparison to d-Glucose

In this study, the Maillard reaction of maltose and d-glucose in the presence of l-alanine was investigated in aqueous solution at 130 °C and pH 5. The reactivity of both carbohydrates was compared in regards of their degradation, browning, and antioxidant activity. In order to identify relevant differences in the reaction pathways, the concentrations of selected intermediates such as 1,2-dicarbonyl compounds, furans, furanones, and pyranones were determined. It was found, that the degradation of maltose predominantly yields 1,2-dicarbonyls that still carry a glucosyl moiety and thus subsequent reactions to HMF, furfural, and 2-acetylfuran are favored due to the elimination of d-glucose, which is an excellent leaving group in aqueous solution. Consequently, higher amounts of these heterocycles are formed from maltose. 3-deoxyglucosone and 3-deoxygalactosone represent the only relevant C₆-1,2-dicarbonyls in maltose incubations and are produced in nearly equimolar amounts during the first 60 min of heating as byproducts of the HMF formation.

Transketolase A from E. coli Significantly Suppresses Protein Glycation by Glycolaldehyde and Glyoxal in Vitro

Short-chained carbonyl species such as glycolaldehyde and its oxidized pendant glyoxal are highly reactive Maillard agents, leading to the formation of protein modifications. These advanced glycation endproducts have gained considerable interest as they have been linked to various pathologies in vivo. The ability of transketolase to use glycolaldehyde as a substrate suggested the possibility to modulate carbonyl-driven Maillard reactions. Model incubations with recombinant transketolase A from Escherichia coli in the presence of bovine serum albumin and glycolaldehyde indeed led to a decrease in glycolaldehyde concentrations paralleled by the enzymatic conversion to erythrulose. As a result, reversibly protein-bound glycolaldehyde and the major final endproduct N⁶-carboxymethyl lysine were significantly reduced by approximately 50%, respectively. Glycolaldehyde is easily oxidized to glyoxal in the presence of amines and oxygen. In the presence of transketolase, the lower amounts of glycolaldehyde therefore also strongly suppressed the formation of glyoxal specific arginine modifications, measured as 5-(2-imino-5-oxo-1-imidazolidinyl)norvaline after acid hydrolysis.

Browning Potential of C6-α-Dicarbonyl Compounds under Maillard Conditions

In this work, the three major C₆-α-dicarbonyl compounds glucosone (GLUC), 1-deoxyglucosone (1-DG), and 3-deoxyglucosone (3-DG) were synthesized and examined under Maillard conditions (aqueous solutions with the addition of l-alanine at 130 °C and pH 5/8). For the first time, the resulting color formation, antioxidant activity, and generation of short-chained α-dicarbonyls were investigated and compared to incubations of d-glucose and d-fructose. An additive effect on the formation of color, an antagonistic effect on the generation of α-dicarbonyl compounds, and a synergistic effect on the antioxidant activity could be observed for the 1-DG/GLUC combination. Despite their common degradation products, different extinctions could be measured, with 3-DG showing the strongest color formation, followed by GLUC and 1-DG. The analyzed α-dicarbonyl compounds have no direct impact on the formation of color but are precursors for most of the colored compounds. The main difference between the three substances is their ability to form different heterocyclic degradation products, such as pyranones (1-DG), furanones (1-DG), furans (GLUC and 3-DG), and the corresponding N-heterocycles in the presence of amino components. This seems to be the main reason for their varying browning potential and antioxidant activity.

Simultaneous Quantitation of Advanced Glycation End Products in Soy Sauce and Beer by Liquid Chromatography-Tandem Mass Spectrometry without Ion-Pair Reagents and Derivatization

The aim of this study was to develop a simple and sensitive method to analyze several advanced glycation end products (AGEs) simultaneously using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and to apply this method to the quantitation of AGEs in brown-colored foods. The developed method enabled to separate and quantitate simultaneously seven AGEs, and was applied to the determination of free AGEs contained in various kinds of soy sauce and beer. The major AGEs in soy sauce and beer were N^ε-carboxymethyllysine (CML), N^ε-carboxyethyllysine (CEL), and N^δ-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine (MG-H1). Using the developed LC-MS/MS method, recovery test on soy sauce and beer samples showed the recovery values of 85.3-103.9% for CML, 95.9-107.4% for CEL, and 69.5-123.2% for MG-H1. In particular, it is the first report that free CML, CEL, and MG-H1 were present in beer. Furthermore, long-term storage and heating process of soy sauce increased CML and MG-H1.

Relevance of Oxygen for the Formation of Strecker Aldehydes during Beer Production and Storage

Off-flavor in beer is often associated with the appearance of staling aldehydes. In this study, the factors amino acid concentration, carbohydrate concentration, Fe²⁺ concentration, and oxygen concentration were investigated in terms of their effect on the formation of carbonyl compounds during storage using response surface methodology. From all factors tested, only amino acid concentration and oxygen concentration promoted Strecker aldehyde formation during storage, while all other carbonyls measured were unaffected. A mixture of glucose/xylose, representing carbohydrate sources, as well as Fe²⁺ concentration were insignificant factors, though carbohydrate additions exhibited a significant role in the formation of 2-furfural. De novo formation of phenylacetaldehyde from phenylalanine during beer storage was observed using labeling experiments and a linear relationship between Strecker aldehydes formed and total packaged oxygen was identified. Capping beers with oxygen barrier crown corks and addition of 10 mg/L EDTA to beers effectively diminished Strecker aldehyde formation. Oxygen was additionally shown to significantly promote Strecker aldehyde formation during sweet wort production. A pathway for the reactive oxygen species-induced degradation of amino acids yielding Strecker aldehydes was proposed and was further scrutinized in buffered model solutions. The insignificant role of Fe²⁺ in the response surface experiments is discussed.

Free and Protein-Bound Maillard Reaction Products in Beer: Method Development and a Survey of Different Beer Types

The Maillard reaction is important for beer color and flavor, but little is known about the occurrence of individual glycated amino acids in beer. Therefore, seven Maillard reaction products (MRPs), namely, fructosyllysine, maltulosyllysine, pyrraline, formyline, maltosine, MG-H1, and argpyrimidine, were synthesized and quantitated in different types of beer (Pilsner, dark, bock, wheat, and nonalcoholic beers) by HPLC-ESI-MS/MS in the multiple reaction monitoring mode through application of the standard addition method. Free MRPs were analyzed directly. A high molecular weight fraction was isolated by dialysis and hydrolyzed enzymatically prior to analysis. Maltulosyllysine was quantitated for the first time in food. The most important free MRPs in beer are fructosyllysine (6.8-27.0 mg/L) and maltulosyllysine (3.7-21.8 mg/L). Beer contains comparatively high amounts of late-stage free MRPs such as pyrraline (0.2-1.6 mg/L) and MG-H1 (0.3-2.5 mg/L). Minor amounts of formyline (4-230 μg/L), maltosine (6-56 μg/L), and argpyrimidine (0.1-4.1 μg/L) were quantitated. Maltulosyllysine was the most significant protein-bound MRP, but both maltulosyllysine and fructosyllysine represent only 15-60% of the total protein-bound lysine-derived Amadori products. Differences in the patterns of protein-bound and free individual MRPs and the ratios between them were identified, which indicate differences in their chemical, biochemical, and microbiological stabilities during the brewing process.

Proteome-Based Analysis of Colloidal Instability Enables the Detection of Haze-Active Proteins in Beer

Colloidal haze is a serious quality defect of bright beers that considerably reduces their shelf life and is thought to be triggered by hordeins, a class of proline-rich barley proteins. In this work, the proteomes of fresh and old beers were investigated in bottled pilsners and compared to the protein inventory of haze to identify specific haze-active proteins. Haze isolates dissolved in rehydration buffer contained high concentrations of proteins and sugars but provided protein gels with weak spot signals. Consequently, a treatment for the chemical deglycation with trifluoromethanesulfonic acid was applied, which resulted in the identification of protein Z4, LTP1, CMb, CMe, pUP13, 3a, and Bwiph as constituents of the haze proteome. Because only one hordein was detectable and the proline content in haze hydrolysates was lower than those of barley prolamins, our results suggest that this class of proteins is of minor importance for haze development.

Influence of yeast strain, priming solution and temperature on beer bottle conditioning

BACKGROUND

Recently, there has been a significant increase in the number of microbreweries. Usually, craft beers are bottle conditioned; however, few studies have investigated beer refermentation. One of the objectives of this study was to evaluate the impacts of different experimental conditions, specifically yeast strain, priming solution and temperature, on the standard quality attributes, the volatile compounds and the sensory profile of the bottle-conditioned beer. The other aim was to monitor the evolution of volatile compounds and amino acids consumption throughout the refermentation process to check if it is possible to reduce the time necessary for bottle conditioning.

RESULTS

The results indicate that the volatile profile was mainly influenced by the strain of yeast, and this may have obscured the possible impacts of the other parameters. Our results also confirm that the two yeast strains showed different metabolic activity, particularly with respect to esters production. Moreover, we found the Safbrew S-33® strain when primed with Siromix® and refermented at 30 °C yielded the fastest formation of higher alcohols while maintaining low production of off-flavours.

CONCLUSIONS

These results suggest a formulation that may reduce the time needed for bottle conditioning without affecting the quality of the final beer which may simultaneously improve efficiency and economic profits. © 2016 Society of Chemical Industry.

Occurrence of (Z)-3,4-Dideoxyglucoson-3-ene in Different Types of Beer and Malt Beer as a Result of 3-Deoxyhexosone Interconversion

In beer, 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) are important sugar degradation products, but little is known about the relevance of the interconversion reaction between these compounds in different types of beer. In the present study, 3-DG was quantitated at concentrations of 12.9-52.7 mg/L and 3-DGal at concentrations of 6.0-26.4 mg/L in different types of beer (pilsner, wheat, bock, dark, and alcohol-free beers). The concentrations in malt beer tended to be higher. Largely overlapping concentration ranges precluded a classification of beers by their 3-deoxyglycosone contents. 3,4-Dideoxyglucoson-3-ene (3,4-DGE) was identified as an important intermediate and quantitated in beer and malt beer for the first time. The E and Z isomers of the corresponding quinoxaline were synthesized by a new synthetic approach and isolated by semipreparative HPLC. An assay was developed for quantitation of (E)- and (Z)-3,4-DGE by HPLC-MS/MS, and the Z isomer was determined at concentrations of 0.3-1.7 mg/L in beer and 0.5-4.8 mg/L in malt beer samples. The E isomer was shown to be of little importance. Concentrations of 5-hydroxymethylfurfural (HMF) were twice as high as those of (Z)-3,4-DGE in beer samples (0.4-3.7 mg/L) but much higher in malt beer samples (1.6-336 mg/L).

Oxidative versus Non-oxidative Decarboxylation of Amino Acids: Conditions for the Preferential Formation of Either Strecker Aldehydes or Amines in Amino Acid/Lipid-Derived Reactive Carbonyl Model Systems

Comparative formation of both 2-phenylethylamine and phenylacetaldehyde as a consequence of phenylalanine degradation by carbonyl compounds was studied in an attempt to understand if the amine/aldehyde ratio can be changed as a function of reaction conditions. The assayed carbonyl compounds were selected because of the presence in the chain of both electron-donating and electron-withdrawing groups and included alkenals, alkadienals, epoxyalkenals, oxoalkenals, and hydroxyalkenals as well as lipid hydroperoxides. The obtained results showed that the 2-phenylethylamine/phenylacetaldehyde ratio depended upon both the carbonyls and the reaction conditions. Thus, it can be increased using electron-donating groups in the chain of the carbonyl compound, small amounts of carbonyl compound, low oxygen content, increasing the pH, or increasing the temperature at pH 6. Opposed conditions (use of electron-withdrawing groups in the chain of the carbonyl compound, large amounts of carbonyl compound, high oxygen contents, low pH values, and increasing temperatures at low pH values) would decrease the 2-phenylethylamine/phenylacetaldehyde ratio, and the formation of aldehydes over amines in amino acid degradations would be favored.