The Effects of Lipid Oxidation Product Acrolein on the Structure and Gel Properties of Rabbit Meat Myofibrillar Proteins

Myofibrillar protein lipoxidation in fish induced by linoleic acid and 4-hydroxy-2-nonenal: Insights from LC-MS/MS analysis

The oxidation of fish lipids and proteins is interconnected. The LOX (lipoxygenase)-catalyzed LA (linoleic acid) oxidation system on MPs (myofibrillar proteins) was established in vitro, to investigate the impact of lipoxidation on the physicochemical properties of fish MPs. By detecting HNE (4-hydroxy-2-nonenal) concentration during LA oxidation, the HNE treatment system was established to investigate the role of HNE in this process. In addition, the site specificity of modification on MPs was detected utilizing LC-MS/MS. Both treatments could induce sidechain modification, increase particle size, and cause loss of nutritional value through the reduction in amino acid content of MPs. The HNE group is more likely to alter the MPs' surface hydrophobicity compared to the LA group. By increasing the exposure of modification sites in MPs, the HNE group has more types and number of modifications compared to the LA group. LA group mainly induced the modification of single oxygen addition on MPs instead, which accounted for over 50 % of all modifications. The LA group induced a more pronounced reduction in the solubility of MPs as compared to the HNE group. In conclusion, HNE binding had a high susceptibility to Lys on MPs. Protein aggregation, peptide chain fragmentation, and decreased solubility occurred in the LA group mainly induced by peroxide generated during lipid oxidation or the unreacted LA instead of HNE. This study fills in the mechanism of lipoxidation on protein oxidation in fish and sheds light on the HNE modification sites of MPs, paving the way for the development of oxidation control technology.

Oxidized myoglobin: Revealing new perspectives and insights on factors affecting the water retention of myofibrillar proteins

The impact of oxidized myoglobin (Mb) on myofibrillar protein (MP) oxidation and water retention was investigated. Results showed that the oxidation of Mb increased with increasing concentration of oxidized linoleic acid (OLA). In the presence of 100 mmol/L OLA, hemin iron decreased by 62.07 % compared to the control group. Further investigation showed that mild oxidation of Mb (≤10 mmol/L OLA) increased the water retention and the absolute value of the zeta potential of MP, whereas excessive oxidation (>10 mmol/L OLA) decreased these properties. With the increase of Mb oxidation, the carbonyl content in MP increased, and α-helices changed to random helix. And the tertiary structure changed. Pearson correlation analysis suggested that oxidized Mb affected the water retention of MP, which was closely related to hemin iron and non-hemin iron. In conclusion, OLA induced Mb oxidation, further promoted MP oxidation and affected its water retention.

Assessing the structural and foaming property changes in egg yolk proteins due to malondialdehyde: Experimental and molecular docking studies

This study evaluated the effects of varying levels of malondialdehyde (MDA) on the structural and foaming properties of the egg yolk proteins (EYPs), and the interaction between them was explored by molecular docking. The results showed that oxidative modification due to MDA increased the carbonyl content of EYPs by 4.49 times. Simultaneously, the total sulfhydryl content was reduced by 21.47%, and the solubility of EYPs was significantly decreased (p < 0.05). Continuous oxidation disorders the previously ordered structure of EYPs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that some proteins underwent crosslinking and aggregation with increased MDA oxidation, aligning with changes in particle size and zeta-potential. Moderate oxidation (<1 mmol/L) enhanced the foaming capacity and foam stability of EYPs. Additionally, molecular docking results uncovered favorable interactions between MDA and specific EYPs, primarily through hydrogen bonding. This research offers valuable insights into managing the functional and quality changes of yolk products during processing.

Structural properties and emulsification of myofibrillar proteins from hairtail (Trichiurus haumela) at different salt ions

The structural properties and emulsification of myofibrillar proteins (MPs) are susceptibly affected by salt ions. The effect of different salt ions on the structural properties and emulsification of MPs from hairtail (Trichiurus haumela) remains unclear. Hairtail MPs were analyzed under different ion treatments of Na+, K+, Ca2+ and Mg2+. MPs at K+ and Na+ treatment showed a similar trend on salt effect due to the unfolding of proteins under salt ions. However, the excessive electrostatic effect of divalent ions could enhance protein aggregation, especially at Ca2+ and Mg2+. The β-sheet of MPs at different salt ions interconverted with α-helix and random coil at ionic strengths from 0.1 mol/L to 1.0 mol/L. The surface hydrophobicity and active sulfhydryl content of MPs increased with the improvement of ionic strengths at 0-0.8 mol/L. Under Ca2+ and Mg2+ treatments, the turbidity of MPs was low compared to that under the treatment of Na+ and K+. Additionally, the emulsification of hairtail MPs treated with different ions was improved at an ionic strength of 0.6 mol/L. This study can contribute to using salts in constructing fish protein-based emulsions for manufacturing emulsified surimi products and promoting the development and utilization of hairtail proteins.

Exploring the interaction between myofibrillar proteins and pyrazine compounds: Based on molecular docking, molecular dynamics simulation, and multi-spectroscopy techniques

Flavor is one of the most important factors that affect consumers' preference for processed meat products. This study aimed to investigate effects of heating on interaction between myofibrillar proteins (MPs) and pyrazine compounds and understand the underlying mechanisms. A combination of multispectral, molecular docking, and molecular dynamics technologies was used to achieve study's aim. Results demonstrated that MPs underwent structural reconstruction and expansion during heating, which significantly altered surface hydrophobicity and SH content. MPs' zeta potential reduced from -7.29 to -10.47 when a short heating time. Additionally, a positive correlation was found between β-sheet content and ability of MPs to adsorb pyrazine compounds. Molecular docking analysis revealed 13 binding sites for pyrazines and MPs. Furthermore, amino acid residues and pyrazine compounds were found to interact by four different forms of forces, primarily van der Waals forces, carbon‑hydrogen bonds, alkyl groups, and π-alkyl groups. Obtained results demonstrated that adequate or optimized heat treatment could expose more binding sites, hence enhancing the binding of MPs to pyrazine compounds. This study may be used to better understand how structural changes in MPs during processing affect MPs' capacity to bind flavor substances, which can help improve flavor of processed meats to encourage their consumption.

Effects of alternating electric field assisted freezing-thawing-aging sequence on longissimus dorsi muscle microstructure and protein characteristics

The current study investigates the influence of alternating electric field (AEF)-assisted freezing-thawing-aging sequence on the muscle microstructure and myofibrillar protein characteristics. Three treatments were used for longissimus dorsi (LD) muscle: only aging (OA), freezing-thawing-aging sequence (FA) and AEF-assisted freezing-thawing-aging sequence (EA). Compared with the FA and EA groups, the OA group showed considerably fewer cracks between muscle fibers and maintained the integrity of the Z-line as observed using scanning and transmission electron microscopy, respectively. Furthermore, the EA treatment effectively decreased myofibrillar fragmentation, myofibrillar protein aggregation, and protein oxidation, as shown by the myofibrillar fragmentation index, turbidity, and total sulfhydryl concentration. Analysis of surface hydrophobicity and the Fourier transform infrared, UV absorption, and fluorescence spectrums indicated that AEF minimized the alterations of protein secondary and tertiary structure alterations during aging after freezing.

Oxidation affects dye binding of myofibrillar proteins via alteration in net charges mediated by a reduction in isoelectric point

In order to study the effect of oxidation on the dye-binding behavior of myofibrillar proteins, selected dyes with different charges (positively charged Sarfarin O (SO), neutral bromophenol blue (BPB), and negatively charged Orange G (OG)) were incubated with myofibrils oxidized by the Fenton system with H₂O₂ (10 mM). Upon oxidation, loss of free thiols, formation of carbonyls, particle size, and hydrophobicity of myofibrillar proteins (MPs) increased. The absolute value of Zeta-potential increased by 14.48 % after oxidation, the myofibrillar proteins shifted to a more acidic isoelectric point (pI) upon oxidation. Oxidation decreased net positive charges of myofibrillar protein and the binding ability of MPs towards OG in the environment with pH less than pI and the affinity of MPs towards SO in the environment with pH more than pI were thus increased. Here we propose a hypothesis that oxidation-induced change in net charges is the driving force affecting the amount of protein-bound dye. This paper aims to examine the effect of oxidation on the net charges of myofibrillar proteins and to provide insight into the mechanism of oxidation-induced changes in protein-bound dyes.

Role of Ovalbumin/β-Cyclodextrin in Improving Structural and Gelling Properties of Culter alburnus Myofibrillar Proteins during Frozen Storage

This study aimed to analyze the cryoprotective effect of a ovalbumin (OVA) and β-cyclodextrin (βCD) mixture (3:1, OVA/βCD) on the structure, rheology and gelling properties of myofibrillar proteins (MPs) during 90 days of frozen storage. A mixture of OVA/βCD at different concentrations (0, 2, 4, and 6%) was added to MPs and stored at −18 °C for 90 days. The addition of OVA/βCD significantly decreased the sulfhydryl contents while it increased the surface hydrophobicity, which was closely connected with tertiary structural changes. Circular dichroism analysis showed that the addition of OVA/βCD enhanced the stability of the secondary structure by inhibiting the decline in the α-helix. Rheological properties analysis indicated that 6% OVA/βCD treatment showed better storage modulus (G’) and loss modulus (G”). In addition, treatment of OVA/βCD showed better gel forming properties than the control group (0%), helping to form a homogeneous and denser gel network. The results proved that 6% OVA/βCD could be act as a promising cryoprotectant, which can improve the structure and gel behavior of Culter alburnus MPs during frozen storage. Moreover, OVA/βCD could be a potential alternative to conventional cryoprotectants at the industrial level to increase the economic and commercial values of seafood products.

Oxidized Milk Induces Spatial Learning and Memory Impairment by Altering Gut Microbiota in Offspring Mice during Pregnancy and Lactation

Early adverse diet exposures are known to be associated with increased risk of learning and memory injury in offspring, yet whether oxidized milk is involved in such an effect has been largely unknown. Here, we focused on oxidized milk intake in mice during pregnancy and lactation to measure the changes in the learning and memory ability in offspring and also probed into the relevant association with gut microbiota. Milk was oxidized with H₂O₂-Cu or HClO, resulting in different degrees of oxidative damage. KM female mice were fed H₂O₂-Cu, HClO, or normal control diets immediately after caging until their offspring were 3-weeks old. Behavioral tests were then performed to test the learning and memory ability, and 16S rRNA sequencing was completed with harvested fecal contents. As analyzed, fecal microflora in mice with oxidized milk was affected, mainly reflected in decreased mucin-degrading bacteria, Akkermansia and Lactobacillus, and in reversely increased pro-inflammatory bacteria Shigella, pathobiont Mucispirillum, nervous associated bacteria Ruminococcus, Escherichia, and Desulfovibrio. In the meantime, the inflammation developed in mice was aggravated accompanied by increased expression of relevant genes, while the genes and proteins associated with the learning and memory ability were down-regulated. Further behavioral tests proved impairment of the learning and memory ability in offspring. In general, milk of oxidative damage is a risk factor of the impaired transgenerational ability in learning and memory, which is associated with gut microbiota and intestinal mucosa conditions. This finding may help support the potential of early adverse diet as a harmful factor in learning and memory.

Mechanisms of change in gel water-holding capacity of myofibrillar proteins affected by lipid oxidation: The role of protein unfolding and cross-linking

This work explored the effects of protein unfolding and cross-linking induced by lipid oxidation (linoleic acid, OLA) on the gel water-holding capacity (WHC) of beef myofibrillar proteins (MP). Medium concentration of OLA (≤6 mM) caused the increase of gel WHC from 55.2% to 65.1%, while relative high OLA concentration (>6 mM) decreased the gel WHC. When the OLA concentrations increased from 0 to 10 mM, the population of immobile water of gel decreased from 92.91% to 78.97%, whereas that of free water increased from 6.13% to 19.80%, suggesting that OLA treatment regardless concentration was harmful for gel WHC. However, medium OLA concentrations (≤6 mM) caused the shifting of α-helixes to β-sheets in MP gel, exerting positive effect on gel WHC. Protein unfolding and cross-linking jointly determined the increased gel WHC at moderate oxidative modification. Additionally, the protein aggregation at high OLA concentration resulted in decreased gel WHC.

Effects of oxidative modification on the functional, conformational and gelling properties of myofibrillar proteins from Culter alburnus

Protein oxidation is a critical process in the deterioration and spoilage of fish and related commodities during processing and storage. In this study, the hydroxyl radical generation system (HRGS) was used to simulate the effect of oxidation on the functional, conformational and gelling properties of topmouth culter (Culter alburnus) myofibrillar proteins (MP). Additionally, the effects of oxidation on the gel-forming abilities of MP were also systematically analyzed from the perspective of intermolecular interaction forces. Oxidation was shown to decrease the total sulfhydryl content, increase the surface hydrophobicity, and induce conformational changes in MP. Rheological analysis showed that oxidation reduced the gel strength. Water holding capacity (WHC) and low-field nuclear magnetic resonance (LF-NMR) analyses showed that low oxidation could enhance water binding of protein matrix, while high-degree oxidation could substantially reduce the gelling properties of MP. The selective solubility of MP gel proved that oxidation could reduce the content of ionic and hydrogen bonds and increase hydrophobic interactions. All the results indicate that oxidation could alter the intermolecular interactions between protein-protein and protein-water molecules, due to irregular unfolding and inhibition of the cross-linking of amino acid side chains, leading to reduction in the quality and function of fish and related products.

Variation in the structure and emulsification of egg yolk high-density lipoprotein by lipid peroxide

To further clarify the effect of the oxidation of egg yolk high-density lipoprotein (EYHDL) on the protein structure and emulsification, 2,2'-azobis (2-methylpropionamidine) dihydrochloride (AAPH) was selected as a representative lipid peroxidation-derived peroxyl radical. The results of Raman spectroscopy indicated that, with the increase in the concentration of AAPH, the EYHDL carbonyl content increased significantly and the free sulfhydryl content declined sharply. Circular dichroism spectroscopy and intrinsic fluorescence indicated that exposure of EYHDL to AAPH led to destruction of the orderly structure and reduction of the structural stability. The particle size distribution and zeta potential indicated that the peroxyl radical caused molecular aggregation. Moderate oxidizing conditions can enhance the emulsification of EYHDL, and high-intensity oxidation decreased emulsification. The research results indicated that EYHDL made a significant change in the oxidation system and led to a change in its structure and emulsification, providing a theoretical basis to clarify the EYHDL oxidation mechanism. PRACTICAL APPLICATIONS: Egg yolk powder is prone to emulsification degradation during storage. The emulsification of egg yolk powder is mainly derived from high-density lipoprotein in egg yolk. Moreover, egg yolk powder contains a large amount of lipids, and, during the processing and storage of egg yolk powder, many lipid peroxyl radicals are inevitably generated. Therefore, it is desired to combine the lipid peroxyl radicals generated during the storage of egg yolk powder with the decrease in emulsifiability. In this paper, we first investigated the effects of peroxyl radicals on the structure and emulsifying properties of high-density lipoproteins and provided a theoretical basis to solve the problem that the emulsifiability of egg yolk powder is significantly reduced during storage.