A comprehensive review of Nε-carboxymethyllysine and Nε-carboxyethyllysine in thermal processed meat products

Formation of advanced glycation end-products and N-nitrosamines in salami of different recipes and fermented at different stages

Most research on the formation of advanced glycation end-products (AGEs) and N-nitrosamines (NAs) in meat products has focused on high-temperature processing. The effects of low-temperature processing on AGEs and NAs formation have rarely been studied. This study investigated the effects of salt addition (0 %, 2 %, and 4 %) and lean-to-fat ratio (10:0, 8:2, and 6:4) on the formation of AGEs and NAs in Salami. We found that the salt in Salami would inhibit CEL formation. And the Lean pork Salami showed the highest Nε-carboxyethyllysine (CEL) and lowest Nε-carboxymethyllysine (CML) contents. For NAs content, it was lowest in Salami with 40 % fat. Principal component analysis and correlation analysis revealed significant correlations between CEL and N-nitrosodiphenylamine (NDPhA) formation in Salami. Additionally, the production of CML was correlated with the extent of fat oxidation, while CEL formation was more strongly associated with protein-related reactions. Furthermore, NAs formation correlated with protein content and protein oxidation.

Intricate relationship among major heat-induced harmful by-products and modulating role of lipid and protein oxidation in seafood: A comprehensive review

Seafood is an important constituent of our diet and well-known for its high-quality proteins and lipids (especially polyunsaturated fatty acids). While thermal processing imparts unique flavors to seafood, it also generates heat-induced harmful by-products (HHBs), such as polycyclic aromatic hydrocarbons (PAHs), heterocyclic aromatic amines (HAAs), and advanced glycation end-products (AGEs), which pose a serious threat to human health in the long run. This manuscript provides an overview of the formation mechanisms of PAHs, HAAs, and AGEs, and their occurrence in seafood. The main body of it deals with their potential crosstalk and the modulatory role of lipid and protein oxidation in their formation. Additionally, major strategies for the control of HHBs as well as their impact on the nutritional and sensory quality of seafood in the last two decades are also reviewed. Finally, challenges associated with the control of multiple HHBs in seafood and future outlooks are discussed. Literature data support that different types of HHBs are formed from different and yet subtly interconnected pathways, such as the Maillard reaction, pyrolysis, and lipid and protein oxidation. In particular, certain precursors (e.g., reactive amino acids) and intermediates (e.g., reactive carbonyls) are key intersections. However, only limited literature has been available thus far on the simultaneous control of multiple HHBs. Given their potential health hazards, more comprehensive studies with the aid of advanced analytical techniques and software will be needed to unravel their intricate relationships, which would facilitate the establishment of strategies to achieve simultaneous control of multiple HHBs.

Riboflavin-mediated ultraviolet photosensitive oxidation of beef myofibrillar proteins with different storage times

The study was designed to investigate the mechanism of Riboflavin (RF)-mediated UVA photosensitive oxidation on beef myofibrillar proteins (MP) oxidized at different storage times. To elucidate the direct relationship between RF and protein oxidation, the mechanism of action was analyzed in terms of amino acid and side chain residues, protein structure, and protein oxidative metabolism. Oxidation of MP resulted in significant changes in the levels of carbonyls, sulfhydryls, Lysine, Arginine, Threonin, and Histidine. The oxidized MP secondary structure was changed, fluorescence intensity decreased, and surface hydrophobicity increased. Metabolomics results revealed that RF-mediated UVA photosensitized oxidation is primarily mediated by Riboflavin metabolism and co-regulated with Phenylalanine metabolism. Moreover, with the increase of frozen storage time, Arginine and proline metabolism was inhibited, and the contents of creatine were significantly reduced, which exacerbated MP oxidative damage. The results provide a theoretical basis for unraveling the mechanism of RF-mediated UVA photosensitive oxidation of MP.

Formation and control of heterocyclic amines and advanced glycation end products in traditional Chinese braised pork belly: The role of food additives

For braised pork belly, a popular traditional Chinese dish, we lack a scientific knowledge to reduce the formation of harmful heterocyclic amines (HAs) and advanced glycation end products (AGEs) while maintaining sensory quality. This study aimed to clarify the factors affecting the formation of free and protein-bound HAs and AGEs during the braised pork belly cooking process using UPLC-MS/MS analysis. The results indicated that soy sauce significantly promoted the formation of HAs, with organic soy sauce exhibiting the strongest promoting effect, increasing HAs by 270.92 %. Early-middle incorporation of sauce juice can attenuate this promoting effect. Spices exerted an inhibitory effect on HAs and AGEs formation, which was enhanced when added in powdered form, although no significant differences were observed across different dosages. Notably, the elevation of crystal sugar levels reduced both HAs and AGEs while enhancing sensory preference. Several umami flavor enhancers, particularly 5'-flavored nucleotide disodium, further inhibited the formation of these harmful compounds. This research deepens the understanding of the association between seasonings additions and the formation of harmful substances in braised meat products, providing valuable insights for developing safer and healthier culinary practices.

Accumulation of Nε-carboxymethyllysine and Nε-carboxyethyllysine in precooked pork during cold storage and subsequent reheating

This research aimed to investigate the levels of Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL) in precooked pork (100 °C, 10 min) as affected by storage (0 °C, 0-11 d) and subsequent reheating (100 °C, 5 min). A longer storage duration led to more CML (average increased: 69-128 %) and CEL (average increased: 11-44 %) in precooked pork, while the reheating resulted in average increases of 86 % CML and 32 % CEL compared to their initial levels in precooked pork. However, the storage duration did not significantly (p > 0.05) affect CML/CEL formation in precooked pork during the subsequent reheating. The levels of CML/CEL and glyoxal/methylglyoxal had no obvious relationship, but CML formation was linked to lipid oxidation in precooked or reheated pork. The accumulation of CML and CEL in precooked meat produced during the initial precooking, storage, and reheating implies the necessity to control their generation in these products.

Differential contribution of Cu2+ and OH- to the formation of Nε-carboxymethyllysine and Nε-carboxyethyllysine in preserved egg white during pickling

In this study, the relationship between advanced glycosylation end products (AGEs) in preserved egg white (PEW) with protein oxidation and precursors induced by OH- and Cu2+ were performed to clarify the differential contribution of OH- and Cu2+ on the formation of AGEs during pickling. It was found that AGEs were more easily formed in PEW rather than yolk, and the accumulation of Nε-carboxymethyllysine (CML) could be promoted through protein oxidation related to carbonyl compounds, tryptophan induced by Cu2+ at early stage, while carbonyl compounds were more conducive to form Nε-carboxyethyllysine (CEL) under synergistic action of Cu2+ and OH-. At later period, Schiff base promoted the formation of CEL and CML in the presence of Cu2+. Meanwhile, the enrichment of CEL and CML could both be promoted by α-dicarbonyl compounds in presence of Cu2+ and/or OH-. This manuscript will provide theoretical guidance for reducing and limiting hazardous compounds in preserved eggs.

Mechanism studies of gliadin-glucose glycation reaction and products formation by heat treatment with different conduction modes

Heat treatments induce protein-reducing sugar glycation reactions easily, leading to protein structural transformations and advanced glycation end products generation. In this study, effects of four heat conduction modes (air, contact, vapour and liquid-conduction) on the spatial conformation and glycation products of gliadin-glucose system were evaluated. The results showed that gliadin tertiary structure expanded and exposed more hydrophobic sites in vapour-conduction, resulting in more glycation sites. Conversely, air-conduction promoted the protein folded, causing a lighter glycation degree and lower glyoxal, methylglyoxal, acrylamide, 5-hydroxymethylfurfural and carboxymethyl lysine contents (following vapour-conduction > contact-conduction > liquid-conduction > air-conduction). The above phenomena were attributed to the different water content in the different conduction modes. Furthermore, the glycation sites identified in vapour-conduction and contact-conduction were approximately two-fold of that in air-conduction. Conclusively, gliadin-glucose systems subjected to air-conduction showed less glycated intensity and hazardous products.

Polyphenols as reactive carbonyl substances regulators: A comprehensive review of thermal processing hazards mitigation

Reactive carbonyl species (RCS) are a class of compounds with one or more C = O structures with highly reactive electrophilic properties. This comprehensive review delves into the multifaceted role of RCS in thermally processed foods, where they serve as both crucial intermediates in the development of food color and flavor, as well as precursors of potentially harmful compounds. By exploring the carbonyl pool concept, the impact of RCS equilibrium on the formation and reduction of hazardous substances such as acrylamide, hydroxymethylfurfural, advanced glycation end-products, and heterocyclic amines was elucidated. The review particularly emphasizes the regulatory effects of polyphenols on the carbonyl pool, highlighting their potential to reduce the levels of RCS and their associated hazards. Furthermore, the dual role of polyphenols in both mitigating and enhancing to the formation of RCS and their associated hazards was discussed. This review offers valuable insights into strategies for inhibiting RCS and their associated hazards.

Formation and kinetic analysis of AGEs in Pacific white shrimp during frying

Advanced glycation end products (AGEs) are complex and heterogeneous compounds closely associated with various chronic diseases. The changes in Nε-carboxymethyllysine (CML), Nε-carboxyethyllysine (CEL), Nε-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1), and fluorescent AGEs (F-AGEs) in fried shrimp during frying (170 °C, 0-210 s) were described by kinetic models. Besides,the correlations between AGEs contents and physicochemical indicators were analyzed to reveal their intrinsic relationship. Results showed that the changes of four AGEs contents followed the zero-order kinetic, and their rate constants were ranked as kCML < kCEL ≈ kMG-H1 < kF-AGEs. Oil content and lipid oxidation were critical factors that affected the AGEs levels of the surface layer. Protein content and Maillard reaction were major factors in enhancing the CML and CEL levels of the interior layer. Furthermore, the impact of temperature on the generation of CML and CEL was greater than that of MG-H1 and F-AGEs.

Effect of Extraction Methods on Chemical Characteristics and Bioactivity of Chrysanthemum morifolium cv. Fubaiju Extracts

Chrysanthemum morifolium cv. Fubaiju (CMF) is regarded as one of the three most renowned varieties of white Chrysanthemum in China, and different extraction methods have significant effects on its composition and activities. Therefore, six extractions were used in this study to assess the effects on extracts. The basic chemical composition showed that hot water extract (Hw) had the highest total phenolic content, alkali water immersion-assisted hot water extract (Al) had the highest content of protein, and enzyme-assisted hot water extract (Enz) had the highest content of carbohydrate. The UPLC-Q-Exactive-MS results evinced the presence of 19 small-molecule compounds, including chlorogenic acid, caffeic acid, tuberonic acid glucoside, luteolin-7-O-rutinoside, and other substances. In addition, the antioxidant test found that the Hw exhibited the best 1,1-diphenyl-2-picrylhydrazyl (DPPH) (82.05 ± 1.59 mM TE/mg) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) (61.91 ± 0.27 mM TE/mg) scavenging ability. The anti-glycation test demonstrated that Enz possessed the most pronounced inhibitory effect on glycation products, including fructosamine and advanced glycation end products (AGEs). Additionally, the Enz also exhibited the most significant inhibitory effect on the protein oxidation product N'-formylkynurenine. The correlation analysis revealed that there was a close relationship between antioxidant properties and glycation resistance of extracts, and tuberonic acid glucoside, 1,3-di-O-caffeoylquinic acid, 1,4-Dicaffeoylquinic acid, quercetin-7-O-β-D-glucopyranoside, and isochlorogenic acid B were key small molecule components that affected activities. In summary, the extracts of CMF can be regarded as an excellent antioxidant and anti-glycosylation agent.

Inhibition of Nε-(carboxyethyl)lysine and Nε-(carboxymethyl)lysine formation in beef, chicken, and fish meat: A comparative study of oven frying and air frying with a marinade-containing Micromeria fruticosa

The objective of this study was to assess the impact of marinating beef, chicken, and fish with Micromeria fruticosa (M. fruticosa) on the inhibition of Nε-(carboxyethyl)lysine (CEL) and Nε-(carboxymethyl)lysine (CML). Furthermore, our objective was to examine how different cooking techniques, temperatures, and durations affect the creation of CEL and CML in these meat products. The study began with the characterization of M. fruticosa. Subsequently, meat samples were marinated using an M. fruticosa-containing marinade and stored at 4 ± 1°C for 24 h. Following storage, the meats underwent cooking in an oven at 200°C for 12 min and in an air fryer at 250°C for 8 min. Subsequently, pH, color, thiobarbituric acid reactive substances (TBARS), as well as CEL and CML analyses were conducted. M. fruticosa had high levels of biological activity and bioactive content. Moreover, increasing the M. fruticosa ratio in the marinade demonstrated a reduction in TBARS, CML, and CEL formation. This study concludes that M. fruticosa can be effectively used as a marinade component for meat, inhibiting the formation of CEL and CML. In conclusion, this research underscores the significant potential of M. fruticosa in reducing the synthesis of advanced glycation end products (AGEs) during meat processing. These results not only enhance our comprehension of the complex relationship between plant extracts and meat quality but also present encouraging prospects for fostering healthier and safer cooking methods.

Inclusion of reeling wastewater-derived sericin peptides in high-protein nutrition bars for antihardening and storage stability

The utilization of agroindustrial wastes to enrich food protein resources and the exploration of their broader applications are crucial for addressing the food crisis and achieving sustainable development goals. In this study, reeling wastewater-derived sericin was hydrolyzed using papain and trypsin to prepare sericin peptide (SRP) and was used as an antihardening ingredient of high-protein nutrition bars (HPNBs). The mechanism of the antihardening effect of SRP was elucidated by investigating the content of advanced glycation end products and protein oxidation products (carbonyl and free sulfhydryl), and the molecular weight change of HPNBs during storage before and after the addition of SRP. Our results confirmed the fortification of HPNBs with SRP, which is beneficial for the promotion and expansion of sericin applications in the food industry, with positive implications for the rational utilization of protein resources and the enrichment of food protein sources.

Simultaneous determination of advanced glycation end products and heterocyclic amines in roast/grilled meat by UPLC-MS/MS

Advanced glycation end products (AGEs) and heterocyclic amines (HAs) are main harmful Maillard reaction products of meat products. Simultaneous quantification of both with high sensitivity, selectivity and accuracy remains a major challenge due to inconsistencies in their pre-treatment and instrumental methods and the different polarity of AGEs and HAs. We developed a method for the simultaneous determination of AGEs and HAs in roast/grilled meat by ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) using dynamic multiple reaction monitoring (D-MRM). The instrument parameters and pre-treatment method were optimized to achieve reasonably good separation and high response for the 11 target analytes within 8 min. From 10 to 200 ng/mL, the limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.3 to 5.5 μg/L and 0.9 to 6.3 μg/L, respectively, and the correlation coefficient (R2) was >0.99. It was acceptable to recoveries, standard deviations (RSDs), and matrix effects. Six types of roast/grilled meat samples were then tested using the developed method.

Effects of seasoning addition and cooking conditions on the formation of free and protein-bound heterocyclic amines and advanced glycation end products in braised lamb

The accumulation of heterocyclic amines (HAs) and advanced glycation end products (AGEs) in thermally processed meats has been arising safety concerns. The effects of cooking conditions and seasoning addition on the formation of HAs and AGEs in Chinese traditional braised lamb were investigated by UPLC-MS/MS analysis. Soy sauce significantly increased the formation of HAs and AGEs, among which light soy sauce had the greatest promoting effect (69.45-15300.62 %). Conversely, spices inhibited HAs and AGEs formation, the inhibition rate of free HAs and AGEs reached 22.06-34.72 % when using 70 % ethanol extract. Hot blanching treatment and adding soy sauce and spices at a later stage could significantly suppress HAs and AGEs production. Flavonoids, including galangin, hesperidin, narirutin, etc., were identified as key effectors in spices. These findings help to promote awareness of the formation of HAs and AGEs in braised lamb and provide valuable insights for optimizing processing techniques to minimize their production.

The effects of using sheep tail fat and cooking time on carboxymethyl-lysine formation and some quality characteristics of heat-treated sucuk

The study's aim was to determine the effect of using sheep tail fat (STF) on carboxymethyl-lysine (CML) content and other properties of heat-treated sucuk (HTS), a type of semi-dry fermented sausage. Three mixtures were prepared: 100% beef fat (BF), 50% BF + 50% STF, and 100% STF. After production (fermentation, heat treatment, and drying), the samples were cooked at 180°C for 0, 1, 3, and 5 min to determine the effect of cooking time on CML, thiobarbituric acid reactive substance (TBARS), total sulfhydryl, and carbonyl contents. The lowest pH value (5.50) was observed in the presence of STF. The most oleic acid (46.02%) was observed in the 100% STF group. The score of taste and general acceptability decreased with increasing STF. Using STF had no significant effect on TBARS, total sulfhydryl, carbonyl, or CML content. These parameters were affected by cooking time. The mean CML content increased from 55.77 to 72.90 μg/g after 5 min of cooking. CML correlated more strongly with TBARS than sulfhydryl or carbonyl.

Exploring the role of Maillard reaction and lipid oxidation in the advanced glycation end products of batter-coated meat products during frying

The Maillard reaction occurs during the frying of batter-coated meat products, resulting in the production of advanced glycosylation products that are harmful to human health. This study investigated the effects of frying temperature (140, 150, 160, 170 and 180 ℃) and time (80, 100, 120, 140 and 160 s) on the quality, advanced glycation end product (AGE) level and the relationship between these parameters in batter-coated meat products were investigated. The results showed that with an increase in frying temperature and time, the moisture content of the batter-coated meat products gradually decreased, the thiobarbituric Acid Reactive Substance (TBARS) values and oil content increased to 0.37 and 21.7 %, respectively, and then decreased, and CML and CEL content increased to 7.30 and 4.86 mg/g, respectively. Correlation analysis showed that the moisture content and absorbance at 420 nm, as well as TBARS values, were highly correlated with the oil content in batter-coated meat products. Additionally, the absorbance at 420 nm and TBARS levels were significantly correlated with AGE levels. Moreover, the AGE content in batter-coated meat products was less variable at lower frying temperatures or shorter frying times, and the influence of temperature on AGE formation was greater than that of time. Overall, these findings may help to better control the cooking conditions of batter-coated meat products based on AGE profiles.

Development of a two-step pretreatment and UPLC-MS/MS-based method for simultaneous determination of acrylamide, 5-hydroxymethylfurfural, advanced glycation end products and heterocyclic amines in thermally processed foods

A two-step pretreatment and UPLC-MS/MS-based method was established to extract and determine 17 thermal processing hazards (TPHs) simultaneously. The first step was to extract acrylamide (AA), 5-hydroxymethylfurfural (HMF) and free heterocyclic amines (HAs). The bound HAs and advanced glycation end products (AGEs) were released by acid hydrolysis in the second step. A fairly good separation was achieved within 7 min. Almost all TPHs showed high correlation coefficients (R2 >0.999) in their respective linear ranges. The accuracy ranged from 98.13 to 100.96%. LODs and LOQs were in the range of 0.01-0.89 µg/L and 0.02-2.96 µg/L, respectively. The method was successfully applied to four representative food products, including high-starch, high-protein, high-fat and high-sugar foods, showing acceptable recoveries, intra-day and inter-day precisions. Moreover, PCA was performed to visualize the association between TPHs and food matrices. The developed method provided technical support for the formation and control researches of TPHs.

Effect of edible oil type on the formation of protein-bound Nε-(carboxymethyl)lysine in roasted pork patties

Protein-bound Nε-(carboxymethyl)lysine (CML), an advanced glycation end product within meat products, poses a potential health risk to humans. The objective of this study was to explore the impact of various edible oils on the formation of protein-bound CML in roasted pork patties. Eleven commercially edible oils including lard oil, corn oil, palm oil, olive oil, flaxseed oil, blended oil, camellia oil, walnut oil, soybean oil, peanut oil, and colza oil were added to pork tenderloin mince, respectively, at a proportion of 4 % to prepare raw pork patties. The protein-bound CML contents in the pork patties were determined by HPLC-MS/MS before and after roasting at 200 °C for 20 min. The results indicated that walnut oil, flaxseed oil, colza oil, olive oil, lard oil, corn oil, blended oil, and palm oil significantly reduced the accumulation of protein-bound CML in pork patties, of which the inhibition rate was in the 24.43 %-37.96 % range. Moreover, the addition of edible oil contributed to a marginal reduction in the loss of lysine. Meanwhile, glyoxal contents in pork patties were reduced by 16.72 %-43.21 % after roasting. Other than blend oil, all the other edible oils restrained protein oxidation in pork patties to varying degrees (between 20.16 % and 61.26 %). In addition, camellia oil, walnut oil, and flaxseed oil increased TBARS values of pork patties by 2.2-8.6 times when compared to the CON group. After analyzing the fatty acid compositions of eleven edible oils, five main fatty acids (palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid) were selected to establish Myofibrillar protein-Glucose-fatty acids systems to simulate the roasting process. The results showed that palmitic acid, oleic acid, linoleic acid, and linolenic acid obviously mitigated the formation of myofibrillar protein-bound CML, exhibiting suppression rates ranging from 10.38 % to 40.32 %. In conclusion, the addition of specific edible oil may curb protein-bound CML production in roasted pork patty by restraining protein or lipid oxidation, reducing lysine loss, and suppressing glyoxal production, which may be attributed to the fatty acid compositions of edible oils. This finding provides valuable guidance for the selection of healthy roasting oils in the thermal processing of meat products.

Processing Stage-Induced Formation of Advanced Glycation End Products in Cooked Sausages with the Addition of Spices

This study aims to evaluate the relationship between the four processing stages of cooked sausage preparation (raw, drying, baking, and steaming) and the formation of advanced glycation end products (AGEs), 1,2-dicarbonyl compounds, and lipid and protein oxidation in sausages with spices. Baking and steaming significantly promoted lipid and protein oxidation. The Nε-carboxymethyllysine (CML) content increased from 4.32-4.81 µg/g in raw samples to 10.68-16.20 µg/g in the steamed sausages. Nε-carboxyethyllysine (CEL) concentrations increased by approximately 1.7-3.7 times after steaming. The methylglyoxal concentration increased dramatically after baking and then rapidly decreased in the steaming stage. Chili promoted the formation of CML and CEL. The CEL concentration increased in samples containing garlic, but yellow mustard and garlic slightly reduced CML concentrations in the cooked sausages. The spices decreased the lipid and protein stability of the cooked sausages, increasing malondialdehyde and protein carbonyls. Lipid oxidation and 3-deoxyglucosone positively correlated with CML and CEL levels. Black pepper had no impact on CML when the sausages were baked but remarkably increased the content of both CML and CEL in the steaming stage. Thus, the impact of spices on sausages depends on both the specific spices used and the category of AGEs formed.

Application of tea polyphenols as additives in brown fermented milk: Potential analysis of mitigating Maillard reaction products

Brown fermented milk (BFM) is favored by consumers in the dairy market for its unique burnt flavor and brown color. However, Maillard reaction products (MRP) from high-temperature baking are also noteworthy. In this study, tea polyphenols (TP) were initially developed as potential inhibitors of MRP formation in BFM. The results showed that the flavor profile of BFM did not change after adding 0.08% (wt/wt) of TP, and its inhibition rates on 5-hydroxymethyl-2-furaldehyde (5-HMF), glyoxal (GO), methylglyoxal (MGO), Nε-carboxymethyl lysine (CML), and Nε-carboxyethyl lysine (CEL) were 60.8%, 27.12%, 23.44%, 57.7%, and 31.28%, respectively. After 21 d of storage, the levels of 5-HMF, GO, MGO, CML, and CEL in BFM with TP were 46.3%, 9.7%, 20.6%, 5.2%, and 24.7% lower than the control group, respectively. Moreover, a smaller change occurred in their color and the browning index was lower than that of the control group. The significance of this study was to develop TP as additives to inhibit the production of MRP in brown fermented yogurt without changing color and flavors, thereby making dairy products safer for consumers.

The Effects of Sheep Tail Fat, Fat Level, and Cooking Time on the Formation of Nε-(carboxymethyl)lysine and Volatile Compounds in Beef Meatballs

This study aimed to determine the effects of fat type (sheep tail fat (STF) and beef fat (BF)), fat levels (10, 20, or 30%), and cooking time (0, 2, 4, and 6 min, dry heat cooking at 180 °C) on the carboxymethyl lysine (CML) content in meatballs. pH, thiobarbituric acid reactive substance (TBARS), and volatile compound analyses were also performed on the samples. The use of STF and the fat level had no significant effect on the pH value. The highest TBARS value was observed with the combination of a 30% fat level and STF. CML was not affected by the fat level. The highest CML content was determined in meatballs with STF at a cooking time of 6 min. In the samples cooked for 2 min, no significant difference was observed between STF and BF in terms of the CML content. STF generally increased the abundance of aldehydes. Aldehydes were also affected by the fat level and cooking time. A PCA provided a good distinction between groups containing STF and BF regardless of the fat level or cooking time. Pentanal, octanal, 2,4-decadienal, hexanal, and heptanal were positively correlated with CML.

Formation of advanced glycation end products of chicken breast meat induced by freeze-thaw cycles and subsequent cooking

The impacts of freeze-thaw (F-T) cycles and cooking on the basic composition, protein and lipid oxidation, and advanced glycation end products (AGEs) of chicken breasts were studied. During F-T cycles, the moisture and protein contents of raw and cooked chicken breasts decreased, and protein and lipid oxidation occurred, increasing carbonyl and TBARS contents. Meanwhile, the contents of methylglyoxal, glyoxal, and hydroxymethylfurfural in raw meat increased by 2.27, 2.27, and 5 times, respectively, whereas glyoxal and hydroxymethylfurfural contents increased by 2.73 and 3 times, respectively, after cooking as F-T cycles increased. The formation of carboxymethyl lysine, pentosidine, and fluorescent AGEs in cooked samples was confirmed using an ELISA kit and fluorescent intensity. The study also revealed that AGEs contents of chicken meat were negatively correlated with moisture contents and positively correlated with carbonyl and TBARS levels. Therefore, F-T cycles and subsequent cooking promoted AGEs formation in cooked meat.

Effects of different heat treatments on Maillard reaction products and volatile substances of camel milk

Camel milk has unique compositional, functional and therapeutic properties compared to cow's milk and also contains many protective proteins with anti-cancer, anti-diabetic and anti-bacterial properties. In this experiment, fresh camel milk was heat-treated at different temperatures and times, and the changes in Millard reaction products were analyzed. Meanwhile, headspace-gas chromatography-ion migration spectrometry (HS-GC-IMS), electronic nose and electronic tongue were used to analyze the changes of volatile components in camel milk after different heat treatments. The results showed that the Maillard reaction was more severe with the increase of heat treatment, and the contents of furosine and 5-hydroxymethylfurfural increased significantly when the heat treatment temperature was higher than 120°C. HS-GC-IMS results showed that the contents of aldehydes and ketones increased obviously with the increase of heat treatment degree. The study clarifies the effects of different heat treatment degrees on Maillard reaction degree and flavor of camel milk, which has practical production guidance significance for the research and industrialization of liquid camel milk products.

Formation of Nε-Carboxymethyl-Lysine and Nε-Carboxyethyl-Lysine in Heated Fish Myofibrillar Proteins with Glucose: Relationship with Its Protein Structural Characterization

The formation of advanced glycation end products (AGEs), including N^ε-carboxymethyl-lysine (CML) and N^ε-carboxyethyl-lysine (CEL), in a fish myofibrillar protein and glucose (MPG) model system at 80 °C and 98 °C for up to 45 min of heating were investigated. The characterization of protein structures, including their particle size, ζ-potential, total sulfhydryl (T-SH), surface hydrophobicity (H₀), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectroscopy (FTIR), were also analyzed. It was found that the covalent binding of glucose and myofibrillar protein at 98 °C promoted protein aggregation when compared with the fish myofibrillar protein (MP) heated alone, and this aggregation was associated with the formation of disulfide bonds between myofibrillar proteins. Furthermore, the rapid increase of CEL level with the initial heating at 98 °C was related to the unfolding of fish myofibrillar protein caused by thermal treatment. Finally, correlation analysis indicated that the formation of CEL and CML had a significantly negative correlation with T-SH content (r = -0.68 and r = -0.86, p ≤ 0.011) and particle size (r = -0.87 and r = -0.67, p ≤ 0.012), but was weakly correlated with α-Helix, β-Sheet and H₀ (r² ≤ 0.28, p > 0.05) during thermal treatment. Overall, these findings provide new insights into the formation of AGEs in fish products based on changes of protein structure.

Investigation on the Contents of Nε-carboxymethyllysine, Nε-carboxyethyllysine, and N-nitrosamines in Commercial Sausages on the Chinese Market

Sausages are among the most popular meat products worldwide. However, some harmful products, such as advanced glycation end-products (AGEs) and N-nitrosamines (NAs), can be formed simultaneously during sausage processing. In this study, the contents of AGEs, NAs, α-dicarbonyls and the proximate composition were investigated in two kinds of commercial sausages (fermented sausages and cooked sausages) in the Chinese market. The correlations among them were further analyzed. The results showed that the fermented and cooked sausages had different in protein/fat contents and pH/thiobarbituric acid reactive substance values due to their different processing technologies and added ingredients. The N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) concentrations varied from 3.67 to 46.11 mg/kg and from 5.89 to 52.32 mg/kg, respectively, and the NAs concentrations ranged from 1.35 to 15.88 µg/kg. The contents of some hazardous compounds, such as CML, N-nitrosodimethylamine, and N-nitrosopiperidine, were observed to be higher in the fermented sausages than in the cooked sausages. Moreover, levels of NAs in some sausage samples exceeded the limit of 10 µg/kg issued by the United States Department of Agriculture, suggesting that particular attention should be paid to mitigating NAs, especially in fermented sausages. The correlation analysis suggested that the levels of AGEs and NAs were not significantly correlated in both kinds of sausages.

Control of the Maillard reaction and secondary shelf-life prediction of infant formula during domestic use

To control the Maillard reaction of infant formula (IF) during secondary shelf-life (SSL) and establish an SSL prediction model, the effects of storage temperatures (25°C, 37°C) and relative humidity (RH) levels (32%, 57%, and 75%) on the Maillard reaction products (MRPs) were evaluated. Visible color changes were observed during storage in samples stored at 37°C and not at 25°C. The available lysine loss was the largest, up to 64.14% and 69.40% after 4 weeks of storage at 37°C and 57% RH. At the end of storage, the 5-hydroxymethylfurfural, 3-deoxyglucuronide, fluorescence of advanced Maillard products and soluble Tryptophan (FAST) index, and N^ε -carboxymethyllysine (CML) of two commercial IFs increased by 0.48-3.32, 1.26-12.65, 0.01-4.87, and 0.30-1.05 times, respectively. During storage, the glyoxal content in two commercial IFs tended to increase and then decrease in the range of 0.21-3.43 mg/100 g. The SSL of IFs was predicted using the multivariate accelerated shelf-life test and the Arrhenius model. At 25°C, the estimated SLL of two commercial IFs were 10-9 and 7-6 weeks at 57% and 75% RH, respectively. MRPs and ΔE* could be used as indicators for predicting the SLL of infant formula. PRACTICAL APPLICATION: The results of the study suggested that the increase in storage temperature and humidity during the SSL can promote the MR of IF, which affects the sensory and safety of IF. Therefore, consumers need to focus on controlling storage conditions during the SSL to avoid degradation of IF quality.

Advanced Glycation End Products and Nitrosamines in Sausages Influenced by Processing Parameters, Food Additives and Fat during Thermal Processing

Advanced glycation end products (AGEs) and nitrosamines (NAs) in sausage are associated with pathogenic and carcinogenic risks. However, the multiple reaction parameters affecting the production of AGEs and NAs during sausage processing remain unclear. This experiment evaluated the effects of processing parameters, food additives and fat ratios on the formation of AGEs and NAs in sausages. The results showed a 2-3-fold increase in N^ε-(carboxymethyl)lysine (CML) and N^ε-(carboxyethyl)lysine (CEL) when the sausage processing temperature was increased from 90 °C to 130 °C, and N-nitrosodimethylamine (NDEA) increased from 3.68 ng/g to 6.41 ng/g. The addition of salt inhibited the formation of AGEs and NAs, and the inhibitory ability of 2 g/100 g of salt was 63.6% for CML and 36.5% for N-nitrosodimethylamine (NDMA). The addition of 10 mg/kg nitrite to sausages reduced CML formation by 43.9%, however, nitrite had a significant contribution to the formation of NAs. The addition of fat only slightly contributed to the production of CML. In addition, the relationship between α-dicarbonyl compounds and the formation of AGEs was investigated by measuring the changes in α-dicarbonyl compounds in sausages. The results showed two trends of AGEs and α-dicarbonyl compounds: AGEs increased with the increase in α-dicarbonyl compounds and AGE level increased but α-dicarbonyl compound level decreased.

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

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

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

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

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

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

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

Effect of Traditional Stir-Frying on the Characteristics and Quality of Mutton Sao Zi

The effects of stir-frying stage and time on the formation of Maillard reaction products (MRP) and potentially hazardous substances with time in stir-fried mutton sao zi were investigated. Furosine, fluorescence intensity, Nε-(1-carboxymethyl)-L-lysine (CML), Nε-(1-carboxyethyl)-L-lysine (CEL), polyaromatic hydrocarbons PAHs), heterocyclic aromatic amines (HAAs), and acrylamides (AA) mainly presented were of stir-fried mutton sao zi. The furosine decreased after mixed stir-frying (MSF) 160 s due to its degradation as the Maillard reaction (MR) progressed. The fluorescent compound gradually increased with time during the stir-frying process. The CML and CEL peaked in MSF at 200 s. AA reached its maximum at MSF 120 s and then decreased. All the 5 HAAs were detected after MSF 200 s, suggesting that stir-frying mutton sao zi was at its best before MSF for 200 s. When stir-frying exceeded the optimal processing time of (MSF 160 s) 200 s, the benzo[a]pyrene peaked at 0.82 μg/kg, far lower than the maximum permissible value specified by the Commission of the European Communities. Extended stir-frying promoted MRP and some hazardous substances, but the content of potentially hazardous substances was still within the safety range for food.

Effects of Konjac Glucomannan on Oil Absorption and Safety Hazard Factor Formation of Fried Battered Fish Nuggets

The purpose of this study was to investigate the effects of konjac glucomannan (KGM) on oil absorption and the formation of safety hazard factors in fried battered fish nuggets by measuring advanced glycation end products (AGEs) and acrylamide contents. Other physicochemical properties were determined to explore the reason for oil absorption and formation of safety hazard factors. The acrylamide was found mainly in the crust. The addition of 0.8% KGM could significantly reduce the acrylamide content (p < 0.05). For the battered sample, the AGEs content was far lower than the unbattered. The addition of 0.8% KGM could significantly reduce the AGEs content in the inner layer (p < 0.05). The microstructure showed that the sample with 0.8% KGM had the most compact crust. The compact crust reduced oil and malondialdehyde contents. Combined with the other indicators, the inhibitory effect of 0.8% KGM on acrylamide was closely related with the decreased extent of oil oxidation and Maillard reaction in the samples with 0.8% KGM. The inhibitory effect of 0.8% KGM on AGEs might originate from its lower oil content.

Formation of AGEs in fish cakes during air frying and other traditional heating methods

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.

Formation of Nε-Carboxymethyl-Lysine and Nε-Carboxyethyl-Lysine in Pacific Oyster (Crassostrea gigas) Induced by Thermal Processing Methods

Advanced glycation end products (AGEs) are important endogenous hazardous substances produced during the thermal processing of foods, which have attracted much attention due to the potential health risks. The current research first investigated the effect of different thermal processing methods (steaming, boiling, sous vide (SV), and sterilizing) on the formation of two typical markers of AGEs, including N^ε-carboxymethyl-lysine (CML) and N^ε-carboxyethyl-lysine (CEL), in Pacific oyster (Crassostrea gigas). The compositions, lipid oxidation, di-carbonyl compounds, and AGEs in 12 kinds of processed oysters were detected, and the Index values (total Z-score) were calculated. The SV treatment at 70°C caused higher processing yield and lower CEL level while sterilizing in oil at 121°C greatly resulted in the formation of CML. The Index value of SV-treated oysters was much lower than steamed, boiled, and sterilized ones. Correlation analysis showed that the CML and CEL levels were positively correlated with fat content, a^* and b^* value (p < 0.05), and negatively correlated with moisture content and L^* value (p < 0.05). Besides, thiobarbituric acid reactive substances had a negative correlation with CML (r = −0.63, p < 0.05) while no significant correlation with CEL (p > 0.05), suggesting that lipid oxidation had a greater effect on the formation of CML but less on the formation of CEL. In summary, SV treatment at 70°C within 15 min was a recommended thermal processing method to reduce the formation of AGEs in oysters.

Maillard reaction harmful products in dairy products: Formation, occurrence, analysis, and mitigation strategies

Various harmful Maillard reaction products such as lactulosyl-lysine (furosine), furfurals, and advanced glycation end products (AGEs) could be formed during the thermal processing of dairy products, which could lead to various chronic diseases. In this review, the furosine, furfurals, and AGEs formation, occurrence, analysis methods, and toxicological and health aspects in various dairy products were summarized to better monitor and control the levels of harmful Maillard reaction products in processed dairy products. It was observed that all types of dairy products, including raw milk, contain harmful Maillard reaction products, with the highest in whey cheese and condensed milk. High-performance liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the common method for the determination of furosine and furfurals and AGEs in dairy products, respectively. However, the simple, rapid, environment-friendly, and accurate methods of determination are still to be developed. Incorporating resveratrol, pectin oligosaccharides (POS) in milk are effective methods to inhibit AGEs formation. This review provides a guide not only for consumers regarding the selection and consumption of dairy products, but also for monitoring and controlling the quality of dairy products.

Comparison of metabolic fate, target organs, and microbiota interactions of free and bound dietary advanced glycation end products

Increased intake of Western diets and ultra-processed foods is accompanied by increased intake of advanced glycation end products (AGEs). AGEs can be generated exogenously in the thermal processing of food and endogenously in the human body, which associated with various chronic diseases. In food, AGEs can be divided into free and bound forms, which differ in their bioavailability, digestion, absorption, gut microbial interactions and untargeted metabolites. We summarized the measurements and contents of free and bound AGE in foods. Moreover, the ingestion, digestion, absorption, excretion, gut microbiota interactions, and metabolites and metabolic pathways between free and bound AGEs based on animal and human studies were compared. Bound AGEs were predominant in most of the selected foods, while beer and soy sauce were rich in free AGEs. Only 10%-30% of AGEs were absorbed into the systemic circulation when orally administered. The excretion of ingested free and bound AGEs was approximately 90% and 60%, respectively. Dietary free CML has a detrimental effect on gut microbiota composition, while bound AGEs have both detrimental and beneficial impacts. Free and bound dietary AGEs changed amino acid metabolism, energy metabolism and carbohydrate metabolism. And besides, bound dietary AGEs altered vitamin metabolism, and glycerolipid metabolism.

Dietary N-epsilon-carboxymethyllysine as for a major glycotoxin in foods: A review

N-epsilon-carboxymethyllysine (CML), as a potential glycotoxin and general marker for dietary advanced glycation end products (dAGEs), exists in raw food and is formed via various formation routes in food processing such as Maillard reaction between the reducing sugars and amino acids. Although comprehensive cause-effect proof is not available yet, current research suggests a potential risk of chronic diseases such as diabetes is associated with exogenous CML. Thus, CML is causing public health concerns regarding its dietary exposure, but there is a lack of explicit guidance for understanding if it is detrimental to human health. In this review, inconsistent results of dietary CML contributed to chronic disease are discussed, available concentrations of CML in consumed foods are evaluated, measurements for dietary CML and relevant analytic procedures are listed, and the possible mitigation strategies for protecting against CML formation are presented. Finally, the main challenges and future efforts are highlighted. Further studies are needed to extend the dietary CML database in a wide category of foods, apply new identifying methods, elucidate the pathogenic mechanisms, assess its detrimental role in human health, and propose standard guidelines for processed food.