Investigation on the Contents of N(ε)-carboxymethyllysine, N(ε)-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.

Characteristic flavor formation of thermally processed N-(1-deoxy-α-d-ribulos-1-yl)-glycine: Decisive role of additional amino acids and promotional effect of glyoxal

The role of amino acids and α-dicarbonyls in the flavor formation of Amadori rearrangement product (ARP) during thermal processing was investigated. Comparisons of the volatile compounds and their concentrations when N-(1-deoxy-α-d-ribulos-1-yl)-glycine reacted with different amino acids or glyoxal (GO) at 100 °C were executed. Additional amino acids, such as glycine (Gly), in ARP models contributed to the diversity of furanoids by the chain elongation of the derived formaldehyde. Whereas the monoanion of additional glutamic acid acted as nucleophile, favored 2-ethyl-3,5-dimethylpyrazine and 2,5-dimethylpyrazine formation; the nonionized amino group of additional lysine were involved in α-dicarbonyls formation, causing pyrazine and methylpyrazine accumulation in the ARP model. Moreover, the high dosage and pH stabilization of additional GO probably promoted the ARP degradation and deoxyosones retro-aldol cleavage, resulting in methylpyrazine rather than furanoids formation. The present work provided the guidance for the controlled flavor formation of ARP in industrial application.

The antioxidant and antiglycation activities of selected spices and other edible plant materials and their decay in sugar-protein systems under thermal stress

Antiglycation activities of herbs and spices, have been described in relation to their in vivo anti-diabetic or anti-aging activity at physiological temperature. Under the hypothesis that those natural antioxidants may inhibit the formation of Maillard intermediates, the behavior of several hydroalcoholic plant extracts was analyzed in sugar-protein systems. Allspice, thyme, green pepper and black pepper extracts were the most efficient inhibitors, decreasing furosine formation by 60, 45, 40 and 30%, respectively. 5-hydroxymethyl-2-furfural formation decreased in the presence of the extracts and protein glycation was inhibited by the thyme extract in advanced stages. Antiglycation activities were related to polyphenols content, to radical scavenging and to iron-reducing power. In the protein-sugar systems studied at the time in which 4000 ppm of furosine were formed, the antioxidant activity dropped between 30 and 40%. Polyphenols inhibit Maillard intermediates formation, revealing the incidence of oxidative pathways, but they are depleted as a function of time.

Cocoa melanoidins reduce the formation of dietary advanced glycation end-products in dairy mimicking system

The control of Maillard reaction in foods is important to preserve protein nutritional quality. In this study, we investigated the effects of melanoidins obtained from different roasted cocoa beans toward the formation of dietary advanced glycation end-products (d-AGEs) in aqueous solution of whey protein (WP) and glucose, glyoxal and methylglyoxal at 35 °C and pH 7.0. Cocoa melanoidins (4 mg/mL) were more effective to inhibit glyoxal-derived d-AGEs than methylglyoxal-derived d-AGEs, with 74.4% and 48% reduction of N-ε-carboxymethyllysine and methylglyoxal-hydroimidazolone formation in WP/glyoxal and WP/methylglyoxal system, respectively. Furthermore, protein-bound N-ε-fructosyllysine, measured through furosine, decreased down to 57.2% in presence of cocoa melanoidins in WP/glucose model system suggesting an effective control of the Maillard reaction in an early stage. These findings highlighted that cocoa melanoidins are functional ingredients able to mitigate protein glycation in dairy products during storage.

Metal cations promote α-dicarbonyl formation in glucose-containing peritoneal dialysis fluids

Heat sterilization of peritoneal dialysis fluids (PDFs) leads to the formation of glucose degradation products (GDPs), which impair long-term peritoneal dialysis. The current study investigated the effects of metal ions, which occur as trace impurities in the fluids, on the formation of six major α-dicarbonyl GDPs, namely glucosone, glyoxal, methylglyoxal, 3-deoxyglucosone, 3-deoxygalactosone, and 3,4-dideoxyglucosone-3-ene. The chelation of metal ions by 2-[bis[2-[bis(carboxymethyl)amino]ethyl]amino]acetic acid (DTPA) during sterilization significantly decreased the total GDP content (585 μM vs. 672 μM), mainly due to the decrease of the glucose-oxidation products glucosone (14 μM vs. 61 μM) and glyoxal (3 μM vs. 11 μM), but also of methylglyoxal (14 μM vs. 31 μM). The glucose-dehydration products 3-deoxyglucosone, 3-deoxygalactosone, and 3,4-dideoxyglucosone-3-ene were not significantly affected by chelation of metal ions. Additionally, PDFs were spiked with eleven different metal ions, which were detected as traces in commercial PDFs, to investigate their influence on GDP formation during heat sterilization. Iron(II), manganese(II), and chromium(III) had the highest impact increasing the formation of glucosone (1.2–1.5 fold increase) and glyoxal (1.3–1.5 fold increase). Nickel(II) and vanadium(III) further promoted the formation of glyoxal (1.3 fold increase). The increase of the pH value of the PDFs from pH 5.5 to a physiological pH of 7.5 resulted in a decreased formation of total GDPs (672 μM vs 637 μM). These results indicate that the adjustment of metal ions and the pH value may be a strategy to further decrease the content of GDPs in PDFs.

Quantification of dicarbonyl compounds in commonly consumed foods and drinks; presentation of a food composition database for dicarbonyls

Dicarbonyls are reactive precursors of advanced glycation endproducts. They are formed endogenously and during food processing. Currently, a comprehensive database on dicarbonyls in foods that covers the entire range of food groups is lacking, limiting knowledge about the amount of dicarbonyls that is ingested via food. The aim of this study was to analyze the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) in commonly-consumed products in a Western diet. We validated a UHPLC-MS/MS method to quantify MGO, GO, and 3-DG. We present a dietary dicarbonyl database of 223 foods and drinks. Total dicarbonyl concentrations were highest in dried fruit, Dutch spiced cake, and candy bars (>400 mg/kg). Total dicarbonyl concentrations were lowest in tea, dairy, light soft drinks, and rice (<10 mg/kg). The presented database of MGO, GO, and 3-DG opens the possibility to accurately estimate dietary exposure to these dicarbonyls, and explore their physiological impact on human health.

Effects of hydroxycinnamic acids on the reduction of furan and α-dicarbonyl compounds

The effects of hydroxycinnamic acids such as cinnamic acid (CNA), p-coumaric acid(CMA), caffeic acid (CFA), and chlorogenic acid (CGA) on the reduction of furan in canned-coffee model systems (CCMS) containing α-dicarbonyls [glyoxal (GO) or methylglyoxal (MGO)] were investigated. The concentration of furan in CCMS containing GO, which was 59.76 μg/L, was reduced by the addition of CFA and CGA to 48.31 μg/L and 41.38 μg/L, respectively; similarly, the furan concentration in model system containing MGO was 45.79 μg/L, and this decreased to 35.41 μg/L (by CFA) and 32.65 μg/L (by CGA), respectively. In addition, the effects of hydroxycinnamic acids on the trapping of GO and MGO were determined. CFA and CGA greatly reduced the concentration of GO to 303.51 μg/L and 267.80 μg/L, respectively (compared to 515.79 μg/L in the control), whereas that of MGO was decreased to 207.01 μg/L and 219.14 μg/L (compared to 417.14 μg/L in the control). The trapping of α-dicarbonyls such as GO and MGO by CFA and CGA could be closely related to furan reduction in CCMS.

Effect of pH on the reaction between naringenin and methylglyoxal: A kinetic study

Methylglyoxal (MGO) is a highly reactive ɑ-dicarbonyl compound that may adversely impact food quality and human health by modifying proteins. The kinetics of the reaction of naringenin with MGO was studied at pH 6-8 and 37 °C by UV-Vis spectrophotometry and reaction products were characterized by liquid chromatography-mass spectrometry (LC-MS/MS). The apparent second order rate constant (k₂) increased at pH above the lowest pKa value of naringenin, indicating deprotonated naringenin as the main reactant. A Lederer-Manasse type reaction mechanism is suggested, with dehydration of the MGO-dihydrate as a rate determining step. The quantitative data obtained in the present study was used to simulate the competitive reaction between MGO and nucleophilic amino acid residues (Lys, Arg and Cys) and naringenin in milk. It is predicted that naringenin will be able to efficiently trap MGO during storage of milk, although the reversible trapping of MGO by Cys residues is initially kinetically favourable.

Formation of allysine in β-lactoglobulin and myofibrillar proteins by glyoxal and methylglyoxal: Impact on water-holding capacity and in vitro digestibility

The ability of α-dicarbonyls, glyoxal (GO) and methyl-glyoxal (MGO) (2 M), to induce the formation of allysine in β-lactoglubulin (LAC), and myofibrillar proteins (MP) (2 mg/mL) during incubation at 80 °C for 48 h, was studied. Both GO and MGO induced the formation of allysine in all tested proteins with GO being more reactive (23.8 and 8.6 nmoles/mg protein in LAC and MP respectively after 6 h) than MGO (2.6 and 3.1 nmoles/mg protein at the same sampling point). LAC seemed to be more susceptible to the glycation reactions than MP. The concentration of allysine decreased at 24 h along with a concomitant increase of advanced-glycation end-products suggesting that allysine may be involved in the formation of fluorescent adducts. The water-holding capacity and trypsin-chymotrypsin digestibility of the proteins decreased during the incubation assay. The mechanisms by which α-dicarbonyls-mediated carbonylation likely influenced the impairment of such protein properties are thoroughly discussed.

Energy restriction and Roux-en-Y gastric bypass reduce postprandial α-dicarbonyl stress in obese women with type 2 diabetes

AIMS/HYPOTHESIS

Dicarbonyl compounds are formed as byproducts of glycolysis and are key mediators of diabetic complications. However, evidence of postprandial α-dicarbonyl formation in humans is lacking, and interventions to reduce α-dicarbonyls have not yet been investigated. Therefore, we investigated postprandial α-dicarbonyl levels in obese women without and with type 2 diabetes. Furthermore, we evaluated whether a diet very low in energy (very low calorie diet [VLCD]) or Roux-en-Y gastric bypass (RYGB) reduces α-dicarbonyl stress in obese women with type 2 diabetes.

METHODS

In lean (n = 12) and obese women without (n = 27) or with type 2 diabetes (n = 27), we measured the α-dicarbonyls, methylglyoxal (MGO), glyoxal (GO) and 3-deoxyglucosone (3-DG), and glucose in fasting and postprandial plasma samples obtained during a mixed meal test. Obese women with type 2 diabetes underwent either a VLCD or RYGB. Three weeks after the intervention, individuals underwent a second mixed meal test.

RESULTS

Obese women with type 2 diabetes had higher fasting and particularly higher postprandial plasma α-dicarbonyl levels, compared with those without diabetes. After three weeks of a VLCD, postprandial α-dicarbonyl levels in diabetic women were significantly reduced (AUC MGO -14%, GO -16%, 3-DG -25%), mainly through reduction of fasting plasma α-dicarbonyls (MGO -13%, GO -13%, 3-DG -33%). Similar results were found after RYGB.

CONCLUSIONS/INTERPRETATION

This study shows that type 2 diabetes is characterised by increased fasting and postprandial plasma α-dicarbonyl stress, which can be reduced by improving glucose metabolism through a VLCD or RYGB. These data highlight the potential to reduce reactive α-dicarbonyls in obese individuals with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01167959.