Comparison of two kinds of peroxyl radical pretreatment at chicken myofibrillar proteins glycation on the formation of Nε-carboxymethyllysine and Nε-carboxyethyllysine

Effects of 2,2'-Azobis(2-methylpropionamidine) Dihydrochloride Stress on the Gel Properties of Duck Myofibrillar Protein Isolate

The aim of this study was to investigate the biochemical properties and gel-forming capacity of duck myofibrillar proteins under the effects of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH)-mediated oxidation. Duck myofibrillar proteins were extracted and treated with different concentrations of AAPH solutions (0, 1, 3, 5, 10 mmol/L) and then analysed for carbonyl content, dynamic rheology, protein profiles and gel-forming properties (colour, water holding capacity, gel strength and microstructure). The results showed that with increasing AAPH concentration, the carbonyl content of the proteins exhibited an increasing trend (p < 0.05); SDS-PAGE pattern changes indicated that moderate oxidation (3 mmol/L AAPH) induced myosin aggregation via covalent bonds including disulfide, enhanced protein-protein interactions, and thus affected the gel strength of the DMPs' heat-induced gels. However, high oxidation (5 and 10 mmol/L AAPH) led to the partial degradation of the myosin heavy chain (MHC) isoforms, as evidenced by lower storage modulus and irregular microstructures, which significantly reduced gelation ability. These results suggest that the internal relationship between alkylperoxyl radical-induced oxidation should be taken into account in the processing of duck meat, as mild protein oxidation is conducive to improving gel quality.

Changes in glycated myofibrillar proteins conformation on the formation of Nε-carboxymethyllysine under gradient thermal conditions

N^ε-carboxymethyllysine (CML), a frequently used marker of advanced glycation end products (AGEs) in food, was generated in food processing easily and caused changes in myofibrillar proteins (MPs) characterization. The relevance between glycosylated MPs structure alternation and CML formation under thermal conditions have been reported. However, the correlation mechanism was not clear yet. In this work, the influence of gradient heating (50℃, 60℃, 70℃, 80℃, and 90℃) on the different degrees of glycated MPs, which determined the correlation with CML formation in protein structural changes of MPs. In the rising stage of the CML level, glycation accelerated the fibrillation and aggregation behavior of MPs during heating and increased surface hydrophobicity and particle size. The protein cross-linking affected the protein modification caused by heating and glycation. This work highlights the substantial influences of glycosylation and thermal treatments on MPs, which transformed the MPs structural characteristics and CML level.

Vegetable extracts: Effective inhibitors of heterocyclic aromatic amines and advanced glycation end products in roasted Mackerel

The formation of hazardous substances, heterocyclic aromatic amines (HAAs) and advanced glycation end products (AGEs), in roasted mackerel with different cooking temperatures (180, 210, 240 °C) and vegetable extracts (celery, carrot and yam extracts) in a preheated oven was investigated. The results indicated that the introduction of vegetable extracts had inhibitory effects on HAAs and AGEs during thermal processing, especially celery extracts. Benefiting from the addition of vegetable extracts, the roasted mackerel keep high quality against lipid/protein oxidation, avoids nutrition loss of polyunsaturated fatty acids, and flavor is promoted. We also examined the variation of key precursors, including creatine, creatinine, reducing sugars, amino acids and attempted to explain the molecular pathway of inhibition of the formation of the hazardous substances by vegetable extracts. The results provide theoretical support to develop technologies for inhibiting hazardous substances formation during fish processing, which is important for food manufacturers and consumers for producing healthier meat products.

Insight into the effect of traditional frying techniques on glycosylated hazardous products, quality attributes and flavor characteristics of grass carp fillets

This study aimed to evaluate the evolution of quality attributes, oxidation index, glycosylated hazardous products, aroma characteristics of grass carp fillets and their relationship under air-frying, roast-frying and pan-frying. With frying progressed, the level of carbonyl protein and lipid oxidation products increased significantly (following air-frying > pan-frying > roast-frying), and the latter decreased subsequently after 6 min. Fillets possessed by frying increased significantly N^ε-carboxymethyl-lysines (CML) and 5-hydroxymethylfurfural (5-HMF) levels, whose increment was pan-frying > air-frying > roast-frying. Compared to raw, eighty-seven volatiles were identified and the total concentrations of those increased gradually in air-frying, but then decreased up to 6 min in roast-frying and pan-frying. Furthermore, significant correlations between CML, TBARS and 5-HMF, quality attributes, oxidation index; volatiles (VIP and/or OAV > 1) and lipid oxidation index were obtained. Conclusively, fillets possessed by air-/roast-frying showed more lipid oxidation and alcohols/aldehydes, while pan-fried enriched CML and pyrazines.

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.

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.

Changing the IgE Binding Capacity of Tropomyosin in Shrimp through Structural Modification Induced by Cold Plasma and Glycation Treatment

Tropomyosin (TM) is the major allergen of shrimp (Penaeus chinensis). Previous studies showed that separate cold plasma or glycation have their drawback in reducing allergenicity of TM, including effectiveness and reliability. In the current study, a new processing combining cold plasma (CP) and glycation was proposed and its effect on changing IgE binding capacity of TM from shrimp was investigated. Obtained results showed the IgE binding capacity of TM was reduced by up to 40% after CP (dielectric barrier discharge, 60 kV, 1.0 A) combined with glycation treatment (4 h, 80 °C), compared with the less than 5% reduction after single CP or glycation treatment. Notably, in contrast to the general way of CP prompting glycation, this study devised a new mode of glycation with ribose after CP pretreatment. The structural changes of TM were explored to explain the decreased IgE binding reactivity. The results of multi-spectroscopies showed that the secondary and tertiary structures of TM were further destroyed after combined treatment, including the transformation of 50% α-helix to β-sheet and random coils, the modification and exposure of aromatic amino acids, and the increase of surface hydrophobicity. The morphology analysis using atomic force microscope revealed that the combined processing made the distribution of TM particles tend to disperse circularly, while it would aggregate after either processing treatment alone. These findings confirmed the unfolding and reaggregation of TM during combined processing treatment, which may result in the remarkable reduction of IgE binding ability. Therefore, the processing of CP pretreatment combined with glycation has the potential to reduce or even eliminate the allergenicity of seafood.

Improving physicochemical properties of myofibrillar proteins from wooden breast of broiler by diverse glycation strategies

The effect of diverse glycation strategies on the physicochemical and structural properties of wooden breast myofibrillar protein (WBMP) were studied. The WBMP was mixed with D-ribose (RI), sodium alginate (SA), and glucosamine (GH) respectively in a weight ratio of 1:2 (w/w) at 70 °C, and was heated for 6 h. Atomic force microscopy and particle size results showed that the glycation reaction in the presence of RI made WBMP to be more evenly dispersed in the solution and had a significantly smaller particle size (78-955 nm, average 361.06 nm) (P < 0.05). There was an increase in WBMP-RI solubility (76.23 ± 0.56%) and α-helix content (51.23 ± 1.1%) than other groups. Compared with WBMP-RI, WBMP-SA and WBMP-GH have poor performance in particle distribution, solubility and emulsification. This study clarified the aldehyde group in aldose was more suitable for the glycation modification of WBMP than the ketone group in ketose.

Effects of Peroxyl Radicals on the Structural Characteristics and Fatty Acid Composition of High-Density Lipoprotein from Duck Egg Yolk

In this study, high-density lipoprotein (HDL) from duck egg yolk was subjected to oxidation with a system based on 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-derived peroxyl radicals. The effects of peroxyl radicals on the protein carbonyl, free sulfhydryl, secondary/tertiary structure, surface hydrophobicity, solubility, particle size distribution, zeta potential and fatty acid composition of HDL were investigated by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared spectroscopy (FTIR), circular dichroism (CD), fluorescence spectroscopy, dynamic light scattering and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The results indicated that the content of protein carbonyl was significantly increased, that of free sulfhydryl was obviously reduced, and the ordered secondary structure was also decreased with increasing AAPH concentration. In addition, the surface hydrophobicity and solubility of HDL showed apparent increases due to the exposure of hydrophobic groups and aggregation of protein caused by oxidation. The fatty acid composition of HDL exhibited pronounced changes due to the disrupted protein–lipid interaction and lipid oxidation by AAPH-derived peroxyl radicals. These results may help to elucidate the molecular mechanism for the effect of lipid oxidation products on the oxidation of duck yolk proteins.

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.