Effects of in vitro oxidation on myofibrillar protein charge, aggregation, and structural characteristics

Improving the stability of myofibrillar proteins undergoing hemoglobin-mediated oxidation by rosmarinic acid or chlorogenic acid: Insights into the underlying mechanisms

In this study, rosmarinic acid (RA) and chlorogenic acid (CGA) were used to improve the stability of myofibrillar protein (MP) undergoing hemoglobin (Hb)-mediated oxidation. Hb-mediated oxidation caused changes in MP's secondary and tertiary structures. RA or CGA suppressed effectively Hb-induced MP oxidation, and maintained MP's spatial conformational stability through interacting with MP's amino acid side chains to form phenolic-protein complexes. Further investigations by multi-spectroscopic techniques, isothermal titration calorimetry, and molecular docking and dynamics simulation revealed the interaction of RA or CGA with Hb through binding to Hb's central hydrophobic cavity via one binding site. The RA/CGA-Hb binding was an enthalpy-driven spontaneous and exothermic process, involving hydrogen bonds and van der Waals forces as the main interactive forces. The Hb-CGA binding might be more stable than Hb-RA binding. This study provides a theoretical basis for the application of RA and CGA in improving meat products quality by regulating Hb-mediated protein oxidation.

Excellent quality acquisition of myofibrillar protein in red shrimp (Solenocera crassicornis) based on regulating the oxidation degree of atmospheric cold plasma treatment

BACKGROUND

Myofibrillar protein (MP) is essential for the texture and taste of shrimp surimi products. The reactive oxygen/nitrogen species (ROS/RNS) produced by atmospheric cold plasma (ACP) might cause oxidative modification of MP. In this study, the effect of different ACP treatment times on the properties of red shrimp MP was investigated in detail.

RESULTS

The mild oxidation induced by ACP treatment for 1 min (ACP-1 min) promoted the unfolding and refolding of the MP structure, which was manifested as a transition from α-helix to β-sheets. Compared with other groups, more hydrogen bonds and hydrophobic interactions in the ACP-1 min group might enhance the interactions between the myosin heavy chain and actin, which was conducive to the formation of a regular and dense three-dimensional network structure. Person correlation analysis revealed that ROS/RNS mediated the changes in the secondary and tertiary structure of MP. In addition, ACP-1 min has high Ca2+-ATPase activity, which reflected that MP maintained structural integrity. While excessive oxidation in the ACP treatments for 3 min and 5 min reduced MP robustness. The stable internal structure in ACP-1 min group gave the MP excellent texture profile (1.79 mJ of adhesiveness and 0.89 mm of springiness) and rheological characteristics (0.373 MPa of storage modulus).

CONCLUSION

Overall, the excellent quality of MP could be obtained by regulating the oxidation degree of ACP, which would provide valuable information for the in-depth and efficient processing of shrimp products. © 2024 Society of Chemical Industry.

Goat Milk Exhibits a Higher Degree of Protein Oxidation and Aggregation than Cow Milk During Cold Storage

Due to their markedly distinct protein compositions and structures, goat milk and cow milk display substantially different characteristics. In this study, the quality and composition of goat milk and cow milk were studied after being refrigerated at 4 °C for 7 days, with a particular focus on protein oxidation and aggregation states. The results revealed that alongside increases in acidity, microbial colony count, and hydrolysis, there was a significant change in the protein aggregation state beginning on the second day. This change was characterized by increased turbidity, an elevated centrifugal sedimentation rate, and a right-shifted particle size distribution. After seven days of refrigeration, the centrifugal sedimentation rate of goat milk increased from 0.53% to 0.97%, whereas that of cow milk rose from 0.41% to 0.58%. The degree of aggregation was significantly greater in goat milk compared to cow milk. Additionally, both protein and lipids exhibited substantial oxidation, with the degree of oxidation more pronounced in goat milk than in cow milk. The malondialdehyde (MDA) content increased from 0.047 μg/mL to 0.241 μg/mL in goat milk and from 0.058 μg/mL to 0.178 μg/mL in cow milk. The results suggest that goat milk was more prone to oxidation, which further reduced its stability. Therefore, in the storage and transportation of dairy products before processing, it is essential not only to monitor sanitary conditions but also to effectively control protein oxidation to enhance the quality of milk processing.

Sustainable development of fishery resources: Precipitation of protein from surimi rinsing wastewater by low-temperature plasma

This study aimed to determine the impact of low-temperature plasma (LTP) on the protein stability and composition in surimi rinsing wastewater (SRW). When SRW (300 mL) was treated with LTP at a power of 420 W and a flow rate of 1.1 L/min for 106 s, the protein precipitation was 76.04 %, the pH was close to the estimated value of the isoelectric point (pI). In comparison with the pI precipitation treatment, non-precipitated proteins in the SRW after LTP precipitation treatment showed significant changes in amino acids susceptible to oxidation but had minor changes in the hydrophobic amino acid content. LTP showed a markedly differentiated response to the different protein types in the SRW, increasing the relative amounts of several enzyme proteins in the non-precipitated protein. The combined effect of the active ingredients provided by LTP on protein conformation and hydrophobic interactions may be responsible for this 'screening' phenomenon.

Effect of Boiling Treatment on Linoleic Acid-Induced Oxidation of Myofibrillar Protein in Grass Carp

The aim of this study was to investigate the promotion of linoleic acid (OLA)-induced myofibrillar protein (MP) oxidation by boiling treatment. The effect of the boiling treatment on grass carp MP oxidation induced by OLA was investigated. The total sulfhydryl content, fluorescence intensity, and amino acid content were reduced with the increasing OLA concentration after the boiling treatment, while the boiled oxidized MP's carbonyl content (4.76 ± 0.14 nmol/mg) was 2.14 times higher than that of the native MP (2.22 ± 0.02 nmol/mg) at an OLA concentration of 10 mM. Additionally, the secondary structure of MP became more disordered, shifting from an α-helix to random coils and β-turns. When the concentration of OLA was higher than 5 mM, both the surface hydrophobicity and water holding capacity (WHC) decreased with the increasing OLA concentration. Furthermore, the boiling treatment led to a reduction in immobile water and an increase in free water content in the MP gel. These findings establish a theoretical basis for regulating MP oxidation to improve fish quality during boiling.

Oxidative regulation and cytoprotective effects of γ-polyglutamic acid on surimi sol subjected to freeze-thaw process

Frozen surimi sol incline to protein oxidation, but the quality control strategies based on oxidation remain limited. Hence, the antioxidant and cryoprotective effects of γ-polyglutamic acid (γ-PGA) on freeze-thawed salt-dissolved myofibrillar protein (MP) sol were investigated. Results showed that γ-PGA could effectively regulate protein oxidation of MP sol during freeze-thawing with lower carbonyl contents and less oxidative cross-linking. Meanwhile, γ-PGA primely maintained sol protein structures, showing reduction of 15.28% of salt soluble protein contents at γ-PGA addition of 0.04% under unoxidized condition. Additionally, compared to the control group without oxidation treatment, cooking loss of heat-induced gel with 0.04% γ-PGA decreased by 47.19%, while gel strength obviously increased by 57.22% respectively. Overall, moderate γ-PGA addition (0.04%) could inhibit protein oxidation of sol, further improving frozen stability of sol through hydrogen bonds and hydrophobic interaction, but excessive γ-PGA was adverse to sol quality due to severe cross-linking between γ-PGA and MP.

Effect of whey protein hydrolysate on the structural and functional stability of surimi myofibrillar protein gels during freeze-thaw cycles

This study investigates the effects of varying concentrations of whey protein hydrolysate (WPH) (5 %, 10 %, 15 %) on surimi myofibrillar protein gels subjected to freeze-thaw (FT) cycles. With an increase in the number of FT cycles, there was a decrease in both ionic and hydrogen bonding, resulting in reduced chewiness and elasticity. At the same time, hydrophobic interactions were strengthened, leading to disruptions in protein secondary structures. In contrast, the addition of WPH significantly improved and stabilized the gels' intermolecular interactions and textural properties, particularly at the 15 % concentration, which demonstrated superior effects compared to both the untreated control and the positive control treated with 0.02 % butylated hydroxyanisole (BHA) (P < 0.05). Furthermore, 15 % WPH effectively preserved the gel's secondary structure and water-holding capacity, significantly outperforming the 0.02 % BHA positive control group (P < 0.05). These findings highlight the potential of WPH to enhance intermolecular interactions and preserve the structural integrity of myofibrillar protein gels during FT cycles, indicating its promising application in food science.

Stability of large yellow croaker (Pseudosciaena crocea) as affected by temperature abuse during frozen storage: Quality attributes, myofibril characteristics, and microstructure

Temperature abuse occurs frequently during transportation and frozen storage, which affects the quality of frozen aquatic products. Recrystallization generated by temperature abuse leads to irreversible damage to the muscle tissue and microstructure, and exacerbates undesirable oxidation reactions, thus reducing the quality of frozen aquatic products. In this study, a modeling system of temperature abuse alternating between -24 °C and -7 °C was established to evaluate the effect of temperature abuse on the stability of frozen large yellow croaker. The results revealed that temperature abuse caused water migration with the extension of storage time, as well as poorer texture, color, and freshness. Furthermore, the structure of myofibrillar protein (MP) was severely damaged, with a gradual decrease in total sulfhydryl groups and Ca2+-ATPase activity, a loosening of the secondary structure, and a disruption of the protein conformation. The confocal laser scanning microscopy (CLSM) analysis also found that temperature abuse exacerbated protein aggregation. Therefore, temperature abuse during transportation and frozen storage could affect the stability of large yellow croaker negatively, and it mainly originated from the growth of ice crystals and the effect of recrystallization. The study was supposed to provide new insights into the improvement of frozen aquatic products quality.

Hydroxyl radical-induced oxidation boosts the gelation of ginkgo seed protein in the presence of hyaluronic acid

Hydroxyl radical-induced oxidation can modify gelling properties of food proteins. In this study, a hydroxyl radical generating system (HRGS), consisting of 0.1 mM Fe3+, 0.1 mM ascorbic acid, and 1, 10, or 20 mM H2O2, was used to oxidize ginkgo seed protein isolate (GSPI) for 4 h at ambient temperature in the presence of 0.3 % (w/v) hyaluronic acid (HA) to enhance its gelation properties. HRGS treatment led to increased protein hydrophobicity, reduced sulfhydryl content, and disulfide bond-mediated protein crosslinking. Moreover, the secondary structure of GSPI varied with H2O2 concentrations. Moderate oxidation (approximately 10 mM H2O2) promoted GSPI aggregation and improved mechanical strength, rheological properties, water holding capacity, and whiteness of GSPI gels. However, excessive oxidation disrupted hydrogen bonding, generated excessive disulfide bonds, hindered active group interaction, inhibited gel network formation, and reduced gel strength. Hence, hydroxyl radical-induced oxidation holds potential for enhancing GSPI gelation within specific concentration ranges. This study suggests that controlled oxidation could be a novel approach for developing protein-based gel products.

Uncovering quality changes of surimi-sol based products subjected to freeze-thaw process: The potential role of oxidative modification on salt-dissolved myofibrillar protein aggregation and gelling properties

Frozen surimi quality generally correlates with oxidation, but impacts of protein oxidation on salt-dissolved myofibrillar protein (MP) sol in surimi remain unclear. Hence, physicochemical and gelling properties of MP sol with different oxidation degrees were investigated subjected to freeze-thaw cycles. Results showed that mild oxidation (≤1 mmol/L) improved unfrozen MP gel quality with lowest cooking loss (3.29 %) and highest hardness (829.76 N). Whereas, oxidized sol suffering freeze-thawing degenerated severely, showing reduction of 23.85 % of salt soluble protein contents with H2O2 concentrations of 10 mmol/L. Shearing before heating influenced gelling properties of freeze-thawed sol, depending on oxidation levels. Oxidized gel with shearing displayed disorganized network structures, whereas gel without shearing displayed relatively complete appearances without holes under high oxidation condition (10 mmol/L). Overall, freeze-thaw process aggravated denaturation extents of MP sol subjected to oxidation, further causing high water loss and yellow color of heat-induced gel, especially to gel with shearing.

Impact of Flammulina velutipes polysaccharide on properties and structural changes of pork myofibrillar protein during the gel process in the absence or presence of oxidation

The present study aimed to investigate the impact of Flammulina velutipes polysaccharide (FVSP) on the rheological properties and structural alterations of myofibrillar protein (MP) and oxidized MP (OMP), utilizing techniques such as rhehometer, fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the unoxidized system, the addition of 5.00% FVSP significantly improved (p < 0.05) the storage and loss moduli of the composite gel and promoted the α-helix to β-sheet transformation. These effects enhanced the protein's gel strength and water-holding capacity (WHC). In the oxidation system, 5.00% FVSP had significant effects (p < 0.05) on repair and improvement of the oxidized MP. These effects inhibited the cross-linking aggregation and degradation of the protein. In addition, the addition of FVSP significantly improved the gel properties of MPs after oxidation (p < 0.05), hindered fracture of the protein gel network structure. In summary, polysaccharides have a substantial effect on the functional characteristics of MP, and FVSP could potentially be applied in meat products.

Utilization of Infrared Drying as Alternative to Spray- and Freeze-Drying for Low Energy Consumption in the Production of Powdered Gelatin

This study evaluated possible utilization of infrared drying (ID) as an alternative to spray- (SD) and freeze-drying (FD) for fish skin-derived gelatins. Physical, functional, thermal, and spectroscopic analyses were conducted for characterization of the resulting gelatin powders. Energy consumption for the applied drying methods were 3.41, 8.46 and 25.33 kWh/kg for ID, SD and FD respectively, indicating that ID had the lowest energy consumption among the studied methods. Gel strength, on the other hand, was lower (398.4 g) in infrared-dried gelatin (ID-FG) compared to that (454.9 g) of freeze-dried gelatin (FD-FG) and that (472.7 g) of spray-dried gelatin (SD-FG). TGA curves indicated that ID-FG showed more resilience to thermal degradation. SDS-PAGE and UV-Vis spectra indicated that slight degradation was observed in the β-configuration of ID-FG. ID-FG and SD-FG gelatins had the highest water holding capacity (WHC), protein solubility and transparency values compared to that of FD-FG. Morphological structures of the samples were quite different as shown by SEM visuals. Ultimately, the findings showed that infrared drying may be a promising alternative for gelatin processing, maintaining product quality and supporting sustainable practices in food and other industries.

Pseudomonas weihenstephanensis through the iron metabolism pathway promotes in situ spoilage capacity of prepared beef steaks during cold storage

In this study, we evaluated the histomorphology, reactive oxygen species (ROS), protein degradation, and iron metabolism characteristics and differential expression analysis of genes for siderophores synthesis and protease secretion in prepared beef steaks inoculated alone or co-inoculated with P. weihenstephanensis, B. thermotrichothrix and M. caseolyticus at 4 °C for 12 days. The results showed that the P. weihenstephanensis was the key bacteria that degraded protein in the process of prepared beef steaks spoilage, which led to protein oxidation by promoting ferritin degradation to release free iron and inducing ROS accumulation. The highest expression of FpvA and AprE was detected in the P. weihenstephanensis group by comparing qRT-PCR of the different inoculation groups. Both qRT-PCR and Western blot revealed that ferritin heavy polypeptide and ferritin light chain polypeptide gene and protein expressions were significantly higher in the P. weihenstephanensis inoculation group compared to the other inoculation groups. Results suggested that FpvA and AprE might play roles in meat spoilage and were potential positional, physiological and functional candidate genes for improving the quality traits of prepared beef steaks. This work may provide insights on controlling food quality and safety by intervening in spoilage pathways targeting iron carrier biosynthesis or protease secretion genes.

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.

Effects of Baking and Frying on the Protein Oxidation of Wheat Dough

Protein oxidation caused by food processing is harmful to human health. A large number of studies have focused on the effects of hot processing on protein oxidation of meat products. As an important protein source for human beings, the effects of hot processing on protein oxidation in flour products are also worthy of further study. This study investigated the influences on the protein oxidation of wheat dough under baking (0-30 min, 200 °C or 20 min, 80-230 °C) and frying (0-18 min, 180 °C or 10 min, 140-200 °C). With the increase in baking and frying time and temperature, we found that the color of the dough deepened, the secondary structure of the protein changed from α-helix to β-sheet and β-turn, the content of carbonyl and advanced glycation end products (AGEs) increased, and the content of free sulfhydryl (SH) and free amino groups decreased. Furthermore, baking and frying resulted in a decrease in some special amino acid components in the dough, and an increase in the content of amino acid oxidation products, dityrosine, kynurenine, and N'-formylkynurenine. Moreover, the nutritional value evaluation results showed that excessive baking and frying reduced the free radical scavenging rate and digestibility of the dough. These results suggest that frying and baking can cause protein oxidation in the dough, resulting in the accumulation of protein oxidation products and decreased nutritional value. Therefore, it is necessary to reduce excessive processing or take reasonable intervention measures to reduce the effects of thermal processing on protein oxidation of flour products.

The Impact of AAPH-Induced Oxidation on the Functional and Structural Properties, and Proteomics of Arachin

The aim of this study was to investigate the effect of 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation on the functional, structural properties and proteomic information of arachin. The results showed that moderate oxidation improved the water/oil holding capacity of proteins and increased the emulsifying stability, while excessive oxidation increased the carbonyl content, reduced the thiol content, altered the structure and thermal stability, and reduced most of the physicochemical properties. Through LC-QE-MS analysis, it was observed that oxidation leads to various modifications in arachin, including carbamylation, oxidation, and reduction, among others. In addition, 15 differentially expressed proteins were identified. Through gene ontology (GO) analysis, these proteins primarily affected the cellular and metabolic processes in the biological process category. Further Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that the "proteasome; protein processing in the endoplasmic reticulum (PPER)" pathway was the most significantly enriched signaling pathway during the oxidation process of arachin. In conclusion, this study demonstrated that AAPH-induced oxidation can alter the conformation and proteome of arachin, thereby affecting its corresponding functional properties. The findings of this study can potentially serve as a theoretical basis and foundational reference for the management of peanut processing and storage.

Physicochemical and structural changes of myofibrillar proteins in muscle foods during thawing: Occurrence, consequences, evidence, and implications

Myofibrillar protein (MP) endows muscle foods with texture and important functional properties, such as water-holding capacity (WHC) and emulsifying and gel-forming abilities. However, thawing deteriorates the physicochemical and structural properties of MPs, significantly affecting the WHC, texture, flavor, and nutritional value of muscle foods. Thawing-induced physicochemical and structural changes in MPs need further investigation and consideration in the scientific development of muscle foods. In this study, we reviewed the literature for the thawing effects on the physicochemical and structural characters of MPs to identify potential associations between MPs and the quality of muscle-based foods. Physicochemical and structural changes of MPs in muscle foods occur because of physical changes during thawing and microenvironmental changes, including heat transfer and phase transformation, moisture activation and migration, microbial activation, and alterations in pH and ionic strength. These changes are not only essential inducements for changes in spatial conformation, surface hydrophobicity, solubility, Ca2+ -ATPase activity, intermolecular interaction, gel properties, and emulsifying properties of MPs but also factors causing MP oxidation, characterized by thiols, carbonyl compounds, free amino groups, dityrosine content, cross-linking, and MP aggregates. Additionally, the WHC, texture, flavor, and nutritional value of muscle foods are closely related to MPs. This review encourages additional work to explore the potential of tempering techniques, as well as the synergistic effects of traditional and innovative thawing technologies, in reducing the oxidation and denaturation of MPs and maintaining the quality of muscle foods.

Lipid oxidation in foods and its implications on proteins

Lipids in foods are sensitive to various environmental conditions. Under light or high temperatures, free radicals could be formed due to lipid oxidation, leading to the formation of unstable food system. Proteins are sensitive to free radicals, which could cause protein oxidation and aggregation. Protein aggregation significantly affects protein physicochemical characteristics and biological functions, such as digestibility, foaming characteristics, and bioavailability, further reducing the edible and storage quality of food. This review provided an overview of lipid oxidation in foods; its implications on protein oxidation; and the assessment methods of lipid oxidation, protein oxidation, and protein aggregation. Protein functions before and after aggregation in foods were compared, and a discussion for future research on lipid or protein oxidation in foods was presented.

Esterified Soy Proteins with Enhanced Antibacterial Properties for the Stabilization of Nano-Emulsions under Acidic Conditions

Soy protein isolate (SPI), including β-conglycinin (7S) and glycinin (11S), generally have low solubility under weakly acidic conditions due to the pH closed to their isoelectric points (pIs), which has limited their application in acidic emulsions. Changing protein pI through modification by esterification could be a feasible way to solve this problem. This study aimed to obtain stable nano-emulsion with antibacterial properties under weakly acidic conditions by changing the pI of soy protein emulsifiers. Herein, the esterified soy protein isolate (MSPI), esterified β-conglycinin (M7S), and esterified glycinin (M11S) proteins were prepared. Then, pI, turbidimetric titration, Fourier transform infrared (FTIR) spectra, intrinsic fluorescence spectra, and emulsifying capacity of esterified protein were discussed. The droplet size, the ζ-potential, the stability, and the antibacterial properties of the esterified protein nano-emulsion were analyzed. The results revealed that the esterified proteins MSPI, M7S, and M11S had pIs, which were measured by ζ-potentials, as pH 10.4, 10.3, and 9.0, respectively, as compared to native proteins. All esterified-protein nano-emulsion samples showed a small mean particle size and good stability under weakly acidic conditions (pH 5.0), which was near the original pI of the soy protein. Moreover, the antibacterial experiments showed that the esterified protein-based nano-emulsion had an inhibitory effect on bacteria at pH 5.0.

Changes in Texture Characteristics and Special Requirements of Sichuan-Style Braised Beef for Industrial Production: Based on the Changes in Protein and Lipid of Beef

This study aimed to investigate the optimal stewing time (0, 30, 60, 90, 120, and 150 min) for industrialized preparation of Sichuan-style braised beef with different demands. With prolonged stewing time, the hardness and chewiness of the braised beef initially increased and then decreased (p < 0.05), whereas springiness and cohesiveness gradually decreased. The moisture content of braised beef and the endogenous fluorescence intensity of braised beef protein significantly decreased (p < 0.05). However, the thiobarbituric acid reaction substances (TBARS) value and protein carbonyl content of braised beef greatly increased (p < 0.05). During the stewing process, the texture properties of Sichuan-style braised beef were affected by the moisture content, oxidation of proteins and lipids, and integrity of the muscle fibers. Considering texture traits, when Sichuan-style pre-braised beef bought by consumers is stewed with other ingredients for about 30 min, its corresponding stewing time is 60 min in industrialized production processes. This process parameter can not only save energy consumption for practical production, but also improve the hardness value of the as-obtained Sichuan-style pre-braised beef, which is conducive to transportation through refraining from cracking of pre-braised beef pieces. When consumers only use simple heating to eat the Sichuan-style pre-braised beef product, stewing times of 120 or 150 min can be considered in industrialized production processes. This work provided a theoretical reference for the industrialized and standardized production of different types of prepared Sichuan-style braised beef.

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.

Conformational Changes in Proteins Caused by High-Pressure Homogenization Promote Nanoparticle Formation in Natural Bone Aqueous Suspension

As a natural calcium resource, animal bone needs to be miniaturized to the nanoscale to improve palatability and absorption capacity. To explore the mechanism of high-pressure homogenization (HPH) in preparing natural bone aqueous nanosuspensions, the relationships between the changes in protein conformation, solubility and quality characteristics of rabbit bone aqueous suspensions (RBAS) prepared by different HPH cycles were studied. The results showed that the improvements in particle size, stability and calcium solubility of RBASs could be mainly attributed to the improvement of protein solubility induced by the changes in protein conformation. HPH treatment led to the denaturation and degradation of protein in rabbit bone, generating soluble peptides and improving the stability of the suspensions by enhancing the surface charge of the particles. When collagen as the main protein was partially degraded, the hydroxyapatite in the bone was crushed into tiny particles. The increase in the particle-specific surface area led to the release of calcium ions, which chelated with the peptides to produce peptide calcium. However, excessive HPH treatment caused the production of protein macromolecular aggregates and affected the quality of RBASs. This study is helpful to promote the application of HPH technology in animal bone nanoprocessing.

The Effect of Pressure-Shift Freezing versus Air Freezing and Liquid Immersion on the Quality of Frozen Fish during Storage

In this study, a self-cooling laboratory system was used for pressure−shift freezing (PSF), and the effects of pressure−shift freezing (PSF) at 150 MPa on the quality of largemouth bass (Micropterus salmoides) during frozen storage at −30 °C were evaluated and compared with those of conventional air freezing (CAF) and liquid immersion freezing (LIF). The evaluated thawing loss and cooking loss of PSF were significantly lower than those of CAF and LIF during the whole frozen storage period. The thawing loss, L* value, b* value and TBARS of the frozen fish increased during the storage. After 28 days storage, the TBARS values of LIF and CAF were 0.54 and 0.65, respectively, significantly higher (p < 0.05) than the 0.25 observed for PSF. The pH of the samples showed a decreasing trend at first but then increased during the storage, and the CAF had the fastest increasing trend. Based on Raman spectra, the secondary structure of the protein in the PSF-treated samples was considered more stable. The α-helix content of the protein in the unfrozen sample was 59.3 ± 7.22, which decreased after 28 days of frozen storage for PSF, LIF and CAF to 48.5 ± 3.43, 39.1 ± 2.35 and 33.4 ± 4.21, respectively. The results showed that the quality of largemouth bass treated with PSF was better than LIT and CAF during the frozen storage.

Effects of oxidation on the physicochemical properties and degradation of mutton myofibrillar proteins

Tenderness affects mutton quality and price, and the degradation of myofibrillar protein (MP) is critical to improve tenderness. We investigated the oxidative modification of mutton MP by hydroxyl radicals (OH) and the effects of this modification on the proteolysis of MP by µ-calpain. As the H₂ O₂ concentrations increased, the carbonyl and dityrosine contents and the surface hydrophobicity of MP all display an increasing trend, whereas the total sulfhydryl and intrinsic fluorescence intensity of MP declines significantly. SDS-PAGE electrophoresis indicates that disulfide bonds and other covalent bonds led to protein cross-linking and aggregation. After adding µ-calpain, with increasing oxidation, the degradation percentage of myosin heavy chain (MHC) increases considerably and actin degradation is promoted, while the proteolysis of troponin-T and desmin is inhibited. These data suggest that·OH can change MP physicochemical properties and its susceptibility to µ-calpain. Future investigations will focus on the effect of oxidation on the degradation of MP by other proteases, such as cathepsins and caspase and the effect of oxidation on these enzymes. PRACTICAL APPLICATION: The calpain system, particularly µ-calpain, plays a pivotal role in postmortem tenderization of meat. Protein oxidative modifications influence meat tenderness mainly by regulating proteolysis. An investigation of the effect of oxidation on the proteolytic susceptibility of MP to degradation by µ-calpain allows for the monitoring of the association between protein oxidation and meat tenderness.

Effect of Peroxyl Radical-Induced Oxidation on Functional and Structural Characteristics of Walnut Protein Isolates Revealed by High-Resolution Mass Spectrometry

The present study aims to investigate the structural and functional properties of oxidated walnut protein isolates (WPI) by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH). The oxidation degree, changes in structural characteristics, processing properties, and protein modifications of WPI were measured. The results showed that oxidation significantly induced structural changes, mainly reflected by the increasing carbonyl content, and decreasing sulfhydryl and free amino groups. Moreover, the secondary structure of WPI was altered in response to oxidation, and large aggregates formed through disulfide cross-linking and hydrophobic interactions. Almost all the property indicators were significantly decreased by oxidation except the foaming property and water/oil holding capacity. Mass spectrometry analysis showed that 16 different modifications occurred in amino acid side chains, and most of the protein groups with higher numbers of modifications were found to be associated with allergies, which was further confirmed by the reduction in antigenicity of the major allergen (Jug r 1) in WPI. Meanwhile, we used oxidation-related proteins for gene ontology (GO) enrichment analyses, and the results indicated that 115, 204 and 59 GO terms were enriched in terms of biological process, molecular function, and cellular component, respectively. In conclusion, oxidation altered the groups and conformation of WPI, which in turn caused modification in the functional properties correspondingly. These findings might provide a reference for processing and storage of walnut protein foods.

Quantifying methionine sulfoxide in therapeutic protein formulation excipients as sensitive oxidation marker

Methionine is a common excipient used in therapeutic protein liquid formulations as stabilizer and antioxidant. The oxidation of methionine to methionine sulfoxide can be regarded as a sensitive marker of oxidative stress for drug product storage conditions. In this study, a sensitive HPLC method for the quantification of methionine sulfoxide in formulated protein product was developed and qualified according to regulatory requirements using a SIELC® Primesep 100 column with UV detection. The separation involves a mixed-mode mechanism including reversed phase and cationic exchange modalities. The operating range of the method was established between 1 µM and 35 µM of methionine sulfoxide. In this testing range, the method was shown to be linear (R² > 0.99), accurate (Recovery 92.9 - 103.6%, average recovery = 99.8 ± 1.4%) and precise (intermediate precision at LoQ, CV = 2.9%). The developed test system was successfully applied to study the effects of temperature and storage conditions on methionine sulfoxide formation in complex therapeutic antibody formulations.

The quality properties of frozen large yellow croaker fillets during temperature fluctuation cycles: improvement by cellobiose and carboxylated cellulose nanofibers

Frozen aquatic products undergo unavoidable quality changes owing to temperature fluctuations during frozen storage and distribution. This study investigated the effects of 1% cellobiose (CB), and 0.5 and 1% carboxylated cellulose nanofibers (CNF) on ice crystal growth and recrystallization of frozen large yellow croaker fillets exposed to temperature fluctuations. Denser and more uniformly distributed ice crystals were observed in the CB- and CNF-treated samples than in the water-treated samples. Furthermore, the addition of CB and CNF suppressed the conversion of bound water to frozen water in the samples during temperature fluctuation cycles, played a positive role in fixing the ionic and hydrogen bonds that stabilize the protein structure, limited the conformational transition from α-helix to β-sheet, and improved protein thermal stability. Based on turbidity, zeta potential, and confocal laser scanning microscopy (CLSM) analyses, the presence of CB and CNF restricted the protein aggregation. Compared with CB, CNF molecules with abundant carboxyl functional groups and longer morphology exhibited better cryoprotective effects. Moreover, the fillets were more improved protected from mechanical damage induced by large ice crystals at a higher CNF concentration. This study reveals the potential of CB and CNF as novel cryoprotectants.

Effect of cellobiose on the myofibrillar protein denaturation induced by pH changes during freeze-thaw cycles

The aim of this study was to investigate myofibrillar protein (MFP) denaturation induced by pH changes during freeze-thaw (FT) cycles, and to propose an effective mitigation strategy. Owing to the selective crystallization of Na₂HPO₄·12H₂O and the consequent pH change, a pH change of 3.32 units was observed when the MFP solution were frozen. The surface hydrophobicity, particle size and confocal laser scanning microscopy showed that the protein molecules gradually unfolded and formed larger protein aggregation as the number of FT cycles increases. Additionally, protein degradation, secondary and tertiary structure alterations suggested that the FT cycle could disrupt structural integrity. The addition of cellobiose could maximize the inhibition of pH changes (decrease of ∼0.62 unit), no Na₂HPO₄·12H₂O crystallization was observed by X-ray diffraction. Cellobiose could minimize FT damage to myofibrillar protein, which was closest to the control. Thus, cellobiose can be used as a new and effective cryoprotectant.

Aggregation and deaggregation: The effect of high-pressure homogenization cycles on myofibrillar proteins aqueous solution

Myofibrillar proteins (MPs) have not been fully used for a long time due to its poor solubility in low ionic strength solutions. The study explored the effect of high pressure homogenization (HPH) cycles under two pressures on the solubility of MPs. The MPs solubility increased with HPH cycles (p < 0.05), the results of turbidity, appearance, droplet size indicated that the increase of solubility was due to MPs depolymerization, excessive HPH cycles (25k psi for 11 cycles) would lead to protein re-aggregation but does not affect solubility (p>0.05). SDS-PAGE suggested that myosin formed soluble polymers with different molecular weights through disulfide bonds during HPH cycles, the polymer consisted of myosin subunits of different molecular weights. Endogenous fluorescence spectra, intermolecular chemical forces, isoelectric point analysis and free amino acids (FAAs) indicated that the dissolution of polymers in low ionic strength media was dominated by polar environment and intermolecular steric hindrance, but not to FAAs.

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.

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.

Effect of drying methods on the solubility and amphiphilicity of room temperature soluble gelatin extracted by microwave-rapid freezing-thawing coupling

The effect of three drying methods (hot air, freeze and spray drying) on the solubility and amphiphilicity of gelatin were investigated and compared. Results showed spray drying gelatin (SDG) and hot air drying gelatin (HDG) showed the lowest and best solubility, respectively. This phenomenon was attributed to the degree of subunits degradation and hydrophobicity. The HDG showed an obvious degradation during the hot air drying and displayed the strongest hydrophilicity, while SDG showed a slight degradation and strongest hydrophobicity. The results of wettability showed that SDG had a better amphiphilicity (92.48°) in comparison with HDG (57.7°) and freeze drying gelatin (VDG, 77.53°), which can effectively reduce the interfacial tension of gelatin, thus significantly improving the stability of foam and emulsion (p < 0.05). These results suggested the drying methods can adjust the amphiphilicity of gelatin, and the SDG displayed a better amphiphilicity, showing good potential applications in foam and emulsion.