Fragmentation pathways during Maillard-induced carbohydrate degradation

Non-enzymatic posttranslational protein modifications in protein aggregation and neurodegenerative diseases

Highly reactive metabolic intermediates and other small molecules frequently react with amino acid side chains, leading to non-enzymatic posttranslational modifications (nPTMs) of proteins. The abundance of these modifications increases under high metabolic activity or stress conditions and can dramatically impact protein structure and function. Although protein quality control mechanisms typically mitigate the effects of these impaired proteins, in long-lived and degradation-resistant proteins, nPTMs accumulate. In some cases, such as cataract development and diabetes, clear links between nPTMs, aging, and disease progression have been established. In neurodegenerative diseases such as Alzheimer's and Parkinson's disease, a key question is whether accumulation of nPTMs is a cause or consequence of protein aggregation. This review focuses on major nPTMs found on proteins with central roles in neurodegenerative diseases such as α-synuclein, β-amyloid, and tau. We summarize current knowledge on the formation of these modifications and discuss their potential impact on disease onset and progression. Additionally, we examine what is known to date about how nPTMs impair cellular detoxification, repair, and degradation systems. Finally, we critically discuss the available methodologies to systematically investigate nPTMs at the molecular level and outline suitable approaches to study their effects on protein aggregation. We aim to foster more research into the role of nPTMs in neurodegeneration by adapting methodologies that have proven successful in studying enzymatic posttranslational modifications. Specifically, we advocate for site-specific incorporation of these modifications into target proteins using advanced chemical and molecular biology techniques.

Multi-response kinetic modelling of the formation of five Strecker aldehydes during kilning of barley malt

Control of aroma formation during production of barley malt is critical to provide consistent and high-quality products for the brewing industry. Malt quality can be affected by the inherent variability of raw material and processing conditions, leading to inconsistent and/or undesirable profiles. Dried green malts were cured isothermally at 65, 78 and 90 °C for 8.4 h, and characteristic aroma compounds (Strecker aldehydes), precursors and intermediate compounds were analysed over time. By kinetic modelling of Strecker aldehydes, based on fundamental chemical pathways, we showed that degradation of Amadori rearrangement products and short-chain dicarbonyls was more sensitive to temperature change due to their higher activation energies compared to other kinetic steps. This study can help maltsters to manipulate formation of Strecker aldehydes, via raw material screening and process control, and hence optimise the organoleptic quality of malts and their products, such as non-alcoholic beers, where these aldehydes play a key role.

Role of galacturonic acid in acrylamide formation: Insights from structural analysis

Acrylamide (AA) is a neoformed compound in heated foods, mainly produced between asparagine (Asn) and glucose (Glc) during the Maillard reaction. Galacturonic acid (GalA), the major component of pectin, exhibits high activity in AA formation. This study investigated the pathway for AA formation between GalA and Asn. Three possible pathways were proposed: 1) The carbonyl group of GalA directly interacts with Asn to produce AA; 2) GalA undergoes an oxidative cleavage reaction to release α-dicarbonyl compounds, which subsequently leads to AA production; 3) 5-formyl-2-furancarboxylic acid, the thermal degradation product of GalA, reacts with Asn to generate AA. Structural analysis revealed that the COOH group in GalA accelerated intramolecular protonation and electron transfer processes, thereby increasing the formation of AA precursors such as decarboxylated Schiff base and α-dicarbonyl compounds, promoting AA formation. This study provides a theoretical basis and new insights into the formation and control of AA.

Qualitative and Quantitative Profiling of Fructose Degradation Products Revealed the Formation of Thirteen Reactive Carbonyl Compounds and Higher Reactivity Compared to Glucose

Fructose occurs in foods and as a metabolite in vivo. It can be degraded, leading to the formation of reactive carbonyl compounds, which may influence food properties and have an impact on health. The present study performed an in-depth qualitative and quantitative profiling of fructose degradation products. Thus, the α-dicarbonyl compounds 3-deoxyglucosone, glucosone, methylglyoxal, glyoxal, hydroxypyruvaldehyde, threosone, 3-deoxythreosone, and 1-desoxypentosone and the monocarbonyl compounds formaldehyde, acetaldehyde, glycolaldehyde, glyceraldehyde, and dihydroxyacetone were detected in fructose solutions incubated at 37 °C. Quantitative profiling after 7 days revealed 4.6-271.6-fold higher yields of all degradation products from fructose compared to glucose. Except for 3-deoxyglucosone, the product formation appeared to be metal dependent, indicating oxidative pathways. CaCl2 and MgCl2 partially reduced fructose degradation. Due to its high reactivity compared to glucose, particularly toward metal-catalyzed pathways, fructose may be a strong contributor to sugar degradation and Maillard reaction in foods and in vivo.

Accelerated Degradation of DiXyl-α,ε-Lys-ARP via Interaction between Extra-Added Xylose and Monosubstituted Lys-ARPs during Maillard Reaction

Lysine (Lys) is capable of forming a di-substituted Amadori rearrangement product (ARP) with xylose (Xyl), designated as diXyl-α,ε-Lys-ARP. DiXyl-α,ε-Lys-ARP degradation was characterized by two steps: Initially, Xyl-α- and Xyl-ε-Lys-ARP were formed through elimination or hydrolysis at specific Nα/Nε positions of the corresponding enol and imine intermediates, which were then further degraded to dicarbonyl compounds and regenerated Lys. Xyl-α- or Xyl-ε-Lys-ARP had a reactive free amino group (ε-NH2 or α-NH2), both of which were still highly reactive and able to undergo further reactions with Xyl. Therefore, the diXyl-α,ε-Lys-ARP/Xyl model system was established to explore the impact of extra-added Xyl on diXyl-α,ε-Lys-ARP degradation behavior. Extra-added Xyl remarkably affected the degradation pathway of diXyl-α,ε-Lys-ARP by capturing the Xyl-α- and Xyl-ε-Lys-ARP to regenerate diXyl-α,ε-Lys-ARP. This interaction between Xyl and mono-substituted Lys-ARPs promoted the shift of chemical equilibrium toward the degradation of diXyl-α,ε-Lys-ARP, thereby accelerating its degradation rate. This degradation was markedly facilitated by the elevated temperature and pH values. Interestingly, the yield of Xyl-α- and Xyl-ε-Lys-ARP was particularly dependent on the pH during diXyl-α,ε-Lys-ARP degradation. Xyl-ε-Lys-ARP was the dominant product at pH 5.5-7.5 while Xyl-α-Lys-ARP possessed a relatively higher content under weak alkaline conditions, which was related to the reactivities of the Nα/Nε positions under various reaction conditions.

The Maillard reactions: Pathways, consequences, and control

The century old Maillard reactions continue to draw the interest of researchers in the fields of Food Science and Technology, and Health and Medical Sciences. This chapter seeks to simplify and update this highly complicated, multifaceted topic. The simple nucleophilic attack of an amine onto a carbonyl group gives rise to a series of parallel and subsequent reactions, occurring simultaneously, resulting into a vast array of low and high mass compounds. Recent research has focused on: (1) the formation and transformation of α-dicarbonyl compounds, highly reactive intermediates which are essential in the development of the desired color and flavor of foods, but also lead to the production of the detrimental advanced glycation end products (AGEs); (2) elucidation of the structures of melanoidins in different foods and their beneficial effects on human health; and (3) harmful effects of AGEs on human health. Considering that MRs have both positive and negative consequences, their control to accentuate the former and to mitigate the latter, is also being conscientiously investigated with the use of modern techniques and technology.

Advances of nanoparticle derived from food in the control of α-dicarbonyl compounds-A review

α-Dicarbonyl compounds (α-DCs) are predominantly generated through the thermal processing of carbohydrate and protein-rich food. They are pivotal precursors to hazard formation, such as advanced glycation end products (AGEs), acrylamide, and furan. Their accumulation within the body will be genotoxicity and neurotoxicity. Recently, significant advancements have been made in nanotechnology, leading to the widespread utilization of nanomaterials as functional components in addressing the detrimental impact of α-DCs. This review focuses on the control of α-DCs through the utilization of nanoparticle-based functional factors, which were prepared by using edible components as resources. Four emerging nanoparticles are introduced including phenolic compounds-derived nanoparticle, plant-derived nanoparticle, active peptides-derived nanoparticle, and functional minerals-derived nanoparticle. The general control mechanisms as well as the recent evidence pertaining to the aforementioned aspects were also discussed, hoping to valuable helpful references for the development of innovative α-DCs scavengers and identifying the further scope of research.

Volatilome and flavor analyses based on e-nose combined with HS-GC-MS provide new insights into ploidy germplasm diversity in Platostoma palustre

Platostoma palustre (Mesona chinensis Benth or Hsian-tsao, also known as "Xiancao" in China), is an edible and medicinal plant native to India, Myanmar, and Indo-China. It is the main ingredient in the popular desserts Hsian-tsao tea, herbal jelly, and sweet herbal jelly soup. P. palustre is found abundantly in nutrient-rich substances and possesses unique aroma compounds. Variations in the contents of volatile compounds among different germplasms significantly affect the quality and flavor of P. palustre, causing contradiction in demand. This study investigates the variation in the volatile compound profiles of distinct ploidy germplasms of P. palustre by utilising headspace gas chromatography-mass spectrometry (HS-GC-MS) and an electronic nose (e-nose). The results showed significant differences in the aroma characteristics of stem and leaf samples in diverse P. palustre germplasms. A total of sixty-seven volatile compounds have been identified and divided into ten classes. Six volatile compounds (caryophyllene, α-bisabolol, benzaldehyde, β-selinene, β-elemene and acetic acid) were screened as potential marker volatile compounds to discriminate stems and leaves of P. palustre. In this study, leaves of P. palustre showed one odor pattern and stems showed two odor patterns under the influence of α-bisabolol, acetic acid, and butyrolactone. In addition, a correlation analysis was conducted on the main volatile compounds identified by HS-GC-MS and e-nose. This analysis provided additional insight into the variations among samples resulting from diverse germplasms. The present study provides a valuable volatilome, and flavor, and quality evaluation for P. palustre, as well as new insights and scientific basis for the development and use of P. palustre germplasm resources.

The Chemical Reactivity of Membrane Lipids

It is well-known that aqueous dispersions of phospholipids spontaneously assemble into bilayer structures. These structures have numerous applications across chemistry and materials science and form the fundamental structural unit of the biological membrane. The particular environment of the lipid bilayer, with a water-poor low dielectric core surrounded by a more polar and better hydrated interfacial region, gives the membrane particular biophysical and physicochemical properties and presents a unique environment for chemical reactions to occur. Many different types of molecule spanning a range of sizes, from dissolved gases through small organics to proteins, are able to interact with membranes and promote chemical changes to lipids that subsequently affect the physicochemical properties of the bilayer. This Review describes the chemical reactivity exhibited by lipids in their membrane form, with an emphasis on conditions where the lipids are well hydrated in the form of bilayers. Key topics include the following: lytic reactions of glyceryl esters, including hydrolysis, aminolysis, and transesterification; oxidation reactions of alkenes in unsaturated fatty acids and sterols, including autoxidation and oxidation by singlet oxygen; reactivity of headgroups, particularly with reactive carbonyl species; and E/Z isomerization of alkenes. The consequences of reactivity for biological activity and biophysical properties are also discussed.

Maillard Reaction Process and Characteristic Volatile Compounds Formed During Secondary Thermal Degradation Monitored via the Change of Fluorescent Compounds in the Reaction of Xylose-Corn Protein Hydrolysate

Until now, no effective method has been found to monitor the Maillard reaction process for complex protein hydrolysates. Dynamic changes in the concentration of α-dicarbonyl compounds, fluorescence intensity, and browning degree were investigated during the Maillard reaction of corn protein hydrolysates. When the fluorescence intensity reached the peak, deoxyosones would continue to be increased by ARP's degradation. However, the reaction node with the highest fluorescence intensity coincided with the turning point of the browning reaction, and the subsequent browning rate remarkably increased. Therefore, the change in fluorescence intensity could be used to monitor the degradation of ARP and the formation of browning melanoidin at different stages of the Maillard reaction of complex systems, thus effectively indicating the process of the Maillard reaction. When Maillard reaction intermediates (MRIs) with maximum fluorescent compounds were heated, the most abundant pyrazines were subsequently achieved. However, furan compounds would be progressively increased during the thermal process of MRIs with continuously enhanced browning.

Efficient Formation of N-(1-Deoxy-d-ribulos-1-yl)-Glutathione via Limited Oxidation and Degradation of Glutathione during the Atmospheric-Vacuum Thermal Reaction

The efficient preparation of the ribose-glutathione (Rib-GSH) Amadori rearrangement product (RG-ARP) as a potent precursor of meaty flavor was studied through the atmospheric-vacuum thermal reaction. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed that the oxidation and degradation of GSH occurred during the preparation of RG-ARP via the atmospheric thermal reaction, especially at a low molar ratio of Rib to GSH and high reaction temperature. The RG-ARP and the ARPs derived from the products of GSH oxidation and degradation with the participation of Rib were identified by MS/MS as N-(1-deoxy-d-ribulos-1-yl)-glutathione, N-(1-deoxy-d-ribulos-1-yl)-cysteinylglycine, and N-(1-deoxy-d-ribulos-1-yl)-glutathione disulfide. The selective formation of RG-ARP was disrupted due to the multiple consumption pathways of GSH and Rib. The removal of water and the reduction of oxygen content during vacuum dehydration exhibited an obvious inhibitory effect on the oxidation of cysteinyl and the cleavage of glutamyl, limiting the oxidation and degradation of GSH. Meanwhile, the rapid evaporation of water promoted the molecular collision between the reactants, which allowed the glycation reaction of GSH to be advanced and fragmentation of RG-ARP to be inhibited at a mild dehydration temperature. Accordingly, the atmospheric-vacuum thermal reaction was proposed to limit the generation of secondary byproducts and enhance the yield of RG-ARP, enabling the RG-ARP yield to reach 49.23% at 80 °C and a molar ratio of 2:1 (Rib/GSH) for 20 min.

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.

Microwaves affect the formation of volatile compounds in peper powder by changing the nucleophilic addition reactions in Maillard reactions

We explored the effect of microwave heating (MWH) and electric heating (ETH) on the volatile compounds (VCs) of pepper (Capsicum annuum L.). The spectral of the produced melanoidins by baking were used to screen samples with similar baking degrees. Mass spectrometry was used to detect the differences of VCs in samples. The results showed a dose-dependent effect between the intensity of absorption and fluorescence of melanoidins, which can be utilized as indicators for assessment baking degree. MWH samples produced larger variety of VCs than ETH. Changes in the variety and content of VCs infer changes in the flavor of pepper. According to the mechanism of Maillard reaction (MR) and MWH, it was deduced that MWH changes the type of chemical reaction in MR by affecting the distribution of valence electrons in the compounds. Therefore, MWH can be used as a novel method to modify the VCs and flavor of peppers.

Regulated Formation of Inhibited Color and Enhanced Flavor Derived from Heated 2-Threityl-Thiazolidine-4-Carboxylic Acid with Additional Cysteine Targeting at Different Degradation Stages

This study explored the addition of cysteine (Cys) affecting the color formation of heated 2-threityl-thiazolidine-4-carboxylic acid (TTCA) models under different reaction conditions and pointed out that temperature was considered to be the key parameter influencing the color inhibition behavior of Cys on TTCA reaction models. Results revealed that additional Cys not only controlled the reaction progress and blocked the formation pathway of browning but also changed the formation rate, intensity, and profile of the flavor generated from the TTCA reaction model. Meanwhile, the mechanism of Cys simultaneously regulating the formation of color and flavor was revealed through monitoring of the characteristic downstream products during TTCA degradation and model reaction systems. At the initial stage, the additional Cys acted as a color inhibitor before the deoxyxylosone degradation, preventing the formation of downstream browning precursors. With the continuous depletion of Cys as well as the generation of furans or α-dicarbonyl compounds, Cys became a flavor enhancer to act on the browning precursors and to provide more sulfur/nitrogen elements for the TTCA thermal reaction system. Therefore, Cys had the potential to act as both color inhibitor and flavor fortifier to match with TTCA for the preparation of a light-colored flavoring base with a desired flavor during thermal processing.

Promotion or Inhibition Effects of Exogenous Glutathione-Degraded Amino Acids on the Formation of 2,3-Butanedione and Pyrazines via Varied Pathways of Interaction with α-Dicarbonyl Compounds Derived from N-(1-Deoxy-d-xylulos-1-yl)-alanine

The contribution of glutathione (GSH) and free amino acids degraded from GSH to the generation of pyrazines and 2,3-butanedione was illustrated during their interaction in the thermal treatment of the Amadori compound of alanine and xylose (ARP). GSH-degraded amino acids, glutamic acid (Glu), cysteine (Cys), and glycine (Gly), but not pyroglutamic acid (pGlu), could effectively capture α-dicarbonyls to facilitate the formation of pyrazines when ARP was heated with GSH. Deoxypentosones, the precursors of 2,3-butanedione, were largely consumed in the ARP-GSH model by the interaction with GSH and its degradative Cys compared with the ARP model. The addition of GSH and deoxypentosones inhibited the further degradation of deoxypentosones, resulting in less formation of 2,3-butanedione and other α-dicarbonyl compounds. Meanwhile, the reaction between GSH-degraded Cys and deoxypentosones to form sulfur-containing compounds such as thiols accelerated the consumption of deoxypentosones; thereby, the formation of 2,3-butanedione was severely interfered. However, this inhibition was compensated for by the GSH-degraded Gly through the addition between Gly and MGO and the subsequent deamination. The involvement of exogenous GSH could simultaneously boost the yields of 2,3-butanedione and pyrazines compared with those of ARP heated alone. As the degree of GSH degradation strengthened in the ARP-thermal-degraded GSH models, the yields of both pyrazines and 2,3-butanedione steadily increased.

Variations in volatile flavour compounds in Crataegi fructus roasting revealed by E-nose and HS-GC-MS

Introduction

Crataegi fructus (CF) is an edible and medicinal functional food used worldwide that enhances digestion if consumed in the roasted form. The odour of CF, as a measure of processing degree during roasting, significantly changes. However, the changes remain unclear, but are worth exploring.

Methods

Herein, the variations in volatile flavour compounds due to CF roasting were investigated using an electronic nose (E-nose) and headspace gas chromatography-mass spectrometry (HS-GC-MS).

Results

A total of 54 components were identified by GC-MS. Aldehydes, ketones, esters, and furans showed the most significant changes. The Maillard reaction, Strecker degradation, and fatty acid oxidation and degradation are the main reactions that occur during roasting. The results of grey relational analysis (GRA) showed that 25 volatile compounds were closely related to odour (r > 0.9). Finally, 9 volatile components [relative odour activity value, (ROAV) ≥ 1] were confirmed as key substances causing odour changes.

Discussion

This study not only achieves the objectification of odour evaluation during food processing, but also verifies the applicability and similarity of the E-nose and HS-GC-MS.

Study on the Mechanism of Phenylacetaldehyde Formation in a Chinese Water Chestnut-Based Medium during the Steaming Process

The white pulp of the Chinese water chestnut (CWC) is crisp and sweet with delicious flavours and is an important ingredient in many Chinese dishes. Phenylacetaldehyde is a characteristic flavoured substance produced in the steaming and cooking process of CWC. The steaming process and conditions were simulated to construct three Maillard reaction systems which consisted of glucose and phenylalanine, and of both alone. The simulation results showed that glucose and phenylalanine were the reaction substrates for the formation of phenylacetaldehyde. The intermediate α-dicarbonyl compounds (α-DCs) and the final products of the simulated system were detected by solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) methods. Through the above methods the formation mechanism of phenylacetaldehyde is clarified; under the conditions of the steaming process, glucose is caramelized to produce Methylglyoxal (MGO), 2,3-Butanedione (BD), Glyoxal (GO) and other α-DCs. α-DCs and phenylalanine undergo a Strecker degradation reaction to generate phenylacetaldehyde. The optimal ratio of the amount of substance of glucose to phenylalanine for Maillard reaction is 1:4. The results can provide scientific reference for the regulation of flavour substances and the evaluation of flavour quality in the steaming process of fruits and vegetables.

Effects of sprouting and fermentation on the formation of Maillard reaction products in different cereals heated as wholemeal

The concentration and composition of reducing sugars and free amino acids as Maillard reaction (MR) precursors change with grain sprouting. The formation of early and advanced glycation products, and α-dicarbonyl compounds as intermediates were monitored during heating native and sprouted wholemeals, as well as during heating of yeast and sourdough fermented native and sprouted wholemeals. Sprouting increased the concentration of all MR products because of an increase in reducing sugar concentrations. Although reducing sugars were lowered due to their consumption by yeasts, fermentation did not lower the furosine concentration. Sourdough fermentation unexpectedly increased furosine because the low pH caused glucose release from polysaccharides. Glyoxal, methylglyoxal and diacetyl were found to be formed as metabolites during yeast and sourdough fermentation. Another factor affecting the MR in sprouted/fermented wholemeals was revealed to be the increased amount of total free amino acids that compete with bound lysine to react with reducing sugars.

Promoted Formation of Pyrazines and Sulfur-Containing Volatile Compounds through Interaction of Extra-Added Glutathione or Its Constituent Amino Acids and Secondary Products of Thermally Degraded N-(1-Deoxy-d-ribulos-1-yl)-Glutathione

An Amadori rearrangement product (ARP) derived from ribose (Rib) and glutathione (GSH) was prepared and identified as N-(1-deoxy-d-ribulos-1-yl)-glutathione by ultraperformance liquid chromatography-tandem mass spectrometry and NMR. Thermal treatment of the ARP aqueous solution was conducted, and a relatively high temperature was found to accelerate the degradation of the ARP. The concentration of furans formed at 120 °C was more than 6.39 times that at 100 °C, and especially, the high temperature favored the formation of furfural and 4-hydroxy-5-methyl-3(2H)-furanone through deoxyosone dehydration. The promoting role of extra-added GSH or its constituent amino acids was investigated in the volatile formation during thermal processing of the ARP. Both, the added GSH and its constituent amino acids, could timely capture glyoxal (GO) and methylglyoxal (MGO) to facilitate Strecker degradation, which improved pyrazine formation. Compared with glycine and glutamic acid, cysteine was the most effective extra-added amino acid to react with GO and MGO to produce pyrazine and methylpyrazine. More importantly, the cysteine degraded from extra-added GSH effectively accelerated the generation of sulfur-containing volatile compounds through the reaction of cysteine degradation products with furans and shorter-chain α-dicarbonyl compounds.

Evaluation of Fructo-, Inulin-, and Galacto-Oligosaccharides on the Maillard Reaction Products in Model Systems with Whey Protein

The present study aimed to investigate the effects of fructo-, inulin-, and galacto-oligosaccharides (FOS, IOS, and GOS) on forming the Maillard reaction products such as browning, α-dicarbonyl compounds, and advanced glycation end products (AGEs). The model solutions at pH 6.8 containing each carbohydrate (mono-, di-, and oligosaccharides) and whey protein were incubated at 50 °C for 8 weeks. In the IOS model, sugars of DP3 or larger were significantly decreased at 4 weeks, whereas at 6 weeks in the FOS model. The residual amount of GOS after 8 weeks was higher than FOS and IOS; however, a large amount of 3-deoxyglucosone was formed compared to the other models. N^ε-Carboxymethyllysine (CML) concentrations in oligosaccharide models were about half of those in monosaccharide and lactose models. The highest concentrations of glyoxal- and methylglyoxal-derived hydroimidazolones 3 (G-H3 and MG-H3) were observed in the IOS model, indicating the involvement of fructose units linked by β-2 → 1 bonds. G-H3 and MG-H3 quantification could be a useful indicator to reflect the modification of an arginine residue by fructose if used acid-hydrolysis for AGE analysis. CML, G-H3, and MG-H3 were considerably formed even in the FOS model, which has no reducing terminal site, suggesting that degradation products of oligosaccharides probably participated in the formation of AGEs.

Comparison of pyrazines formation in methionine/glucose and corresponding Amadori rearrangement product model

The generation of pyrazines in a binary methionine/glucose (Met/Glc) mixture and corresponding methionine/glucose-derived Amadori rearrangement product (MG-ARP) was studied. Quantitative analyses of pyrazines and methional revealed that MG-ARP generated more methional compared to Met/Glc, whereas lower content and fewer species of pyrazines were observed in the MG-ARP model. Comparing the availability of α-dicarbonyl compounds generated from the Met/Glc model, methylglyoxal (MGO) was a considerably effective α-dicarbonyl compound for the formation of pyrazines during MG-ARP degradation, but glyoxal (GO) produced from MG-ARP did not effectively participate in the corresponding formation of pyrazines due to the asynchrony on the formation of GO and recovered Met. Diacetyl (DA) content was not high enough to form corresponding pyrazines in the MG-ARP model. The insufficient interaction of precursors and rapid drops in pH limited the formation of pyrazines during MG-ARP degradation. Increasing reaction temperature could reduce the negative inhibitory effect by promoting the content of precursors.

Exploring polymerisation of methylglyoxal with NH3 or alanine to analyse the formation of typical polymers in melanoidins

To investigate the formation of typical melanoidin polymers, methylglyoxal (MGO) with NH₃ or alanine (Ala) was used to form coloured compounds, with glyoxal or acetone used as controls. The products were characterised using chromatography, mass spectrometry, and spectroscopy. Spectroscopic results showed that the coloured compounds formed were similar to melanoidins in food. GC-MS results showed that the MGO-based reaction generated similar volatile compounds using the Maillard reaction. Mass spectrometry showed that the molecular weights of structural units in the polymers were mainly 162, 169, and 176 Da, and these could be reassembled using the basic units derived from MGO alone or in combination with nitrogen. Hence, polymers recombined using basic structural units should be considered while determining melanoidin biomarkers. The preparation of coloured compounds using MGO with NH₃ can be used as a novel method to produce the control compounds for melanoidin after process optimization.

Preparation and Taste Characteristics of Kokumi N-Lactoyl Phenylalanine in the Presence of Phenylalanine and Lactate

N-l-Lactoyl phenylalanine (N-l-lactoyl-Phe) has been identified as a taste-active contributor in many fermented foods. However, its preparation, taste property, and content in foodstuffs are little known to date. In the current study, two preparation technologies of N-l-lactoyl-Phe including heating and enzymatic methods were investigated. Other investigations include its taste property and quantification in several fermented foods. The results indicated that the heating preparation and enzymatic preparation only produced N-l-lactoyl-Phe instead of N-d-lactoyl-Phe in the presence of l-lactate/d-lactate and l-phenylalanine (Phe). A high yield (58.0% ± 0.7%) of N-l-lactoyl-Phe was achieved under the following conditions: Phe, lactate, CaO, and water at molar ratios of 1:8:0.3:9 kept at 100 °C for 3 h. With nine enzymes, a maximum yield of 21.2% ± 0.3% was achieved in the aqueous solution under mild operating conditions: 0.18 M Phe, 0.90 M lactate, 5 g/L Debitrase HYW 20, pH 8, and 55 °C for 24 h. The sensory evaluation revealed that N-l-lactoyl-Phe in water enhanced the salty and umami intensity. It also enhanced the thickness, mouthfulness, and continuity of salt solution, model broth, and chicken broth, revealing that N-l-lactoyl-Phe was a kokumi-active compound. The kokumi thresholds of N-l-lactoyl-Phe in these solutions were 50, 50, and 25 mg/L, respectively. N-l-Lactoyl-Phe was quantified in traditional Chinese fermented foods as 30.12 ± 0.28 mg/kg in preserved pickles, 14.11 ± 0.14 mg/kg in soybean paste, 4.87 ± 0.16 mg/kg in fermented bean, 0.71 ± 0.11 mg/kg in rice vinegar, and 20.34 ± 0.18 mg/kg in soy sauce. These results revealed the potential of N-l-lactoyl-Phe as a taste enhancer, presenting a new opportunity for the food industry.

Nitrogen Enrichment during Soil Organic Matter Burning and Molecular Evidence of Maillard Reactions

Wildfires in forested watersheds dramatically alter stored and labile soil organic matter (SOM) pools and the export of dissolved organic matter (DOM). Ecosystem recovery after wildfires depends on soil microbial communities and revegetation and therefore is limited by the availability of nutrients, such as nitrogen-containing and labile, water-soluble compounds. However, SOM byproducts produced at different wildfire intensities are poorly understood, leading to difficulties in assessing wildfire severity and predicting ecosystem recovery. In this work, water-extractable organic matter (WEOM) from laboratory microcosms of soil burned at discrete temperatures was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to study the impacts of fire temperature on SOM and DOM composition. The molecular composition derived from different burn temperatures indicated that nitrogen-containing byproducts were enriched with heating and composed of a wide range of aromatic features and oxidation states. Mass difference-based analysis also suggested that products formed during heating could be modeled using transformations along the Maillard reaction pathway. The enrichment of N-containing SOM and DOM at different soil burning intensities has important implications for ecosystem recovery and downstream water quality.

Exploring Chemical Markers Related to the Acceptance and Sensory Profiles of Concentrated Liquid Coffees: An Untargeted Metabolomics Approach

In this study, we aimed to apply an untargeted LC/QTOF-MS analysis for the identification of compounds that positively and negatively affect the acceptance of coffee beverages from liquid coffee concentrates (CLCs) before and after storage. The metabolomic results were integrated with physicochemical and sensory parameters, such as color, pH, titratable acidity, and oxygen contents, by a bootstrapped version of partial least squares discriminant analysis (PLS-DA) to select and classify the most relevant variables regarding the rejection or acceptance of CLC beverages. The OPLS-DA models for metabolite selection discriminated between the percent sensory acceptance (the Accepted group) and rejection (the Rejected group). Eighty-two molecular features were considered statistically significant. Our data suggest that coffee sample rejection is associated with chlorogenic acid hydrolysis to produce ferulic and quinic acids, consequently generating methoxybenzaldehydes that impact the perceived acidity and aroma. Furthermore, acceptance was correlated with higher global scores and sweetness, as with lactones such as feruloyl-quinolactone, caffeoyl quinolactone, and 4-caffeoyl-1,5-quinolactone, and significant oxygen levels in the headspace.

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.

High-Resolution Mass Spectrometry Analysis of Melanoidins and Their Precursors Formed in a Model Study of the Maillard Reaction of Methylglyoxal with l-Alanine or l-Lysine

Despite more than 100 years of research, formation of food melanoidins from carbohydrates and amino acids in the course of the Maillard reaction is still not fully understood. Experiments with relevant precursors are commonly used to limit the pathways of the complex reaction and to elucidate the formation mechanisms of the colored end-products. Here as a simple model, methylglyoxal was incubated with l-alanine or l-lysine in aqueous solutions at 100 °C and pH 5. The reaction mixtures were analyzed for color formation, molecular weight distribution, and conversion of methylglyoxal. High-resolution mass spectrometry was used to characterize the variety of products formed. With the help of Kendrick and van Krevelen analyses, the complex data sets were investigated for common substructures and reaction patterns. This study revealed that methylglyoxal forms oligomers via aldol reaction under involvement of its prevalent reaction products such as formaldehyde, acetaldehyde, acetol, and aminoacetone with amino acids.

Degradation of 2-Threityl-Thiazolidine-4-Carboxylic Acid and Corresponding Browning Accelerated by Trapping Reaction between Extra-Added Xylose and Released Cysteine during Maillard Reaction

2-Threityl-thiazolidine-4-carboxylic acid (TTCA), a nonvolatile precursor of flavor and color, is considered to be more stable than its isomeric Amadori compound (ARP). The degradation behavior of TTCA favors higher temperatures and pH. In order to adjust and control the thermal degradation of TTCA to improve its food processing adaptability, a TTCA-Xyl thermal reaction model was constructed to explore the effect of extra-added Xyl on the thermal degradation behavior of TTCA. The results confirmed that the extra-added Xyl was involved in the degradation pathway of TTCA and accelerated its depletion, thus promoting the formation of characteristic downstream products of TTCA including some α-dicarbonyl compounds, and consequently accelerating the browning formation. The isotope-labeling technique was further applied to confirm that the added Xyl could trap the Cys released from the decomposition of ARP and formed additional TTCA, which could promote the movement of chemical equilibrium and gradually accelerate the degradation rate of TTCA as well as melanoidins formation. The higher pH value could even promote this phenomenon.

Kinetic studies of 5-(hydroxymethyl)-furfural formation and change of the absorption at 420 nm in fruit juices for the improvement of pasteurization plants

Preservation of juices is essential to obtain microbial safe products. There are various established methods as pasteurization. Heretofore, only the kinetic figures of microbial inactivation were considered but not those of reaction impairing the chemical quality. For a gentler processing, knowledge of the kinetics of relevant chemical conversion reactions is necessary. 5-(Hydroxymethyl)-furfural (HMF) formation and the color change of juices are important attributes. The non-isothermal Rhim method was used to determine the activation energy and pre-exponential factor for HMF formation in different juices and an isothermal method for the reaction order. Values for the activation energy from 133 to 303 kJ/mol were obtained with a zeroth reaction order. A correlation between HMF and the color change could be found. Based on the kinetic figures, lines with equal effects for the chemical changes and for the lethal effect on microorganisms were calculated. Time-temperature settings for the gentlest treatment could be found.

Novel Amidine Protein Cross-Links Formed by the Reaction of Glyoxal with Lysine

One crucial aspect of the Maillard reaction is the formation of reactive α-dicarbonyl structures like glyoxal, which are prone toward further reactions with proteins, e.g., the N⁶-amino group of lysine. The initially formed labile glyoxal-imine was previously established as a key intermediate in the formation of the advanced glycation end products N⁶-carboxymethyl lysine (CML), glyoxal lysine amide (GOLA), glyoxal lysine dimer (GOLD), and N⁶-glycolyl lysine (GALA). Here, we introduce a novel amidine cross-link structure N¹,N²-bis-(5-amino-5-carboxypentyl)-2-hydroxy-acetamidine (glyoxal lysine amidine, GLA), which is formed exclusively from glyoxal through the same isomerization cascade. After independent synthesis of the authentic reference standard, we were able to quantitate this cross-link in incubations of 40 mM N²-t-Boc-lysine with glyoxal and various sugars (40-100 mM) under mild conditions (pH 7.4, 37 °C) using an HPLC-MS/MS method. Furthermore, incubations of proteins (6 mg/mL) with 50 mM glyoxal confirmed the cross-linking by GLA, which was additionally identified in acidic hydrolyzed proteins of butter biscuits after HPLC enrichment.

Carbon dots from roasted chicken accumulate in lysosomes and induce lysosome-dependent cell death

Thermal processing may generate toxicants. Carbon dots (CDs) from baked foods are toxic to cells; however, their molecular mechanism is still unexplored to date. The present study investigated the effects of CDs from roasted chicken breasts on normal rat kidney (NRK) and Caco-2 cells. The average size of CDs heated at 200 °C and 300 °C was about 2.8 nm and 1.2 nm, respectively. The element and surface groups of CDs were analyzed via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), respectively. It was confirmed that the CDs were internalized in lysosomes and induced apoptosis. Furthermore, Z-VAD-FMK did not decrease the rate of apoptosis. The acquired data further confirmed that these internalized CDs enlarged lysosomes, decreased the lysosomal enzyme degradation activity and increased the lysosomal pH value. An increase in the co-localization of RIPK3 in lysosomes in the CD-treated groups was observed. The CD treatment increased the protein level of receptor interaction protein 1 (RIPK1) and receptor interaction protein 3 (RIPK3). Overall, CDs from the baked chicken breast induced lysosomal membrane permeabilization and initiated lysosome-dependent cell death and necroptosis. Our results elucidated the toxic mechanism of CDs from baked chicken breast and implied that food thermal processing at a lower temperature is beneficial to human health.

Investigations on the formation of Maillard reaction products in sweet cookies made of different cereals

In this study, the content of Maillard reaction products from its initial, intermediate and final stage (5-hydroxymethylfurfural, α-dicarbonyl compounds, furosine, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine) was measured in sweet cookies made of wholegrain flour of eight genotypes of small-grain cereals (bread wheat, durum wheat, soft wheat, hard wheat, triticale, rye, hulless barley and hulless oat) and four corn genotypes (white-, yellow- and red-colored standard seeded corn and blue-colored popping corn). Furthermore, the effect of the initial content of sugars, total proteins, free and total lysine in flour on the formation of Maillard reaction products was investigated using the principle component analysis. 3-deoxyglucosone was the predominant α-dicarbonyl compound in all cereal cookies and the highest content was measured in those made from flour of different colored corn genotypes (on average, 98.35, 151.28 and 172.85 mg/kg after baking for 7, 10 and 13 min, respectively). Heating dough at 180 °C for 7, 10 and 13 min differently affected the content of 5-hydroxymethylfurfural and α-dicarbonyl compounds in the cereal cookies. The 5-hydroxymethylfurfural content gradually increased, while a reduction in 3-deoxyglucosone content was observed in the cookies baked for 13 min except for those made from soft wheat, hulless oat, red- and blue-colored corn. After 7 min of heating, the content of furosine measured in the cereal cookies reached its maximum (from 320.9 mg/kg in yellow-colored corn-based cookies to 585.7 mg/kg in hulless oat-based cookies), while N-ε-carboxymethyllysine and N-ε-carboxyethyllysine showed the opposite trend. The highest content of advanced glycation end products was detected in cookies also made from hulless oat flour rich in proteins (16.80%) and total lysine (10670.3 mg/kg). The interrelationship analysis showed that the initial content of sugars in flour of cereals affected 5-hydroxymethylfurfural and 3-deoxyglucosone formation in the cookies. In addition, a high correlation between protein-bound Maillard reaction products in the cookies and the total proteins and the total lysine content in the flours was found.

Effect of Methionine on the Thermal Degradation of N-(1-Deoxy-d-fructos-1-yl)-methionine Affecting Browning Formation

The effect of additional dl-methionine (Met) on the thermal degradation of a methionine-glucose-derived Amadori rearrangement product (MG-ARP) was investigated under different reaction conditions. The resulting color formation and changes in the concentrations of MG-ARP, Met, and α-dicarbonyl compounds were investigated. Additional Met did not affect the degradation rate of MG-ARP but got involved in subsequent reactions and resulted in a decrease in the contents of C₆-α-dicarbonyl compounds. During MG-ARP degradation, the formation of glyoxal (GO) and methylglyoxal (MGO) was facilitated by additional Met, through retro-aldolization reaction of C₆-α-dicarbonyl compounds. This effect of Met addition was dependent on the reaction temperature, and the consistent conclusion could be made in a buffer system. The improvement of GO and MGO formation as color precursors caused by the additional Met contributed to the acceleration of browning formation.

Odour-active compounds in liquid malt extracts for the baking industry

An odorant screening by gas chromatography–olfactometry (GC–O) and a crude aroma extract dilution analysis (AEDA) applied to the volatiles isolated from a light and a dark liquid malt extract (LME) by solvent extraction and solvent-assisted flavour evaporation (SAFE) identified 28 odorants. Fifteen major odorants were subsequently quantitated and odour activity values (OAVs) were calculated as ratio of the concentration to the respective odour threshold value (OTV). Important odorants in the light LME included 3-(methylsulfanyl)propanal (OAV 1500), (E)-β-damascenone (OAV 430), and 4-ethenyl-2-methoxyphenol (OAV 91). In the dark LME, sotolon (OAV 780), 3-(methylsulfanyl)propanal (OAV 550), (E)-β-damascenone (OAV 410), acetic acid (OAV 160), and maltol (OAV 120) were of particular importance. To get an insight into the changes during malt extract production, the quantitations were extended to the malt used as the starting material for both LMEs. Addition of a minor amount of water to malt before volatile extraction was shown to be effective to cover the free as well as the bound malt odorants. Results showed that some LME odorants originated from the starting material whereas others were formed during processing. Important process-induced LME odorants included (E)-β-damascenone and 4-ethenyl-2-methoxyphenol in the light LME as well as maltol, sotolon, (E)-β-damascenone, and 2-methoxyphenol in the dark LME. In summary, the odorant formation during LME production was shown to be more important than the transfer of odorants from the malt.

Oxidative Fragmentation of Aspalathin Leads to the Formation of Dihydrocaffeic Acid and the Related Lysine Amide Adduct

In the present study, the degradation of C-glucosidic dihydrochalcone aspalathin as the major phenolic compound in rooibos (Aspalathus linearis) was investigated. Analyses by gas chromatography-mass spectrometry of aqueous aspalathin-lysine incubations after silylation showed the formation of dihydrocaffeic acid [3-(3,4-dihydroxyphenyl)-propionic acid] under oxidative conditions as a novel degradation product up to 10 mol %. High-performance liquid chromatography analyses revealed the concurrent formation of the dihydrocaffeic acid lysine amide at about 30-fold lower concentrations, which was unequivocally verified by synthesis of an authentic reference standard. The amide was also verified in aspalathin-protein incubations after enzymatic hydrolysis by high-performance liquid chromatography-tandem mass spectrometry analyses. Thus, the covalent interaction of phenolic plant compounds with proteins under mild conditions (ambient temperatures and neutral pH) was confirmed for the first time. Acid and free amide were also quantitated in rooibos teas with significantly higher values in fermented varieties. The mechanism of formation was clarified to be initiated by singlet oxygen and to include a rearrangement-fragmentation mechanism with 1,2,3,5-tetrahydroxybenzene as the counterpart.

Characterization of the Soluble Products Formed during the Hydrothermal Conversion of Biomass-Derived Furanic Compounds by Using LC-MS/MS

To reveal the hydrothermal conversion routes of the biomass-derived furanic compounds, the soluble products formed during the hydrothermal conversion of 5-hydroxymethylfurfural (HMF), furfural, and furfuryl alcohol were analyzed by liquid chromatography-mass spectrometry (LC-MS) and LC-MS/MS. Multiple carbocyclic compounds containing hydroxy group and carbonyl group were detected, with a molecular mass in the range of 154-272 Da and carbon chain of the length 8-15. The formation of these soluble carbocyclic compounds was proposed to involve hydrolytic ring-opening of the furanic ring, intermolecular aldol condensation, intramolecular aldol condensation, and C-C cleavage reaction. The C-C cleavage reaction was proposed to occur on the dicarbonyl structure of the formed primary polymers.

Trapping Methylglyoxal by Myricetin and Its Metabolites in Mice

Trapping of methylglyoxal (MGO) has been determined to be one of the potential mechanisms for dietary polyphenols to prevent chronic diseases. In this study, myricetin was demonstrated to efficiently trap MGO to generate mono- and di-MGO adducts under in vitro conditions. Furthermore, the mono- and di-MGO adducts of myricetin were detected in urine and fecal samples collected from myricetin-treated mice based on LC-MS analysis. More importantly, the mono-MGO adducts of the mono- and di-methylated myricetin were also found in these mouse samples. Further dose-dependent studies demonstrated that myricetin and its methylated metabolites significantly trapped MGO in a dose-dependent manner with the 400 mg/kg dose having the highest trapping efficacy (mono-MGO-myricetin: 272.0 ± 90.9 nM in urine and 1.05 ± 0.67 μg/g in feces; mono-MGO-mono-Me-myricetin: 135.2 ± 77.6 nM in urine and 1.16 ± 0.65 μg/g in feces; and mono-MGO-di-Me-myricetin: 17.0 ± 5.9 nM in urine and 0.19 ± 0.04 μg/g in feces) compared to the 100 and 200 mg/kg doses. In conclusion, this study demonstrates for the first time the in vivo trapping efficacy of myricetin, suggesting that intake of myricetin-containing foods has the potential to scavenge MGO in vivo and to prevent MGO-induced harmful effects to human health.

Formation of Taste-Active Pyridinium Betaine Derivatives Is Promoted in Thermally Treated Oil-in-Water Emulsions and Alkaline pH

The oil-water interface can be used as an efficient reaction controller in foods by carrying specific reactants and products in either the hydrophobic or hydrophilic phase. The formation of the taste-active compounds N-(1-carboxyethyl)-6-hydroxymethyl-pyridinium-3-ol inner salt (alapyridaine) and 1-(1-carboxyethyl)-3-hydroxy-pyridinium inner salt is influenced by the presence of a dispersed saturated triglyceride oil phase and by the pH of the aqueous phase. At pH 6.5, the formation of both betaines was 1.24 and 6 times higher in emulsions than in aqueous solution after 4 min at 140 °C. In alkaline emulsions (pH = 9.5, 4 min), the concentrations of alapyridaine and 1-(1-carboxyethyl)-3-hydroxy-pyridinium ion were 6.2 and 3.8 times higher, respectively, than in unbuffered emulsions as a result of the interaction between the polar head group of the surfactant and pyridinium rings. Here, we reported for the first time the effects of multiphase systems on the formation of nonvolatile, taste-active end products.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Quality Criteria for Studies on Dietary Glycation Compounds and Human Health

Current reports increasingly associate dietary "advanced glycation end products" ("AGEs") resulting from the Maillard reaction (glycation) between reducing sugars and amino compounds in foods with pathophysiological consequences, such as chronic inflammation, atherosclerosis, and metabolic syndrome. Heated foods are therefore suggested to pose a potential risk for human health. However, studies in this field are very often based on questionable quantitative data and inadequate structural characterization. To improve the situation, the present perspective suggests quality criteria for future studies and the assessment of the currently available literature.

Melanoidins from Coffee, Cocoa, and Bread Are Able to Scavenge α-Dicarbonyl Compounds under Simulated Physiological Conditions

Free amino residues react with α-dicarbonyl compounds (DCs) contributing to the formation of advanced glycation end products (AGEs). Phenolic compounds can scavenge DCs, thus controlling the dietary carbonyl load. This study showed that high-molecular weight cocoa melanoidins (HMW-COM), HMW bread melanoidins (HMW-BM), and especially HMW coffee melanoidins (HMW-CM) are effective DC scavengers. HMW-CM (1 mg/mL) scavenged more than 40% DCs within 2 h under simulated physiological conditions, suggesting some physiological relevance. Partial acid hydrolysis of HMW-CM decreased the dicarbonyl trapping capacity, demonstrating that the ability to react with glyoxal, methylglyoxal (MGO), and diacetyl was mainly because of polyphenols bound to macromolecules. Caffeic acid (CA) and 3-caffeoylquinic acid showed a DC-scavenging kinetic profile similar to that of HMW-CM, while mass spectrometry data confirmed that hydroxyalkylation and aromatic substitution reactions led to the formation of a stable adduct between CA and MGO. These findings corroborated the idea that antioxidant-rich indigestible materials could limit carbonyl stress and AGE formation across the gastrointestinal tract.

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.

Identification of key aroma-active compounds in sesame oil from microwaved seeds using E-nose and HS-SPME-GC×GC-TOF/MS

The study investigated the volatile compounds of sesame oil and the effects of microwave processing (0-8 min with 1-min intervals), mainly focusing on the integral flavor characteristics and individual aroma-active compounds. A total of 82 characteristic odors were identified using GC×GC-TOF/MS. Fifteen volatile compounds with the highest odor activity values (OAV > 100) were selected as the key odors contributing to the flavor profile of microwaved sesame oil, including 2-methyl-propanal (pungent, malt, green), 2-methyl-butanal (cocoa, almond), furaneol (caramel), 1-octen-3-one (mushroom), 4-methyl-3-penten-2-one (sweet), 1-nonanol (fat, citrus, green), 2-methyl-phenol (phenol), 2-methoxy-phenol (smoke, sweet), 2-methoxy-4-vinylphenol (clove, curry), 2,5-dimethyl-pyrazine (cocoa, roasted nut, roast beef), 2-furfurylthiol (coffee, roast), 2-thiophenemethanethiol (sulfur), methanethiol (gasoline, garlic), methional (cooked potato), and dimethyl trisulfide (fish, cabbage). The OAVs significantly increased with a longer microwave process. Meanwhile, PCA results based on E-nose and cluster analysis results based on GC×GC-TOF/MS were similar to distinguish flavor formation during the microwave process. PRACTICAL APPLICATIONS: Sesame oils were prepared by a microwave process. Aroma-active compounds with the highest OAVs in sesame oils were not clear. Identification of key aroma compounds of sesame oils could adopt a comprehensive assessment method in combination with E-nose and individual odors detection. Microwave pretreatment as a new processing technology for sesame oil extraction could reduce the time consumption and produce a unique fragrant flavor compared to the traditional roasting process.