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

Glucose addition and oven-heating of pork stimulate glycoxidation and protein carbonylation, while reducing lipid oxidation during simulated gastrointestinal digestion

In the present study, it was investigated if glucose addition (3 or 5%) to pork stimulates glycoxidation (pentosidine, PEN), glycation (Maillard reaction products, MRP), lipid oxidation (4-hydroxy-2-nonenal, 4-HNE; hexanal, HEX; thiobarbituric acid reactive substances, TBARS), and protein oxidation (protein carbonyl compounds, PCC) during various heating conditions and subsequent in vitro gastrointestinal digestion. An increase in protein-bound PEN level was observed during meat digestion, which was significantly stimulated by glucose addition (up to 3.3-fold) and longer oven-heating time (up to 2.5-fold) of the meat. These changes were accompanied by the distinct formation of MRP during heating and digestion of the meats. Remarkably, stimulated glyc(oxid)ation was accompanied by increased protein oxidation, whereas lipid oxidation was decreased, indicating these reactions are interrelated during gastrointestinal digestion of meat. Glucose addition generally didn't affect these oxidative reactions when pork was packed preventing air exposure and oven-heated until a core temperature of 75 °C was reached.

Modification of casein with oligosaccharides via the Maillard reaction: As natural emulsifiers

In the present study, different oligosaccharides (fructooligosaccharide (FOS), galactooligosaccharide (GOS), isomaltooligosaccharide (IMO), and xylooligosaccharide (XOS)) were modified on casein (CN) via Maillard reaction. The CN-oligosaccharide conjugates were evaluated for modifications to functional groups, fluorescence intensity, water- and oil-holding properties, emulsion foaming properties, as well as general emulsion properties and stability. The results demonstrated that the covalent combination of CN and oligosaccharides augmented the spatial repulsion and altered the hydrophobic milieu of proteins, which resulted in a diminution in water-holding capacity, an augmentation in oil-holding capacity, and an enhancement in the emulsification properties of proteins. Among them, CN-XOS exhibited the most pronounced changes, with the emulsification activity index and emulsion stability index increasing by approximately 72% and 84.3%, respectively. Furthermore, CN-XOS emulsions have smaller droplet sizes and higher absolute potential values than CN emulsions. Additionally, CN-XOS emulsions demonstrate remarkable stability when ion concentration and pH are varied. These findings indicate that oligosaccharides modified via Maillard reaction can be used as good natural emulsifiers. This provides a theoretical basis for using oligosaccharides to modify proteins and act as natural emulsifiers.

Natural antioxidants (rosemary and parsley) in microwaved ground meat patties: effects of in vitro digestion

BACKGROUND

Minimizing food oxidation remains a challenge in several environments. The addition of rosemary extract (150 mg kg-1) and lyophilized parsley (7.1 g kg-1) at equivalent antioxidant activity (5550 μg Trolox equivalents kg-1) to meat patties was assessed in terms of their effect during microwave cooking and after being subjected to an in vitro digestion process.

RESULTS

Regardless of the use of antioxidants, cooking caused a decrease of the fat content as compared to raw samples, without noticing statistical differences in the fatty acid distribution between raw and cooked samples [44%, 47% and 6.8%, of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA), respectively]. However, the bioaccessible lipid fraction obtained after digestion was less saturated (around 34% SFA) and more unsaturated (35% MUFA +30% PUFA). Cooking caused, in all types of samples, an increased lipid [thiobarbituric acid reactive substances (TBARS)] and protein (carbonyls) oxidation values. The increase of TBARS during in vitro digestion was around 7 mg malondialdehyde (MDA) kg-1 for control and samples with parsley and 4.8 mg MDA kg-1 with rosemary. The addition of parsley, and particularly of rosemary, significantly increased the antioxidant activity (DPPH) of cooked and digested microwaved meat patties.

CONCLUSION

Whereas rosemary was effective in minimizing protein oxidation during cooking and digestion as compared to control samples, parsley could only limit it during digestion. Lipid oxidation was only limited by rosemary during in vitro digestion. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of Sustained Fructose Consumption on Gastrointestinal Function and Health in Wistar Rats: Glycoxidative Stress, Impaired Protein Digestion, and Shifted Fecal Microbiota

The gastrointestinal tract (GIT) is the target of assorted pathological conditions, and dietary components are known to affect its functionality and health. In previous in vitro studies, we observed that reducing sugars induced protein glycoxidation and impaired protein digestibility. To gain further insights into the pathophysiological effects of dietary sugars, Wistar rats were provided with a 30% (w/v) fructose water solution for 10 weeks. Upon slaughter, in vivo protein digestibility was assessed, and the entire GIT (digests and tissues) was analyzed for markers of oxidative stress and untargeted metabolomics. Additionally, the impact of sustained fructose intake on colonic microbiota was also evaluated. High fructose intake for 10 weeks decreased protein digestibility and promoted changes in the physiological digestion of proteins, enhancing intestinal digestion rather than stomach digestion. Moreover, at colonic stages, the oxidative stress was harmfully increased, and both the microbiota and the intraluminal colonic metabolome were modified.

The pro-oxidant action of high-oxygen MAP on beef patties can be counterbalanced by antioxidant compounds from common hawthorn and rose hips

The objective of this research was to evaluate the effectiveness of antioxidant-rich extracts from rose hip (Rosa canina L.; RC) and hawthorn (Crataegus monogyna Jacq.; CM) at minimizing the oxidative damage to proteins and lipids in beef patties subjected to a high‑oxygen (HiOx-MAP) and vacuum (Vacuum) packaging atmosphere. The extracts of RC and CM were characterized by quantifying bioactive compounds, namely, phenolic compounds, tocopherols and vitamin C. Both fruits had high concentrations of bioactive compounds, with RC having the highest total phenolic and vitamin C content. Yet, CM was the most efficient in protecting beef patties against protein carbonylation, reducing, as a result, the instrumental toughness in cooked beef patties. The use of CM and RC extracts in beef patties significantly improved consumer purchase intention in HiOx-MAP packaging systems. The use of CM and RC extracts or their combination in future research would be an effective antioxidant means to decrease the pro-oxidative effects caused by HiOx-MAP in red meat.

Sustainable polylactide materials with the function of blocking a specific wavelength of light based on aloe-emodin

Polylactide, a biodegradable polymer, can alleviate white pollution, but the use of polylactide in food packaging is limited by high transmittance to light with a specific wavelength, UV (185-400 nm) and short-wavelength visible (400-500 nm) light. Herein, the polylactide end-capped with renewable light absorber aloe-emodin (PLA-En), is blended with commercial polylactide (PLA) to fabricate the polylactide film with the function of blocking light with a specific wavelength, PLA/PLA-En film. Only 40 % of light around 287 and 430 nm transmits through PLA/PLA-En film incorporating 3 mass% of PLA-En, while the film still maintains good mechanical properties and high transparency more than 90 % at 660 nm because of the good compatibility with PLA. The PLA/PLA-En film exhibits stable light-blocking properties under light irradiation and anti-solvent migration under the immersion of fat simulant. Almost no PLA-En migrated out of the film with the molecular weight of PLA-En only 2.89 × 104 g/mol. Compared with PLA film and commercial PE plastic wrap, the designed PLA/PLA-En film exhibits a better preservative effect on riboflavin and milk for inhibiting the production of 1O2. This study offers a green strategy for developing UV and short-wavelength light protective food package film based on renewable resource.

Effect of different stunning methods on antioxidant status, myofibrillar protein oxidation, and gelation properties of large yellow croaker during postmortem

Post-mortem muscle biochemical processes play a crucial role on fish fillets quality and they are strictly linked to stunning methods. The improper stunning methods before slaughter could cause the fish to deteriorate more quickly during cold storage. This study aimed to investigate the effect of stunning methods (hit on the head, T₁; gill cut, T₂; immersion in ice/water slurry, T₃; CO₂ narcosis, T₄; 40% CO₂ + 30 % N₂ + 30% O₂, T₅) on myofibrillar proteins (MPs) of large yellow croaker. The results indicated that T₂ and T₃ samples were significantly damaged compared with other samples, which reflected that the activities of total superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were significantly damaged during cold storage in T₂ and T₃ samples. And the gill cut and immersion in ice/water slurry resulted in the generation of protein carbonyl, the decrease of Ca²⁺-ATPase, free ammonia and protein solubility, and the production of dityrosine during storage. In addition, MPs gel of T₂ and T₃ samples showed the decrease of water hold capacity (WHC) and whiteness, structure destruction, and water migration. The T₄ samples had the least damage of MPs and gel structure during cold storage.

Moderate Protein Oxidation Improves Bovine Myofibril Digestibility by Releasing Peptides in the S2 Region of Myosin: A Peptidomics Perspective

This study aimed to investigate the influence of protein oxidation on the digestive properties of beef myofibrillar protein (MP). MP was treated with a hydroxyl radical-generating system containing various concentrations of H₂O₂. The increased content in a free sulfhydryl group and surface hydrophobicity indicated that oxidation treatment with 1 mM H₂O₂ induced unfolding of MP. Reducing and nonreducing SDS-PAGE results suggested that 10 mM H₂O₂ oxidation treatment resulted in aggregation of MP; meanwhile, the disulfide bond was the major covalent bond involved in aggregation. Peptidomics showed that peptides in the digestion products of MP were mainly derived from myosin tail. Moderate oxidation (1 mM H₂O₂) facilitated the release of peptide in the rod portion (S2) of myosin, whereas excessive oxidation (10 mM H₂O₂) inhibited peptide release in the light meromyosin region. This work presents insightful information for the crucial impact of oxidation on meat protein digestibility from the peptidomics perspective.

Kilning invokes oxidative changes in malt proteins

Beneath glycation, oxidation reactions may take place at cereal proteins during production of malt. The extent of oxidative chemical changes at malt proteins has not yet been studied. In the present short communication, malt protein was characterized by the determination of free thiol groups and degree of methionine oxidation as well as the sites that are reactive to covalent modification by 2,4-dinitrophenylhydrazine (DNPH, “protein carbonylation”). Protein carbonylation in pale malts was around 1.5 nmol/mg protein and increased with increasing malt colour. Investigations on the protein pellet isolated for determination of carbonylation revealed that solubility and colour may disturb the quantification of carbonyl sites in roasted malts. Free thiols decreased with increasing malt colour already in pale malts (EBC < 10). The formation of methionine sulfoxide (MetSO) was intensified with increasing malt colour. An amount of 7–20% of methionine was converted to MetSO in pale and dark malt, whereas nearly 60% of methionine was oxidized to MetSO in roasted malts. The formation of methionine sulfone was negligible. This study shows that malt proteins suffer from oxidation during kilning, and future studies will have to show whether this supports the pro- or antioxidant activity of malt.

Dietary oxidized beef protein alters gut microbiota and induces colonic inflammatory damage in C57BL/6 mice

This study aimed to investigate the effect of oxidized beef protein on colon health. C57BL/6 mice were fed diets containing in vitro oxidized beef protein (carbonyl content 5.83/9.02 nmol/mg protein) or normal beef protein (control group, carbonyl content 2.27 nmol/mg protein) for 10 weeks. Histological observations showed that oxidized beef protein diet induced notable inflammatory cell infiltrations in colon. The analysis of high-throughput sequencing indicated oxidized beef protein largely altered the composition of gut microbiota (GM) by increasing proinflammatory bacteria (Desulfovibrio, Bacteroides, Enterorhabdus) while reducing beneficial bacteria (Lactobacillus, Akkermansia). In addition, oxidized beef protein remarkably increased protein fermentation in the colon, which was evidenced by the elevated i-butyrate, i-valerate, and ammonia levels in feces. Furthermore, consuming oxidized beef protein destroyed colon barrier functions by decreasing tight junction proteins expression. These changes in colonic ecosystem activated the proinflammatory pathway of lipopolysaccharide/toll-like receptor-4/nuclear factor kappa B (LPS/TLR-4/NF-κB), eventually leading to colonic inflammatory damage in mice. Taken together, these results imply that consuming oxidized beef protein detrimentally regulates GM and impairs colon health.

Glucose boosts protein oxidation/nitration during simulated gastric digestion of myofibrillar proteins by creating a severe pro-oxidative environment

The severe pro-oxidative environment in the stomach promotes oxidation of dietary components. The pro-oxidant molecular mechanisms of reducing sugars on this environment are unknown. To investigate the mechanisms involved in protein oxidation and nitration during a simulated gastric digestion (porcine pepsin, 37 °C, 2 h) of meat proteins, these were exposed to several dietary reactive components namely myoglobin, glucose, glyoxal, myoglobin + glucose and myoglobin + glyoxal. Two versions of each experimental unit were prepared depending on the addition or absence of nitrite. Compared to control (only meat proteins), myoglobin + glucose showed the highest pro-oxidative and pro-nitrosative effect (p < 0.001), likely caused by an increase in ROS derived from the degradation of glucose during assay. Nitrite promoted the occurrence of protein nitration but decreased protein oxidation in myoglobin-added groups (p < 0.001) by, plausibly, stabilizing heme iron. These results indicate the relevant role of glyco-oxidation during digestion of red meat with other dietary components such as reducing sugars.

Effect of Malondialdehyde on the Digestibility of Beef Myofibrillar Protein: Potential Mechanisms from Structure to Modification Site

Lipid oxidation and protein oxidation occur side by side in meat. Here, the effect of malondialdehyde (MDA), the major product of lipid oxidation, on the digestibility of beef myofibrillar proteins (MP) was studied. MP samples were incubated with 0, 0.1, 0.3, 0.5, and 0.7 mM MDA at 4 °C for 12 h and then subjected to in vitro gastrointestinal digestion. The result showed that MDA remarkably reduced the digestibility of MP (p < 0.05). MDA treatments significantly increased carbonyl and Schiff base contents in MP (p < 0.05). The microstructure observed by atomic force microscopy showed that MDA treatments resulted in the aggregation of MP. Non-reducing and reducing electrophoresis suggested the aggregation was mainly caused by covalent bonds including disulfide bond and carbonyl−amine bond. Proteomics analysis proved that the myosin tail was the main target of MDA attack, meanwhile, lysine residues were the major modification sites. Taken together, the above results imply that MDA induces protein oxidation, aggregation, and blockage of hydrolysis sites, consequently leading to the decrease in both gastric and gastrointestinal digestibility of MP.

Deciphering Changes in the Structure and IgE-Binding Ability of Ovalbumin Glycated by α-Dicarbonyl Compounds under Simulated Heating

As a complex reaction, biological consequences of the Maillard reaction (MR) on dietary proteins need to be deciphered. Despite previous studies on the structural and antigenic properties of ovalbumin (OVA) by MR, associated changes induced by specific MR intermediates and their downstream products are largely unknown. This study focused on the impacts of glycation by α-dicarbonyl compounds (α-DCs), intermediates of MR and precursors of advanced glycation end-products (AGEs), on the structural and IgE-binding properties of ovalbumin (OVA) under simulated heating. Methylglyoxal (MGO), glyoxal (GO), and butanedione (BU) were selected as typical α-DCs to generate glycated OVA with different AGE-modifications (AGE-Ms). The results showed that reactions between OVA and α-DCs generated OVA-AGE with various degrees of modification and conformational unfolding, and the reactivity of α-DCs followed the order GO > MGO > BU. Depending on the precursor type, the levels of 10 specific AGEs were verified, and the amounts of total AGEs increased with heating temperature and α-DC dosage. Compared to native OVA, glycated OVA showed reduced IgE-binding levels but with sRAGE-binding ligands, the extent of which was associated with the contents of total AGEs and Nε-carboxymethyllysine, and changes in certain protein conformational structures. High-resolution mass spectrometry further identified different AGE-Ms on the Lys and Arg residues of OVA, confirming variations in the glycation sites and their associations with the immunoreactive epitopes of OVA under different conditions.

Molecular mechanisms of the disturbance caused by malondialdehyde on probiotic Lactobacillus reuteri PL503

This study aimed to provide insight into the molecular and genetic mechanisms implicated in the responses of Lactobacillus reuteri against the oxidative stress induced by malondialdehyde (MDA) by analysing protein oxidation and assessing the uspA and the dhaT genes. Four experimental groups were evaluated depending on the concentration of MDA added in Man, Rogosa and Sharpe (MRS) broth: Control (L. reuteri), 5 µM (L. reuteri + 5 µM MDA), 25 µM (L. reuteri + 25 µM MDA) and 100 µM (L. reuteri + 100 µM MDA). Three replicates were incubated at 37 °C for 24 h in microaerophilic conditions and sampled at 12, 16, 20 and 24 h. The upregulation of the uspA gene by L. reuteri indicates the recognition of MDA as a potential DNA-damaging agent. The dhaT gene, encoding a NADH-dependent-oxidoreductase, was also upregulated at the highest MDA concentrations. This gene was proposed to play a role in the antioxidant response of L. reuteri. The incubation of L. reuteri with MDA increased the production of ROS and caused thiol depletion and protein carbonylation. L. reuteri is proposed to detoxify pro-oxidative species while the underlying mechanism requires further elucidation.

Protein carbonylation in food and nutrition: a concise update

Protein oxidation is a topic of indisputable scientific interest given the impact of oxidized proteins on food quality and safety. Carbonylation is regarded as one of the most notable post-translational modifications in proteins and yet, this reaction and its consequences are poorly understood. From a mechanistic perspective, primary protein carbonyls (i.e. α-aminoadipic and γ-glutamic semialdehydes) have been linked to radical-mediated oxidative stress, but recent studies emphasize the role alternative carbonylation pathways linked to the Maillard reaction. Secondary protein carbonyls are introduced in proteins via covalent linkage of lipid carbonyls (i.e. protein-bound malondialdehyde). The high reactivity of protein carbonyls in foods and other biological systems indicates the intricate chemistry of these species and urges further research to provide insight into these molecular mechanisms and pathways. In particular, protein carbonyls are involved in the formation of aberrant and dysfunctional protein aggregates, undergo further oxidation to yield carboxylic acids of biological relevance and establish interactions with other biomolecules such as oxidizing lipids and phytochemicals. From a methodological perspective, the routine dinitrophenylhydrazine (DNPH) method is criticized not only for the lack of accuracy and consistency but also authors typically perform a poor interpretation of DNPH results, which leads to misleading conclusions. From a practical perspective, the biological relevance of protein carbonyls in the field of food science and nutrition is still a topic of debate. Though the implication of carbonylation on impaired protein functionality and poor protein digestibility is generally recognized, the underlying mechanism of such connections requires further clarification. From a medical perspective, protein carbonyls are highlighted as markers of protein oxidation, oxidative stress and disease. Yet, the specific role of specific protein carbonyls in the onset of particular biological impairments needs further investigations. Recent studies indicates that regardless of the origin (in vivo or dietary) protein carbonyls may act as signalling molecules which activate not only the endogenous antioxidant defences but also implicate the immune system. The present paper concisely reviews the most recent advances in this topic to identify, when applicable, potential fields of interest for future studies.

Effect of L-calcium lactate, zinc lactate, and ferric sodium EDTA on the physicochemical and functional properties of liquid whole egg

The study aimed to evaluate the physicochemical and functional properties of liquid whole egg (LWE) with L-calcium lactate (L-Ca), zinc lactate (L-Zn), and sodium ferric EDTA (NaFeEDTA), and to compare with NaCl addition to determine the application potential of these mineral supplements. Results showed that salts addition significantly influenced the foaming, emulsifying, and gelling properties of LWE, which was possible through affecting the pH, particle size, surface hydrophobicity, apparent viscosity, and solubility. The addition of all the four salts reduced pH but increased the d_4,3 diameter of LWE. Additionally, the addition of 200 mM L-Ca and 6 mM L-Zn significantly improved the emulsifying capacity by 41.73% and 13.6%, the foaming capacity by 26.57% and 10%, and the protein solubility by 13.89% and 12.70%, respectively. In the meantime, mineral supplements tend to produce lower hardness gel, especially with 25 mM L-Ca and 8 mM L-Zn, and the hardness was decreased from 2401.13 to 1138.29 and 1175.59 g, respectively. A relative decrease in hardness was desirable in gelled egg products. Moreover, the addition of NaCl and L-Ca showed a higher redness and yellowness, but the addition of NaFeEDTA showed an undesirable color in dark brown, which may be not accepted by the public. In summary, L-Ca and L-Zn had great potential for application in LWE, which was more appropriate than adding NaCl. This study provides a basis for improving the functional properties of LWE products in the future. PRACTICAL APPLICATION: The addition of L-Ca and L-Zn to liquid whole egg (LWE) could improve the foaming and emulsifying capacity of LWE as well as produce a lower hardness gel, which may be more conducive to the production of cake, custards, and meat products. Meantime, it is more in line with people's pursuit of a healthy diet.

Critical overview of the use of plant antioxidants in the meat industry: Opportunities, innovative applications and future perspectives

The number of articles devoted to study the effect of "natural antioxidants" on meat systems has remarkably increased in the last 10 years. Yet, a critical review of literature reveals recurrent flaws in regards to the rationale of the application, the experimental design, the characterisation of the plant sources, the discussion of the molecular mechanisms and of the potential benefits. The selection of the appropriate source of these antioxidants and the identification of their bioactive constituents, are essential to understand their mode of action and set effective and safe doses. The methodological approach should also be planned with care as the recorded effects and main conclusions largely depend on the accuracy and specificity of the methods. This article aims to critically review the recent advances in the application of plant antioxidants in meat and meat products and briefly covers current trends of innovative application and future trends.

Effect of methylglyoxal on the alteration in structure and digestibility of α-lactalbumin, and the formation of advanced glycation end products under simulated thermal processing

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.

Adverse Effects of Thermal Food Processing on the Structural, Nutritional, and Biological Properties of Proteins

Thermal processing is one of the most important processing methods in the food industry. However, many studies have revealed that thermal processing can have detrimental effects on the nutritional and functional properties of foods because of the complex interactions among food components. Proteins are essential nutrients for humans, and changes in the structure and nutritional properties of proteins can substantially impact the biological effects of foods. This review focuses on the interactions among proteins, sugars, and lipids during thermal food processing and the effects of these interactions on the structure, nutritional value, and biological effects of proteins. In particular, the negative effects of modified proteins on human health and strategies for mitigating these detrimental effects from two perspectives, namely, reducing the formation of modified proteins during thermal processing and dietary intervention in vivo, are discussed.

Allysine and α-Aminoadipic Acid as Markers of the Glyco-Oxidative Damage to Human Serum Albumin under Pathological Glucose Concentrations

Understanding the molecular basis of the disease is of the utmost scientific interest as it contributes to the development of targeted strategies of prevention, diagnosis, and therapy. Protein carbonylation is a typical feature of glyco-oxidative stress and takes place in health disorders such as diabetes. Allysine as well as its oxidation product, the α-amino adipic acid (α-AA) have been found to be markers of diabetes risk whereas little is known about the chemistry involved in its formation under hyperglycemic conditions. To provide insight into this issue, human serum albumin was incubated in the presence of FeCl3 (25 μM) and increasing glucose concentrations for 32 h at 37 °C. These concentrations were selected to simulate (i) physiological fasting plasma concentration (4 mM), (ii) pathological pre-diabetes fasting plasma concentration (8 mM), and pathological diabetes fasting plasma concentration (12 mM) of glucose. While both allysine and α-AA were found to increase with increasing glucose concentrations, the carboxylic acid was only detected at pathological glucose concentrations and appeared to be a more reliable indicator of glyco-oxidative stress. The underlying chemical mechanisms of lysine glycation as well as of the depletion of tryptophan and formation of fluorescent and colored advanced glycation products are discussed.

Effectiveness of Sprayed Bioactive Fruit Extracts in Counteracting Protein Oxidation in Lamb Cutlets Subjected to a High-Oxygen MAP

High-oxygen packaging atmosphere (High-Ox-MAP) promotes meat protein oxidation and leads to texture deterioration. This study was conceived to assess the extent to which sprayed fruit extracts could inhibit the oxidative damage to proteins in lamb cutlets subjected to High-Ox-MAP (10 days/4 °C) and subsequent roasting (10 min/180 °C). Extracts from oaknut (Quercus ilex subsp. ballota; QI), rose hips (Rosa canina L.; RC), common hawthorn (Crataegus monogyna Jacq.; CM) and strawberry tree (Arbutus unedo L.; AU) were characterized for bioactive compounds (phenolic subclasses, tocopherols and ascorbic acid) and in vitro bioactivities. While the four fruits showed relevant antioxidant potential, CM had the highest phenolics and tocopherol content and that was reflected in efficient antiradical activity. The in vitro activity of this fruit to inhibit meat protein oxidation was, however, lower than that displayed by the other fruits. Taking the results altogether, CM was also found to be most efficient in protecting lamb cutlets from lipid oxidation. All fruits were able to inhibit thiols oxidation except RC, which seemed to reduce protein thiols. Among fruits, QI was the most efficient in protecting lamb cutlets against protein carbonylation as a plausible involvement of ellagitannins. The inhibition of protein oxidation by QI was reflected in significantly lower instrumental hardness in cooked lamb cutlets. Spraying lamb cutlets with extracts from QI, RC and CM improved consumers' purchase intention after chilled storage. This antioxidant strategy seems to be a feasible and efficient solution to the pro-oxidative effects caused by High-Ox-MAP in red meat.

Analysis of Protein Oxidation in Food and Feed Products

Food and feed proteins are subject to oxidation reactions during production, processing, and storage. Several individual oxidized amino acids have been described in model systems and food; however, protein oxidation in food is still mostly assessed by the analysis of protein carbonylation. In the present review, the chemistry of protein oxidation and its implications for protein functionality, food flavor, and nutritional physiology are briefly summarized. Limitations of generic methods targeting redox-relevant functional groups and properties of typical reaction products, such as the determination of protein carbonyls and fluorescence spectroscopy, are presented. Methods for the quantitation of individual oxidation products of susceptible amino acids, such as cysteine, methionine, phenylalanine, tyrosine, and tryptophan, are reported. Special regard is paid to limitations resulting from the required hydrolysis procedures and unintended formation of the analytes during sample pretreatment. If available, results from food analysis obtained by different methods are compared. Suggestions and requirements for future works on protein oxidation in food and nutrition are given.

Noxious effects of selected food-occurring oxidized amino acids on differentiated CACO-2 intestinal human cells

The harmful effects of food-occurring oxidized amino acids, namely, aminoadipic acid (AAA), dityrosine (DTYR), L-kynurenine (KN), kynurenic acid (KA) and 3-nitrotyrosine (3NT), were studied on differentiated CACO-2 cells by flow cytometry and quantification of glutathione (GSH), and allysine. Cells were exposed to food-relevant doses (200 μM) of each compound for 4 or 72h and compared to a control (no stimulated cells). All oxidized amino acids induced apoptosis and results indicated that underlying mechanisms depended on the chemical nature of the species. AAA, KN and KA caused ROS generation and severe oxidative stress in 96%, 98% and 89% of exposed cells (77% in control cells), leading to significant GSH depletion and allysine accretion (1.5, 1.5 and 1.6 nmol allysine/mg protein, respectively at 4h; control: 0.22 nmol/mg protein; p < 0.05). DTYR and 3NT induced significant apoptosis to 29% and 25% of cells (control: 16%; p < 0.05) and necrosis to 28% and 26% of cells (control: 23%) at 72h by ROS-independent mechanisms. KN and KA were found to induce a cycle arrest effect on CACO-2 cells. These findings emphasize the potential harmful effects of the intake of oxidized proteins and amino acids and urge the necessity of carrying out further molecular studies.

Study on quality characteristics of cassava flour and cassava flour short biscuits

In this paper, the basic components, nutrient composition, and processing characteristics of cassava flour were determined. In addition, the effects of xanthan gum and inulin on the pasting properties, microstructure, and thermal properties of cassava flour were studied. Biscuits were prepared using cassava flour as the main raw material and the optimal technology and formula for the biscuits were determined by single-factor and orthogonal tests. The effects of xanthan gum and inulin on the quality of cassava flour short biscuits were also investigated, and volatile components in the biscuits were determined using electronic nose technique. The addition of xanthan gum improved the pasting properties and microstructure of cassava flour, and improved the taste and increased hardness and brittleness of the biscuits, making their quality similar to that of commercially available short biscuits. The addition of inulin inhibited the setback of starch and improved starch gelatinization. However, inulin was not suitable for processing of cassava flour biscuits as it decreased their hardness, brittleness, and taste. The optimal formula and baking conditions of cassava flour short biscuits were as follows: cassava flour 100 g, water 24 g, shortening 25 g, sugar 30 g, baking powder 0.6 g, salt 1 g, and egg 25 g; the surface fire and primer fire temperatures were 180°C, and the baking time was 9 min. In addition, although the main aroma volatile components present in cassava flour and low gluten wheat flour short biscuits were similar, the proportions of each component were different.

Effect of hydroxyl radicals on biochemical and functional characteristics of myofibrillar protein from large yellow croaker (Pseudosciaena crocea)

The oxidative modification effect of hydroxyl radicals generated by an H₂ O₂ oxidative solution on the biochemical and functional characteristics of myofibrillar protein (MP) from large yellow croaker (Pseudosciaena crocea) was investigated. The results showed that MP of large yellow croakers was vulnerable to hydroxyl radicals. Incubation of MP with increased concentration of H₂ O₂ led to the gradual formation of carbonyl derivatives, disulphide bonds and dityrosine, and loss of available lysine, sulphydryl, and free ammonia. Surface hydrophobicity increased, while tryptophan residues decreased, indicating a conformational transition of MP. SDS-PAGE demonstrated that both disulphide and nondisulphide bonds were involved in MP aggregation. The MP functionalities were also affected by hydroxyl radicals, including reduced solubility, gelling, and emulsifying properties. Mild oxidation (0.1 mM H₂ O₂ ) slightly improved MP gel strength and water-holding capacity, while excessive oxidation caused a reduction in gel properties. The results suggested that the MP oxidation should be controlled. PRACTICAL APPLICATIONS: Protein oxidation mediated by hydroxyl radicals is one of the most crucial reasons affecting the quality of large yellow croaker during processing and storage. Additionally, it is well known that the quality of protein in fish systems directly determines the quality stability and nutritional value of the fish products. Hence, the study explored how the hydroxyl radicals influenced the physicochemical and functional properties of fish MP. The changes in amino acid residues (carbonyl, available lysine, sulphydryl, free ammonia, tryptophan residues, etc.) of MP and its gelling and emulsifying properties after oxidation not only benefit the awareness of quality deterioration and quality control of large yellow croaker, but also provide a basis for the understanding of protein oxidation on the nutritional value of aquatic products and human health.

Metabolite Profile Differences Among Different Storage Time in Beef Preserved at Low Temperature

Storage temperature influences meat color stability and quality. This study was performed to quality change-associated metabolites profiles using a nontargeted liquid chromatography-mass spectrometry (LC-MS/MS)-based method. Beef longissimus dorsi samples were purchased immediately after slaughter, and then stored at room temperature, 4 °C and 0 °C. Water holding capacity (WHC), moisture content and pH value of the muscle samples were detected. Muscle samples and quality control samples were then prepared for nontargeted LC-MS/MS system, followed by identification of distinct metabolites. Pearson correlation coefficients between metabolites and quality indexes were calculated. Storage reduced pH values of beef, and room temperature and 4 °C displayed the lowest pH value. Moisture content and WHC in beef muscles, especially WHC declined obviously during the first 24 hr. The significantly altered metabolites profiles in meat samples at 0, 3.5, and 7 days during 4 °C storage were identified using LC-MS/MS. Most metabolites showed linear changes during storage (0 to 7 days). Using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, we found 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine were increased, and 2-(S-glutathionyl)acetyl glutathione and glutathione were decreased in beef during 4 °C storage. Correlation analysis showed there were significantly correlations between metabolites and meat quality indexes (WHC, moisture content, and pH). In summary, 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine, proved to be harmful to human body, accumulated gradually, especially after 3.5 days during storage at 4 °C. While the contents of beneficial substances, including 2-(S-glutathionyl)acetyl glutathione and glutathione, were decreased, which provided reference for the nutrition guidance of using beef meat.

Modification of Glutenin and Associated Changes in Digestibility Due to Methylglyoxal during Heat Processing

Glutenin is the main protein of flour and is a very important source of protein nutrition for humans. Methylglyoxal (MGO) is an important product of the Maillard reaction that occurs during the hot-processing of flour products, and it reacts with glutenin to facilitate changes in glutenin properties. Here, the effects of MGO on glutenin digestion during the heating process were investigated using a simulated MGO-glutenin system. MGO significantly reduced the digestibility of glutenin. The structure of MGO-glutenin and physicochemical properties were studied to understand the mechanism of the decrease of digestibility. These data suggest that changes in digestibility were caused by decreases in surface hydrophobicity and increases in disulfide bonds. MGO induces strong aggregation of glutenin after heating that led to the masking of cleavage sites for proteases. Moreover, carbonyl oxidation induced by MGO leads to intermolecular cross-linking of glutenin that increasingly masks or even destroys cleavage sites, further decreasing digestibility.

Structural modification and digestibility change of β-lactoglobulin modified by methylglyoxal with the simulated reheating of dairy products

A methylglyoxal (MG)-β-lactoglobulin (bLG) model was established to simulate reheating conditions (60-100 °C) to investigate the modification effect that α-dicarbonyl compounds had on protein structure and on the digestibility of milk protein. The results showed that bLG can be modified by MG, and the modification degree increased with the increase in reheating temperature. The reacted lysine and arginine as well as the generated protein-bound N^Ɛ-carboxymethyllysine and N^Ɛ-carboxyethyllysine in the modified bLG also increased with temperature. The high-resolution mass spectrometry results revealed that the modification site is at the lysine and arginine residue of bLG. Additionally, nine types of modifications were detected, and N^Ɛ-carboxyethyllysine was the dominant modification product. The in vitro digestibility of MG-modified bLG clearly decreased with the increase in reheating temperature. This result was consistent with the degree of structural modification and could be explained by the specific action sites (lysine and arginine) of the digestive enzyme, which were modified by MG.

Effects of oxidative modification on textural properties and gel structure of pork myofibrillar proteins

Isolated myofibrillar protein (MP) was treated by the oxidation system of FeCl₃ (0.01 mM) at four different H₂O₂ concentrations (0, 1, 10, 20 mM). The oxidation degree was determined by measuring the carbonyl and total sulphydryl values. The structure and physicochemical properties of MP gels were investigated by water holding capacity (WHC) evaluation, sodium dodecyl sulfate-polyacryl amide gel electrophoresis (SDS-PAGE), texture profile analysis (TPA), Raman spectroscopy, and NMR transverse relaxation (T₂). The results of carbonyls and total sulphydryls indicated that oxidation degree of MP increased with increasing H₂O₂ concentration. TPA showed that moderate oxidation (10 mM H₂O₂) could improve the hardness, springiness, gumminess and cohesiveness of MP gels, but not contribute to the maintenance of their WHC, probably due to severe depolymerization of MPs, unfolding of α-helix, exposure of the hydrophobic groups and the migration of protein-associated water (T_2b) and intra-myofibrillar water (T₂₁) to the longer relaxation time.