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Abstract
The Maillard reaction or nonenzymatic browning is of outstanding importance for the formation of flavour and colour of heated foods. Corresponding reactions, also referred to as "glycation", are known from biological systems, where the formation of advanced glycation endproducts (AGEs) shall play an important pathophysiological role in diabetes and uremia. In this review, pathways leading to the formation of individual protein-bound lysine and arginine derivatives in foods are described and nutritional consequences resulting from this posttranslational modifications of food proteins are discussed.
... 4 One key reaction for the sensory changes, especially for the appearance of bready, caramel, and sweet impressions, is the Maillard reaction. 5 Dicarbonyl compounds are formed 6,7 during its advanced phase. Regarding this substance class, 3deoxyglucosone (3-DG) is the major compound in beer, its process intermediates, and malt. ...
... 16 AGEs are formed by the reaction of dicarbonyls with selected amino acids and characterize the final stage of the Maillard reaction. 7 For example, pyrraline is formed from lysine (Lys) during reaction with 3-DG. 17 Further, Lys reacts with MGO to N ε -carboxyethyllysine (CEL) 18,19 and with GO to N ε -carboxymethyllysine (CML). ...
... Article aging, which indicates that the Maillard reaction is already in the final stage in fresh beer. 7 Surprisingly, the reference beer showed reduced contents of MGH1 and pyrraline after 6 months of natural beer aging. It is assumed that both substances may have been degraded by reactions such as Strecker degradation or nucleophilic additions of their free amino groups during aging. ...
3-Deoxyglucosone (3-DG) is a Maillard reaction intermediate, which forms known beer aging compounds such as Strecker aldehydes. However, the role of 3-DG in beer aging stability has not been described yet. To investigate the influence of 3-DG toward beer aging stability, different concentrations of 3-DG were added to the freshly brewed beer at the beginning of storage. Analysis of well-known degradation products of 3-DG such as 3-deoxygalactosone (HPLC-UV), 5-hydroxymethylfurfural (HPLC-UV), Strecker aldehydes (GC-MS), and free glycated amino acids (HPLC-MS/MS) during beer aging revealed that a higher initial 3-DG concentration increases the formation of the products. In this study, the significant importance of 3-DG as a key precursor compound in beer aging has been shown, especially the increase of Strecker aldehydes.
... Several potential mechanisms have been proposed to explain the relationship between HGI and NAFLD. First, advanced glycation end-products (AGEs) are covalent complexes composed of non-enzymatic reactions between amino acids and reducing sugars or oxidized lipids 31 . The role of the HGI in reflecting AGEs is partially evident. ...
... Increasing evidence suggests that AGEs activity on receptor for AGEs downstream pathways might facilitate pro-inflammatory responses and damage signaling pathways of insulin, thereby promoting the evolution and worsening of NAFLD 33,34 . Additionally, AGEs are also associated with the severity of fibrosis in patients with NAFLD 31 . ...
Aims/introduction:
The hemoglobin glycation index (HGI) represent the disparity between actual glycated hemoglobin measurements and predicted HbA1c. It serves as a proxy for the degree of non-enzymatic glycation of hemoglobin, which has been found to be positively correlated with diabetic comorbidities. In this study, we investigated the relationship between HGI and non-alcoholic fatty liver disease (NAFLD), along with other relevant biological markers in patients with diabetes.
Materials and methods:
This cross-sectional study consisted of 3,191 adults diagnosed with type 2 diabetes mellitus. We calculated the predicted glycated hemoglobin levels based on fasting blood glucose levels. Multivariate binary logistic regression analysis was conducted to examine the correlation between the HGI and NAFLD. Hepatic steatosis was diagnosed using ultrasonography.
Results:
Among all participants, 1,784 (55.91%) were diagnosed with NAFLD. Participants with confirmed NAFLD showed elevated body mass index, diastolic blood pressure, liver enzyme, total cholesterol, triglyceride, low-density lipoprotein and uric acid levels compared with those without NAFLD. In the unadjusted model, participants in the last tertile of HGI were 1.40-fold more likely to develop NAFLD than those in the first tertile (95% confidence interval 1.18-1.66; P < 0.001). In the fully adjusted model, those in the last tertile of HGI had a 39% increased risk of liver steatosis compared with confidence interval in the first tertile of HGI (95% confidence interval 1.12-1.74; P < 0.001).
Conclusions:
A higher HGI suggests an elevated risk of developing NAFLD in patients with type 2 diabetes.
... 5-HMF, as one of Maillard reaction intermediates, was mainly generated via the Amadori products of Maillard reactions through enolization (in the presence of amino group) or the fragmentation of sugars [2]. AGEs are usually identified as the products of the advanced stage of the Maillard reactions, including N ε -(carboxymethyl) lysine (CML), N ε -(carboxyethyl)lysine (CEL), two of the most well-known and important AGEs, which formed by the reaction of α-dicarbonyl compounds (α-DCs) with lysine/arginine side chains or oxidative cleavage of Amadori products [5,6]. ...
... α-DCs are easily formed from sugars without the involvement of amines by caramelization or Amadori compounds in the Maillard reaction and were considered as the precursor of AGEs [5]. In this study, the main α-DCs in milk including GO, MGO, 3-DG, and 2,3-BD were measured. ...
Traditional thermal processing often denatures protein, causing loss of active ingredients and nutrients in dairy products, even the formation of 5-hydroxymethylfurfural (5-HMF) and advanced glycation end products (AGEs). In this study, the high hydrostatic pressure (HHP) combined with moderate heat (50 °C) pre-incubation (MHHP) was utilized to explore the alternative processing to reduce the levels of 5-HMF and AGEs in milk. The mandatory microbial indicators including total viable count, coliform, Staphylococcus aureus, and Salmonella were assessed concurrently to ensure microbiological safety. Single-factor experiments of HHP (200–600 MPa, 3–20 min) suggested that HHP intensity was negatively correlated with the levels of 5-HMF and AGEs, while positively correlated with microbial inactivation of mandatory microbial indicators. Through orthogonal experiments, 50 °C pre-incubation for 20 min followed by 600 MPa for 15 min was ascertained as the optimal processing. Compared with commercially thermal processed milk, the levels of 5-HMF and AGEs in MHHP milk were significantly reduced (p < 0.05), but no significant difference in turbidity and pH. The MHHP treatment commendably preserved the protein content of milk compared to ultrahigh-temperature treatment. There were significant differences in the color and turbidity of milk due to different processing (p < 0.05). These results can provide the basic data to establish the novel processing for producing the high-quality milk in dairy industry.
Graphical Abstract
... A study with electrospun fibers from pea protein isolate and maltodextrin showed that furosines could already be detected in both the unheated fibers (1.1 mg/g protein) and the heated fibers, which had three times the content after 12 h at 65 °C and 75% RH [31]. Furosine, which can be formed in the first stage of the Maillard reaction from degradation of the Schiff base, can indicate an ongoing conjugation [42]. Table 1. ...
... A study with electrospun fibers from pea protein isolate and maltodextrin showed that furosines could already be detected in both the unheated fibers (1.1 mg/g protein) and the heated fibers, which had three times the content after 12 h at 65 • C and 75% RH [31]. Furosine, which can be formed in the first stage of the Maillard reaction from degradation of the Schiff base, can indicate an ongoing conjugation [42]. ...
Fibers of potato protein and polysaccharides were obtained by needleless electrospinning. Mixtures of maltodextrin DE2 (dextrose equivalent) (0.8 g/mL), DE21 (0.1 g/mL), and different concentrations of potato protein (0.05, 0.1, 0.15, and 0.2 g/mL) were used for fiber production. Glycation was performed via the Maillard reaction after thermal treatment (0/6/12/24/48 h, 65 °C, 75% relative humidity). The effects of electrospinning and heating on trypsin inhibitor activity (IA) were studied. The results of the IA assay showed that electrospinning and glycation caused significant differences in IA among blends, heating times, and the interaction of blend and heating time (p < 0.001). The higher the protein content in the fibers, the higher the IA. The lowest IA was found in the mixture with the lowest protein content after 48 h. In other blends, the minimum IAs were found between 6 and 12 h of heating. The determination of the free lysine groups showed a nonsignificant decrease after heating. However, higher free lysine groups per protein (6.3-9.5 g/100 g) were found in unheated fibers than in the potato protein isolate (6.0 ± 0.5 g/100 g). The amide I and amide II regions, detected by the Fourier transform infrared spectra, showed only a slight shift after heating.
... A competing reaction pathway for dicarbonyls and amino acids is the final stage of the Maillard reaction [12]. Here, the amino groups of arginine or lysine can react with dicarbonyls forming "advanced glycation end products" (AGEs). ...
... Glycated amino acids are formed in the late phase of the Maillard reaction and are considered their end products [12]. Since the formation also occurs in dicarbonyl compounds, it represents a concurrence reaction to the Strecker degradation. ...
Flavor instability of beer is affected by the rise of aroma-active aldehydes during aging. Aldehydes can be either released from bound-state forms or formed de novo. This second part of our study focused on the de novo formation of aldehydes during the Maillard reaction, Strecker degradation, and oxidation reactions. Key precursor compounds for de novo pathways are free amino acids. This study varied the potential for reactions by varying free amino acid content in fresh beer using different proteolytic malt modification levels (569–731 mg/100 g d. m. of soluble nitrogen) of the used malt in brewing trials. Overall, six pale lager beers were produced from three malts (different malt modification levels), each was made from two different barley varieties and was naturally and forcibly aged. It was found that higher malt modification levels in fresh beer and during beer aging increased amino acid and dicarbonyl concentrations as aging precursors and Strecker aldehyde contents as aging indicators. Dicarbonyls were degraded during aging. Advanced glycation end products as possible degradation products showed no consistent formation during aging. Therefore, Strecker reactions were favored during beer aging. No alternative oxidative formation of Strecker aldehydes from their corresponding alcohols could be confirmed. Along with the preceding part one of our investigation, the results of this study showed that de novo formation and release occur simultaneously. After 4 months of natural aging, aldehyde rise is mainly accounted for by de novo formation.
... Another recent investigation highlighted the potential association of telomere attrition with high HGI, possibly via the mediating effect of TNF-α [31]. Advanced glycation end products (AGEs) are covalent complexes consisting of non-enzymatic reactions between amino acids and reducing sugars or oxidized lipids [32]. Hence, the role of the HGI in reflecting AGE levels is partially obvious. ...
An increasing number of studies have reported the close relation of the hemoglobin glycation index (HGI) with metabolism, inflammation, and disease prognosis. However, the prognostic relationship between the HGI and patients with sepsis remains unclear. Thus, this study aimed to analyze the association between the HGI and all-cause mortality in patients with sepsis using data from the MIMIC-IV database. In this study, 2605 patients with sepsis were retrospectively analyzed. The linear regression equation was established by incorporating glycated hemoglobin (HbA1c) and fasting plasma glucose levels. Subsequently, the HGI was calculated based on the difference between the predicted and observed HbA1c levels. Furthermore, the HGI was divided into the following three groups using X-tile software: Q1 (HGI ≤ − 0.50%), Q2 (− 0.49% ≤ HGI ≤ 1.18%), and Q3 (HGI ≥ 1.19%). Kaplan–Meier survival curves were further plotted to analyze the differences in 28-day and 365-day mortality among patients with sepsis patients in these HGI groups. Multivariate corrected Cox proportional risk model and restricted cubic spline (RCS) were used. Lastly, mediation analysis was performed to assess the factors through which HGI affects sepsis prognosis. This study included 2605 patients with sepsis, and the 28-day and 365-day mortality rates were 19.7% and 38.9%, respectively. The Q3 group had the highest mortality risk at 28 days (HR = 2.55, 95% CI: 1.89–3.44, p < 0.001) and 365 days (HR = 1.59, 95% CI: 1.29–1.97, p < 0.001). In the fully adjusted multivariate Cox proportional hazards model, patients in the Q3 group still displayed the highest mortality rates at 28 days (HR = 2.02, 95% CI: 1.45–2.80, p < 0.001) and 365 days (HR = 1.28, 95% CI: 1.08–1.56, p < 0.001). The RCS analysis revealed that HGI was positively associated with adverse clinical outcomes. Finally, the mediation effect analysis demonstrated that the HGI might influence patient survival prognosis via multiple indicators related to the SOFA and SAPS II scores. There was a significant association between HGI and all-cause mortality in patients with sepsis, and patients with higher HGI values had a higher risk of death. Therefore, HGI can be used as a potential indicator to assess the prognostic risk of death in patients with sepsis.
... The existence of these kinds of compounds in foods has received more and more attention in recent years, primarily due to the role they play in the formation of color, aroma, and flavor profiles in a number of foods [4]. Furthermore, they are active components that decorate the free amino or mercapto groups in the side chains of a protein covalently in the course of food processing and storage, leading to the formation of advanced glycation end products (AGEs) and cross-linking in various foods, which induce minus impact on the properties and stability of the proteins [5,6]. α-DCs are also found in the body fluids of human beings. ...
α-Dicarbonyl compounds (α-DCs) are commonly present in various foods. We conducted the investigation into concentration changes of α-DCs including 3-deoxyglucosone (3-DG), glyoxal (GO), and methylglyoxal (MGO) in fresh fruits and decapped commercial juices during storage at room temperature and 4 °C, as well as in homemade juices during storage at 4 °C. The studies indicate the presence of α-DCs in all samples. The initial contents of 3-DG in the commercial juices (6.74 to 65.61 μg/mL) are higher than those in the homemade ones (1.97 to 4.65 μg/mL) as well as fruits (1.58 to 3.33 μg/g). The initial concentrations of GO and MGO are normally less than 1 μg/mL in all samples. During storage, the α-DC levels in the fruits exhibit an initial increase followed by a subsequent decrease, whereas, in all juices, they tend to accumulate continuously over time. As expected, 4 °C storage reduces the increase rates of the α-DC concentrations in most samples. From the viewpoint of the α-DC contents, fruits and homemade juices should always be the first choice for daily intake of nutrients and commercial juices ought to be mostly avoided.
... Foods that contribute large amounts of d-AGEs and precursors of these include: dry heat-cooked milk powder, meats, fish, and chicken (Inan-Eroglu et al. 2020;Tristan Asensi et al. 2023); flour-based products subjected to high temperatures (bread, cookies, processed cereals) (Henle 2005); sweet sauces (Gil and Bengmark 2007), and sweet carbonated beverages containing corn syrup (Wang et al. 2017a). Alcoholic beverages and fermented foods also contain significant levels of d-AGEs because microorganisms readily produce and release these compounds (Vistoli et al. 2013). ...
Advanced glycation end products (AGEs) are a diverse group of compounds that are formed as a result of the non-enzymatic reaction between a reducing sugar such as glucose and the free NH2 groups of an amino acid in a protein or other biomolecule. The chemical reaction, by which these products are generated, is known as the Maillard reaction and occurs as a part of the body’s normal metabolism. Such a reaction is enhanced during diabetes due to hyperglycemia, but it can also occur during the preparation, processing, and preservation of certain foods. Therefore, AGEs can also be obtained from the diet (d-AGE) and contribute to an increase of the total serum pool of these compounds. They have been implicated in a wide variety of pathological processes, mainly because of their ability to induce inflammatory responses and oxidative stress increase. They are extensively accumulated as a part of the normal aging, especially in tissues rich in long half-life proteins, which can compromise the physiology of these tissues. d-AGEs are abundant in diets rich in processed fats and sugars. This review is addressed to the current knowledge on these products and their impact on the immunomodulation of various mechanisms that may contribute to exacerbation of the diabetes pathophysiology.
... The Maillard reaction is divided into three stages: I) Formation of flavor precursors, II) Formation of aromatic substances, and III) Formation of brown pigments [28]. In the initial stage, the formation of Schiff base occurs, resulting from the conversion of colorless Amadori compounds from free amino groups and the reducing sugar fraction of carbohydrates [29]. As the reaction progresses, the degradation of intermediate compounds occurs through condensation with free amino acids, leading to the formation of Strecker aldehydes [30]. ...
The trapiá, although it is a species present in almost the entire Brazilian territory, has limited consumption due to the absence of commercial plantations and general unawareness of its properties, aggravated by the difficulty of processing due to rapid enzymatic browning that affects the pulp when handled. In this study, the influence of enzymatic inactivation through thermal blanching on the changes in luminosity, bioactive compounds, and antioxidant activity of trapiá pulp was evaluated. Blanching showed optimal effects when the thermal process was applied for a duration of 15 min, as confirmed by the qualitative determination of peroxidase (POD), indicating the interruption of enzymatic activity. The study of instrumental luminosity kinetics (color parameter) of the sample without thermal blanching treatment (control) and with blanching indicated a degradation process over time governed by a first-order model. The thermal process influenced the levels of bioactive compounds, resulting in increased flavonoids, anthocyanins, and β-carotene. Blanching also led to an increase in antioxidant activity measured by ABTS and DPPH methods, with a significant increase in DPPH radical scavenging activity, reaching 96% higher than the unblanched pulp.
... The primary amino group in the side chains of lysine is the most reactive precursor amine in proteins, so a large number of AGEs derived from lysine can be formed during food processing (Zhu et al., 2018). However, clearly defined and quantified AGEs are very limited, especially in processed foods (Henle, 2005;Zhu et al., 2018). ...
Advanced glycation end products (AGEs) are a large number of heterogeneous compounds formed by the glycation of proteins, fats or nucleic acids. Endogenous AGEs have been associated with various health problems such as obesity, type 2 diabetes mellitus and cardiovascular disease. Inflammation is thought to be one of the main mechanisms in the development of these disorders. Although AGEs are produced endogenously in the body, exogenous sources such as smoking and diet also contribute to the body pool. Therefore, when the AGE pool in the body rises above physiological levels, different pathological conditions may occur through various mechanisms, especially inflammation. While the effects of endogenous AGEs on the development of inflammation have been studied relatively extensively, and current evidence indicates that dietary AGEs (dAGEs) contribute to the body's AGE pool, it is not yet known whether dAGEs have the same effect on the development of inflammation as endogenous AGEs. Therefore, this review aimed to evaluate the results of cross‐sectional and intervention studies to understand whether dAGEs are associated with inflammation and, if there is an effect on inflammation, through which mechanisms this effect might occur.
... In addition, lysine may react with the HMF precursor(s) to form Amadori compounds or bind to HMF to form brown pigments. 62 Moreover, lysine can react with 3,4-dideoxyglucosone-3-ene, one of the precursors of HMF, to form pyrazine. 63 Figure 3(A)-(E) shows that fructose, glucose, asparagine, and glutamine had the least significant promotion effect on GS and 2,3-BD compared with other intermediates. Fructose, glucose, asparagine, and glutamine spiking only increased GS by 18%, 16%, 24%, and 27%, and 2,3-BD by 12%, 5%, 15%, and 16%, respectively. ...
BACKGROUND
Lotus rhizome juice (LRJ) is susceptible to the Maillard reaction (MR) and caramelization, which tend to cause a reduction in quality and lower consumer acceptance of the product. 1,2‐Dicarbonyl compounds (DCs) and heterocyclic compounds have attracted increasing attention as key intermediates responsible for the formation of brown pigments during MR and caramelization. However, little is known about the effects of these two types of compounds on brown pigments in LRJ during sterilization. This study quantified the changes in brown intensity (A420), DCs, and heterocyclic compounds before and after spiking, and identified the precursors and intermediates for brown pigment formation as well as the formation pathways of the intermediates.
RESULTS
The spiking experiments suggested that spiking with fructose resulted in more 3‐deoxyglucosone (3‐DG) and 2,3‐dihydro‐3,5‐dihydroxy‐6‐methyl‐4(H)‐pyran‐4‐one (DDMP), while that with lysine led to more glucosone (GS) and 2,3‐butanedione (2,3‐BD) in LRJ. The addition of glucose, asparagine, and glutamine promoted the formation of 5‐hydroxymethylfurfural (HMF) significantly, whereas the addition of glucose, lysine, and asparagine resulted in more norfuraneol. Spiking with reducing sugars and amino acids promoted both glyoxal (GO) and methylglyoxal (MGO), and the effect of glucose on GO was particularly significant. Correlation analysis showed that A420 had the highest correlation with 3‐DG in the fructose‐ and lysine‐spiked group, and with HMF in the glucose‐, asparagine‐, and glutamine‐spiked groups.
CONCLUSION
This study revealed that fructose, glucose, asparagine, glutamine, and lysine were essential precursors of MR and caramelization in LRJ during sterilization. 3‐Deoxyglucosone and DDMP were mainly produced by caramelization with fructose as the primary precursor, whereas GS and 2,3‐BD were primarily formed via MR with lysine catalysis. The MR and caramelization were the main formation pathways of HMF (catalyzed by asparagine and glutamine) and norfuraneol (catalyzed by lysine and asparagine), with glucose as the critical precursor. Methylglyoxal was mainly produced by MR or caramelization, and caramelization was the main formation pathway of GO, with glucose as the precursor. Dor brown pigment formation from fructose and lysine, 3‐DG was identified as the most crucial intermediate, while for that from glucose, asparagine, and glutamine, HMF was found to be the most important intermediate. © 2023 Society of Chemical Industry.
... Prolonged hyperglycemia in patients with diabetic leads to an increase in reducing sugars and accelerates the formation of advanced glycation end products (AGEs), eventually causing AGEs accumulation [20]. AGEs are destructive heterogeneous molecules that are irreversibly generated during the nonenzymatic glycation process [21]. Due to these oxidative stress or proinflammatory effects, AGEs have been implicated in the pathogenesis of multiple complications of type 2 diabetes mellitus (T2DM) [22]. ...
Hyperglycemia is an independent risk factor for the rapid progression of nonalcoholic steatohepatitis (NASH) to liver fibrosis with an incompletely defined mechanism. Ferroptosis is a novel form of programmed cell death that has been identified as a pathogenic mechanism in various diseases. However, the role of ferroptosis in the development of liver fibrosis in NASH with type 2 diabetes mellitus (T2DM) is unclear. Here, we observed the histopathological features of the progression of NASH to liver fibrosis as well as hepatocyte epithelial-mesenchymal transition (EMT) in a mouse model of NASH with T2DM and high-glucose-cultured steatotic human normal liver (LO2) cells. The distinctive features of ferroptosis, including iron overload, decreased antioxidant capacity, the accumulation of reactive oxygen species, and elevated lipid peroxidation products, were confirmed in vivo and in vitro. Liver fibrosis and hepatocyte EMT were markedly alleviated after treatment with the ferroptosis inhibitor ferrostatin-1. Furthermore, a decrease in the gene and protein levels of AGE receptor 1 (AGER1) was detected in the transition from NASH to liver fibrosis. Overexpression of AGER1 dramatically reversed hepatocyte EMT in high-glucose-cultured steatotic LO2 cells, whereas the knockdown of AGER1 had the opposite effect. The mechanisms underlying the phenotype appear to be associated with the inhibitory effects of AGER1 on ferroptosis, which is dependent on the regulation of sirtuin 4. Finally, in vivo adeno-associated virus-mediated AGER1 overexpression effectively relieved liver fibrosis in a murine model. Collectively, these findings suggest that ferroptosis participates in the pathogenesis of liver fibrosis in NASH with T2DM by promoting hepatocyte EMT. AGER1 could reverse hepatocyte EMT to ameliorate liver fibrosis by inhibiting ferroptosis. The results also suggest that AGER1 may be a potential therapeutic target for the treatment of liver fibrosis in patients with NASH with T2DM. Chronic hyperglycemia is associated with increased advanced glycation end products, resulting in the downregulation of AGER1. AGER1 deficiency downregulates Sirt4, which disturbs key regulators of ferroptosis (TFR-1, FTH, GPX4, and SLC7A11). These lead to increased iron uptake, decreasing the antioxidative capacity and enhanced lipid ROS production, ultimately leading to ferroptosis, which further promotes hepatocyte epithelial-mesenchymal transition and fibrosis progression in NASH with T2DM.
... Advanced glycation end products (AGEs) are a group of molecules formed nonenzymatically, after the initial attachment of reducing sugars to amino groups of proteins, lipids, or nucleic acids [1]. Long-lived tissues are more prone to AGEs accumulation, and sustain damage due to the formation of cross-links, the modification of proteins, or from inflammation due to their binding to the receptor for AGEs (RAGE) [2][3][4]. ...
Background:
Advanced glycation end products (AGEs) are involved in age-related diseases, but the interaction of gut microbiota with dietary AGEs (dAGEs) and tissue AGEs in the population is unknown.
Objective:
Our objective was to investigate the association of dietary and tissue AGEs with gut microbiota in the population-based Rotterdam Study, using skin AGEs as a marker for tissue accumulation and stool microbiota as a surrogate for gut microbiota.
Design:
Dietary intake of three AGEs (dAGEs), namely carboxymethyl-lysine (CML), N-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MGH1), and carboxyethyl-lysine (CEL), was quantified at baseline from food frequency questionnaires. Following up after a median of 5.7 years, skin AGEs were measured using skin autofluorescence (SAF), and stool microbiota samples were sequenced (16S rRNA) to measure microbial composition (including alpha-diversity, beta-dissimilarity, and taxonomic abundances) as well as predict microbial metabolic pathways. Associations of both dAGEs and SAF with microbial measures were investigated using multiple linear regression models in 1052 and 718 participants, respectively.
Results:
dAGEs and SAF were not associated with either the alpha-diversity or beta-dissimilarity of the stool microbiota. After multiple-testing correction, dAGEs were not associated with any of the 188 genera tested, but were nominally inversely associated with the abundance of Barnesiella, Colidextribacter, Oscillospiraceae UCG-005, and Terrisporobacter, in addition to being positively associated with Coprococcus, Dorea, and Blautia. A higher abundance of Lactobacillus was associated with a higher SAF, along with several nominally significantly associated genera. dAGEs and SAF were nominally associated with several microbial pathways, but none were statistically significant after multiple-testing correction.
Conclusions:
Our findings did not solidify a link between habitual dAGEs, skin AGEs, and overall stool microbiota composition. Nominally significant associations with several genera and functional pathways suggested a potential interaction between gut microbiota and AGE metabolism, but validation is required. Future studies are warranted, to investigate whether gut microbiota modifies the potential impact of dAGEs on health.
... During the early stage of these reactions, Amadori products are released which, contrary to Maillard reaction end products, are hydrolysed back to lysine in the presence of strong acids (such as that used for the amino acid analysis in the present study). Consequently, although the absorption of Amadori products is low (Henle, 2005), they can lead to an overestimation of available lysine (Moughan, 2003). That is the reason why in the second experiment reactive lysine (lysine not engaged in Maillard reaction) was specifically determined in order to obtain a more accurate measure of bioavailable lysine. ...
The development of plant-based protein foods may facilitate the decrease in animal product consumption in western countries. Wheat proteins, as a starch coproduct, are available in large amounts and are good candidates for this development. We investigated the effect of a new texturing process on wheat protein digestibility and implemented strategies aimed at enhancing the lysine content of the product developed. Protein true ileal digestibility (TID) was determined in minipigs. In a preliminary experiment, the TID of wheat protein (WP), texturized wheat protein (TWP), TWP enriched with free lysine (TWP-L), or with chickpea flour (TWP-CP) was measured and compared to beef meat proteins. In the main experiment, minipigs (n = 6) were fed a dish (blanquette type) containing 40 g of protein in the form of TWP-CP, TWP-CP enriched with free lysine TWP-CP+L, chicken filet, or texturized soy, together with quinoa (18.5 g of protein) in order to improve meal supply of lysine. Wheat protein texturing did not affect total amino acid TID (96.8 % for TWP vs 95.3 % for WP), which was not different from that of beef meat (95.8 %). Chickpea addition did not affect protein TID (96.5 % for TWP-CP vs 96.8 % for TWP). The Digestible Indispensable Amino Acid Score for adults of the dish combining TWP-CP+L with quinoa was 91, whereas it was 110 and 111 for the dishes containing chicken filet or texturized soy. The above results show that, by optimizing lysine content through the formulation of the product, wheat protein texturization can enable the development of protein-rich products of nutritional quality compatible with quality protein intake in the context of a complete meal.
... 18 AGEs comprise a heterogeneous pro-oxidant and cytotoxic group of compounds formed from the Maillard reaction. 20 Nutrient composition and food processing methods are the most critical factors determining the content of exogenous AGEs. Roasting, frying, and grilling produce more AGEs, such as carboxymethyl-lysine and methylglyoxal, in food than boiling or steaming. ...
Background: Insulin resistance (IR), even in its subclinical state, is a significant risk factor for the onset and progression of coronary artery disease (CAD). IR is a multifactorial condition, and dietary composition is a factor associated with its development. Elevated advanced glycation end products (AGEs) in the body, secondary to highly processed food consumption, can impair glucose metabolism. The present study investigated whether a restricted AGE diet could affect insulin sensitivity and anthropometric indices reflecting visceral adipose tissue in nondiabetic CAD patients.
Methods: This trial randomly allocated 42 angioplasty-treated patients to follow either low-AGE or control diets based on the AHA/NCEP guidelines for 12 weeks. Serum levels of total AGEs, insulin, HbA1c, and fasting blood sugar, as well as anthropometric measurements, were evaluated before and after the intervention. The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and anthropometric indices were calculated according to the proposed formula. The patients’ health status was assessed using the Seattle Angina Questionnaire (SAQ) at baseline and after the intervention.
Results: Our study showed a significant reduction in anthropometric indices in the low-AGE group after 12 weeks. Insulin levels and IR decreased during the low-AGE diet. No significant changes were observed in the other serum biochemical markers. All SAQ domains significantly decreased in both groups, except for Treatment Satisfaction.
Conclusion: A low-AGE diet for 12 weeks had beneficial effects on HOMA-IR and insulin levels in patients with CAD. Regarding the fundamental role of AGE in IR development and body fat distribution, AGE restriction may positively affect these patients.
... This is explained by the ease of their release as a result of cellulose degradation in the cell walls, plant structure decomposition [94], and the hydrolysis of molecular complexes and the dissociation of bonds between food ingredients [95], which consequently leads to the release of polyphenols associated with dietary fiber [94] and increased levels of free phenolic compounds, among others [94,96]. In addition, under the influence of a heat treatment, new biologically active compounds are synthesized, including as a result of the Maillard reaction [97]. ...
Quince (Cydonia oblonga Miller) is a plant that is commonly cultivated around the world, known for centuries for its valuable nutritional and healing properties. Although quince fruit are extremely aromatic, due to their high hardness and sour, astringent, and bitter taste, they are not suitable for direct consumption in an unprocessed form. However, they are an important raw material in fruit processing, e.g., in the production of jams, jellies, and juices. Quince fruits fall under the category of temperate fruits, so their shelf life can be predicted. Considering that technological processing affects not only the organoleptic properties and shelf life but also the functional properties of fruits, the aim of this research was to determine the impact of various types of technological treatments on the physicochemical and bioactive properties of quince fruit. In fresh, boiled, and fried fruits and in freshly squeezed quince fruit juice, basic parameters, such as the content of dry matter, moisture, soluble solids (°Brix), pH, total acidity, water activity, and color parameters (L*a*b*) were determined. The content of key bioactive ingredients, i.e., tannins, carotenoids, flavonoids, phenolic acids, and total polyphenols, was also determined, as well as the antioxidant activity of raw and technologically processed (cooked, fried, and squeezed) quince fruits. The conducted research showed that fresh quince fruit and processed quince products can be a very good source of bioactive ingredients in the diet, such as tannins (3.64 ± 0.06 mg/100 g in fresh fruit; from 2.22 ± 0.02 mg/100 g to 5.59 ± 0.15 g/100 g in products), carotenoids (44.98 ± 0.18 mg/100 g in fresh fruit; from 141.88 ± 0.62 mg/100 g to 166.12 ± 0.62 mg/100 g in products), and polyphenolic compounds (246.98 ± 6.76 mg GAE/100 g in fresh fruit; from 364.53 ± 3.76 mg/100 g to 674.21 ± 4.49 mg/100 g in products). Quince fruit and quince products are also characterized by high antioxidant properties (452.41 ± 6.50 µM TEAC/100 g in fresh fruit; 520.78 ± 8.56 µM TEAC/100 g to 916.16 ± 6.55 µM TEAC/100 g in products). The choice of appropriate technological processing for the quince fruit may allow producers to obtain high-quality fruit preserves and act a starting point for the development of functional products with the addition of quince fruit in its various forms, with high health-promoting values and a wide range of applications in both the food and pharmaceutical industries.
... The presence of α-dicarbonyl compounds in glucosecontaining peritoneal dialysate is catching attention due to its potential undesirable effects in vivo (Wieslander et al., 1995). They were reported that altered digestibility and nutritional value of protein by forming advanced glycation end products (AGEs) during glycosylation reactions in protein synthesis and were associated with some diseases (Henle, 2005). ...
... AGE initiates phosphorylation of ERKl/2 and MAPKs by interacting with cell-expressed RAGE receptors, which subsequently leads to abnormal activation of NF-κB, a major regulatory transcription factor of inflammation, which is involved in the expression of inflammatory cytokines and is associated with the occurrence of diabetes-related complications and a variety of chronic diseases. These include cardiovascular diseases, neurodegenerative diseases, arthritis, tumors, and their complications (31)(32)(33). Inflammation and oxidative stress are closely related in the pathogenesis of various chronic diseases, and the RAGE/MAPK/NF-KB signaling pathway is the main signaling pathway regulating inflammation and oxidative stress (34). NF-κB has been found to be a nuclear B factor binding to immunoglobulin κ site, which is a conserved inducible transcription factor family. ...
Background:
Although we have a good understanding of the diagnosis and treatment of pheochromocytoma and paraganglioma (PPGL), the underlying pathogenesis and molecular pathways of PPGL need to be further studied. This study aimed to use bioinformatics to analyze the role of immune-related genes (IRGs) in the pathogenesis of PPGL.
Methods:
GSE19422 and GSE60459 microarray data were obtained from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified using the "limma" package in R, and genes overlapping with IRGs were screened using the "VennDiagram" package. A protein-protein interaction (PPI) network was constructed in the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, and the core genes were identified by Cytoscape, followed by enrichment analysis and receiver operating characteristic (ROC) curve analysis to evaluate the diagnostic efficacy of the core genes. In addition, the level of immune cell infiltration of PPGL was analyzed and the target drug of the core gene was predicted.
Results:
A total of 1,105 DEGs were identified from the 2 datasets, of which 94 were IRGs, suggesting that the occurrence of PPGL involved immune-related pathways. Through PPI and Cytoscape, a total of 2 core genes: fibroblast growth factor 2 (FGF2), FYN proto-oncogene (FYN), and vascular cell adhesion molecule 1 (VCAM1) were identified, and the ROC curve showed that these 3 core genes had good efficacy in the diagnosis of PPGL, and more than 50 potential therapeutic drugs could be predicted based on these 3 core genes. Subsequent immunoinfiltration analysis showed that mast cells activated were significantly elevated in patients with PPGL, negatively correlated with macrophages M2, and positively correlated with the level of dendritic cells activated.
Conclusions:
This study found that immunity is closely related to the occurrence of PPGL, and that FGF2, FYN, and VCAM1 may be potential biomarkers and therapeutic targets of PPGL.
... Even in healthy individuals, circulating AGE levels are correlated with their intake, contributing to the endogenous pool of AGEs and activation of inflammatory signals [14][15][16]. Intestinal absorption of glycotoxins and AGEs has been shown, as well as their deposition in tissues [17]. In foods, the initial steps of the Maillard reaction originate from such Amadori products as fructoselysine and lactuloselysine and AGEs, which are estimated to be consumed on a scale of daily 500-1200 mg in the diet. ...
Glycotoxins include the group of advanced glycation end-products (AGEs) and their precursors, most of them highly reactive intermediary compounds of sugar metabolism. Glycotoxins and products of the Maillard reaction are present in high concentrations in foods rich in sugars and processed at high temperatures and are often associated with the flavour of the food. Proteins undergoing this type of molecular modification are targets for gut peptidases and may be absorbed into circulation. AGEs are associated with the toxic effects of glucose in diabetic patients, and some studies have shown that they also contribute to metabolically unhealthy obesity and prediabetes development. Restriction of dietary glycotoxins was shown to improve insulin resistance in humans. However, the real contribution of dietary AGEs to such mechanisms is still not understood. This review summarizes the current knowledge about glycotoxin formation from dietary sugars, their digestion throughout the gastrointestinal system, and the mechanisms of their intestinal absorption.
... Briefly, Maillard reaction can be divided into three stages. In the initial stage, Schiff base is formed due to the reaction between free amino groups of protein and reducing sugar of carbohydrate, which then convert into colourless Amadori compounds ( Henle, 2005 ). The formation of Amadori compounds can be used as an indicator of the initial stage. ...
Pea protein isolate (PPI)-maltodextrin (MD) conjugates were prepared by using controlled Maillard reaction at 90 °C in the solution state (wet-heating route). The degree of conjugation between PPI and MD was measured in terms of evolved colour, UV absorbance, and molecular weight change. Results showed that the degree of Maillard reaction increased with the increase in pH and reaction time; however, the PPI-MD conjugation was optimised and was successfully controlled within the initial stage at pH 7.5 and 8.0 to avoid the formation of melanonids. The random coil content of PPI significantly increased upon conjugation with MD producing more flexible structure. The functional properties of PPI in terms of solubility, surface change (zeta-potential), and emulsifying properties of PPI were significantly improved after conjugation with MD. The highest solubility PPI-MD conjugates was observed at 5 h of reaction. The canola oil-in-water (O/W) emulsion stabilised by PPI-MD 5 h conjugate at 2% of emulsifier concentration and homogenised at 60 MPa for 3 passes had the highest physical stability when subjected to 25-60 °C. These findings indicate that Maillard reaction can be controlled in the initial stage via the wet-heating route and the resulting conjugates can be much effective emulsifiers than plant proteins.
... Bu kararsız ara ürünler, daha kararlı olan Amadori/Heyns ürünlerine dönüştükten sonra, glioksal (GO), metilglioksal (MGO) ve 3-deoksiglukozon (3-DG) gibi oldukça reaktif α-dikarbonil bileşiklerine dönüşmektedir (Poulsen vd., 2013). Bu bileşikler de lizin, arginin, histidin ve sistein gibi amino asitlerin amino grupları ile reaksiyona girerek, N-εkarboksimetillizin (CML), N-ε-karboksietillizin (CEL) ve pentosidin gibi ileri glikasyon son ürünlerini oluşturmaktadır (Henle, 2005;Luevano-Contreras ve Chapman-Novakofski, 2010). AGE öncülleri, hem gıdalarda (eksojen) hem de insan vücudunda (endojen) oluşabilmektedir (Sharma vd., 2015). ...
Objective: Advanced glycation end products (AGEs) are compounds formed by the Maillard reaction, oxidation of proteins and lipids during food processing, and have toxic effects on human body. The most critical AGE precursors are glyoxal (GO) and methylglyoxal (MGO). This study aims to detect sugar components in the content of various sauces, to determine the pre-and post-digestion amounts of GO and MGO in sauces with an in vitro gastrointestinal digestion model, to evaluate the effect of sugar component type and amount on AGE precursor formation, and to reveal the GO and MGO bioaccessibility of various sauces. Materials and methods: In the study, 20 different sauce samples were obtained from various markets in Istanbul, and the analyses were carried out by HPLC.
... They then degrade into highly reactive α-DCs, such as GO, MGO, and 3-deoxyglucosone (3-DG) (Poulsen et al., 2013). The final AGEs, such as N-ε-carboxymethyllysine, N-εcarboxyethyllysine, and pentosidine, can be formed from lysine, arginine, histidine, and cysteine residues and the amino groups of proteins (Henle, 2005;Luevano-Contreras & Chapman-Novakofski, 2010). GO and MGO are the most abundant α-DCs found in processed foods and biological systems (Liu et al., 2011). ...
Abstract The precursors glyoxal (GO) and methylglyoxal (MGO) of advanced glycation end products (AGEs) or advanced lipoxidation end products (ALEs) occur exogenously and endogenously. These α-dicarbonyl compounds, GO and MGO, can be formed from Maillard reactions during food processing as well as protein and lipid peroxidation. The purpose of the present study was to determine and evaluate the in vitro formation of AGEs and ALEs precursors, GO and MGO, in high-fat processed meat products. Before digestion, GO and MGO amounts in the samples ranged between 59.0 and 81.0 µg/100 g and between 11.7 and 47.0 µg/100 g, respectively. After in vitro digestion, GO and MGO formation ranged between 147.0 and 514.1% and 156.0 and 6912.3%, respectively. It is believed that prooxidant components, such as oxygen, enzymes, or heme-proteins, in the gastrointestinal tract promote lipid oxidation; therefore, GO and MGO can be formed. A higher rate of MGO increase was observed in starch containing meatball (chicken) and nugget samples in the gastrointestinal tract. It is thought that the carbohydrates in the meat samples may have contributed to the amount of GO and MGO formed. Thus, reducing fat and starch may produce low levels of GO and MGO formation in the foods during processing or digestion.
... In vivo accumulation of advanced glycation endproducts (AGEs), a heterogeneous group of sugar-modified amino groups within proteins and other macromolecules, may drive the pathophysiology of type 2 diabetes (1-6) and its associated vascular dysfunction (7)(8)(9)(10)(11). In addition to the endogenous formation of AGEs, AGEs also form in foods, especially those rich in sugar and protein or fat, when exposed to heat (12). Since heating of food is widely employed due to favorable effects on sterility, flavor, and color, diets consumed in Westernized societies significantly contribute to the body's exposure to AGEs (13). ...
Background:
Accumulation of advanced glycation endproducts (AGEs) may contribute to the pathophysiology of type 2 diabetes and its vascular complications. AGEs are widely present in food, but whether restricting AGE intake improves risk factors for type 2 diabetes and vascular dysfunction is controversial.
Research design and methods:
Abdominally obese but otherwise healthy individuals were randomly assigned to a specifically designed 4-week diet low or high in AGEs in a double blind parallel-design. Insulin sensitivity, secretion, and clearance were assessed by a combined hyperinsulinemic-euglycemic and hyperglycemic clamp. Micro- and macrovascular function, inflammation, and lipid profile were assessed by state-of-art in vivo measurements and biomarkers. Specific urinary and plasma AGEs Nε-(carboxymethyl)lysine (CML), Nε-(1-carboxyethyl)lysine (CEL), and Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) were assessed by mass spectrometry.
Results:
In 73 individuals (22 males, mean ± SD age and BMI 52 y ± 14, 30.6 kg/m2 ± 4.0), intake of CML, CEL, and MG-H1 differed 2.7, 5.3, and 3.7-fold between the low and high AGE diets, which led to corresponding changes of these AGEs in urine and plasma. Despite this, there was no difference in insulin sensitivity, secretion, or clearance, micro- and macrovascular function, overall inflammation, or lipid profile between the low and high dietary AGE groups (all p for treatment effects > 0.05).
Conclusions:
This comprehensive RCT demonstrates very limited biological consequences of a 4-week diet low or high in AGEs in abdominally obese individuals.
Trial registration:
clinicaltrials.gov: NCT03866343, trialregister.nl: NTR7594.
Funding:
Diabetesfonds and ZonMw.
... The initial step involves a condensation reaction between the amino group of a lysine or arginine residue and the carbonyl group of a reducing sugar to form a Schiff base adduct during thermal processing. Subsequent rearrangement of the Schiff base results in a stable intermediate known as an Amadori product [15,16]. Amadori intermediates can be subjected to further reactions with a variety of other molecules, such as fragmentation, oxidation, enolization, dehydration and cyclization, to form more advanced products, including colourants, aromas and AGEs. ...
There is increasing evidence for the role of intestinal permeability as a contributing factor in the pathogenesis of diabetes; however, the molecular mechanisms are poorly understood. Advanced glycation endproducts, of both exogenous and endogenous origin, have been shown to play a role in diabetes pathophysiology, in part by their ligation to the receptor for advanced glycation endproducts (RAGE), leading to a proinflammatory signalling cascade. RAGE signalling has been demonstrated to play a role in the development of intestinal inflammation and permeability in Crohn’s disease and ulcerative colitis. In this review, we explore the role of AGE-RAGE signalling and intestinal permeability and explore whether activation of RAGE on the intestinal epithelium may be a downstream event contributing to the pathogenesis of diabetes complications.
... In addition to its endogenously formation, AGEs and their precursors are also absorbed from exogenous sources, such as cigarette smoke and through the consumption of highly heated processed foods [3]. Globalization and industrialized methods of processing dramatically alter foods to give desirable properties as longer shelf life, sterility, flavor and color, thus increasing exposure to AGEs [4,5]. AGEs are related to modifying chemical and functional properties of most diverse biological structures and their formation is accelerated in diseases such as diabetes as a result of chronic hyperglycemia and increased oxidative stress [6]. ...
Glycation process refers to reactions between reduction sugars and amino acids that can lead to formation of advanced glycation end products (AGEs) which are related to changes in chemical and functional properties of biological structures that accumulate during aging and diseases. The aim of this study was to perform and analyze in vitro glycation by fructose and methylglyoxal (MGO) using salivary fluid, albumin, lysozyme, and salivary α-amylase (sAA). Glycation effect was analyzed by biochemical and spectroscopic methods. The results were obtained by fluorescence analysis, infrared spectroscopy (total attenuated reflection—Fourier transform, ATR-FTIR) followed by multivariate analysis of principal components (PCA), protein profile, immunodetection, enzymatic activity and oxidative damage to proteins. Fluorescence increased in all glycated samples, except in saliva with fructose. The ATR-FTIR spectra and PCA analysis showed structural changes related to the vibrational mode of glycation of albumin, lysozyme, and salivary proteins. Glycation increased the relative molecular mass (Mr) in protein profile of albumin and lysozyme. Saliva showed a decrease in band intensity when glycated. The analysis of sAA immunoblotting indicated a relative reduction in intensity of its correspondent Mr after sAA glycation; and a decrease in its enzymatic activity was observed. Carbonylation levels increased in all glycated samples, except for saliva with fructose. Thiol content decreased only for glycated lysozyme and saliva with MGO. Therefore, glycation of salivary fluid and sAA may have the potential to identify products derived by glycation process. This opens perspectives for further studies on the use of saliva, an easy and non-invasive collection fluid, to monitor glycated proteins in the aging process and evolution of diseases.
... 2013). Bu bileşikler lizin, arginin, histidin ve sistein gibi amino asitlerin amino grupları ile reaksiyona girer ve N-ε-karboksimetillizin (CML), N-ε-karboksietillizin (CEL) ve pentosidin gibi AGE son ürünleri dönüşür (Henle 2005;Luevano-Contreras ve Chapman-Novakofski, 2010). GO ve MGO işlenmiş gıdalarda ve biyolojik sistemlerde en çok bulunan α-dikarbonil bileşikleridir (Liu vd. ...
... Recently it was shown that both compounds are formed simultaneously and the Maillard reaction is initiated in malt production (5). Therefore, as demonstrated, the Maillard reaction goes further, focusing on the formation of dicarbonyls (38). ...
The metabolite 3-deoxyglucosone (3-DG) is formed by carbohydrate caramelisation or the Maillard reaction. 3-DG is a precursor in the Strecker reaction forming beer ageing compounds, such as 2-methylbutanal or 3-methylbutanal. Although 3-DG is known as intermediate, recent studies have focused on 3-DG in beer. Foremost, the thermal load during wort boiling provides the best conditions for 3-DG formation and degradation, however, the reactivity of the dicarbonyl during the boiling process has not yet been explained. As a key intermediate, 3-deoxyglucosone could be a critical indicator for beer ageing stability. The 3-DG formation and reactivity during wort production depends on its precursor reactants (amino acids and glucose). The concentration in wort of these substances was varied using two malts with different malt modification along with two different mashing programmes. 3-Deoxyglucosone reactivity was observed by analysing dehydratisation to HMF (HPLC-UV), interconversion to 3-deoxygalactosone (3-DGal, HPLC-UV) and selected Strecker aldehydes (GC-SPME-MS). This study shows that wort boiling is the most important process in 3-DG formation as it contributes 47% of the final content compared with malting (28%) and mashing (25%). With degradation reactions, 3-DG is mainly interconverted to 3-DGal and, contrary to the literature, it could not be confirmed that enhanced 3-deoxyglucosone content affects Strecker reactions. The interconversion reaction during wort boiling determines the dicarbonyl potential of beer and influences the ageing stability. © 2021 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling.
... In the final stage of Maillard reaction, α-dicarbonyl compounds can give rise to modification of protein/peptide bound amino acids and subsequently form advanced glycation end-products [47]. The reaction between the reactive side of amino acids such as lysine, and α-dicarbonyl compounds results in the formation AGEs such as CML and CEL that are the markers of the advanced stage of Maillard reaction. ...
This study aims to investigate the formation mechanism of α-dicarbonyl compounds and glycation products in sesame seeds during roasting. The changes in the concentrations of sucrose, bound lysine, α-dicarbonyl compounds, N-ε-fructoselysine, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine were observed in sesame samples roasted at 180, 200 and 220 °C for different time intervals to form a comprehensive kinetic model consisting of elementary steps for these products. Model results indicated that N-ε-carboxyethyllysine was originated from the reaction between methylglyoxal and bound lysine while N-ε-carboxymethyllysine formation was formed predominantly by the oxidation of N-ε-fructoselysine compared to the reaction of glyoxal with bound lysine. In addition, N-ε-fructoselysine was found to be mostly contributed to the formation of 1-deoxyglucosone, which was the most important precursor of methylglyoxal and diacetyl formation in roasted sesame seeds. 3-Deoxyglucosone and glyoxal were mainly formed from the glucose degradation. Among the reaction steps, the degradation of 1-deoxyglucosone was found to be the fastest one. In this study, the multiresponse kinetic modelling approach, which provided a better understanding the important pathways on the formation of advanced glycation end-products, was reported first in a real food system.
... In addition to this endogenous formation, AGEs are abundantly present in sugar-and protein-rich food items exposed to dry heat (15). In 450 individuals with an elevated risk of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD), a higher habitual intake of these dietary AGEs was associated with higher concentrations of AGEs in plasma (16). ...
Background
Advanced glycation end products (AGEs), a heterogeneous group of bioactive compounds, are thought to contribute to arterial stiffness, which in turn is a causal factor in the pathogenesis of stroke, myocardial infarction, and heart failure. Whether AGEs derived from food also contribute to arterial stiffness is not clear.
Objectives
We investigated whether higher intake of dietary AGEs is associated with arterial stiffness.
Methods
In this cross-sectional observational study in 2255 participants of The Maastricht Study (mean ± SD age: 60 ± 8 y, 51% male, mean ± SD BMI: 26.9 ± 4.4 kg/m2, n = 1326 normal glucose metabolism, n = 341 prediabetes, and n = 585 type 2 diabetes mellitus), we estimated intake of the dietary AGEs Nε-(carboxymethyl)lysine (CML), Nε-(1-carboxyethyl)lysine (CEL), and Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) by a validated FFQ coupled to our ultra-performance liquid chromatography tandem mass spectrometry dietary AGE database. Arterial stiffness was determined using carotid-femoral pulse wave velocity (cfPWV), carotid distensibility coefficient (DC), and carotid Young's elastic modulus (YEM). We performed multiple linear regression analyses adjusting for potential confounders (demographic, hemodynamic, cardiovascular, and dietary factors).
Results
In the fully adjusted models we observed no statistically significant associations between intake of the dietary AGEs CML, CEL, and MG-H1 and arterial stiffness expressed as cfPWV, carotid DC, and carotid YEM.
Conclusions
In adults aged 40–75 y, habitual intake of the dietary AGEs CML, CEL, and MG-H1 is not associated with arterial stiffness measured as cfPWV, carotid DC, or carotid YEM.
... The Maillard reaction (MR) is common during heat processing of food, especially dairy processing and baking. Diverse Maillard reaction products (MRPs) are generated during early, middle, and late stage of MR, including N(ε)-2-furoylmethyl-l-lysine (furosine), pyrraline, N(6)-(1-carboxyethyl)-l-lysine (CEL), fructolysine (FL), pronyl-lysine, N(ε)-carboxymethyl-l-lysine (CML), pentosidine, and 5-hydroxymethylfurfural (5-HMF; Henle, 2005;Huang et al., 2015;Ledl & Schleicher, 1990). MRPs can not only affect the sensory attributes of thermally processed foods, changing their appearance, flavor, aroma, and texture, but also damaging the nutritional value (Fan et al., 2018). ...
As classical MRPs, the toxic effects of furosine, pyralline, and 5‐hydroxymethylfurfural (5‐HMF) in liver tissue are evaluated and the related mechanism is investigated here, and the protective effects of lactoferrin on liver injury caused by Maillard reaction products (MRPs) with furan ring are proved in vitro and in vivo. First, we detect the concentrations of furosine, pyralline, and 5‐HMF in several foods using ultrahigh‐performance liquid chromatography (UHPLC). Then, the effects of the three MRPs on liver cells (HL‐7702) viability, as well as liver tissue, are performed and evaluated. Furthermore, the regulations of three MRPs on necroptosis‐related pathway in liver cells are investigated. Additionally, the effects of lactoferrin in alleviating liver injury, as well as regulating necroptosis pathway, were evaluated. Results elucidate that lactoferrin protects liver injury caused by MRPs with furan ring structure through activating RIPK1/RIPK3/p‐MLKL necroptosis pathway and downstream inflammatory reaction.
... Byonic and database retrieval parameters which were set according to references which were shown in Tables S1 and S2 (Arena et al., 2014;Henle, 2005;Mittelmaier & Pischetsrieder, 2011;Renzone et al., 2015;Tu et al., 2017). ...
α‐Dicarbonyl compounds (α‐DCs) are a class of compounds generated during the thermal processing of food. Due to the high reactivity, α‐DCs were endowed with the ability to react with food components thus lowering nutrition value and even leading to a potential risk for food safety. In this study, methylglyoxal (MG), the most abundant α‐DCs, was selected to investigate the alteration effects on the structure and digestibility of α‐lactalbumin (αLA) under thermal processing (60–100°C). The results showed that the modification degree of αLA by MG increased with the rise of processing temperature, accompanied by the significant changes in molecular weight, intrinsic fluorescence, and secondary structures of αLA. High‐resolution mass spectrometry analysis identified that lysine (Lys) and arginine (Arg) are the modification sites, and Nε‐(carboxyethyl)‐L‐lysine is the main modification type. Since the Lys and Arg are also the cleavage sites of trypsin, the digestibility of MG modified αLA (MG‐αLA) by trypsin correspondingly decreased with an increase of processing temperature. The reacted Lys and Arg residues, and the protein‐bound AGEs were quantified, and the contents were found to be highly dependent on the temperature.
This study delves into the dynamics of dietary Advanced Glycation End-products (dAGEs) on host health and gut microbiota. Using 13C-labeled Carboxymethyllysine (CML) bound casein, we identify bound AGEs as the...
Food allergy is a multifactorial interplay process influenced not only by the structure and function of the allergen itself but also by other components of the food matrix. For food, before it is thoroughly digested and absorbed, numerous factors make the food matrix constantly change. This will also lead to changes in the chemistry, biochemical composition, and structure of the various components in the matrix, resulting in multifaceted effects on food allergies. In this review, we reveal the relationship between the food matrix and food allergies and outline the immune role of the components in the food matrix, while highlighting the ways and pathways in which the components in the food matrix interact and their impact on food allergies. The in-depth study of the food matrix will essentially explore the mechanism of food allergies and bring about new ideas and breakthroughs for the prevention and treatment of food allergies.
The irreversible glycation of proteins produces advanced glycation end products (AGEs) which are triggered to bind the receptor for AGE (RAGE), thereby activating mitogen-activated protein kinase/nuclear factor-κB signaling pathway and stimulating proinflammatory cytokines, ultimately leading to chronic disorders. In this study, we focus the promoting effect of Nε-carboxymethyl-lysine (CML), one of the most dietary AGEs, on non-alcoholic fatty liver disease (NAFLD) and evaluated NAFLD-related biomarkers. Oxidative stress and hepatic steatosis were assessed in oleic acid (OA)-induced HepG2 cells. Using OA-induced HepG2 cells, we show that CML results in oxidative stress and steatosis and drives major changes in hepatic lipid metabolism. Administration of CML exacerbated NAFLD-related symptoms by increasing body and liver weight gain, serum alanine aminotransferase and lipid levels, and insulin resistance in mild high-fat diet-induced mice. Moreover, hepatic histological analysis data, such as staining, western blotting, and RNA-seq, indicate that CML aggravates NAFLD in association with activation of the de novo lipogenesis pathway, consistent with the in vitro assays. Our findings could contribute to model studies related to the prevention and treatment of NAFLD progression due to excessive consumption of dietary AGEs.
Due to unique chemical structure, flavonoids are secondary metabolites with numerous biological activities. Thermal processing of food usually produces some chemical contaminants, which cause an adverse effect on food quality and nutrition. Therefore, it is vital to reduce these contaminants in food processing. In this study, current researches around the inhibitory effect of flavonoids on acrylamide, furans, α-dicarbonyl compounds and heterocyclic amines (HAs) were summarized. It has been shown that flavonoids inhibited the formation of these contaminants to varying degrees in chemical or food models. The mechanism was mainly associated with natural chemical structure and partly with antioxidant activity of flavonoids. Additionally, methods and tools of analyzing interactions between flavonoids and contaminants were discussed. In summary, this review demonstrated potential mechanisms and analytical strategies of flavonoids in food thermal processing, providing new insight of flavonoids applying on the food engineering.
The human body is exposed to dietary advanced glycation end products (AGEs) – dAGEs ingested with food and the endogenous AGEs, which are continuously formed in vivo. Clinical and experimental studies concluded that dAGEs, which are abundant in the Western diet, are directly absorbed in circulation, accumulate in the tissues, and add to the endogenous AGEs to significantly increase the systemic AGEs burden. The interaction between AGEs and the receptor – RAGE – is a key factor in the initiation of intracellular signaling pathways, with the subsequent formation of free radicals and the release of pro-inflammatory cytokines. The pro-inflammatory and prooxidant systemic effects of AGEs promote the development of chronic general diseases. Based on the correlations between AGEs intake, circulatory levels, and the risk of systemic pathology, AGEs measured in the body fluids could be used as biomarkers for the diagnosis and screening of metabolic syndrome and aging. The AGEs-restricted nutrition and physical exercise have beneficial effects and are recommended to promote health across all ages.
In the present work, the contribution of lipid peroxidation on modifications of lysine and arginine residues of proteins was investigated. Lipid peroxidation had a major impact on malondialdehyde-derived protein modifications; however, the influence on glyoxal and methylglyoxal-derived modifications in flat wafers was negligible. Therefore, vegetable oils (either linseed oil, sunflower oil, or coconut oil) were added to respective batters, and flat wafers were baked (150 °C, 3-10 min). Analysis of malondialdehyde indicated oxidation in linseed wafers, which was supported by the direct quantitation of three malondialdehyde protein adducts in the range of 0.09-23.5 mg/kg after enzymatic hydrolysis. In contrast, levels of free glyoxal and methylglyoxal were independent of the type of oil added, which was in line with the analysis of 13 advanced glycation end products. Comprehensive incubations of 40 mM N2-t-Boc-lysine (100 mM phosphate buffer, pH 7.4) with either 10% oil or an equimolar concentration of carbohydrates led to magnitudes higher (103-105) amounts of N6-carboxymethyl lysine, N6-glycolyl lysine, and N6-carboxyethyl lysine in the latter. Furthermore, malondialdehyde exceeded glyoxal and methylglyoxal in incubations of pure oils at 150 °C by factors of 30 and 100, respectively.
This study investigated the formation of advanced glycation end products (AGEs) in fish cakes under air frying, deep frying, pan frying and baking. The results showed that the AGEs contents on the surface of fish cakes significantly increased with prolonging heating time. The AGEs contents under different methods were following: deep frying > air frying ≈ pan frying > baking. However, the AGEs contents in the interior of fish cakes were hardly influenced by the methods and time. The correlation analysis showed that the AGEs contents were negatively correlated with the moisture content, positively correlated with the yellowness (b*) value, oil content and oxidation products. Additionally, the air-fried fish cake exhibited a denser texture compared to the others, and its colour was similar to the deep-fried ones. Conclusively, the air-fried fish cake showed low oil and AGEs contents, and similar colour to the deep-fried fish cake.
Abstract This study aims to investigate the glyoxal (GO), and methylglyoxal (MGO), and the effect of the types of sugar components on GO and MGO formation in Turkish delight and baklava. The values of GO and MGO ranged from 326 to 1842 µg/100 g, and from 31 to 517 µg/100 g in Turkish delight, respectively. The values of GO and MGO in baklava ranged from 344 to 815 µg/100 g, and between 19 and 358 µg/100 g, respectively. One of the baklava samples may contained high fructose corn syrup (HCFS) given the presence of significantly higher amount of MGO than that of other samples. Increased sugar concentration, processing time, storage, and HCFS in Turkish delight and baklava may affect the GO and MGO formations. Longer storage time may influence the increase of MGO formation in Turkish delight. Therefore, these products should be consumed less or formulated with agents that reduce AGEs.
Les produits déshydratés permettent d’optimiser la conservation et le transport des aliments. Les poudres alimentaires distribuées au consommateur affichent des garanties nutritionnelles en termes d’apports qualitatif et quantitatif. Cependant, l’apport nutritionnel du produit après reconstitution et cuisson, n’est pas garanti. Ce travail se concentre sur l’évaluation des pertes en vitamines dues aux procédés de transformation alimentaire en lien avec l’effet de la matrice alimentaire. Ces pertes mesurées après le traitement thermique ne sont pas négligeables, rendant l’encapsulation nécessaire pour répondre à l’objectif de la thèse de garantir une teneur en vitamines suffisante après reconstitution et traitement thermique du produit alimentaire déshydraté. Différentes matrices ont été testées à l’échelle laboratoire et industrielle. Parmi ces matrices, certaines comme les protéines laitières et l’amidon se sont avérées très intéressants et ont permis la préservation de la vitamine C du traitement thermique. Pour finaliser l’étude, il a été indispensable de prendre en compte le stockage des poudres de la vitamine C encapsulée avant et après leur commercialisation. Pour assurer leur teneur suffisante en vitamine C lors ce stockage, un vieillissement accéléré a été effectué. Cette thèse a permis d’apporter des réponses concrètes au problème industriel posé, qui était de garantir la teneur en vitamine C des produits commercialisés après reconstitution et traitement thermique
Context:
Most methods for assessing dietary intake have considerable measurement error. Dietary biomarkers are objective tools for dietary assessment. Dietary biomarkers of dietary patterns have not been well described, despite modern dietary guidelines endorsing dietary patterns.
Objective:
This systematic review sought to describe the dietary biomarkers commonly used to assess dietary patterns, and the novel biomarkers of dietary patterns identified by exploratory studies.
Data sources:
MEDLINE, Embase, Cochrane Central, PreMEDLINE, and CINAHL databases were searched.
Data extraction:
Data extraction and bias assessment were undertaken in duplicate.
Data analysis:
A qualitative approach was applied, without statistical analysis.
Conclusion:
In controlled settings, dietary biomarkers of single nutrients or of individual foods or food groups are commonly used to assess compliance with dietary patterns. However, currently, there are no dietary biomarkers or biomarker profiles that are able to identify the specific dietary pattern that has been consumed by an individual. Future work should seek to validate novel dietary biomarkers and biomarker profiles that are indicative of specific dietary patterns and their characteristics. A dietary biomarker panel consisting of multiple biomarkers is almost certainly necessary to capture the complexity of dietary patterns.
Systematic review registration:
PROSPERO registration no. CRD42019129839.
Glucose and its metabolites provide building blocks for cellular structures and modifications occurring on proteins, lipids and nucleotides. The underlying reactions consist of glycosylations controlled by hundreds of enzymes following a specific yet incompletely understood architecture of cell physiology and glycations as random, not controlled modifications occurring in an oxidative environment. In both cases attachments of glucose or its metabolites can modulate the tertiary structure of proteins as required for cellular physiology or cause disturbance with disease driving pathology. In this review we will discuss the relevance of glucose dependent cellular modifications for cardiovascular complications.
The obesity rate in the United States is 42.4% and has become a national epidemic. Obesity is a complex condition that is influenced by socioeconomic status, ethnicity, genetics, age, and diet. Increased consumption of a Western diet, one that is high in processed foods, red meat, and sugar content, is associated with elevated obesity rates. Factors that increase obesity risk, such as socioeconomic status, also increase consumption of a Western diet because of a limited access to healthier options and greater affordability of processed foods. Obesity is a public health threat because it increases the risk of several pathologies, including atherosclerosis, diabetes, and cancer. The molecular mechanisms linking obesity to disease onset and progression are not well understood, but a proposed mechanism is physiological changes caused by altered lipid peroxidation, glycolysis, and protein metabolism. These metabolic pathways give rise to reactive molecules such as the abundant electrophile methylglyoxal (MG), which covalently modifies nucleic acids and proteins. MG-adducts are associated with obesity-linked pathologies and may have potential for biomonitoring to determine the risk of disease onset and progression. MG-adducts may also play a role in disease progression because they are mutagenic and directly impact protein stability and function. In this review, we discuss how obesity drives metabolic alterations, how these alterations lead to MG production, the association of MG-adducts with disease, and the potential impact of MG-adducts on cellular function.
The chemistry of Maillard or browning reactions of glycated proteins was studied using the model compound, N alpha-formyl-N epsilon-fructoselysine (fFL), an analog of glycated lysine residues in protein. Incubation of fFL (15 mM) at physiological pH and temperature in 0.2 M phosphate buffer resulted in formation of N epsilon-carboxymethyllysine (CML) in about 40% yield after 15 days. CML was formed by oxidative cleavage of fFL between C-2 and C-3 of the carbohydrate chain and erythronic acid (EA) was identified as the split product formed in the reaction. Neither CML nor EA was formed from fFL under a nitrogen atmosphere. The rate of formation of CML was dependent on phosphate concentration in the incubation mixture and the reaction was shown to occur by a free radical mechanism. CML was also identified by amino acid analysis in hydrolysates of both poly-L-lysine and bovine pancreatic ribonuclease glycated in phosphate buffer under air. CML was also detected in human lens proteins and tissue collagens by HPLC and the identification was confirmed by gas chromatography/mass spectroscopy. The presence of both CML and EA in human urine suggests that they are formed by degradation of glycated proteins in vivo. The browning of fFL incubation mixtures proceeded to a greater extent under a nitrogen versus an air atmosphere, suggesting that oxidative degradation of Amadori adducts to form CML may limit the browning reactions of glycated proteins. Since the reaction products, CML and EA, are relatively inert, both chemically and metabolically, oxidative cleavage of Amadori adducts may have a role in limiting the consequences of protein glycation in the body.
N-(Carboxymethyl)lysine (CML) is an advanced glycation end product formed on protein by combined nonenzymatic glycation and
oxidation (glycoxidation) reactions. We now report that CML is also formed during metal-catalyzed oxidation of polyunsaturated
fatty acids in the presence of protein. During copper-catalyzed oxidation in vitro, the CML content of low density lipoprotein increased in concert with conjugated dienes but was independent of the presence
of the Amadori compound, fructoselysine, on the protein. CML was also formed in a time-dependent manner in RNase incubated
under aerobic conditions in phosphate buffer containing arachidonate or linoleate; only trace amounts of CML were formed from
oleate. After 6 days of incubation the yield of CML in RNase from arachidonate was 0.7 mmol/mol lysine compared with only 0.03 mmol/mol lysine for protein incubated under the same conditions with glucose.
Glyoxal, a known precursor of CML, was also formed during incubation of RNase with arachidonate. These results suggest that
lipid peroxidation, as well as glycoxidation, may be an important source of CML in tissue proteins in vivo and that CML may be a general marker of oxidative stress and long term damage to protein in aging, atherosclerosis, and diabetes.
Pyrraline, an advanced Maillard product, was used to evaluate heat damage from the manufacture and storage of enteral formulas and model systems.
Two types of enteral formula, with the same components but different protein content, were analyzed untreated (mixture of ingredients) and after pre-sterilization, standardization, and in-bottle sterilization processing steps. The commercial formulas (in-bottle sterilization formulas) were stored at 30 °C for 36 weeks or 55 °C for 12 weeks.
Model systems were prepared with similar ingredients to those used in formula manufacture (whey proteins and lactose or dextrinomaltose) and were heated at 120 °C for 30 min.
In-bottle sterilization produced an increase in the pyrraline content of the formulas of 6.7 and 20.7%. Storage at 55 °C for 12 weeks produced increases in pyrraline content of 41 and 58%, and storage at 30 °C for 36 weeks produced increases of 44 and 52%. Pyrraline was not detected in model systems prepared with whey proteins, lactose, or dextrinomaltose when they were heated at 120 °C for 30 min. However, a significant increase in pyrraline content was observed after the heat treatment of commercial whey proteins.
Advanced glycation end products (AGEs) are linked with the development of diabetic retinopathy; however, the pathogenic mechanisms are poorly defined. Vascular endothelial growth factor (VEGF) levels are increased in ischemic and nonischemic diabetic retina, and VEGF is required for the development of retinal and iris neovascularization. Moreover, VEGF alone can induce much of the concomitant pathology of diabetic retinopathy. In this study, we found that AGEs increased VEGF mRNA levels in the ganglion, inner nuclear, and retinal pigment epithelial (RPE) cell layers of the rat retina. In vitro, AGEs increased VEGF mRNA and secreted protein in human RPE and bovine vascular smooth muscle cells. The AGE-induced increases in VEGF expression were dose- and time-dependent, inhibited by antioxidants, and additive with hypoxia. Use of an anti-VEGF antibody blocked the capillary endothelial cell proliferation induced by the conditioned media of AGE-treated cells. AGEs may participate in the pathogenesis of diabetic retinopathy through their ability to increase retinal VEGF gene expression.
Glucose reacts nonenzymatically with proteins in vivo, chemically forming covalently attached glucose-addition products and cross-links between proteins. The excessive accumulation of rearranged late-glucose-addition products, or advanced glycosylation end products (AGEs), is believed to contribute to the chronic complications of diabetes mellitus.
To elucidate the relation of AGEs to diabetic complications, we used a radioreceptor assay to measure serum and tissue AGEs in diabetic (Types I and Type II) and nondiabetic patients with different levels of renal function. Serum AGEs were measured as a low-molecular-weight (less than or equal to 10 kd) peptide fraction and a high-molecular-weight (greater than 10 kd) protein fraction.
The mean (+/- SD) AGE content of samples of arterial-wall collagen from 9 diabetic patients was significantly higher than that of samples from 18 nondiabetic patients (14.5 +/- 5.2 vs. 3.6 +/- 1.5 AGE units per milligram, P less than 0.001). Moreover, diabetic patients with end-stage renal disease had almost twice as much AGE in tissue as diabetic patients without renal disease (21.3 +/- 2.8 vs. 11.5 +/- 1.9 AGE units per milligram, P less than 0.001). The AGE levels in both serum fractions were elevated in the patients with diabetes, and the levels of AGE peptides correlated directly with serum creatinine (P less than 0.001) and inversely with creatinine clearance (P less than 0.005), suggesting that levels of AGE peptides increased with the severity of diabetic nephropathy. In six patients with diabetes who required hemodialysis, the levels of AGE peptides were five times higher than in eight normal subjects (82.8 +/- 9.4 vs. 15.6 +/- 3.4 AGE units per milliliter, P less than 0.001). In another group of diabetic patients the mean serum creatinine level, which decreased by 75 percent during a session of hemodialysis, whereas the level of AGE peptides decreased by only 24 percent. Serum levels of AGE peptides were normal in two patients with normal serum creatinine levels after renal transplantation.
AGEs accumulate at a faster-than-normal rate in arteries and the circulation of patients with diabetes; the increase in circulating AGE peptides parallels the severity of renal functional impairment in diabetic nephropathy.
The extent of the advanced Maillard reaction (MR) involving protein-bound lysylketoses degradation that occurs in pasta drying was studied by evaluating furosine and lysylpyrrolaldehyde (LPA). By enzymatic hydrolysis followed by solid-phase extraction and ion pair reversed-phase high-performance liquid chromatography (IP-RP HPLC) with 297-nm detection, protein-bound LPA was separated without interference and quantified in pasta products using carboxy-2-pyrrolaldehyde as the external standard. Model doughs containing different amounts of cold or [U-14C]-labeled glucose or maltose and pasta processed under different heating conditions were considered. A close relationship between the accumulation behaviors of furosine and protein-bound LPA was observed, confirming that LPA is a main derivative of lysylketoses residues. Further degradation of LPA was detected only under thermal treatments not applicable in pasta drying. Under the pasta processing conditions of a semipilot plant, and with semolina of known origin and free sugar composition, LPA formation was enhanced (>12 mg/100 g of protein) when the drying cycle included temperatures close to 80° C or higher, and pasta moisture values were close to 15% or lower. Under low-temperature (50° C) conditions, no LPA was produced. Another key parameter was the concentration of reducing sugars, the most effective being glucose. Although other aminoketoses besides lysylketoses are probably formed and degraded, furosine and LPA evaluation seems to sufficiently describe the MR extent occurring on pasta protein. Considering the undesirable sensorial changes of pasta attributable to extensive MR, the possible antinutritional properties reported for LPA, and the wide range of LPA values (from 0 to over 40 mg/100 g of protein) found in commercial spaghetti, a better control of the advanced MR in this food is advisable.
Following complete enzymic hydrolysis, simultaneous determination of protein-bound advanced-stage Maillard compounds in addition to the Amadori products lactuloselysine and fructoselysine as well as the common amino acids including tryptophan was achieved by ion-exchange chromatography with photodiode array measurement and subsequent ninhydrin detection. Direct ultraviolet detection at the absorption maximum allowed the quantification of pyrraline (λmax=297 nm), an acid labile lysine derivative with a pyrrole structure, at levels lower than 2 mg/kg protein. Values for pyrraline in a number of commercially available foods (milk products, bakery goods, pasta products) ranged from not detectable up to 3500 mg/kg protein. Pyrraline proved to be a suitable indicator for the advanced stages of the Maillard reaction in foods. In samples of severely heated whey powder, four previously unknown UV-active compounds were detected. Their formation correlated with heating time and temperature. One of these compounds could be identified as maltosine, a pyridone derivative of lysine of the 1-deoxyosone pathway, which up to now has not been described in protein hydrolysates.
A product easily converted to glyoxal was found in an early stage of the reaction of sugar with amine in ethanol. Glyoxaldicyclohexylimine was isolated from the reaction mixture of D-glucose with cyclohexylamine. This finding suggested the formation of a similar type glyoxaldialkylimine in other reactions of sugar with amine. This two-carbon compound was assumed to be produced directly from sugar or glycosylamine, and a new pathway for sugar fragmentation was proposed.
Glucose chemically attaches to proteins and nucleic acids without the aid of enzymes. Initially, chemically reversible Schiff base and Amadori product adducts form in proportion to glucose concentration. Equilibrium is reached after several weeks, however, and further accumulation of these early nonenzymatic glycosylation products does not continue beyond that time. Subsequent reactions of the Amadori product slowly give rise to nonequilibrium advanced glycosylation end-products which continue to accumulate indefinitely on longer-lived molecules. Excessive formation of both types of nonenzymatic glycosylation product appears to be the common biochemical link between chronic hyperglycemia and a number of pathophysiologic processes potentially involved in the development of long-term diabetic complications. The major biological effects of excessive nonenzymatic glycosylation include: inactivation of enzymes; inhibition of regulatory molecule binding; crosslinking of glycosylated proteins and trapping of soluble proteins by glycosylated extracellular matrix (both may progress in the absence of glucose); decreased susceptibility to proteolysis; abnormalities of nucleic acid function; altered macromolecular recognition and endocytosis; and increased immunogenicity.
Hitzegeschädigte Proteine mit einem hohen Gehalt an Fruktoselysin, dem wichtigsten Reaktionsprodukt von Lysin mit Glukose oder Laktose, wurden zusammen mit Darminhalt von Ratten inkubiert. Als Kontrollen dienten Ansätze, die zur Abtötung der Mikroorganismen mit Sublimat versetzt waren. Wie die Versuche ergaben, sind Mikroorganismen aus dem Verdauungstrakt befähigt, das fur höhere Tiere nicht spaltbare und nicht resorbierbare Fruk-toselysin abzubauen.
Wir danken der Deutschen Forschungsgemeinschaft für Unterstützung der Versuche.
Degradation of fructoselysine by the intestinal flora
Heat damaged proteins with high contents of fructoselysine were incubated with gut contents of rats. Controls has been mixed before incubation with sublimate in order to stop the action of microorganisms. Fructoselysine is neither utilized by the animal nor absorbed as an intact molecule. Our results show however, that fructoselysine was deaminated by the microorganisms of the rats intestinal tract.
Dégradation de la fructoselysine par la flore intestinale
On incube avec le contenu intestinal de rats, des protéines dénaturées à la chaleur, à forte teneur en fructoselysine, qui est le produit de réaction le plus important de la lysine avec le glucose ou le lactose. Comme contrôles, on emploie les préparations qu'on a combinées avec du sublimé pour détruire les microorganismes. Comme les résultats l'ont montré, les microorganismes du tractus digestif sont capables de dégrader la fructoselysine ne pouvant être scindée, ni résorbée par les animaux supérieurs.
Desintegración de la fructosalisina mediante la flora intestinal
Junto con contenido entérico de ratas se incubaron proteínas, dañadas por el calor, con uncontenido elevado en fructosalisina, el producta de reacción más importante de la lisina con la glucosa o lactosa. Como testigos se utilizaron siembras que se habian tratado con sublimado para matar los micro-organismos. Como prueban estos ensayos, los microbios del tracto digestivo son capaces de desintegrar la fructosalisina, que los animales superiores no escinden ni resorben.
The two possible 3-deoxy-D-hexosones were
prepared in high yields by the decomposition of diketoseamino acids in dilute
aqueous solution at pH 5 and 100 °C. Small amounts of the corresponding
epimeric aldoses were also isolated.
1,1'-(Carboxymethylamino)bis-[1-deoxy-D-fructose],
the preparation of which has been improved, gave 3-deoxy-D-erythrohexosone
which was characterized as the 2,4-dinitro- and 2,5-dichlorophenylosazones and
triacetates, and as the 4-nitrophenyl-osazone. The 4-nitro- and 2,4-dinitrophenylosazones
were identical with those prepared from 3-deoxy-D-ribohexose. 1,1'-(Carboxymethylamino)bis-[1-deoxy-D-tagatose]
yielded 3-deoxy-D-threohexosone characterized as the 2,4-dinitrophenylosazone
and triacetate and 2,5-dichlorophenylosazone.
Chromatographic evidence suggests that
3-deoxyhexosones are also formed during the decomposition of other substituted
1-amino-1-deoxyketoses.
A mechanism for the formation of
3-deoxyhexosones and of the epimeric aldoses from diketoseamino acids is
proposed.
The postulated intermediate in the formation of d-glucosaccharinic acid, 1-deoxy-d-erythro-2,3-hexodiulose (1), has been synthesised. The substance, which was stable only in acidic solution, yielded “α”-d-glucosaccharinic acid and d-erythronic acid on treatment with base; with calcium hydroxide, the former acid was preponderant, and, with sodium hydroxide, the latter acid preponderated. “β”-d-Glucosaccharinic acid was formed in traces only.
alpha -Dicarbonyl compounds are of major interest in food chemistry and biochemistry as important precursors of, for example, protein modifications and flavor. Due to their high reactivity most of the published structures were identified and quantitated as stable derivatives after reaction with trapping reagents. However, the present study showed for the first time that the trapping reagents are of dramatic impact on the final qualitative and quantitative alpha -dicarbonyl spectrum. As important representatives, aminoguanidine and o-phenylenediamine were used to compare trapping characteristics and to monitor the dicarbonyl structures arising from the degradation of an Amadori compound. Dicarbonyl structures with a reductone moiety could not be or were only insufficiently detected by slow-reacting reagents such as aminoguanidine. On the other hand, fast-reacting chemicals such as o-phenylenediamine imposed high oxidative stress on the investigated system and led to enhanced or false positive formation of dicarbonyl compounds generated by oxidative pathways.
When lactose is heated with Nα-acetyllysine or other amines for a short time, e.g. 15 min under reflux, a main product can be detected by HPLC/DAD. The product has a UV maximum at 319 nm, indicating an aminoreductone structure (AR). AR was isolated and identified as 1-[Nε-(Nα-acetyllysinyl)]-1,2-dehydro-4-deoxy-3-hexulose. The analogous derivative of butylamine has previously been obtained from maltose. The product is the main UV absorbing material for several hours of heating and at various reaction temperatures. When lactose is heated with milk proteins, such as β-lactoglobulin, formation of AR can be observed by measuring a new UV maximum of the modified protein at 319 nm. Since AR can also be found after a short heating time and since it is the main product at various reaction conditions, it was concluded that the new product can be of importance for the Maillard reaction during milk processing. Keywords: Maillard reaction; lactose; milk products; aminoreductone
Much research is devoted to the elucidation of mechanisms in the Maillard reaction. Model studies with reactive intermediates and 13C-labelled precursors have contributed significantly to our understanding of flavour formation in the Maillard reaction. Several examples are discussed here: The formation of methyl pyrazines and 2-acetyl-1-pyrroline, the role of ARP's and deoxyglycosones and the formation of carbohydrate fragments from reducing sugars, 3-deoxy-glucosone and ARP's. It is concluded that carbohydrate fragments, and also flavour substances derived therof, are formed from the starting reducing sugars (or the corresponding imines), deoxyglycosones, and possibly ARP's. A general scheme for flavour formation in the Maillard reaction is proposed.
The reactions that occur during the cooking, baking, and preservation of foods of all kinds are of great importance for the production of aroma, taste, and color. However, more recently it has been shown that these reactions may be accompanied by a reduction in nutritive value and the formation of toxic compounds. For these reasons, the very complex reactions between reducing sugars and the free amino groups of amino acids or proteins, known as non-enzymatic browning or the Maillard reaction, have again caught the interest of chemists. The Maillard reaction came to be seen in a new light as it was realized that it actually occurred in the human body. As a general rule, the longer the half-life of a protein, the larger the amount of its Maillard products found, i.e., important factors are the ‘age’ or persistence of the protein in the body and the glucose concentration, particularly in diabetics. Many of the symptoms developed by diabetics resemble those of premature aging, which leads to the possibility that glucose, because of its reactivity towards proteins, is fundamentally involved in the normally slow progress of aging.
During the Maillard reaction, the reducing sugars first react with the free amino groups of the amino acids. With aldoses, 1-amino-l-deoxyketoses (ketose-amino acids, Amadori compounds) are the first stable intermediates to be formed. In malts ten different Amadori compounds could be determined that formed during the kiln-drying of malt. Dependent on the kiln-drying conditions, the different types of malt contain different amounts and proportions of these compounds. During the brewing process (mashing, mash wort cooking) about half of the Amadori compounds are decomposed, whereas during fermentation no changes can be observed. Therefore the amount and composition of Amadori compounds detected in beer may indicate the type of malt used. During the production of brewing couleurs, ammonia or ammonium compounds react with sugars and deoxyfructosazines are formed. In brewing coleurs, relatively high amount of these pyrazine derivatives (2–6 g/100 g) could be found. An analytical method is described for the quantitative determination of deoxyfructosazines, indicating an addition of brewing couleur to beer.
Lactuloselysine (ε-N-deoxylactulosyl-L-lysine) and fructoselysine (ε-N-deoxyfructosyl-L-lysine), formed by Maillard reaction, were identified in enzymic hydrolysates of casein from stored ultra-heat-treated (UHT) milk. Furosine (ε-N-(2-furoylmethyl-L-lysine) and pyridosine (ε-(3-hydroxy-4-oxo-6-methyl-1-pyridinyl)-L-norleucine) were identified in the corresponding acid hydrolysates. Enzymic hydrolysis of the caseins, gel filtration and preparative scale amino acid analysis were used to isolate the compounds which were then identified by reference to synthesized authentic compounds. Lactuloselysine formation was extensive and involved 10–30% of lysine residues in UHT milks stored at 30–37 °C for 6 months to 3 years. Fructoselysine concentration was generally about 10% of the lactuloselysine concentration.
a2 Institut für Verfahrenstechnik der Bundesanstalt für Milchforschung, 2300 Kiel 1, FRG(Received November 19 1985)(Accepted June 09 1986)
When Nα-acetyl-l-arginine was heated with glyoxal in aqueous solution at pH 7.0 in the presence of furan-2-carboxaldehyde, an intense red-brown color developed. The compound mainly evoking this color was identified as (S,S)-1-[4-(acetylamino)-4-carboxy-1-butyl]-2-imino-4-[(Z)-(2-furyl)methylidene]-5-{2-[1-[4-(acetylamino)-4-carboxy-1-butyl]-4-[(E)-(2-furyl)methylidene]-5-oxo-1,3-imidazol-2-inyl]}azamethylidene-1,3-imidazolidine (1, BISARG) by application of several one- and two-dimensional NMR experiments and, in addition, by LC/MSn measurements and UV−vis spectroscopy. This is the first time that a chromophoric compound comprising four linked rings with two arginine moieties incorporated was identified in a Maillard reaction system. This novel type of chromophore indicates the possibility that food melanoidins might be generated by protein oligomerization via colored cross-linking structures, for example, between two arginine residues. Keywords: Arginine; furan-2-carboxaldehyde; glyoxal; Maillard reaction; colored compounds; cross-link amino acid; melanoidins
Enzymatic and nonenzymatic browning reactions of amino acids and proteins with carbohydrates, oxidized lipids, and oxidized phenols cause deterioration of food during storage and processing. The loss in nutritional quality and potentially in safety is attributed to destruction of essential amino acids, decrease in digestibility, inhibition of proteolytic and glycolytic enzymes, interaction with metal ions, and formation of antinutritional and toxic compounds. Studies in this area include influence of damage to essential amino acids on nutrition and food safety, nutritional damage as a function of processing conditions, and simultaneous formation of deleterious and beneficial compounds. These compounds include kidney-damaging Maillard reaction products, mutagens, carcinogens, antimutagens, antioxidants, antibiotics, and antiallergens. This overview covers the formation, nutrition, and safety of glycated proteins, characterized browning products, and heterocyclic amines. Possible approaches to inhibiting browning reactions and preventing adverse effects of browning during food processing and food consumption, including protection against adverse effects of heterocyclic amines by N-acetylcysteine, caffeine, chlorophyll, conjugated linoleic acid, lignin, and tea extracts, are also described. This research subject covers a complex relationship of the chemistry, biology, and pathology of browning products and the impact on human nutrition and health. Future study should differentiate antinutritional and toxicological relationships, define individual and combined potencies of browning products, and develop means to prevent the formation and to minimize the adverse manifestations of the most antinutritional and toxic compounds. Such studies should lead to better and safer foods and improved human health. Keywords: Browning prevention; food browning; food safety; glycated proteins; glycosylation; heterocyclic amines; human health; Maillard products; nutrition
Many different types of organic reactions lead to the production of brown pigments at moderate temperatures. In spite of many reviews of the subject, there has been no comprehensive organization of the reactions. In this review some relationships are shown to exist among the carbonyl-amino, the nonamino, and the oxidative types of browning. Recent findings have provided the basis for an integration of the several isolated partial theories of browning (Maillard, sugar fission, ascorbic acid, furaldehyde) heretofore proposed. The significance of the occurrence of the Amadori rearrangement in the Maillard reaction is stressed, and a mechanism for browning in sugar-amine systems based upon the rearrangement is outlined. Attention is directed to the little-studied but important role of dehydrogenated reductones in both enzymatic and nonenzymatic browning reactions. Investigations of browning reactions in model systems during the past 3 years are reviewed, with the pertinent older studies, and the results of most of these are shown to fit into the proposed scheme of reactions. A classified directory to the major part of 201 references on browning in nitrogenous model systems (1940 to March 1953) is included.
Lysine is often inactivated by ‘Maillard-type’ reactions in food proteins; the values obtained for it by different methods cannot be compared because the chemical behaviour of inactivated lysine is unknown. In this paper, the behaviour of an important form of inactivated lysine, namely its 1-deoxyketosyl derivatives, during acid hydrolysis as well as on the different assays for available lysine (F-DNB, TNBS, pipsylchloride and guanidination) is studied. The relative proportions of regenerated lysine and of formed furosine and pyridosine are established as a function of the conditions of hydrolysis. The validity of the methods used to estimate available lysine from its 1-deoxyketosyl derivatives is discussed.
Bei der Umsetzung von Fructose mit wäßrigem Ammoniak sowie insbesondere auch mit wasserfreiem flüssigen Ammoniak entsteht d- Glucosamin. Die Identifizierung erfolgte durch das analytische und chromatographische Verhalten sowie durch Darstellung des nach Kupplung mit Phenylisocyanat und Ringschluß mit Essigsäure erhaltenen 1-Phenyl-4-[d-arabo-tetraoxybutyl]-imidazolons-(2) und durch Überführung in die N-Carbobenzoxy-Verbindung. Die biochemischen Zusammenhänge der Hexosamin-Bildung werden erörtert.
In Krebs-Ringer phosphate buffer, the rate of formation of methylglyoxal from glycerone phosphate and glyceraldehyde 3-phosphate was first order with respect to the triose phosphate with rates constant values of 1.94 ± 0.02 × 10−5 s−1 (n= 18) and 1.54 ± 0.02 × 10−4 s−1 (n= 18) at 37°C, respectively. The rate of formation of methylglyoxal from glycerone phosphate and glyceraldehyde 3-phosphate in the presence of red blood cell lysate was not significantly different from the nonenzymatic value (P > 0.05). Methylglyoxal formation from glycerone phosphate was increased in the presence of triose phosphate isomerase but this may be due to the faster non-enzymatic formation from the glyceraldehyde 3-phosphate isomerisation product. For red blood cells in vitro, the predicted non-enzymatic rate of formation of methylglyoxal from glycerone phosphate and glyceraldehyde 3-phosphate may account for the metabolic flux through the glyoxalase system. The reactivity of glycerone phosphate and glyceraldehyde 3-phosphate towards the non-enzymatic formation of methylglyoxal under physiological conditions suggests that methylglyoxal formation is unavoidable from the Embden-Meyerhof pathway.
Glyoxal, methylglyoxal and diacetyl were identified as reaction products from non-enzymatic browning of D-glucose (Glc),
D-fructose (Fru), maltose and maltulose. The α-dicarbonyl compounds were quantified throughout the reaction. Monosaccharides
formed more dicarbonyl fragments than disaccharides and Glc formed more than Fru. It is suggested that Fru tends to yield
cyclic products rather than fragmentation products under the reaction conditions used. Furthermore, a mechanism for the fragmentation
of disaccharides is proposed.
Following enzymic hydrolysis, sensitive and unambiguous determination of the protein-bound Maillard compound pyrraline, a lysine derivative with a pyrrol structure, was achieved by ion-exchange chromatography with photodiode array measurement and subsequent ninhydrin detection. The method allows the simultaneous quantification of pyrraline in addition to the common amino acids, as well as acid-labile components such as the Amadori products and tryptophan, at levels lower than 500 g/kg protein. Values of pyrraline in controlled heated samples first increased linearly with heating time, followed by a significant decomposition after long-term heating. In severely heat-treated samples (110 C for 5 h), up to 5.6% of the initial lysine residues had reacted to the pyrrolaldehyde.Die Bestimmung des proteingebundenen Maillard-Produktes Pyrralin, eines Lysinderivats mit Pyrrolstruktur, gelang in enzymatischen Hydrolysaten von Proteinen mittels lonenaustauschchromatographie und kombinierter Photodiodenarraymessung und Ninhydrinanfrbung. Das Verfahren erlaubt die gleichzeitige Bestimmung von Pyrralin neben den brigen Hydrolysataminosuren sowie surelabilen Verbindungen wie den Amadori-Produkten und Tryptophan bis zu Gehalten von 500 g pro kg Protein. Pyrralingehalte in kontrolliert erhitzten Proben stiegen zunchst linear mit der Erhitzungszeit und nahmen nach starkem Erhitzen deutlich ab. Unter drastischen Erhitzungsbedingungen (110C/5 h) reagierten 5,6% der Lysinreste zum Pyrrolaldehyd.
The 1,2-dicarbonyl compounds 3-deoxyglucosulose (3-DG), methylglyoxal (MGO) and glyoxal (GO) were measured for the first time in 21 honey samples as the corresponding quinoxalines after derivatization with orthophenylenediamine using RP-HPLC and UV-detection. Compared to 5-hydroxymethylfural (HMF), which was also quantified, and ranged between 0.6 and 44mg/kg, up to 100-fold higher amounts of 3-DG were found, ranging from 79 to 1,266mg/kg. During storage of honey at 35C and 45C, a linear increase of 3-DG was observed. Values for GO and MGO were in the ranges 0.2–2.7mg/kg and 0.4–5.4mg/kg respectively, and were not affected by storage. Using semi-preparative RP-HPLC, glucosone, a 1,2-dicarbonyl compound previously unknown to occur in foods was isolated from a honey sample and characterized by LC-MS and NMR spectroscopy.
A ninhydrin-positive compound was detected in acid hydrolysates of various alkali-treated bakery products (pretzels, snack bars), eluting immediately after pyridosine in amino acid chromatograms. Following preparative isolation from a food sample and independent synthesis, the compound was unequivocally identified by fast-atom bombardement-mass spectrometry,1H- and13C-nuclear magnetic resonance as a protein-bound imidazolone, existing in two tautomeric forms, namelyN
δ-(5-methyl-4-oxo-5-hydroimidazol-2-yl) -L-ornithine andN
δ-(4-methyl-5-oxo-4-hydroimidazol-2-yl) -L-ornithine. The acid-labile amino acid derivative is formed by direct condensation of the guanido group of arginine and methylglyoxal, a sugar degradation product, and represents a previously unknown post-translational protein modification. For a number of commercially available alkali-treated bakery products, the amounts of the imidazolone after complete enzymic digestion ranged between 900 and 1300 mg per 100g protein, indicating that between 20 and 30% of the arginyl residues might react with methylglyoxal during the bakery process.
The behavior of different lysine Amadori compounds during acid hydrolysis was investigated in order to determine the molar yield of furosine and the other hydrolysis products. Based on this, the conversion factors for calculating the content of Amadori compound and lysine modification before hydrolysis can be derived. For that purpose, the peptide-bound Amadori compounds Nk-(1-deoxy-D-fructosyl)-, Nk-(1-deoxy-D-tagatosyl)-, Nk-(1-deoxy-D-lactulosyl)- and Nk-(1-deoxy-D-maltulosyl)hippuryllysine as well as free Nk-(1-deoxy-D-fructosyl)lysine were synthesized. For isolation of peptide-bound Amadori compounds, an optimized enzyme-enhanced reversed phase-high pressure liquid chromatography procedure was developed. Pyridosine and Nk-(carboxymethyl)hippuryllysine were synthesized as reference materials. After acid hydrolysis with 6 M hydrochloric acid the, molar yields of furosine were determined to be 32% for fructosyllysine, 34% for lactulosyl- and maltulosyllysine and 42% for tagatosyllysine. Hydrolysis with 8 M hydrochloric acid resulted in a higher yield of furosine for Amadori compounds containing a fructosyl-moiety, 46% for fructosyllysine, 50% for lactulosyllysine and 51% for maltulosyllysine. Compared with this, the molar yield for furosine was not affected by concentration of hydrochloric acid in the case of tagatosyllysine. Based on these conversion factors a reliable calculation of the amount of Amadori compound or lysine modification and with it the evaluation of the progress of the "early" Maillard reaction in foods and biological samples is possible via the quantification of lysine and furosine after acid hydrolysis.
After heating N--hippuryl-L-arginine (Hip-Arg) with varying amounts of lactose for 1–4h at 100C, a previously unknown arginine derivative could be detected by RP-HPLC and UV-detection. Following semi-preparative isolation, the compound was unequivocally identified as 2-(2-benzoylamino-acetylamino)-5-[5-(3-hydroxypropyl)-4-oxo-imidazolon-2-yl]-L-ornithine (Hippuryl-PIO, Hip-PIO) by electrospray-time of flight-mass spectroscopy as well as one- and two-dimensional 1H- and 13C-nuclear magnetic resonance. Hip-PIO was exclusively formed during incubation of Hip-Arg with disaccharides containing a 1,4-glycosidic linkage. As reference for amino acid analysis, free PIO was synthesized starting from N-(tert-butoxycarbonyl)-L-arginine (t-Boc-Arg) via t-Boc-PIO and final hydrolysis with acetic acid. Preliminary evidence for the formation of protein-bound PIO, which proved to be acid-labile, was obtained using amino acid analysis with ninhydrin detection for enzymatic hydrolysates of casein samples which had been heated in the presence of lactose at 100C. The ornithinoimidazolinone PIO represents a new type of post-translational protein modification formed during food processing, which might be responsible for the major part of arginine derivatisation in disaccharide-containing foods like milk.
Pentosidine, a crosslink amino acid in which one arginine and one lysine residue are linked together by a pentose, has been
detected in foods for the first time using ion-exchange chromatography with direct fluorescence detection and subsequent ninhydrin
derivatization. The method allows the simultaneous quantification of pentosidine along with all other amino acids of acid
hydrolyzates at levels lower than 50 μg kg protein. Levels of pentosidine in all food samples investigated were very low (milk
products between not detectable and 2–5 mg/kg protein; roasted coffee and some bakery products up to 35 mg/kg protein), indicating
that pentosidine does not play a major part in the polymerization of food proteins.
A new method for the evaluation of the extent of lysine modification caused by the Maillard reaction is presented, based on the direct determination of the Amadori product lactuloselysine plus unmodified lysine after complete enzymatic hydrolysis by ion-exchange chromatography. Using a simple mathematical relation, the amount of modified lysine in milk products can be estimated without knowledge of the initial lysine value before heating or storage.Eine neue Methode zur Ermittlung der durch die Maillard-Reaktion verursachten Lysinmodifizierung wird vorgestellt. Das Verfahren beruht auf der direkten Bestimmung des Amadoriproduktes Lactuloselysin sowie dem Gehalt an unmodifiziertem Lysin nach enzymatischer Totalhydrolyse durch Ionenaustauschchromatographie. ber eine einfache mathematische Beziehung kann der Anteil an modifiziertem Lysin in Milchprodukten ermittelt werden, ohne da hierzu der Ausgangsgehalt an Lysin vor einer thermischen Behandlung oder Lagerung bekannt sein mu.
The identification of a coloured substructure of melanoidin-type colorants is reported in the present paper. Brown-orange
melanoidins with mass >10000 daltons were isolated from a thermally treated aqueous solution of casein and furan-2-carboxaldehyde
using ultracentrifugation. After complete enzymatic digestion of the protein skeleton, two intense red coloured compounds
were detected in the melanoidin hydrolysate by HPLC. These compounds were identified as the previously unknown chromophoric
amino acid (S)-2-amino-6-{4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl) methylidene]-2,3-dihydro-3-oxo-1H-pyrrol-1-yl}hexanoic
acid and its 2-[(Z)-(2-furyl)methylidene] isomer, by using several NMR techniques, by MS, UV, and IR spectroscopy. The identification
of these novel compounds verifies the idea that melanoidin-type colorants can be generated by a cross-linking reaction between
a low molecular weight chromophore and a non-coloured high molecular weight biopolymer.