Structural Changes In Myofibrillar Proteins Research Articles

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Thawed drip and its membrane-separated components: Role in retarding myofibrillar protein gel deterioration during freezing-thawing cycles

Myofibrillar proteins are crucial for gel formation in processed meat products such as sausages and meat patties. Freeze-thaw cycles can alter protein properties, impacting gel stability and product quality. This study aims to investigate the potential of thawed drip and its membrane-separated components as potential antifreeze agents to retard denaturation, oxidation and gel deterioration of myofibrillar proteins during freezing-thawing cycles of pork patties. The thawed drip and its membrane-separated components of > 10 kDa and < 10 kDa, along with deionized water, were added to minced pork at 10 % mass fraction and subjected to increasing freeze–thaw cycles. Results showed that the addition of thawed drip and its membrane separation components inhibited denaturation and structural changes of myofibrillar proteins, evidenced by reduced surface hydrophobicity and carbonyl content, increased free sulfhydryl groups, protein solubility and α-helix, as compared to the deionized water group. Correspondingly, improved gel properties including water-holding capacity, textural parameters and denser network structure were observed with the addition of thawed drip and its membrane separation components. Denaturation and oxidation of myofibrillar proteins were positively correlated with gel deterioration during freezing-thawing cycles. We here propose a role of thawed drip and its membrane separation components as cryoprotectants against myofibrillar protein gel deterioration during freeze-thawing cycles.

Inhibitive effect of trehalose and sodium pyrophosphate on oxidation and structural changes of myofibrillar proteins in silver carp surimi during frozen storage

This work investigated the cryoprotective effect of trehalose (TH) and sodium pyrophosphate (SPP) alone and in combination on myofibrillar protein (MP) oxidation and structural changes in silver carp surimi during 90 days of frozen storage (-20 °C). TH combined with SPP was significantly more effective than single TH or SPP in preventing MP oxidation (P < 0.05), showing a higher SH content (6.05 nmol/mg protein), and a lower carbonyl (4.24 nmol/mg protein) and dityrosine content (1280 A.U.). SDS-PAGE results indicated that TH combined with SPP did not differ significantly from TH and SPP in inhibiting protein degradation but was more effective in inhibiting protein crosslinking. Moreover, all cryoprotectants could stabilise the secondary and tertiary structures and inhibit unfolded and aggregation of MP, with the combination of TH and SPP being the best. It's worth noting that TH combined with SPP had a synergistic effect on inhibiting the decrease in α-helix content and gel-forming ability, and the increase in surface hydrophobicity. Overall, TH combined with SPP could significantly inhibited MP oxidation and structural changes in surimi during frozen storage and improve the gel-forming ability, which was significantly better than single TH or SPP.

Oxidation affects pH buffering capacity of myofibrillar proteins via modification of histidine residue and structure of myofibrillar proteins

The pH buffering capacity is an important functionality of muscle proteins, and muscle foods are susceptible to being oxidized during storage and processing. In order to study the effect of oxidation on the pH buffering capacity of myofibrillar proteins, myofibrils extracted from snakehead fish (Channa argus) were oxidized with H2O2. Results showed that increased oxidation led to loss of free sulfhydryl groups, formation of carbonyl groups, increased surface hydrophobicity, and aggregation of myofibrillar proteins. In addition, there was a significant reduction in the content of histidine in oxidized myofibrillar proteins. The pH buffering capacity of myofibrillar proteins significantly decreased from 3.14 ± 0.03 mM H+/(mL × ΔpH) down to 2.55 ± 0.03 mM H+/(mL × ΔpH) after oxidation with 50 mM H2O2. Both oxidized myofibrillar proteins and histidine showed a high pH buffering capacity at pH near 5.8, which is the histidine pKa value. Here, we hypothesize that oxidation-induced changes in the pH buffering capacity of myofibrillar proteins were driven by oxidative modification of histidine and structural changes of myofibrillar proteins. The significance of this study to food industry may be the awareness that protein oxidation may affect pH through changes in buffering capacity. And the use of antioxidants, especially those targeting at histidine will be promising in addressing this issue.

Dual cryoprotective and antioxidant effects of young apple polyphenols on myofibrillar protein degradation and gelation properties of bighead carp mince during frozen storage.

Commercial cryoprotectants can delay quality loss in frozen fish mince, but they are associated with a sweet taste and high calorie content. Young apple polyphenols (YAP), extracted from unripe apples, show potential as an alternative cryoprotectant. This study evaluated the cryoprotective effect of YAP at varying levels (0.3%, 0.7%, and 1%) in unwashed bighead carp mince. The changes in sulfhydryl content, carbonyl content, thiobarbituric acid reactive substances, intrinsic fluorescence intensity, and Fourier transform infrared spectrum indicated that YAP retarded oxidation and structural changes in myofibrillar proteins during the first 8 weeks of frozen storage, as well as lipid oxidation, which protected the structure of myofibrillar protein. At higher concentrations (0.7% and 1%), YAP maintained gel properties, gel springiness, and water-holding capacity of the gel prepared from frozen fish mince, potentially through the promotion of cross-linking of myofibrillar proteins. Overall, YAP can be used as a cryoprotectant and antioxidant in fish mince. PRACTICAL APPLICATION: Our research found that young apple polyphenols have the potential to be an alternative to commercial cryoprotectants. Young apple polyphenols may be used as a sugar-free and healthy cryoprotectant for frozen fish mince production in the future.

Myofibril degradation and structural changes in myofibrillar proteins of porcine longissimus muscles during frozen storage

The effect of frozen time and the temperature on myofibril degradation and the structure of myofibrillar proteins of porcine longissimus muscles were investigated. With extended frozen time and increased temperature, the muscle fibres became broken; the muscle cells became irregularly arranged; and the fragmentation index value, number of ionic bonds, and number of hydrogen bonds of the samples significantly decreased. Meanwhile, the myofibril fragmentation index value, number of hydrophobic interactions, and number of disulphide bonds significantly increased (P < 0.05). After 12 months of storage, the intensities of I760/I1003, I850/I830, I1450/I1003, and I2945/I1003 in the samples frozen at −8 °C were reduced by 4.36 %, 1.28 %, 1.86 %, and 0.74 %, respectively. A reduction in the maximum absorption peak and a red shift were observed in the ultraviolet spectrum. Therefore, frozen storage resulted in significant damage to the tissue microstructureand caused accelerated protein degradation, and the loss of protein structural integrity.

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.

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

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

Analysis of inhibition of guava (Psidium guajava l.) leaf polyphenol on the protein oxidative aggregation of frozen chicken meatballs based on structural changes

This study compared the effects of guava leaf polyphenol (GLP) on the aggregation and structural changes of myofibrillar proteins (MPs) from chicken meatballs, frozen for 6 months, with that of tea polyphenol (TP). The high antioxidation ability of 450 mg/L GLP was manifested by changes in 1, 1-diphenyl-2-picrylhydrazyl (DDPH), 2, 2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, and the ferric reducing antioxidant power (FRAP) in vitro. Compared with the control, the carbonyl, disulfide bond content, particle size, zeta potential and turbidity of sample with GLP decreased by 25.9 %, 17.7 %, 18.2 %, 11.4 % and 11.7 %, respectively, while the solubility of the sample, after freezing it for 6 months, increased by 14.8 %. Meanwhile, in sustaining the structural stability of MPs, the GLP-treated group exhibited better microstructure (scanning electron microscopy, SEM), lower free amino and sulfhydryl loss, higher α-helix structure and fluorescence intensity than the control. Our results showed that GLP significantly inhibited MP aggregation, and was superior to TP in terms of its particle size, solubility, and turbidity, sulfhydryl content (P < 0.05). Overall, it was demonstrated that GLP has the potential to inhibit protein aggregation and enhance structural stability during frozen storage.

Inhibitive effect of cryoprotectants on the oxidative and structural changes in myofibrillar proteins of unwashed mince from silver carp during frozen storage

Silver carp is a type of Asian carp that poses a threat to the United States. Unfortunately, producing Asian carp surimi in the US has been unsuccessful due to the high cost. Thus, exporting Asian carp to China and other Asian countries in the form of frozen deboned fish mince (without washing) would be a new way to create commercial value. This study was to explore the effects of compound cryoprotectants CC (sucrose, sorbitol, and sodium tripolyphosphate) and CC + SD (salted egg white) on unwashed silver carp mince during frozen storage. In the presence of CC, unwashed mince exerted benefits on gel property and water holding property. CC was able to retard protein oxidation as indicated by the retarded carbonyl content and lower loss in sulfhydryl content. Based on indicators of content of salt-soluble protein, α-helix, myosin heavy chain and intrinsic fluorescence intensity, CC addition inhibited protein aggregation by protecting the protein structure. The inclusion of SD did not show a cryoprotective effect or synergistic antioxidant effect with sucrose-sorbitol, but SD improved the gel strength within 4 weeks of freezing. Thus, CC can provide cryoprotective protection during frozen storage of silver carp mince. CC + SD provides a reference for long-distance transport and off-site production of frozen silver carp mince.

Fluctuated low temperature combined with high-humidity thawing to retain the physicochemical properties and structure of myofibrillar proteins from porcine longissimus dorsi

The physicochemical and structural changes in myofibrillar proteins (MPs) from porcine longissimus dorsi under low temperature combined with high-humidity thawing (4 °C, 90% RH, LHT) and fluctuated low temperature combined with high-humidity thawing (2 → 6 → 2 °C, 90% RH, FLHT) treatments were compared with those under refrigerator thawing (RT). The changes in the thermal stability and viscoelasticity of the MPs after FLHT treatment was insignificant (P < 0.05) compared with the corresponding properties of the fresh samples. In addition, FLHT resulted in a desirable water distribution, the highest total sulfhydryl content, and the lowest carbonyl content compared to the other treatments, suggesting that it effectively decreases protein oxidation. FLHT also led to slight changes in the aggregation and integrity of the MPs. Furthermore, a stable tertiary structure was obtained through FLHT. In contrast, the largest variations in all indicators of the MPs were observed following RT. These results confirmed that FLHT reduced the physicochemical deterioration of MPs from porcine muscle, thereby indicating the potential of FLHT for application in the thawing of meat.

Physicochemical and structural changes in myofibrillar proteins from porcine longissimus dorsi subjected to microwave combined with air convection thawing treatment

The effect of microwave combined with air convection thawing (MAT) on the properties and tertiary structure of myofibrillar proteins (MPs) from porcine longissimus dorsi muscle was investigated and compared with single treatments (air thawing, microwave thawing) and fresh meat (FM). Among the thawing treatments, the carbonyl content, dityrosine content, and surface hydrophobicity of MPs in MAT were the lowest, whereas the total sulfhydryl content, water-holding capacity, and Ca2+-ATPase activity were the highest, suggesting that MAT retained MPs properties better. MAT possessed a more stable tertiary structure and exhibited slight changes in MPs aggregation and degradation. There was an insignificant difference (P > 0.05) in the immobilized water and free water between the MAT samples and FM, indicating a tighter interaction between water and muscle protein in MAT. Thus, MAT could retain the physicochemical and structural properties of MPs, which provided a combination of thawing treatments for application in meat industry.

Cryoprotective effect of egg white proteins and xylooligosaccharides mixture on oxidative and structural changes in myofibrillar proteins of Culter alburnus during frozen storage

The purpose of this research was to investigate the cryoprotective role of EWP-XO in the prevention of oxidative and structural changes in the myofibrillar proteins (MPs). Different concentrations of egg white protein and xylooligosaccharide (EWP-XO) mixture (0, 2, 4 and 6%) were added to the MPs of Culter alburnus fish during frozen storage (−18 °C) of 60 days. During the study, it was observed that EWP-XO significantly (P < .05) reduced the Ca-ATPase activity, which is greatly related with tertiary structural changes. Meanwhile, carbonyl contents of MPs increased in line with frozen storage (control samples). Meanwhile, samples treated with 6% EWP-XO showed less increase in carbonyl content indicating the decreased protein oxidation. The addition of EWP-XO efficiently inhibited the decline in the sulfhydryl contents. Furthermore, through circular dichroism analysis it was confirmed that the addition of EWP-XO increased the secondary structural stability by preventing the reduction in α-helix content. Microstructural analysis confirmed the preservation of a well-structured protein network that reduced the porosity and protein aggregation of MPs gel. It was concluded that 6% EWP-XO was an effective cryoprotectant mixture, which preserved the functional and structural properties of Culter alburnus during 60 days of frozen storage period.

The effectiveness of egg white protein and β-cyclodextrin during frozen storage: Functional, rheological and structural changes in the myofibrillar proteins of Culter alburnus

This study focused on the effects of egg white protein (EWP) and β-cyclodextrin (βCD) mixture (3:1, EWP/βCD) at 0, 2, 4 and 6% concentrations on fish (Culter alburnus) myofibrillar proteins (MP) during 60 days of frozen storage (−18 °C) by analyzing functional, rheological and structural changes in MP and MP gels. After 60 days of storage, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy revealed a decrease in the MP α-helix content, and EWP/βCD addition improved the MP secondary structural properties by inhibiting protein aggregation induced by exposure of hydrophobic residues. Particularly, the 6% EWP/βCD treatment significantly decreased (P < 0.05) the pores and spaces of MP gels formed during frozen storage, resulting in a denser network. Moreover, compared with the control (0%), EWP/βCD addition significantly increased (P < 0.05) the gel hardness, springiness, gumminess and cohesiveness as well as whiteness and water holding properties. Dynamic rheological analysis showed that 6% EWP/βCD also increased the MP storage modulus (G’) and loss modulus (G”). This research provides useful information for increasing the commercial life of fish products by frozen storage and contributes to the potential application of EWP/βCD as a low-sweetness cryoprotectant for Culter alburnus fish.

Effect of vacuum impregnation of red sea bream (Pagrosomus major) with herring AFP combined with CS@Fe3O4 nanoparticles during freeze-thaw cycles

This study examined the effect of herring antifreeze protein (hAFP) combined with chitosan magnetic nanoparticles (CS@Fe3O4), applied through vacuum impregnation, on protein conformation and moisture state of red sea bream during freeze-thaw cycles. DSC and dynamic rheology were used to analyze physicochemical changes. Raman, intrinsic fluorescence and second derivative UV spectrometry were used to explore the structural changes of myofibrillar proteins. Surface hydrophobicity, particle size and zeta-potential were used to analyze protein aggregation and denaturation. AV, POV, and TBA were used to determine the degree of lipid oxidation. LF-NMR and MRI were used to test water migration and distribution. The results indicated that pretreatment of red sea bream through vacuum impregnation with hAFP combined with CS@Fe3O4 solutions could minimize freeze-thaw damage, prevent protein and lipid oxidation. Therefore, these results confirm the importance of hAFP as a valuable food additive in frozen foods.

Investigation on Structural Changes of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix) during Frozen Storage

Investigation on Structural Changes of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix) during Frozen Storage

Structural Evaluation of Myofibrillar Proteins during Processing of Cantonese Sausage by Raman Spectroscopy

Structural changes of myofibrillar proteins from raw pork muscle and Cantonese sausage at different processing periods were elucidated using Raman spectroscopy. Fourier deconvolution combined with iterative curve fitting were used to analyze the amide I Raman band. Results from amide I, amide III, and C-C stretching vibrations in 890-1060 cm(-1) showed that α-helix decreased accompanied by an increase in β-sheet structure during the first 18 h, and a rebuilding process of secondary structures was observed at the rest stage due to proteolysis. The hierarchical cluster analysis results of amide I and amide III confirmed this rebuilding process. Changes in a doublet near 850 and 830 cm(-1) suggested that some tyrosine residues became buried in a more hydrophobic environment due to intermolecular interactions. Raman spectra in the 2855-2940 cm(-1) region suggested that the environment of aliphatic side chains might have been changed during the final stage and further confirmed above rebuilding process.

Raman spectroscopic study of the effects of microbial transglutaminase on heat-induced gelation of pork myofibrillar proteins and its relationship with textural characteristics

The effects of microbial transglutaminase (MTG) on heat-induced gelation of pork myofibrillar proteins (PMP) structural changes, textural properties were studied by Raman spectroscopy and texture profile analysis (TPA), respectively. And the relationships between the structural changes and textural characteristics were estimated by principal component analysis (PCA). Changes in the Raman spectra were interpreted as the occurrence of secondary structural changes in myofibrillar proteins with MTG added. Modifications in the amide I (1600–1700cm−1) regions indicated a significant (p<0.05) decrease in α-helix content, accompanied by a significant (p<0.05) increase in β-sheets, β-turns and random coil content due to the addition of the enzyme. Obvious texture property changes were also determined by TPA. All these changes showed a strong, irreversible heat-induced gel formed due to the addition of MTG. The application of a dimensionality reducing technique such as PCA proved to be useful to determine the most influential properties of heat-induced gel. Significant (p<0.05) correlations were found between these structural changes and the textural characteristics (hardness) in PMP system with the addition of MTG by PCA. The hardness was related positively to fraction of β-sheet, β-turns and random coil, and negatively to normalized intensity of 760cm−1 and fraction of α-helix. The samples are closely grouped in a cluster defined by level of MTG.

Raman spectroscopic study of heat-induced gelation of pork myofibrillar proteins and its relationship with textural characteristic

Structural changes, textural properties and their relationships in pork myofibrillar proteins (PMP) were studied by Raman spectroscopy, texture profile analysis (TPA) and principal component analysis (PCA). Raman spectroscopy analysis revealed the occurrence of secondary structural changes in myofibrillar proteins. Modifications in the amide I (1600–1700 cm −1) and amide III (1200–1300 cm −1) regions indicated a significant ( p < 0.05) decrease in α-helix content, accompanied by a significant ( p < 0.05) increase in β-sheets, β-turns and random coil content. Texture property changes were also determined by TPA. All these features contributed to the formation of strong, irreversible heat-induced gels. The application of a dimensionality reducing technique such as PCA proved to be useful to determine the most influential properties of heat-induced gel. Significant ( p < 0.05) correlations were found between these structural changes and the textural characteristic (hardness) in the pork myofibrillar proteins system by PCA.