Maillard Reaction Products in Different Types of Brewing Malt

Effects of Fortified Wheat Bran Arabinoxylan on the Quality of Wheat Malt Beer

Arabinoxylan, a key non-starch polysaccharide in wheat bran, significantly influences the quality and health benefits of wheat beer. This study aimed to investigate how wheat bran addition (0-20%) affects water-extracted arabinoxylan (WEAX) content and beer quality in 100% wheat malt beer. The study integrated physicochemical analyses (polysaccharide composition, WEAX molecular weight), process parameters (wort filtration time, foam stability), and sensory evaluation to establish structure-function relationships. Results showed that the WEAX content in beer increased from 1.36 mg/mL in pure malt beer (0% bran) to 2.25 mg/mL with 20% bran addition. Bran addition shortened wort filtration time by 20-45%. The molecular weight of WEAX was mainly 2936-7062 Da, enhancing foam expansion (36.18%) and stability (15.54%) due to elevated polymerization and arabinose-to-xylose (A/X) ratios. WEAX fractions (7062-10,134 Da and 859-2936 Da) correlated positively with beer turbidity and viscosity. Sensory analysis identified 15% bran as optimal for balanced quality. These findings demonstrate that bran addition enhances WEAX content, polymerization, and A/X ratios, improving foam performance, reducing filtration time, and optimizing beer quality without altering arabinogalactan, glucan, or mannose polymer content.

Influence of Malted Chickpea on the Composition of Volatiles in Hummus

In recent years, research has shown that malting legume seeds can be a viable modification method; however, very few applications of legume malts are currently available. This research aimed to determine whether using malted chickpeas can significantly impact the volatile composition of the produced hummus, as aroma is one of the crucial factors in the acceptance of food products. Five chickpea malts produced by germination by a different amount of time (24 h, 48 h, 72 h, 96 h, and 120 h) were used as a substrate for the production of hummuses and were compared to the hummus produced from unmalted chickpeas. Hummuses produced from the chickpea malt germinated for 96 h and 120 h were characterized by a higher concentration of most volatiles than the control sample, while the hummuses produced from chickpea malts germinated for 24 h, 48 h, and 72 h were characterized by a lower concentration of volatiles.

Latent Association Between Diets and Glioma Risk: A Mendelian Randomization Analysis

BACKGROUND

Gliomas, particularly high-grade gliomas such as glioblastoma, represent a major challenge due to their poor prognosis. While dietary factors have been proposed as potential modulators of glioma risk, causal inference has been hindered by confounding and reverse causality in observational studies. This study employs Mendelian randomization to investigate the causal relationship between dietary factors and glioma risk.

METHODS

A two-sample MR framework was applied, utilizing genome-wide association study data for 22 dietary exposures and glioma risks, including both GBM and non-GBM subtypes. Instrumental variables (genetic variants) were identified for each dietary factor to address confounding and pleiotropy. Causal inference was conducted using inverse-variance weighted regression, complemented by MR-Egger and MR-PRESSO analyses to assess and correct for potential pleiotropy.

RESULTS

A positive causal association was observed between the intake of cooked vegetables and the GBM risk (OR = 6.55, 95% CI: 1.86-23.12, p = 0.00350). While alcohol intake demonstrated a protective effect for non-GBM risk (OR = 0.770, 95% CI: 0.61-0.97, p = 0.029), beer was substantially linked to an increased risk of non-GBM gliomas (OR = 4.82, 95% CI: 1.84-12.59, p = 0.0014). Other dietary factors did not exhibit significant causal associations.

CONCLUSIONS

These findings suggest that certain dietary factors, including cooked vegetable intake, beer consumption, and alcohol intake, may exert a causal influence on glioma risk. This study provides new insights into the potential dietary determinants of glioma and underscores the need for further investigation into modifiable risk factors for glioma prevention.

Identification of Lactose-Derived α-Dicarbonyl Compounds in Dairy Products and Elucidation of Their Formation Mechanism

α-Dicarbonyl compounds (α-DCs) generated from carbohydrates play a key role in food quality and safety as precursors. Lactose contributes to α-DCs generation in dairy products; however, α-DCs with intact lactose carbons have not been investigated so far. This study aimed to identify lactose-derived α-DCs, clarify the mechanism of its formation using model incubations, and investigate the distribution and contents of α-DCs in dairy products. From the heated lactose and lysine solution, four new α-DCs derivatives were isolated by column chromatography and preparative HPLC and identified as lactosone, 1-deoxylactosone (1-DL) and its epimer, and 1,5-dideoxylactoson-4-ene (1,5-DDLE) by MS and NMR analyses. 1-DL, 1-DL epimer, and 1,5-DDLE were specifically formed from Amadori compounds of lactose and could be indicators of lactose-associated Maillard reaction. These α-DCs were abundantly contained in thermally processed dairy products, especially infant formulas and whey protein, and affected by ingredients and manufacturing process.

Formation of Chlorinated Carbohydrate Degradation Products and Amino Acids during Heating of Sucralose in Model Systems and Food

Sucralose is an artificial sweetener whose stability during the thermal treatment of food is controversially discussed. In the present work, sucralose was subjected to different kinds of heat treatment either as such, in the presence of protein, or as an ingredient of food. Compared with sucrose, sucralose showed remarkable instability and discoloration after heating at 85-90 °C for 1 h. A chlorinated furan-3-one and different chlorinated dicarbonyl compounds were identified by High-performance liquid chromatography-time-of-flight mass spectrometry (HPLC-TOF-MS) for the first time, indicating that both the 4-chlorogalactosyl residue and the 1,6-dichlorofructosyl residue give rise to novel chlorinated sugar degradation products. When sucralose was heated in the presence of protein, the formation of 3-chlorotyrosine was detected, indicating that sucralose can invoke chlorination of other biomolecules. The influence of the addition of sucralose (0.03-0.1%) to dough on pH value, color development, and HMF formation was tested in baking experiments (muffins, coconut macaroons, cookies). A significantly higher HMF concentration was observed in bakery products, including sucralose, and a chlorinated 1,2-dicarbonyl compound was detected qualitatively in baked cookies. This work shows that sucralose is not stable during baking processes at high temperatures and low moisture contents, thereby confirming recommendations from the German Institute of Risk Assessment not to use sucralose for baking.

Control Formation of Furans and Pyrazines Resulting from Dual Glycation Sites in Nα,Nε-Di(1-deoxy-d-xylulos-1-yl)lysine via Elevating Thermal Degradation Temperatures

Lysine (Lys) glycated by xylose (Xyl) at α-NH2 [Nα(1-deoxy-D-xylulos-1-yl)lysine (Nα-Xyl-Lys ARP)] or ε-NH2 [Nε-(1-deoxy-D-xylulos-1-yl)lysine (Nε-Xyl-Lys ARP)] significantly impacted the thermal degradation pathways of Amadori rearrangement products (ARPs). Nα-Xyl-Lys ARP was found to undergo retro-aldolization on the sugar fragment more readily to form glyoxal/methylglyoxal than Nε-Xyl-Lys ARP. Furans and pyrazines formation during the degradation of the diglycated lysine [Nα,Nε-di(1-deoxy-d-xylulos-1-yl)lysine (Nα,Nε-di-Xyl-Lys ARP)] was delayed at 120 °C relative to Nε-Xyl-Lys ARP. This was attributed to the complex degradation of Nα,Nε-di-Xyl-Lys ARP, which slowed the substantial formation of deoxypentosones and the effective release of Lys. At 140 °C, the dual glycated Nα,Nε-di-Xyl-Lys ARP was more conducive to promoting the redistribution of electrons and facilitating molecular rearrangement. This accelerated the efficient decomposition of dual glycated groups in Nα,Nε-di-Xyl-Lys ARP and enabled glyoxal to actively participate in Strecker degradation. Thus, the production of furans and pyrazines was substantially increased, and the variety of pyrazines was expanded from three types to eight types. An appropriate increase to pH 7.5 effectively avoided the overprotonation of hydroxyl and amino groups (pH 5.5), simultaneously enhancing furans and pyrazines yield while minimizing the formation of pyridines under alkaline conditions.

Stability of the Glycated Amino Acid 6-(2-Formyl-5-hydroxymethyl-1-pyrrolyl)-l-norleucine (Pyrraline) During Oxidation

Food proteins may be modified during processing and storage through reactions with reducing sugars (Maillard reaction, glycation) or by reactive oxygen species (protein oxidation). Little is known about particular reactions at the interface of glycation and oxidation. In the present study, the glycated amino acid pyrraline (6-(2-formyl-5-hydroxymethyl-1-pyrrolyl)-l-norleucine) and the proteinogenic amino acids tyrosine and tryptophan were subjected to different types of oxidation. The stability of the amino acids was assessed by HPLC with UV detection, whereas oxidation products were assigned by HPLC with triple quadrupole or time-of-flight mass spectrometric detection. Conditions that lead to oxidation of aromatic proteinogenic amino acids can also lead to oxidation of pyrraline. Pyrraline was particularly unstable in the presence of permanganate, hypochlorite, and under hydroxyl radical-generating conditions (iron, ethylenediaminetetraacetic acid, ascorbic acid). Evidence obtained by high-resolution mass spectrometry revealed the oxidation of pyrraline to 6-(2,5-diformyl-1-pyrrolyl)-l-norleucine, 6-(2-carboxy-5-hydroxymethyl-1-pyrrolyl)-l-norleucine, 6-(2-formyl-5-carboxy-1-pyrrolyl)-l-norleucine, and 6-(2,5-dicarboxy-1-pyrrolyl)-l-norleucine in the presence of potassium permanganate. The latter product was isolated by semipreparative HPLC and characterized by NMR. Under hydroxyl radical-generating conditions, pyrraline is hydroxylated at the ring under formation of 6-(2-formyl-4-hydroxy-5-hydroxymethyl-1-pyrrolyl)-l-norleucine or 6-(2-formyl-3-hydroxy-5-hydroxymethyl-1-pyrrolyl)-l-norleucine. This study shows that the so-called "advanced glycation end products" are no end products of the Maillard reaction, but may undergo further chemical degradation reactions.

From Conventional to Craft Beer: Perception, Source, and Production of Beer Color-A Systematic Review and Bibliometric Analysis

Beer is a popular beverage consumed globally, and studies have emphasized the benefits of moderate consumption as well as its sensory effects on consumers. Color is a crucial sensory attribute, being the first aspect a consumer notices when assessing a beer's quality. This review seeks to offer detailed insights into how brewing methods, raw materials, and the chemical diversity of beer influence the production of beer color. The chemical mechanisms responsible for color development and how consumers and color systems perceive the color of beer were assessed. A systematic review following the PRISMA methodology, coupled with a bibliometric analysis, was performed using (Rayyan 2022) and (VOSviewer 1.6.20) software to assess and evaluate the scientific research retrieved from the Web of Science Core Collection. The findings highlight the significant roles of malt types, heat brewing processes, control of chemical parameters, and innovative brewing techniques in conventional beer color production. Novel chromophores like perlolyrine, pyrrolothiazolate, and furpenthiazinate are thought to affect Pilsen-style beers, along with melanoidins, Strecker aldehydes, and 5-hydroxymethylfurfural (HMF) in conventional beers. In craft beers, such as fruit- or herb-based beers, flavonoids like anthocyanins, along with other natural pigments and synthetic colorants, are identified as the primary sources of color. However, studies related to the influence of chromophores like perlolyrine, pyrrolothiazolate, and furpenthiazinate on beer color are scarce, and emerging additives, such as pigments from microorganisms, spices, exotic herbs, and leaves of plants, on craft beer offer insights for future research.

Metabolization of Free and Peptide-Bound Oxidized Methionine Derivatives by Saccharomyces cerevisiae in a Model System

In the brewing process, methionine is a decisive amino acid for (off-)flavor formation. A significant part of methionine is oxidized to methionine sulfoxide (MetSO) in malt. We hypothesized that MetSO and MetSO2 are metabolized to volatile compounds during yeast fermentation and examined whether the yeast Saccharomyces cerevisiae is able to catabolize l-MetSO and l-MetSO2 in free and dipeptide-bound forms. We also investigated the stability of l-methionine sulfoximine and S-methylmethionine. Cell viability in the presence of the test compounds was at least 90%. Both free and peptide-bound test substances were metabolized by Saccharomyces cerevisiae. l-MetSO was degraded most rapidly as the free amino acid, while l-MetSO2 was degraded most rapidly bound in dipeptides. We observed a different degradation behavior of the (R) and (S) diastereoisomers for l-MetSO and l-methionine sulfoximine. Furthermore, we detected methionol as the only metabolite of MetSO. Methionol sulfoxide was not formed. MetSO2 was not converted to methionol or methionol sulfone but to the respective α-hydroxy acid. We conclude that the reduction of MetSO to methionine proceeds faster than transamination. The occurrence of MetSO or MetSO2 in brewing malt will not lead to the formation of hitherto unknown volatile metabolites of the Ehrlich pathway.

Preliminary research on the flavor substance and antioxidant capacity of beers produced with baking Qingke

The addition of baked Qingke improves the flavor profile of beer. In this study, beer was brewed using Qingke baked at various temperatures. The beer produced with Qingke baked at 180 °C achieved the highest sensory score (40/50), an alcohol content of 6.92% (v/v), a total phenolic content of 446.42 mg/L, melanoidin concentration of 98.22 g/L, a color value of 10.88 EBC, and exhibited satisfactory antioxidant activity. Analysis of volatile compounds using HS-SPME-GC-MS revealed 48 compounds, of which esters accounted for 63% and alcohols accounted for 27% of the total content. The flavor profile of the beer varied across different baking temperatures. Pyrazines and aldehydes were predominantly present in samples baked at higher temperatures (T3, T4, and T5). Correlation analysis showed that the baking flavor in the beer was primarily correlated with 2, 5-dimethyl-pyrazine, trimethyl-pyrazine, phenylacetaldehyde, and ethyl 9-decenoate (R > 0.9).

Metabolization of Free Oxidized Aromatic Amino Acids by Saccharomyces cerevisiae

The aromatic amino acids tryptophan, phenylalanine, and tyrosine are targets for oxidation during food processing. We investigated whether S. cerevisiae can use nonproteinogenic aromatic amino acids as substrates for degradation via the Ehrlich pathway. The metabolic fate of seven amino acids (p-, o-, m-tyrosine, 3,4-dihydroxyphenylalanine (DOPA), 3-nitrotyrosine, 3-chlorotyrosine, and dityrosine) in the presence of S. cerevisiae was assessed. All investigated amino acids except dityrosine were metabolized by yeast. The amino acids 3-nitrotyrosine and o-tyrosine were removed from the medium as fast as p-tyrosine, and m-tyrosine, 3-chlorotyrosine, and DOPA more slowly. In summary, 11 metabolites were identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). DOPA, 3-nitrotyrosine, and p-tyrosine were metabolized predominantly to the Ehrlich alcohols, whereas o-tyrosine and m-tyrosine were metabolized predominantly to α-hydroxy acids. Our results indicate that nonproteinogenic aromatic amino acids can be taken up and transaminated by S. cerevisiae quite effectively but that decarboxylation and reduction to Ehrlich alcohols as the final metabolites is hampered by hydroxyl groups in the o- or m-positions of the phenyl ring. The data on amino acid metabolism were substantiated by the analysis of five commercial beer samples, which revealed the presence of hydroxytyrosol (ca. 0.01-0.1 mg/L) in beer for the first time.

Role of Proteins in the Formation of Melanoidins during Coffee Roasting

The objective of the study was to investigate structural changes in the protein-rich, high-molecular-weight fraction of coffee during roasting and their contribution to the melanoidin formation in the course of the Maillard reaction. For this purpose, high- and low-molecular-weight fractions of one raw and five coffee beans with an increased roasting degree were analyzed in terms of general (color, molecular weight, functionality, elemental composition) and specific parameters (amino acid composition, Maillard reaction products). It could be demonstrated that the high -molecular-weight fraction undergoes significant changes during roasting, where proteins appear to play an important role in melanoidin formation due to their diverse nucleophilic side chains. Modification of the amino acid side chains with known Maillard reaction products (MRPs) occurs in the early stages of roasting and decreases rapidly as color development progresses. The decrease suggests that MRPs are involved in further reactions and thus extend the functionality of the amino acid side chains, opening further possibilities for protein modification. Overall, the large number of reaction pathways leads to the formation of a well-mixed, continuous melanoidin spectrum covering a wide range of molecular masses. In this process, cross-linking and fragmentation reactions oppose each other, leading to an approximation of the molecular weight.

Amadori compounds: analysis, composition in food and potential health beneficial functions

Amadori compounds (ACs) are key intermediates of the Maillard reaction, and found in various thermally processed foods. Simultaneous analysis of multiple ACs is challenging due to the complex amino acid and carbohydrate compositions, and the different food matrices. Most studies focus on the effects of ACs on food flavor and related sensory properties, but not their biological functions. However, increasing evidence shows that ACs possess various beneficial effects on human health, thus a comprehensive review on the various biological activities is warranted. In this review, we summarized the composition and content of ACs in different foods, their formation and degradation reactions, and discussed the latest advances in analytical methods of ACs and their biological functions related to human health. Limitations and research gaps were identified and future perspectives on ACs research were proposed. This review points to the needs of systematic and comprehensive in vitro and in vivo studies on human health related biological functions of ACs and their mechanisms of action, particularly the synergistic effects with other food components and drugs, and roles in intestinal health and metabolic syndrome.

Variation in quality of grains used in malting and brewing

Cereal grains have been domesticated largely from food grains to feed and malting grains. Barley (Hordeum vulgare L.) remains unparalleled in its success as a primary brewing grain. However, there is renewed interest in "alternative" grains for brewing (and distilling) due to attention being placed on flavor, quality, and health (i.e., gluten issues) aspects that they may offer. This review covers basic and general information on "alternative grains" for malting and brewing, as well as an in-depth look at several major biochemical aspects of these grains including starch, protein, polyphenols, and lipids. These traits are described in terms of their effects on processing and flavor, as well as the prospects for improvement through breeding. These aspects have been studied extensively in barley, but little is known about the functional properties in other crops for malting and brewing. In addition, the complex nature of malting and brewing produces a large number of brewing targets but requires extensive processing, laboratory analysis, and accompanying sensory analysis. However, if a better understanding of the potential of alternative crops that can be used in malting and brewing is needed, then significantly more research is required.

The formation and structural characteristics of melanoidins from fermenting and distilled grains of Chinese liquor (baijiu)

Chinese liquor (baijiu) is a typical fermented food. In which production, melanoidins are formed in fermenting grains during low-temperature fermentation with long-term, and in distilled grains with high-temperature distillation for short-term. Here, the formation and structural characterization of melanoidins in these two distinct stages were first investigated through chemical composition analysis and spectroscopic identification. Our research showed that proteins and phenols continuously participate in melanoidin formation during fermentation and distillation processes. Distillation could produce melanoidins with larger amounts, darker colors, higher molecular weights, and more stable states than fermentation. The chemical composition including 10 carbohydrates, 17 amino acids, 5 free phenolic acids, and 7 bound phenolic acids was successfully identified in melanoidins. Ion chromatography was proposed to be an efficient method to investigate carbohydrates in melanoidins. Moreover, the potential impact of microorganisms on melanoidins was first revealed to be the possible utilization of glucose in melanoidins.

Simultaneously Enhanced Formation of Pyrazines and Furans during Thermal Degradation of the Glycyl-l-glutamine Amadori Compound by Selected Exogenous Amino Acids and Appropriate Elevated Temperatures

The Amadori compound of glucose and glycyl-l-glutamine (Gly-Gln-ARP) was prepared and characterized by UPLC-MS/MS and NMR. Gly-Gln-ARP could be thermally degraded into Gly-Gln and other secondary reaction products like glycyl-l-glutamic acid and its ARP via deamidation. The thermal processing temperature exerted a tremendous influence on the flavor formation of ARP. Furans were mainly formed at 100 °C, while an elevated temperature of 120 °C facilitated the massive accumulation of α-dicarbonyl compounds through the retro-aldolization of deoxyglucosone, and then increased the formation of pyrazines. The extra-added amino acids further promoted the formation of pyrazines at 120 °C, especially Glu, Lys, and His, further increasing the total concentration of pyrazines to 457 ± 6.26, 563 ± 65.5, and 411 ± 59.2 μg/L, respectively, exceeding the pure heated control at 140 °C (296 ± 6.67 μg/L). The total concentration of furans was enhanced to (20.7 × 10³) ± 8.17 μg/L by extra-added Gln. Different increasing effects were observed on the type and flavor intensity of formed pyrazines and furans from different extra-added amino acids.

Metabolization of the glycation compounds 3-deoxyglucosone and 5-hydroxymethylfurfural by Saccharomyces yeasts

The Maillard reaction products (MRPs) 3-deoxyglucosone (3-DG) and 5-hydroxymethylfurfural (HMF), which are formed during the thermal processing and storage of food, come into contact with technologically used yeasts during the fermentation of beer and wine. In order for the yeast cells to work efficiently, handling of the stress-inducing carbonyl compounds is essential. In the present study, the utilization of 3-DG and HMF by 13 Saccharomyces yeast strains (7 brewer’s yeast strains, 1 wine yeast strain, 6 yeast strains isolated from natural habitats) was investigated. All yeast strains studied were able to metabolize 3-DG and HMF. 3-DG is mainly reduced to 3-deoxyfructose (3-DF) and HMF is completely converted to 2,5-bishydroxymethylfuran (BHMF) and 5-formyl-2-furancarboxylic acid (FFCA). The ratio of conversion of HMF to BHMF and FFCA was found to be yeast strain-specific and no differences in the HMF stress tolerance of the yeast strains and species were observed. After incubation with 3-DG, varying amounts of intra- and extracellular 3-DF were found, pointing to a faster transport of 3-DG into the cells in the case of brewer’s yeast strains. Furthermore, the brewer’s yeast strains showed a significantly higher 3-DG stress resistance than the investigated yeast strains isolated from natural habitats. Thus, it can be shown for the first time that Saccharomyces yeast strains differ in their interaction of 3-DG induced carbonyl stress.

Graphical abstract

Kilning invokes oxidative changes in malt proteins

Beneath glycation, oxidation reactions may take place at cereal proteins during production of malt. The extent of oxidative chemical changes at malt proteins has not yet been studied. In the present short communication, malt protein was characterized by the determination of free thiol groups and degree of methionine oxidation as well as the sites that are reactive to covalent modification by 2,4-dinitrophenylhydrazine (DNPH, “protein carbonylation”). Protein carbonylation in pale malts was around 1.5 nmol/mg protein and increased with increasing malt colour. Investigations on the protein pellet isolated for determination of carbonylation revealed that solubility and colour may disturb the quantification of carbonyl sites in roasted malts. Free thiols decreased with increasing malt colour already in pale malts (EBC < 10). The formation of methionine sulfoxide (MetSO) was intensified with increasing malt colour. An amount of 7–20% of methionine was converted to MetSO in pale and dark malt, whereas nearly 60% of methionine was oxidized to MetSO in roasted malts. The formation of methionine sulfone was negligible. This study shows that malt proteins suffer from oxidation during kilning, and future studies will have to show whether this supports the pro- or antioxidant activity of malt.

Amino acids and glycation compounds in hot trub formed during wort boiling

The aim of this study was to investigate the amino acid composition and the amount of individual glycation compounds in hot trub formed during boiling of wort prepared from different malts. Compared to the initial amino acid composition of the used malts, some Maillard reaction products (namely MG-H1, pyrraline) and hydrophobic amino acids (leucine, isoleucine, valine, phenylalanine) accumulated in the hot trub, whereas hydrophilic amino acids remained in the boiled wort. For MG-H1, a threefold increase was observed during wort boiling, whereas the other Maillard reaction products, namely CML, CEL, pyrraline and maltosine increased only slightly (1.1–2-fold). Furosine as a hallmark for peptide-bound Amadori compounds showed a small decrease. The results suggest that mainly glycated amino acids derived from small dicarbonyl compounds such as methylglyoxal and glyoxal are formed during wort boiling. Furthermore, the studies indicate that the modification of the protein structure as a result of the Maillard reaction has an influence on the hydration of the denatured proteins during the wort boiling process, thus affecting the coagulation process and, therefore, precipitation of the hot trub. The work carried out contributes to the understanding of the chemical reactions influencing the amino acid and Maillard reaction product transfer from malt to beer.

Graphical abstract

Maillard Reaction Products with Anti-Tobacco Mosaic Virus Activities Generated in Processed Thermopsis lanceolata R. Br. Seed Extract

Six novel Maillard reaction products (MRPs) (1-6) were isolated from the processed Thermopsis lanceolata R. Br. seed extract, along with one biogenetically related intermediate (7). Compounds 1-4 possessed three rare dimerization patterns constructed by cytisine, whereas compounds 5 and 6 represented the first example of the addition products of cytisine and 5,6-dihydroxy-4-hexanolide. Their structures were elucidated by comprehensive spectroscopic data analysis and quantum chemistry calculations including GIAO ¹³C{¹H} NMR and ECD calculation, combined with single-crystal X-ray diffraction analysis. Biologically, compound 3 displayed significant anti-tobacco mosaic virus activity compared with the positive control ningnanmycin.

Temperature-Dependent Catalysis of Glycylglycine on Its Amadori Compound Degradation to Deoxyosone

The Amadori rearrangement product derived from xylose-glycylglycine (XGG-ARP) is reactive to be attacked by another glycylglycine to generate a xylose-glycylglycine cross-linking product (XGG-CP) as a secondary product of the ARP. In this research, the role of additional glycylglycine in the XGG-ARP degradation was studied, and the dependence of glycylglycine on temperature was further clarified. The yields of XGG-CP and its degradation products were significantly affected by the molar ratio of glycylglycine to XGG-ARP. At the similar total concentration of reactant XGG-ARP and glycylglycine, the yields of XGG-CP, 3-deoxyxylosone, and furfural were dramatically decreased as the molar ratio of glycylglycine to XGG-ARP was increased. However, when the reaction temperature was increased to 120 °C, the increased additional glycylglycine percentage showed an obvious catalytic effect on the XGG-ARP degradation to deoxyosone and thus improved the furfural yield as well. The results revealed that an increased glycylglycine dosage level enhanced both the conversion of XGG-ARP to XGG-CP and the conversion of XGG-CP to 3-deoxyosone. The high-temperature-induced unequal acceleration for XGG-CP formation and degradation at a high glycylglycine dosage further led to a catalytic effect on the ARP degradation to deoxyosone. The concentration of 3-deoxyosone was increased by 37.5% when the molar ratio of glycylglycine to XGG-ARP increased from 1:2 to 2:1 at a temperature of 120 °C.

Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min^-1, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g^-1 BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g^-1 carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL^-1) and arabinose (1.039 mg mL^-1) as main sugars, while low contents of furfural (310.7 µg mL^-1), 5-hydroxymethylfurfural (<1 mg L^-1), and organic acids (0.343 mg mL^-1) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g^-1 proteins, where tryptophan (215.55 µg mL^-1), aspartic acid (123.35 µg mL^-1), valine (64.35 µg mL^-1), lysine (16.55 µg mL^-1), and glycine (16.1 µg mL^-1) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.

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.

Time-Course Comparative Metabolome Analysis of Different Barley Varieties during Malting

Malt production is one of the important uses of barley, and its quality differs greatly depending on the barley varieties used. In this study, ultraperformance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry technology was used to investigate the temporal changes of metabolites during malting in two barley varieties: Franklin (malt barley) and Yerong (non-malt barley). Also, differences in metabolite profiles were compared in the kilned malt between two other malt barley varieties (Copeland and Planet) and two non-malt varieties (ZD10 and Hua30). Results showed that degradation of trisaccharide and accumulation of UDP-glucose and mannose-1-phosphate are the key metabolic events during steeping, with Franklin showing earlier and greater changes. Earlier increase of sugars and amino acids in Franklin is associated with its faster germination rate. Comparative metabolome analysis of kilned malt from the different barley varieties indicated that malt barley accumulated more sugars, hordatine-glucoside, and oxoproline, and non-malt barley accumulated more polyphenols and monogalactosylmonoacylglycerol. These results improved the understanding of the genotypic difference in the formation of malt quality at the metabolomic level.

Chemical Stability of Proteins in Foods: Oxidation and the Maillard Reaction

Protein is a major nutrient present in foods along with carbohydrates and lipids. Food proteins undergo a wide range of modifications during food production, processing, and storage. In this review, we discuss two major reactions, oxidation and the Maillard reaction, involved in chemical modifications of food proteins. Protein oxidation in foods is initiated by metal-, enzyme-, or light-induced processes. Food protein oxidation results in the loss of thiol groups and the formation of protein carbonyls and specific oxidation products of cysteine, tyrosine, tryptophan, phenylalanine, and methionine residues, such as disulfides, dityrosine, kynurenine, m-tyrosine, and methionine sulfoxide. The Maillard reaction involves the reaction of nucleophilic amino acid residues with reducing sugars, which yields numerous heterogeneous compounds such as α-dicarbonyls, furans, Strecker aldehydes, advanced glycation end-products, and melanoidins. Both protein oxidation and the Maillard reaction result in the loss of essential amino acids but may positively or negatively impact food structure and flavor. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

The post-translational modification landscape of commercial beers

Beer is one of the most popular beverages worldwide. As a product of variable agricultural ingredients and processes, beer has high molecular complexity. We used DIA/SWATH-MS to investigate the proteomic complexity and diversity of 23 commercial Australian beers. While the overall complexity of the beer proteome was modest, with contributions from barley and yeast proteins, we uncovered a very high diversity of post-translational modifications (PTMs), especially proteolysis, glycation, and glycosylation. Proteolysis was widespread throughout barley proteins, but showed clear site-specificity. Oligohexose modifications were common on lysines in barley proteins, consistent with glycation by maltooligosaccharides released from starch during malting or mashing. O-glycosylation consistent with oligomannose was abundant on secreted yeast glycoproteins. We developed and used data analysis pipelines to efficiently extract and quantify site-specific PTMs from SWATH-MS data, and showed incorporating these features into proteomic analyses extended analytical precision. We found that the key differentiator of the beer glyco/proteome was the brewery, with beer from independent breweries having a distinct profile to beer from multinational breweries. Within a given brewery, beer styles also had distinct glyco/proteomes. Targeting our analyses to beers from a single brewery, Newstead Brewing Co., allowed us to identify beer style-specific features of the glyco/proteome. Specifically, we found that proteins in darker beers tended to have low glycation and high proteolysis. Finally, we objectively quantified features of foam formation and stability, and showed that these quality properties correlated with the concentration of abundant surface-active proteins from barley and yeast.

Occurrence, Formation from d-Fructose and 3-Deoxyglucosone, and Activity of the Carbohydrate-Derived β-Carbolines in Foods

β-Carbolines are naturally occurring bioactive alkaloids. In this work, carbohydrate-derived β-carbolines (βCs), 1-(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers (1a/b), 1-(1,4,5-trihydroxypent-1-yl)-β-carboline (2), 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline (3), and 1-(1,2,3,4,5-pentahydroxypent-1-yl)-β-carboline (4) were identified and analyzed in commercial foods. The concentrations of βCs 1-4 in foods ranged from undetectable to 11.4 μg/g levels, suggesting their intake in the diet. Processed foods contained higher amounts than fresh or unprocessed foods, and the highest content was found in processed tomato and fruit products, sauces, and baked foods. βCs 1-3 were formed in foods during heating, and 1a/b were the main compounds. The formation of carbohydrate-derived βCs was studied in model reactions of tryptophan and carbohydrates. They formed in reactions of tryptophan with glucose under acidic conditions at temperatures higher than 80 °C. The formation of 1a/b was favored, but 2-3 increased at high temperatures. Noticeably, the βCs 1-3 formed in the reactions of tryptophan with fructose or sucrose, and the formation from fructose was much higher than from glucose. Thus, fructose was the main carbohydrate involved in the formation of 1-3, whereas sucrose gave these βCs after acid hydrolysis. It is shown for the first time that the mechanism of formation of βCs 1-3 occurs from the sugar intermediate 3-deoxyglucosone that reacts with tryptophan affording these carbohydrate-derived βCs. A mechanism of reaction to give βCs 1-3 is proposed that relies on the tautomerism (keto-enediol or enamine-imine) of intermediates involved in the reaction. Carbohydrate βCs 1-4 were assessed as inhibitors of monoamine oxidase (MAO), as antioxidants, and for their interaction with DNA. They were not good inhibitors of MAO-A or -B, were poor antioxidants, and did not appreciably interact with DNA.