Lysine-Derived Protein-Bound Heyns Compounds in Bakery Products

Key factors influencing the formation of α-dicarbonyls and dietary advanced glycation end products in bread and commercial bakery products: Impacts of sugar, lipid and gluten protein

α-Dicarbonyls and dietary advanced glycation end products (dAGEs) are potentially harmful compounds formed from the Maillard reaction. Bakery products often contain high levels of α-dicarbonyls and dAGEs due to thermal processing. Additionally, the ingredients used in dough might significantly influence the formation of these compounds. Our findings indicated that adding sucrose notably increased the formation of α-dicarbonyls and methylglyoxal-derived dAGEs in bread, while the incorporation of butter and olive oil had negligible effects. In contrast, substituting high-gluten flour with medium- and low-gluten flour reduced the formation of α-dicarbonyls and dAGEs in bread. Furthermore, correlation analyses revealed a significant positive relationship between total dAGEs content and total sugar content in commercial bakery products, with no significant correlation found with total protein and fat content. This study suggests that the sugar content listed on nutrition labels could serve as a practical indicator for estimating dAGE levels in bakery products.

Enhancing cooking and eating quality of semi-dried brown rice noodles through Lactobacillus fermentation and moderate lysine addition

Various concentrations of lysine were added to Lactobacillus fermentum-fermented brown rice flour to examine their effects on the sensory evaluation, color, pH, cooking quality, and texture of the resulting noodles. The potential mechanisms were explored through analyses of water distribution, thermodynamic properties, crystallinity, and microstructural observations using low-field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Low concentrations of lysine (1 % and 3 %) effectively mitigated sourness while maintaining a color similar to natural brown rice noodles, with minimal structural damage and good cooking quality. The 3 % lysine group received the highest sensory scores (73.3 ± 5.4), likely due to moderate lysine-mediated starch network formation and improved water retention. While, a high lysine concentration (5 %) resulted in an undesirable reddish-brown color, poor texture and cooking quality. This is likely due to the formation of rigid lysine-mediated starch structures, which made the noodles brittle.

Dietary glycation compounds - implications for human health

The term "glycation compounds" comprises a wide range of structurally diverse compounds that are formed endogenously and in food via the Maillard reaction, a chemical reaction between reducing sugars and amino acids. Glycation compounds produced endogenously are considered to contribute to a range of diseases. This has led to the hypothesis that glycation compounds present in food may also cause adverse effects and thus pose a nutritional risk to human health. In this work, the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG) summarized data on formation, occurrence, exposure and toxicity of glycation compounds (Part A) and systematically assessed potential associations between dietary intake of defined glycation compounds and disease, including allergy, diabetes, cardiovascular and renal disease, gut/gastrotoxicity, brain/cognitive impairment and cancer (Part B). A systematic search in Pubmed (Medline), Scopus and Web of Science using a combination of keywords defining individual glycation compounds and relevant disease patterns linked to the subject area of food, nutrition and diet retrieved 253 original publications relevant to the research question. Of these, only 192 were found to comply with previously defined quality criteria and were thus considered suitable to assess potential health risks of dietary glycation compounds. For each adverse health effect considered in this assessment, however, only limited numbers of human, animal and in vitro studies were identified. While studies in humans were often limited due to small cohort size, short study duration, and confounders, experimental studies in animals that allow for controlled exposure to individual glycation compounds provided some evidence for impaired glucose tolerance, insulin resistance, cardiovascular effects and renal injury in response to oral exposure to dicarbonyl compounds, albeit at dose levels by far exceeding estimated human exposures. The overall database was generally inconsistent or inconclusive. Based on this systematic review, the SKLM concludes that there is at present no convincing evidence for a causal association between dietary intake of glycation compounds and adverse health effects.

Glycation reactions of methylglyoxal during digestion in a dynamic, in vitro model of the upper gastrointestinal tract (TIM-1)

The 1,2-dicarbonyl compound methylglyoxal (MGO) can react with and thereby impair the function of proteins and DNA, leading to pathophysiological pathways in vivo. However, studies on the bioavailability of dietary MGO and its reactions during digestion have diverging results. Therefore, simulated digestion experiments of MGO, protein, and creatine were performed in the dynamic, in vitro model of the upper gastrointestinal tract (TIM-1). This multicompartment model continuously adjusts pH values and has realistic gastrointestinal transit times while also removing water and metabolites by dialysis. Samples were analyzed with HPLC-UV for MGO and HPLC-MS/MS for creatine and glycated amino compounds. MGO reacted with creatine during simulated digestion in TIM-1 to form the hydroimidazolone MG-HCr in similar amounts as in a human intervention study. 28%-69% of MGO from the meal were passively absorbed in TIM-1, depending on the addition of creatine and protein. Simultaneous digestion of MGO with ovalbumin led to the formation of the lysine adduct N ε -carboxyethyllysine (CEL) and the methylglyoxal-derived hydroimidazolone of arginine (MG-H1). The formation of both compounds decreased with added creatine. Hence, glycation compounds are formed during digestion and significantly contribute to other ingested dietary glycation compounds, whose physiological consequences are critically discussed.

Formation of Protein-Bound Maillard Reaction Products during the Storage of Manuka Honey

Honey from the nectar of the Manuka tree (Leptospermum scoparium) grown in New Zealand contains high amounts of antibacterial methylglyoxal (MGO). MGO can react with proteins to form peptide-bound Maillard reaction products (MRPs) such as Nε-carboxyethyllysine (CEL) and "methylglyoxal-derived hydroimidazolone 1" (MG-H1). To study the reactions of MGO with honey proteins during storage, three manuka honeys with varying amounts of MGO and a kanuka honey (Kunzea ericoides) spiked with various MGO concentrations up to 700 mg/kg have been stored at 37 °C for 10 weeks, and the formation of protein-bound MRPs has been analyzed via high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) following isolation of the protein fraction and enzymatic hydrolysis. During storage, contents of protein-bound CEL and MG-H1 increased continuously, directly depending on the MGO content. For honeys with large amounts of MGO, a slower formation of Nε-fructosyllysine (FL) was observed, indicating competing reactions of glucose and MGO with lysine. Furthermore, the lysine modification increased with storage independently from the MGO concentration. Up to 58-61% of the observed lysine modification was explainable with the formation of CEL and FL, indicating that other reactions, most likely the formation of Heyns products from lysine and fructose, may play an important role. Our results can contribute to the authentication of manuka honey.

Glucose-Histidine Heyns compound: Preparation, characterization and fragrance enhancement

N-(2-Deoxy-D-glucos-2-yl)-L-histidine (Glu-His), one of Heyns rearrangement products (HRPs), was prepared by condensation, dehydration and rearrangement using l-Histidine and d-Fructose as raw materials with methanol as solvent. The response surface method (RSM) was used to improve yield of product and the optimal reaction condition was as following: the original ratio of Fru:His was 1.2:1 and the temperature and time of reaction was 73.2 °C and 4.7 h, and the yield of final product was 74.10% with the purity of 99.7%. The structure of product was identified by IR, NMR and conformed as C12H19N3O7 (317.1 Da) by high-resolution mass spectrometry (HRMS) and UPLC-MS/MS. The pyrolysis behavior of Glu-His showed that its initial pyrolysis temperature was 145.2 °C and the total weight loss reached 70.61% at 800 °C. The number of pyrolysis products increased with the increase of temperature, and the main pyrolysis products were pyrans, furans, pyrazines, pyrroles, pyridines, indoles and etc. with burnt-sweet, baking, nutty, sweet and floral aroma features. At last, the fragrance enhancement effect of Glu-His in the preparation of reconstructed tobacco stem (RTS) was investigated and the result of sensory evaluation showed that the smoke of RTS cigarettes brought about more sweet and moist, less irritation, better flavor and comfort with the addition of Glu-His (0.25%, w/w).

Advanced Glycation End Products: A Comprehensive Review of Their Detection and Occurrence in Food

The Maillard reaction (MR) is a complicated chemical process that has been extensively studied. Harmful chemicals known as advanced glycation end products (AGEs), with complex structures and stable chemical characteristics, are created during the final stage of the MR. AGEs can be formed both during the thermal processing of food and in the human body. The number of AGEs formed in food is much higher compared to endogenous AGEs. A direct connection exists between human health and the build-up of AGEs in the body, which can result in diseases. Therefore, it is essential to understand the content of AGEs in the food we consume. The detection methods of AGEs in food are expounded upon in this review, and the advantages, disadvantages, and application fields of these detection methods are discussed in depth. Additionally, the production of AGEs in food, their content in typical foods, and the mechanisms influencing their formation are summarized. Since AGEs are closely related to the food industry and human health, it is hoped that this review will further the detection of AGEs in food so that their content can be evaluated more conveniently and accurately.

Rye Bread Crust as an Inducer of Antioxidant Genes and Suppressor of NF-κB Pathway In Vivo

Heat-processed food, like bread, containing high amounts of advanced glycation end products (AGEs), is controversially discussed regarding the effects on health and disease. In in vitro and in vivo experiments, AGEs can induce proinflammatory NF-κB and/or the anti-inflammatory NRF2 pathways. The aim of this study was to investigate how gene expression is influenced in vivo upon short as well as long-term feeding of mice with control and bread crust-food (BC). For that, the liver, kidney and heart from two days- and eight days-fed mice were isolated and gene arrays were performed. Fewer genes were affected in terms of expression after two days of BC feeding than after eight days. We observed, especially in the heart and to lesser extent in the liver, an induction of antioxidant response by BC. Among the significantly up-regulated genes identified in the heart were transcripts encoding for cardioprotective and antioxidative proteins like metallothionein 2, uncoupling protein 3 and pyruvate dehydrogenase kinase 4. In contrast, in the liver, genes encoding for inflammatory drivers like thioredoxin-interacting protein, lncRNA Mtss1 and ubiquitin-specific protease 2 were down-modulated. However, an increased expression of immunoglobulins was observed in the kidney. Furthermore, in vivo imaging analyses with NF-κB-luciferase-reporter mice uncovered a rather anti-inflammatory response, especially after three and seven days of the feeding study. Our results suggest that bread crust exerts antioxidant and anti-inflammatory effects in the model organism mouse in an organ-specific manner.

Heat-induced formation of advanced glycation end-products in ground pork as affected by the addition of acetic acid or citric acid and the storage duration prior to the heat treatments

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Organic acids affected advanced glycation end-product (AGE) levels in heated pork.

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Heat-induced AGEs in pork with citric acid (ca 0.5–1%) were reduced by 30–54%.

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Adding acetic acid at the same level led to 14–48% reduction of AGEs.

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The reduction of AGEs corresponded to decreased levels of TBARS and Schiff bases.

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Marinating time (pork & acid) did not affect the acid’s inhibiting effect for AGEs.

The heat-induced (121 °C, 10 or 30 min) formation of two potentially hazardous advanced glycation end-products (AGEs), protein-bound N^ɛ-carboxymethyllysine (CML) and N^ɛ-carboxyethyllysine (CEL), in pork as affected by citric or acetic acid (0.5, 1 g/100 pork) and the storage duration (0 °C, 0 – 8 d) prior to the heating was investigated. A longer storage time of raw pork resulted in higher levels of AGEs produced during the later heating, likely due to the accumulation of some AGE precursors during the storage. Depending on the acid level and heating time, adding acid in pork led to 30 – 54% (citric acid) or 14 – 48% (acetic acid) average reduction of heat-induced production of CML/CEL, which corresponded to the reduction of thiobarbituric acid reactive substances and Schiff bases. The marinating time of raw pork with an acid did not significantly affect (P = 0.959 – 0.998) the acid’s inhibition effect on heat-induced formation of CML/CEL.

Chromatographic separation of glycated peptide isomers derived from glucose and fructose

Amino groups in proteins can react with aldehyde groups in aldoses or keto groups in ketoses, e.g., D-glucose and D-fructose, yielding Schiff bases that rearrange to more stable Amadori and Heyns products, respectively. Analytical strategies to identify and quantify each glycation product in the presence of the corresponding isomer are challenged by similar physicochemical properties, impeding chromatographic separations, and by identical masses including very similar fragmentation patterns in tandem mass spectrometry. Thus, we studied the separation of seven peptide families, each consisting of unmodified, glucated, and fructated 15mer to 22mer peptides using reversed-phase (RP) and hydrophilic interaction chromatography (HILIC). In RP-HPLC using acidic acetonitrile gradients, unglycated peptides eluted ~ 0.1 to 0.8 min after the corresponding glycated peptides with four of seven peptides being baseline separated. Isomeric glucated and fructated peptides typically coeluted, although two late-eluting peptides were partially separated. Neutral eluents (pH 7.2) improved the chromatographic resolution (R_s), especially in the presence of phosphate, providing good and often even baseline separations for six of the seven isomeric glycated peptide pairs with fructated peptides eluting earlier (R_s = 0.7 to 1.5). Some glucated and unmodified peptides coeluted, but they can be distinguished by mass spectrometry. HILIC separated glycated and unmodified peptides well, whereas glucated and fructated peptides typically coeluted. In conclusion, HILIC efficiently separated unmodified and the corresponding glycated peptides, while isomeric Amadori and Heyns peptides were best separated by RP-HPLC using phosphate buffered eluents.

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.

Differentiation and Quantitation of Coeluting Isomeric Amadori and Heyns Peptides Using Sugar-Specific Fragment Ion Ratios

d-glucose and d-fructose present in blood, tissues, and organs of all mammals can react with amino groups, leading to glucated (Amadori) and fructated (Heyns) products, i.e., proteins glycated at lysine residues. While typically present at low concentration in humans, metabolic diseases including diabetes elevate sugar levels, favoring glycation and consecutive reactions leading to advanced glycation end products (AGEs) linked to diabetic complications and cardiovascular diseases. Analytical methods able to differentiate and to individually quantify Amadori- and Heyns-modified proteins in complex sample mixtures, e.g., serum, are still very limited. Here, we show that the reported and supposedly specific neutral losses displayed in tandem mass spectra of Heyns peptides cannot be used for a reliable differentiation as they were also observed for Amadori peptides. However, the combination of several neutral loss signals in fragment ion ratios at both precursor and fragment ion signals allowed the differentiation and relative quantitation of coeluting isomeric Amadori and Heyns peptides at different concentrations and peptide ratios. This was also true for digested human plasma. Thus, the presented strategy allows the quantitation of Amadori and Heyns peptides in complex samples, especially by spiking isotope-labeled peptides. This will allow searching for glucated and fructated biomarkers in clinical samples.

AGE-Rich Bread Crust Extract Boosts Oxidative Stress Interception via Stimulation of the NRF2 Pathway

Advanced glycation end products (AGEs) result from a non-enzymatic reaction of proteins with reactive carbohydrates. Heat-processed food, such as bread, contains high amounts of AGEs. The activation of the NF-κB signaling pathway by bread crust extract (BCE) is well understood. However, it is largely unknown whether NRF2, the master regulator of oxidative stress resistance in mammalian cells, is affected by BCE. We have investigated the molecular mechanisms by which BCE induces antioxidant gene expression in cellular models. Our data showed that soluble extracts from bread crust are capable of stimulating the NRF2 signaling pathway. Furthermore, NRF2 pathway activation was confirmed by microarray and reporter-cell analyses. QRT-PCR measurements and Western blot analyses indicated an induction of antioxidative genes such as HMOX1, GCLM and NQO1 upon BCE treatment. Moreover, BCE pretreated cells had a survival advantage compared to control cells when exposed to oxidative stress. BCE induces phosphorylation of AKT and ERK kinase in EA.hy926 cells. By mass spectrometry, several new, potentially active modifications in BCE were identified. Our findings indicate that BCE activates NRF2-dependent antioxidant gene expression, thus provoking a protection mechanism against oxidative stress-mediated tissue injury. Hence, BCE can be considered as functional food with antioxidative and cardioprotective potential.

Discovery of Polyhydroxyalkyl Pyrazine Generation upon Coffee Roasting by In-Bean Labeling Experiments

The major non-volatile reaction products formed from free amino acids during the early stage of coffee roasting were investigated using biomimetic in-bean experiments with labeled and unlabeled free amino acids. Comprehensive untargeted screening by ultra-high performance liquid chromatography-electrospray-ionization-quadrupole time-of-flight-tandem mass spectrometry (UHPLC-ESI-QToF-MS) in data-independent acquisition (DIA) mode was carried out and modeling by orthogonal partial least-squares discriminant analysis (OPLS-DA) helped in revealing 11 pyrazine structures identified in coffee for the first time. 2-(2',3',4'-Trihydroxybutyl)-(5/6)-methyl-pyrazine (1) and 2,(5/6)-bis(2',3',4'-trihydroxybutyl)-pyrazine (2) were the most prominent compounds, while 2-(3',4'-dihydroxybutyl)-(5/6)-methyl-pyrazine (5) and 2-(2',3',4'-trihydroxybutyl)-(5/6)-(2'-hydroxyethyl)-pyrazine (10) were not even previously identified in other food matrices. The structures could be verified by means of additional biomimetic in-bean experiments with labeled sucrose leveraging the carbon module labeling (CAMOLA) approach. Based on these results, plausible formation pathways could be formulated fitting into the known Maillard reaction mechanisms. Sucrose was highlighted as the predominant precursor of the carbon backbone of all identified pyrazines butonly 33-55% of the nitrogen atoms originated from free amino acids.

Solid-phase synthesis of D-fructose-derived Heyns peptides utilizing Nα-Fmoc-Lysin[Nε-(2-deoxy-D-glucos-2-yl),Nε-Boc]-OH as building block

Aldoses and ketoses can glycate proteins yielding isomeric Amadori and Heyns products, respectively. Evidently, d-fructose is more involved in glycoxidation than d-glucose favoring the formation of advanced glycation endproducts (AGEs). While Amadori products and glucation have been studied extensively, the in vivo effects of fructation are largely unknown. The characterization of isomeric Amadori and Heyns peptides requires sufficient quantities of pure peptides. Thus, the glycated building block N^α-Fmoc-Lys[N^ε-(2-deoxy-d-glucos-2-yl),N^ε-Boc]-OH (Fmoc-Lys(Glc,Boc)-OH), which was synthesized in two steps starting from unprotected d-fructose and Fmoc-l-lysine hydrochloride, was site-specifically incorporated during solid-phase peptide synthesis. The building block allowed the synthesis of a peptide identified in tryptic digests of human serum albumin containing the reported glycation site at Lys233. The structure of the glycated amino acid derivatives and the peptide was confirmed by mass spectrometry and NMR spectroscopy. Importantly, the unprotected sugar moiety showed neither notable epimerization nor undesired side reactions during peptide elongation, allowing the incorporation of epimerically pure glucosyllysine. Upon acidic treatment, the building block as well as the resin-bound peptide formed one major byproduct due to incomplete Boc-deprotection, which was well separated by reversed-phase chromatography. Expectedly, the tandem mass spectra of the fructated amino acid and peptide were dominated by signals indicating neutral losses of 18, 36, 54, 84 and 96 m/z-units generating pyrylium and furylium ions.

Food Protein Sterylation: Chemical Reactions between Reactive Amino Acids and Sterol Oxidation Products under Food Processing Conditions

Sterols, especially cholesterol and phytosterols, are important components of food lipids. During food processing, such as heating, sterols, like unsaturated fatty acids, can be oxidized. Protein modification by secondary products of lipid peroxidation has recently been demonstrated in food through a process called lipation. Similarly, this study was performed to assess, for the first time, the possibility of reactions between food proteins and sterol oxidation products in conditions relevant for food processing. Therefore, reaction models consisting of oxysterol (cholesterol 5α,6α-epoxide) and reactive amino acids (arginine, lysine, and methionine) were incubated in various conditions of concentration (0–8 mM), time (0–120 min), and temperature (30–180 °C). The identification of lysine adducts through thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC) with a diode array detector (DAD), and electrospray ionization (ESI) mass spectrometry (MS) evidenced a reaction with lysine. Moreover, the HPLC-ESI with tandem mass spectrometry (MS/MS) analyses allowed observation of the compound, whose mass to charge ratio m/z 710.5 and fragmentation patterns corresponded to the reaction product [M + H]⁺ between cholesterol-5α,6α-epoxide and the ε-amino-group of N_α-benzoylglycyl-l-lysine. Moreover, kinetic studies between N_α-benzoylglycyl-l-lysine as a model for protein-bound lysine and cholesterol 5α,6α-epoxide were performed, showing that the formation of lysine adducts strongly increases with time, temperature, and oxysterol level. This preliminary study suggests that in conditions commonly reached during food processing, sterol oxidation products could react covalently with protein-bound lysine, causing protein modifications.

Formation of protein-bound Nε-carboxymethyllysine and Nε-carboxyethyllysine in ground pork during commercial sterilization as affected by the type and concentration of sugars

This research was aimed to investigate the formation of protein-bound N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) in ground pork at 121 °C (5-30 min) as affected by sugars (1-9% w/w, glucose, fructose, lactose, and sucrose).The addition of reducing sugar significantly (P < 0.05) increased the levels of CML and CEL in heat treated pork samples. Even adding 1% of glucose in pork could lead to 3.8 and 4.0 times increase in the formation rate constant (zero-order) of CML and CEL, respectively. In a typical commercial sterilization process (121 °C, 30 min), adding glucose, fructose or lactose in pork resulted in an average increase of 224-581%, 26-276%, and 8-189% CML, and 217-720%, 213%-15.8 times, and 20-150% CEL, respectively, depending on the sugar concentration. Sucrose did not promote the formation of CML and CEL in pork during heating.

Quantitation of α-Dicarbonyls and Advanced Glycation Endproducts in Conventional and Lactose-Hydrolyzed Ultrahigh Temperature Milk during 1 Year of Storage

A comprehensive quantitative characterization of Maillard reaction products was carried out for conventional (CON) and lactose-hydrolyzed (LH) ultrahigh temperature (UHT) milk during storage at 20, 30, and 40 °C for 1 year. The accumulation of 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) in LH-UHT milk ranged from 20-fold (at 20 °C) to 44-fold (at 40 °C) higher than that in CON-UHT milk. High temperature storage (40 °C) significantly accelerated the accumulation of 3-DG, 3-DGal, and 5-hydroxymethyl furfural but not the majority of the analyzed advanced glycation endproducts (AGEs). The concentrations of major AGEs including N-ε-carboxymethyllysine (CML), N-ε-carboxyethyllysine (CEL), methylglyoxal-hydroimidazolone isomers (MG-H1/H3), glyoxal-hydroimidazolone isomers (G-H1/H3), and G-H2 detected in CON milk during storage were in the range 12-700, 1-14, 8-45, 4-13, and 1-30 μM, respectively, while they were 30-570, 2-88, 17-150, 9-20, and 5-34 μM, respectively, in LH milk. Pyrraline, S-(carboxymethyl)cysteine (CMC), and glyoxal-lysine dimer were detected in lower levels, while MG-H2, methylglyoxal-lysine dimer, argpyrimidine, glyoxal-lysine-amide, glycolic acid-lysine-amide, and pentosidine were not detected in any of the milk samples. This work demonstrates for the first time that five of the analyzed AGEs (CML, CEL, MG-H1/H3, G-H1/H3, and G-H2) could be selected as markers for evaluation of the extent of the Maillard reaction in UHT milk. These results contribute to a better understanding of how Maillard reactions progress during storage of UHT milk and can be used to develop strategies to inhibit Maillard reactions in LH milk.

Formation of advanced glycation endproducts in foods during cooking process and underlying mechanisms: a comprehensive review of experimental studies

Advanced glycation endproducts (AGE) are a group of complex and heterogeneous molecules, sharing some common characteristics such as covalent cross-link formation among proteins, the effect of transforming the colour of food products into yellow-brown colours and fluorescence formation. AGE are linked to many diseases including diabetes, renal diseases, CVD, liver diseases, neuro-degenerative and eye disorders, female reproductive dysfunction, and even cancer. AGE are formed endogenously but are also provided from exogenous sources including diet and tobacco. Western diet, rich in processed and/or heat-treated foods, fat and sugar, increases the exposure to AGE. The foods that contain high levels of fat and protein are generally rich in terms of AGE, and are also prone to AGE formation during cooking compared with carbohydrate-rich foods such as vegetables, fruits, legumes and whole grains. The present article aimed to review the literature about the effects of different cooking methods and conditions on the AGE content of food and AGE formation mechanisms using a comprehensive approach.

Studies on the Formation of 3-Deoxyglucosone- and Methylglyoxal-Derived Hydroimidazolones of Creatine during Heat Treatment of Meat

Dicarbonyl compounds such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG) are formed via caramelization and the Maillard reaction in food during heating or in vivo as byproducts of glycolysis. Recently, it was shown that creatine, an amino compound linked to the energy metabolism in vertebrate muscle, reacts rapidly with methylglyoxal under physiological conditions to form N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine (MG-HCr), a methylglyoxal-derived hydroimidazolone of creatine. Based on the observation that heated meat contains only small amounts of MGO and 3-DG when compared to many other foodstuffs, the aim of this study was to investigate a possible reaction of creatine with 3-DG and MGO in meat. From incubation mixtures consisting of 3-DG and creatine, a new hydroimidazolone of creatine, namely N-(4-butyl-1,2,3-triol-5-oxo-1-imidazolin-2-yl)sarcosine (3-DG-HCr), was isolated and characterized via spectroscopic means. To quantitate 3-DG-HCr and MG-HCr, meat and fish products were analyzed via HPLC-MS/MS using isotopically labeled standard material. Whereas samples of raw fish and meat contained only trace amounts of the hydroimidazolones (below 5 μg/kg), up to 28.3 mg/kg MG-HCr and up to 15.3 mg/kg 3-DG-HCr were found in meat and fish products. The concentrations were dependent on the heat treatment and presumably on the smoking process. In comparison to the lysine and arginine derivatives CEL, pyrraline, and MG-H1, the derivatization rate of creatine as MG-HCr and 3-DG-HCr was higher than of lysine and arginine, which clearly demonstrates the 1,2-dicarbonyl scavenging properties of creatine in meat.

Glycation of Plant Proteins: Regulatory Roles and Interplay with Sugar Signalling?

Glycation can be defined as an array of non-enzymatic post-translational modifications of proteins formed by their interaction with reducing carbohydrates and carbonyl products of their degradation. Initial steps of this process rely on reducing sugars and result in the formation of early glycation products-Amadori and Heyns compounds via Schiff base intermediates, whereas their oxidative degradation or reactions of proteins with α-dicarbonyl compounds yield a heterogeneous group of advanced glycation end products (AGEs). These compounds accompany thermal processing of protein-containing foods and are known to impact on ageing, pathogenesis of diabetes mellitus and Alzheimer's disease in mammals. Surprisingly, despite high tissue carbohydrate contents, glycation of plant proteins was addressed only recently and its physiological role in plants is still not understood. Therefore, here we summarize and critically discuss the first steps done in the field of plant protein glycation during the last decade. We consider the main features of plant glycated proteome and discuss them in the context of characteristic metabolic background. Further, we address the possible role of protein glycation in plants and consider its probable contribution to protein degradation, methylglyoxal and sugar signalling, as well as interplay with antioxidant defense.

Metabolic engineering strategies for enhanced shikimate biosynthesis: current scenario and future developments

Shikimic acid is an important intermediate for the manufacture of the antiviral drug oseltamivir (Tamiflu®) and many other pharmaceutical compounds. Much of its existing supply is obtained from the seeds of Chinese star anise (Illicium verum). Nevertheless, plants cannot supply a stable source of affordable shikimate along with laborious and cost-expensive extraction and purification process. Microbial biosynthesis of shikimate through metabolic engineering and synthetic biology approaches represents a sustainable, cost-efficient, and environmentally friendly route than plant-based methods. Metabolic engineering allows elevated shikimate production titer by inactivating the competing pathways, increasing intracellular level of key precursors, and overexpressing rate-limiting enzymes. The development of synthetic and systems biology-based novel technologies have revealed a new roadmap for the construction of high shikimate-producing strains. This review elaborates the enhanced biosynthesis of shikimate by utilizing an array of traditional metabolic engineering along with novel advanced technologies. The first part of the review is focused on the mechanistic pathway for shikimate production, use of recombinant and engineered strains, improving metabolic flux through the shikimate pathway, chemically inducible chromosomal evolution, and bioprocess engineering strategies. The second part discusses a variety of industrially pertinent compounds derived from shikimate with special reference to aromatic amino acids and phenazine compound, and main engineering strategies for their production in diverse bacterial strains. Towards the end, the work is wrapped up with concluding remarks and future considerations.

Bacteria in the ageing gut: did the taming of fire promote a long human lifespan?

Unique among animals as they evolved towards Homo sapiens, hominins progressively cooked their food on a routine basis. Cooked products are characterized by singular chemical compounds, derived from the pervasive Maillard reaction. This same reaction is omnipresent in normal metabolism involving carbonyls and amines, and its products accumulate with age. The gut microbiota acts as a first line of defence against the toxicity of cooked Maillard compounds, that also selectively shape the microbial flora, letting specific metabolites to reach the blood stream. Positive selection of metabolic functions allowed the body of hominins who tamed fire to use and dispose of these age-related compounds. I propose here that, as a hopeful accidental consequence, this resulted in extending human lifespan far beyond that of our great ape cousins. The limited data exploring the role of taming fire on the human genetic setup and on its microbiota is discussed in relation with ageing.